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Experiencing innovative biomaterials for buildings: Potentialities of mosses
Journal Pre-proof Experiencing innovative biomaterials for buildings: potentialities of mosses Katia Perini, Paola Castellari, Andrea Giachetta, Claudia Turcato, Enrica Roccotiello PII:
S0360-1323(20)30066-4
DOI:
https://doi.org/10.1016/j.buildenv.2020.106708
Reference:
BAE 106708
To appear in:
Building and Environment
Received Date: 6 November 2019 Revised Date:
24 January 2020
Accepted Date: 30 January 2020
Please cite this article as: Perini K, Castellari P, Giachetta A, Turcato C, Roccotiello E, Experiencing innovative biomaterials for buildings: potentialities of mosses, Building and Environment, https:// doi.org/10.1016/j.buildenv.2020.106708. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2020 Elsevier Ltd. All rights reserved.
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Experiencing innovative biomaterials for buildings: potentialities of mosses
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Katia Perini*a, Paola Castellaria, Andrea Giachettaa, Claudia Turcatob, Enrica Roccotiellob
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*Corresponding author: [email protected] a
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b
Polytechnic School of the University of Genoa, Architecture and Design Department, Italy
University of Genoa, Department of Earth Life and Environmental Sciences, Laboratory of Plant Biology, Genoa, Italy
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Abstract
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Vertical greening systems and green roofs provide ecosystem services in the urban context. Despite
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the important benefits they provide, economic (initial and maintenance costs) and environmental
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issues may limit the widespread diffusion of these greening systems. Mosses can be a low-cost and
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low-maintenance alternative green envelope for large-scale application on existing urban and
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industrial buildings thanks to their low requirements in terms of growing substrates, low amount of
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water and nutrients needed, and high desiccation tolerance. The study assesses the’ growing ability
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of mosses on building materials and low-cost materials, by means of growing tests performed under
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controlled environmental conditions on horizontal and vertical surfaces. Moss growth depends
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mainly on the physical characteristics of the materials, although an acidic moss mixture improves
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species richness. Results show different surface coverage: capillary matting > cement plaster > lime
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plaster > terracotta brick > slate > quartzite. The water retention capacity and its homogeneous
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distribution on the growing surface are the limiting factors for moss growth.
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1. Introduction
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Urban areas pose significant environmental issues that have to be addressed, i.e. poor air quality
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with high levels of PMx, NO2, O3 (European Environment Agency, 2018), the Urban Heat Island
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phenomenon (Nakamatsu and Tsutsumi, 2002), the extreme alteration of urban surfaces (waterproof
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artificial surfaces with low albedo) and water resources and the deterioration of the urban ecosystem
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(Rees, 1997).
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Urban greening is able to mitigate Urban Heat Island phenomenon (Alexandri et al., 2008; Armson
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et al., 2012; Onishi et al., 2010), collect fine dusts and mitigate the vertical dispersion of gaseous
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pollutants in urban canyons, with a consequent improvement in air, water and soil quality (Dover,
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2018a; Perini and Roccotiello, 2018). Moreover, plants contribute to decrease the superficial water
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flow (Livesley et al., 2014) and remove water pollutants (Jackson and Boutle, 2008), to improve
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human wellbeing (Fjeld et al., 1998; Grahn and Stigsdotter, 2003; Ulrich, 1984) and support
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biodiversity on an urban scale (Atkins, 2018).
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Vertical greening systems and green roofs can provide ecosystem services within densely built
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fabrics, to address a range of challenges facing urban areas (Dover, 2018b; Manso and Castro-
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Gomes, 2015a). In addition, green envelopes work as thermal (Sadineni et al., 2011) and acoustic
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protection (Wong et al., 2010) and as passive systems for energy savings (Coma et al., 2017; Pérez
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et al., 2014a), contributing to building sustainability performances (Eumorfopoulou and Kontoleon,
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2009; Ottelé et al., 2011). However, installation and maintenance costs of green infrastructure
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systems, specifically vertical greening systems, are not always balanced within their life span by the
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(economic) benefits provided (Ottelé et al., 2011; Pérez et al., 2014b; Perini and Rosasco, 2013;
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Rosasco and Perini, 2019).
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Table 1: Main characteristics of green roofs and vertical greening systems (Bellomo, 2003; Fernández-
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Cañero et al., 2018; Manso and Castro-Gomes, 2015b; Medl et al., 2017; Ottelé et al., 2011; Pérez and
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Coma, 2018; Perini and Rosasco, 2016*, 2013; Rosasco, 2018**)
48 49 50 51 52
Green roofs Extensive
Vertical greening systems
Semi-intensive
Intensive
Direct green façade
Indirect green façade – Ground based
Indirect green façade – Wall based
Living Wall Boxes
Living Wall Felt
Depends on plant species
Depends on plant species and supporting material
Depends on planter boxes size, plant species and supporting materials
94 kg/m² + plant species
13 kg/m² + plant species
Creepers planted in the ground and cling directly to the wall
Light support structures for creepers of stainless steel or similar (cables, nets, trellis)
Planter boxes at different heights connected by means of light supporting structures for creepers
Container elements (galvanized steel, polyethylene, or recycled plastic) with organic substrate
Textile or nonwoven felt with pockets. Hydroponics.
-
-
-
-
Scheme/sk etch
Weight
Layers / materials / supportin g structure
2
50-150 Kg/m
Vegetation, substrate (thickness 6-20 cm), filter, drainage, root barrier, protection and water retention layers. Only accessible for maintenance (slope < 100%)
2
120-350 Kg/m
2
>350 Kg/m
Vegetation, substrate Vegetation, substrate (thickness 10-25 (thickness > 25 cm), cm), filter, drainage, filter, drainage, root root barrier, barrier, protection protection and water and water retention retention layers. layers. Pedestrian areas but with a moderate use (slope < 20%)
Pedestrian / recreation areas (slope < 5%)
Succulent, herbaceous and grasses
Herbaceous, grasses and shrubs, perennials
Herbaceous, grasses, shrubs and trees, perennials
Growing speed
Fast
Fast
Medium
Slow
Medium-slow
Medium-fast
Maintena nce
Low
Moderate
High
Low (2-5 €/m²/year)
Low (2-5 €/m²/year)
Low (5-7,5 €/m²/year)
Irrigation
Never or periodically
Periodically
Regularly
Use
Plant characteri stics
Costs
140-250 €/m² *
Mostly climbing and hanging plants
Periodically depending on plants and climate
22-39 €/m² **
127-270 €/m² **
190-365 €/m² (depending on system conception and material) **
Epiphytic, lithophytic and Bromeliads, ferns, succulent, herbaceous, small shrubs, climbers and even vegetables Fast Medium-high (40-100 €/m²/year)
High (40-100 €/m²/year)
Computerized irrigation (1-5 l/m2/day)
210-590 €/m² (depending on system conception and material) **
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Among the systems available on the market (Table 1), living wall systems can support a wide
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variety of plant species. An automated irrigation system covering the entire surface provides water
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and nutrients, according to the position and requirements of each plant species (Fernández-Cañero
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et al., 2018). Green façades based on climbers are generally cheaper and easy to maintain
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(Fernández-Cañero et al., 2018; Perini and Rosasco, 2013), but it is worth mentioning that, although
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the growing speed depends on several parameters (e.g., climate conditions, plant health, amount of
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soil available and species), it can range from 50 to 200 cm/year (Bellomo, 2003). Therefore
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climbers planted on the ground in front of a building can take few years to cover the whole
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buildings’ surface.
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Currently, few studies have been carried out on overcoming the economic limitations of vertical
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greening systems, including the development of a new living concrete material, which allows plants
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to grow directly on it, resulting in a 50% reduction in installation costs, compared to living wall
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systems, and a reduction in costs of maintenance (Riley et al., 2019).
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Since the effect of vegetation in cities is more important the more widespread it is, research is
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needed to find low-cost and low maintenance green envelopes for large-scale application in
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existing urban (e.g. social housing) or industrial buildings, where environmental and architectural
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regeneration interventions are often requested.
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Although mosses can cover and, in some cases, damage buildings, recent studies highlighted their
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potential use to protect buildings and other urban surfaces (Kaufman, 2016; Park and Murase,
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2008). Studies on insertion of mosses onto green roofs demonstrate good stormwater management
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of some moss species (Anderson et al., 2010; Brandão et al., 2017), the ability to decrease surface
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temperatures (Aisar et al., 2017), contribution to the mitigation of the UHI phenomenon (Khalid et
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al., 2017) and the feature of being more durable, resistant, light-weight and easy to maintain than
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vascular plants (Burszta-Adamiak et al., 2019).
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Mosses are the second most species-rich group of plants, after the enormously richer Angiosperms.
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a distinct lineage of Bryophytes that consist in about 12,750 recognized species worldwide (Crosby
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et al., 1999). Mosses have a mop-like structure, dominance of vegetative reproduction and thin
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“false” roots (rhizoids) that adhere to building surfaces (Aleffi and Tacchi, 2008). Mosses are an
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almost perfect sink for some elements, being able to tolerate high levels of salinity (salt crusts),
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metals (e.g., copper mosses) and air pollutants (ability to accumulate PMx), for this reason some
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taxa are commonly used as bioindicators for air quality monitoring (Aleffi and Tacchi, 2008;
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Szczepaniak and Biziuk, 2003).
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Higher plants have several useful characteristics, already extensively listed above, that cannot be
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found in mosses. However, mosses can survive in unfavourable environmental conditions because
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of their ecological needs in terms of growing substrates, low amount of water and nutrients
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required, ability to absorb liquids up to 20 times their weight and vegetative desiccation tolerance
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(Wood, 2007). Research is needed to clarify the possible use of mosses as green envelopes of
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building, growing directly on building materials, and to find the most performing species able to
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sustain stressful conditions such as those found on building surfaces (e.g., wind, solar radiation, air
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pollution, etc.).
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1.1 Aim of the study
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The aim of the study is to evaluate whether mosses could be suitable as a green envelope system,
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i.e. able to grow under limited water requirements and to cover horizontal/vertical surfaces, and
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under which environmental conditions. Spontaneous growth of mosses on buildings under certain
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microclimatic conditions is quite common, but research is needed to develop a promising new
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building coverage system and material.
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This research assesses the growing ability of mosses directly on building commonly used materials
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and low-cost materials, with different physical characteristics (structure and porosity). Tests were
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performed under controlled environmental conditions on horizontal and vertical surfaces to evaluate
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moss growth rate and homogeneity, level of maintenance required (water needs, physical and
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chemical influence of moss mixture- i.e., neutro-acidic for buttermilk moss-mixture, pH 5, or
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alkaline for water-moss mixture, pH 8), moss mixture performance with respect to biomass
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production. Verifying the growing capacity of mosses on such materials represents the first step for
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the evaluation of potential uses and performances of mosses as green envelopes.
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2. Materials and Methods
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The most promising moss taxa were selected by means of field sampling and literature screening.
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Five building materials were chosen for the subsequent experiments, allowing the identification of
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the characteristics needed for the mosses to grow. The study includes two experiments, on both
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horizontal and vertical surfaces, implemented in a growth chamber, described below. 2.1 Moss sampling
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Several taxa were collected in October-November 2018 from different edaphic conditions (e.g.,
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from soil to plaster, from low to high water availability, from shadow to full sunlight) at 350 m a.s.l.
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Details on the sampled mosses and related conditions are summarized in table 2. The pHs of the
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different substrates were also evaluated. Taxa were identified according to Cortini Pedrotti (Cortini
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Pedrotti, 2001). In moss sampling, it is not possible to count the number of individuals precisely,
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due to their small size. For this reason 10x10 cm moss samples were collected (Eldridge et al.,
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2003).
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Table 2: Determination of the sampled plant taxa and their respective habitats (Cortini Pedrotti, 2001).
124 Taxon
Family
Geographical coordinates
Sampling habitat
Common habitat
Isothecium myosuroides Brid.
Brachytheciaceae
44°29’06.28’’ N 8°50’15.18’’E
Soil, shady rocks, under shrubs. Dry stone wall mortar, sunny position.
Barbula unguiculata Hedw.
Pottiaceae
44°29’15.63’’ N 8°50’21.10’’E
Rhynchostegium confertum (Dicks.) Schimp.
Brachytheciaceae
44°29’14.45’’ N 8°50’20.77’’E
Hypnum jutlandicum Holmen & Warncke
Hypnaceae
44°29’16.64’’ N 8°50’21.29’’E
Hypnum sp.
Hypnaceae
44°29’16.19’’ N 8°50’21.15’’E
Rock, sunny position.
Brachythecium salebrosum (Hoffm. ex F. Weber & D. Mohr) Schimp.
Brachytheciaceae
44°29’13.43’’ N 8°50’19.55’’E
Isothecium alopecuroides (Lam. ex Dubois) Isov.
Brachytheciaceae
44°29’11.23’’ N 8°50’18.29’’E
Wood, shaded position in the undergrow th, wet environme nt. Concrete wall, sunny position.
Dry stone wall shaded by brambles and creepers. Rock, semishaded position.
Soil, base of trees, shady rocks, acid environments; from the plain to the mountain. Neutral or baserich, disturbed and open habitats such as the edges of paths, gardens, fields and old walls. Stones, rocks, walls, old stumps, damp, and shaded environments, both basic and acid. Soil, rocks, tree base, rotting wood, edge of marshes, dry or wet environments, exposed or shaded. Wide variety of habitats and climatic zones. It typically grows on tree trunks, logs, walls, rocks and other surfaces. It prefers acidic environments and is quite tolerant of pollution (Vujičić et al. 2011). Soil, rocks, stumps, base trees, humus forests, shaded environments, acids.
Base of trees, stumps and damp rocks, shady forests, along streams of water, rarely on stony ground.
125 126
2.2 Selection of plant taxa
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Among the sampled species, a screening was carried out to evaluate the greatest resistance to
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climatic conditions based on the ecological characteristics of each taxa as a discriminating factor.
129
Basing on literature and ecological requirements (wide species distribution, low water requirements,
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good coverage, high adaptability to different temperatures), Barbula unguiculata was the species
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chosen for subsequent growing experiment due to its ability to be more resistant than other sampled
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taxa with respect to high light radiation level and strong dehydration, and to be able to grow on
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walls and rocks with alkaline pHs (Segal, 2013). 2.3 Selection of building materials
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Five common (building) materials were selected, considering structure and porosity of the surface
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(Dassori, 2011). In addition to building materials – i.e. quartzite, plaster, slate, and brick – capillary
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matting, and gauze were chosen because of their application for floricultural purposes or their
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previous use to grow mosses (Park and Murase 2008), respectively. As shown in Table 3, the
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materials selected have different uses (e.g. coating, external and internal flooring, masonry,
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finishing of exterior and interior walls, growing plants) and physical characteristics. To implement
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the experiment, quartzite, slate, bricks and plaster were treated with the addition of gauze, as
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reported in literature (Kaufman, 2016). Lime and cement-based plasters were treated with a trowel
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to obtain a rougher surface, to allow better adhesion of the moss mixture.
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Table 3: Materials used for the experiment and related uses, characteristics and eventual surface treatment (Dassori 2011). Photo
Material
Common use
Physical characteristics
Surface treatment waterproof with a structured As is surface
Quartzite plates
coatings
Slate plates
roofing, external and waterproof with a structured As is internal flooring, surface coverings
Full bricks masonry, floors in terracotta coverings
and very porous with a structured As is surface
Lime based finishing of exterior very porous with a structured with a trowel finishing and interior walls surface. Holds moisture to obtain a plaster rougher surface
Finishing finishing of exterior very porous with a structured plaster based and interior walls surface. Holds moisture on white cement
Capillary matting
Gauze
with a trowel to obtain a rougher surface
water irrigation system in fabric, covered with a As is. for indoor plants, seed perforated plastic membrane The capillary trays, greenhouses on both sides, retains moisture matting was tested both by keeping both membranes and by removing one used to support rooting cotton net that promotes As is. of moss rhizoids on a rhizoid attachment and The gauze vertical surface moisture retention was applied (Kaufman, 2016) on half of each traditional building material considered
148 149
2.4 Experimental design and set up
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Two experiments in growth chamber were set up to establish the response in terms of biomass
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development on the different building materials used as growing support for the moss mixture,
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under controlled temperature and light and adequate water supply on horizontal and vertical
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surfaces. Since water could be a limiting factor in the development of new (vegetative) biomass and
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water flows easily on vertical surfaces, the experiment on horizontal surface was carried out first.
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The cultivation methods used direct application of the moss mixture onto the material surfaces.
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The tests were divided into two experiments (Figure 1): 1) horizontal surface to identify the moss
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response in terms of growth, with homogeneous water distribution and incident light (i.e. the light
158
that directly falls on the leaf surfaces), and to obtain information on the optimal water supply and
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better growing support for the moss mixture to develop new biomass and 2) vertical surface to test
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the same species with different water distribution and mixture response to gravity. The experiment
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on vertical surface was conducted on the most promising materials obtained after the test on
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horizontal surface.
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The experimental design can be applied to other species, adapting the supply of water and light.
164 165 166
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Figure 1: scheme of the experimental set-up.
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2.4.1
Test on horizontal surface
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The moss was cleaned from substrate residues and weighed. Dried B. unguiculata was hydrated
170
with 1:2 (w/v) deionized water. After removing the excess of water, the moss increased by about
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2/3 its weight.
172
Two types of moss application were prepared.
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1). Moss: water (1:2) mixture obtained by blending hydrated mosses;
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2). Moss: water: buttermilk 1:2:0.2 obtained by blending hydrated mosses with the addition
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of buttermilk.
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The mixtures of gametophytes of B. unguiculata were placed with a spatula to obtain a spot (about
177
1 mm thick and 5x5 cm wide) on the surfaces on different materials used. Each spot weighs
178
approximately 3.80 g, corresponding to 1.52 kg/m². Half of them were covered with gauze, except
179
for the capillary matting, for each growing surface 8 replicates were done (n=8 each covered
180
material and n=8 each uncovered material, as explained in figure 1).
181
Each application spot was clearly separated from the others, to avoid cross-contamination.
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The felt was placed in an open Petri dishes (glass-made) with and without its upper semi-waterproof
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film and submitted to hydration up to 70% WHC.
184
The mosses applications were monitored once a day, for 4 months (i.e. development of new
185
biomass , reached after about 3 months and kept under control for 1 month). Each spot was
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hydrated by spraying the surface with approximately 4 ml of deionized water for the first 40 days.
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The capillary matting was imbibed with the same amount of water.
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Afterwards, the amount of water was increased to 6.5 ml due to the thickening of the moss cushions
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with the production of new biomass.
190
Each material was moved regularly every 2 days to ensure that each of them received the same
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amount of light as the others.
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Gametophytes mixture was incubated in a growth chamber at 18±2°C, 20 µM/m²s light intensity,
193
photoperiod 12/12, 60% of relative humidity.
194
Each spot was photographed once a week to study the evolution of each application.
195
2.4.2
Test on vertical surface
196
Once the most effective materials, in terms of adhesion of the moss mixture and water capacity and
197
distribution, and application techniques, in term of growing capacity and new biomass production,
198
were established with horizontal experimentation, tests began on the vertical surface.
199
The materials were also chosen based on their characteristic surface roughness, to avoid moss
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washout. The materials (covered and uncovered with gauze) selected for the vertical experiments
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were: brick, lime-based plaster, cement-based plaster and capillary matting without waterproof
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membrane. For each material 8 replicates were made. Each replicate consisted of a portion of
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material approximately 5x5 cm and they were glued in groups of 4 on a 20x20 cm PVC panel.
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It was decided to adopt the compound consisting of moss and water, based on the results obtained in
205
the previously reported experiment. Application on the materials was performed differently from
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the tests carried out during the first phase, that is by dipping a brush in the compound and spreading
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the moss on the different materials.
208
The panels were hung from the grids inside the growth chamber, so that each of them received
209
direct light from the lamps.
210
Each spot was sprayed once a day with 10 ml of deionized water and panels were rotated every 3
211
days and moved off the shelf to partially reproduce less controlled conditions, such as in a natural
212
environment.
213
In addition, a constant daily water supply was provided on capillary matting. Capillary matting
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strips were applied to transfer water from a beaker to capillary matting samples on 8 replicates.
215
2.4.3
Data acquisition and processing
216
In order to analyse the surface covered by mosses, high resolution photographs were taken for each
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sample. In order to compare the surface covered by each sample, a portion corresponding to 4 x 4
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cm was extracted from the photographs and analysed with Adobe Photoshop and ImageJ software.
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ImageJ (http://imagej.nih.gov/ij/) allowed quantifying the coverage percentage of moss with respect
220
to the whole image.
221
2.4.4
Data analysis
222
One-way ANOVA with Tukey post-hoc test was performed to evaluate significant differences
223
among the selected moss mixture and substrates for the mosses applications on horizontal surface.
224
Results were presented as average (±standard deviations).
225 226
3. Results and Discussion
227
After two months of incubation new moss biomass was produced. The first results show that the
228
growing support is important for its physical characteristics because of its high-water retention and
229
homogeneous water distribution ability. Vertical surfaces have more physical limitations in terms of
230
water distribution and adhesion of moss mixture to the surface.
231
On horizontal surfaces the moss grows with preference: Capillary matting (67%) > cement plaster
232
(56%) > lime plaster (47%) > terracotta brick (35%) > slate (31%) > quartzite (8%).
233
The tests result on horizontal surfaces, under constant light conditions, show that the limiting
234
factors are given by the water distribution and by the physical (i.e., surface roughness and porosity
235
of the substrate that imply a better adhesion of the moss mixture) rather than the chemical (i.e.,
236
buttermilk-moss mixture vs. water-moss mixture) characteristics.
237
The coverage analyses on horizontal surfaces after 4 months show that capillary matting has the
238
highest performances in terms of moss growth, up to a maximum of 72% (samples with buttermilk
239
without waterproofing layer, table 4). The second interesting response is given by finishing cement
240
plaster where moss coverage reaches a maximum of 67% (samples with buttermilk and gauze and
241
water without gauze, table 4). The last potentially useful growing substrate is the finishing lime-
242
based plaster where moss coverage is up to 47% (samples with buttermilk and gauze, table 4). The
243
average moss coverage on terracotta bricks, slate and quartzite is not satisfying (35, 31 and 8%,
244
respectively, table 4).
245 246
Table 4: Binary images of the samples and mosses coverage (horizontal surfaces).
247 248 249
Error! Not a valid link.
250
ability (biomass production) of B. unguiculata (under controlled environmental conditions in a plant
251
growth chamber) on horizontal and vertical surfaces, mainly depends on the moss mixture together
252
with water accumulation and distribution (with and without gauze) and, subsequently, by physical
253
characteristics of the growing support for the moss mixture.
254
The one-way ANOVA (Fig. 2) highlights significant coverage differences among the moss mixtures
255
for different building surfaces. The highest moss coverage is shown on cement plaster, specifically
256
for buttermilk moss mixture and water moss mixture.
This study shows that mosses can grow on common building and low-cost materials. The growing
80
70
Coverage (%)
60
50
40
30
20
10
0 B
BG
W
WG
Moss mixture
257
Quartzite
Slate
Brick
Lime plaster
cement plaster
258 259
Figure 2. One-way ANOVA of moss coverage (%) respect to moss mixture (B: buttermilk mixture; BG:
260
buttermilk mixture with gauze; W: water mixture; WG: water mixture with gauze) on the different building
261
materials used as substrates. n=8 each moss mixture.
262 263 264
However, the qualitative stereomicroscope analysis shows that quartzite, brick, lime and cement
265
plaster seems to favour the almost exclusive presence of B. unguiculata, although a different taxon
266
(pleurocarpous moss, i.e., branched) is quite ubiquitous (with low coverage) in the different
267
substrates and mixtures. On the other hand, capillary matting houses numerous morphologically
268
distinguishable taxa favouring higher biodiversity, especially in the presence of a more acid
269
environment (obtained by adding buttermilk to the moss mixture). They can therefore be more
270
interesting in ecological terms.
271
The tests result on vertical surfaces allow verifying that, in the presence of strong steepness, the
272
water retention and distribution capacity of the substrate represents the major limiting factor for the
273
growth of moss and production of new biomass. On vertical surface, two main problems persist: (1)
274
washing away of the mixture over time on slate, quartzite, plaster and, in part, on brick if they are
275
not covered with a gripping support such as gauze (applied on the surface); (2) water absorption and
276
distribution capacity (key factor more evident than in horizontal tests).
277
Clearly different results were obtained between irrigation once a day (1.5 ml/cm2) with water
278
sprayed on moss spot and capillary water irrigation with no dehydration phase (1.9 ml/cm2), with
279
the same materials: constant irrigation led to the formation of faster biomass (i.e. growth period of 2
280
months vs. 15 days). The coverage analyses on the vertical water capillary matting (water mixture,
281
without waterproofing layer) revealed a low performance of this material when used vertically
282
(10.4%). Capillary matting system has the best overall performance. Even if this is the only material
283
on which moss grew vertically, an adequate irrigation system will help overcome the low coverage
284
on vertical surface linked to unequal water distribution.
285
A possible way to limit the washing away on vertical surfaces could be a mixture added with
286
colloidal substances that allows moss to generate new biomass (especially during the initial
287
adhesion and growth phase). Since the irrigation system remains the focal point for obtaining a
288
functional vertical greening system with low water costs, a little and constant water supply is more
289
efficient, especially during the first biomass production, with a subsequent decrease once the moss
290
cushion is formed (as it can retain moisture more easily).
291
Compared to Kaufman 2016, in which methods were tested to allow moss adhesion to jersey road
292
barriers, the present study highlights that the moss mixture can adhere to porous surfaces and
293
structured verticals - i.e. capillary matting, gauzed surfaces - but needs further study about the
294
smoothest surfaces - i.e. traditional building materials. Moreover, it highlights the need to design a
295
specific water system to guarantee the production of new biomass without the washing away
296
phenomenon, and at the same time to guarantee good evapotranspiration capacity, as indicated in
297
Park and Murase 2008, for lowering superficial temperature of buildings.
298
Mosses may contribute to ecosystem services provision in urban areas (Aisar et al., 2017; Anderson
299
et al., 2010; Brandão et al., 2017; Burszta-Adamiak et al., 2019; Khalid et al., 2017). In particular,
300
B. unguiculata is able to withstand high concentrations of pollutants (e.g., CKD emitted by cement
301
plant contains 40%–50% CaO, 12%–17% SiO2, 6%–9% K2O, 4%–8% SO3, 3%–5% Al2O3, 2%–
302
4% MgO, 2.8%–3.2% Fe2O3, in small amounts Mn, Zn, Cu and B) such as alkaline cement-dust
303
pollution (Paal and Degtjarenko, 2015) and is particularly tolerant to drying (Guo and Zhao, 2017).
304
The tests conducted show that, on horizontal surfaces compared to vertical ones, moss can grow on
305
a greater quantity of materials and it can be hydrated less frequently, since the water does not flow
306
away from the surface. However, it is possible to grow moss even on vertical surfaces by finding
307
the right support material (more porous to prevent the moss from being washed away, like capillary
308
matting) and minimal but constant irrigation, especially during the first phase, in which vegetative
309
reproduction takes place. The search for a suitable moss species (able to withstand variations in
310
light intensity, temperature and humidity), optimal support materials and the type of irrigation are
311
therefore the focal points for the success of the tests.
312
4. Conclusions
313
B. unguiculata can grow on commonly used building materials and alternative low-cost materials.
314
The growing ability (biomass production and surface covered) of the selected species depends on
315
the physical characteristics of the growing support for the moss mixture. The chemical composition
316
of the substrate does not influence moss coverage but the presence of a more acidic environment
317
(obtained with the addition of buttermilk in the moss mixture) increases the species richness. The
318
most influential physical characteristics involve water, in terms of retention capacity and
319
homogeneous distribution.
320
The tests under controlled environmental conditions showed that:
321
-
is capillary matting. On horizontal surfaces,
322 323
-
-
328
on vertical surfaces attention should be paid to water distribution and adhesion of moss mixture to the surface;
326 327
interesting results were also found for cement-based plaster (coverage of 56% on average) and lime-based plaster (coverage of 47% on average);
324 325
the most performing material for the moss growth on both horizontal and vertical surfaces
-
Irrigation system design to allow constant water provision is important for moss growth: low and constant water supply provides faster moss biomass development.
329
The results obtained so far show that the use of mosses in built environments could represent an
330
interesting and affordable solution for both horizontal and vertical surfaces. This type of greening –
331
with a single layer and low-cost materials – could allow overcoming the limits deriving from the
332
installation costs and maintenance needs of many greening systems available on the market (table 1)
333
(Perini and Rosasco, 2013). Although research is needed to quantify the ecosystem services which
334
moss walls and roofs could provide in urban areas (Aisar et al., 2017; Anderson et al., 2010; Heim
335
et al., 2014; Paal and Degtjarenko, 2015), this study shows an interesting potential for the
336
development of a system. This approach could stimulate the greening of existing buildings with low
337
budget availability, such as residential buildings in low income suburbs and neighbourhoods,
338
industrial areas, etc.
339
The tests also highlighted some challenges for the future development of a moss greening system,
340
i.e. water distribution and adhesion of moss mixture. Future research should be oriented on such
341
aspects. The adaptability of mosses to different environmental conditions will also be tested on site
342
and the performances will be evaluated.
343
This interdisciplinary study between plant biology and architecture provides a more comprehensive
344
way to identify new perspectives for greening urban surfaces.
345
346
Acknowledgements
347
The research was supported by PRA 2018 funding (Progetti di Ricerca di Ateneo 2018),
348
provided by the University of Genoa – DAD. Thanks are expressed to Davide Dagnino for
349
his helpful support during mosses identification.
350 351
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475
Highlights •
Mosses can be a low-cost and low-maintenance alternative to green envelope
•
Mosses have high vegetative desiccation tolerance and low growing requirements
•
Capillary matting, cement and lime plaster are suitable for horizontal moss growth
•
Water distribution limits mosses’ growth on vertical applications
Declaration of interests ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. ☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:
S0360-1323(20)30066-4
DOI:
https://doi.org/10.1016/j.buildenv.2020.106708
Reference:
BAE 106708
To appear in:
Building and Environment
Received Date: 6 November 2019 Revised Date:
24 January 2020
Accepted Date: 30 January 2020
Please cite this article as: Perini K, Castellari P, Giachetta A, Turcato C, Roccotiello E, Experiencing innovative biomaterials for buildings: potentialities of mosses, Building and Environment, https:// doi.org/10.1016/j.buildenv.2020.106708. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2020 Elsevier Ltd. All rights reserved.
1
Experiencing innovative biomaterials for buildings: potentialities of mosses
2
Katia Perini*a, Paola Castellaria, Andrea Giachettaa, Claudia Turcatob, Enrica Roccotiellob
3
*Corresponding author: [email protected] a
4 5 6 7
b
Polytechnic School of the University of Genoa, Architecture and Design Department, Italy
University of Genoa, Department of Earth Life and Environmental Sciences, Laboratory of Plant Biology, Genoa, Italy
8
Abstract
9
Vertical greening systems and green roofs provide ecosystem services in the urban context. Despite
10
the important benefits they provide, economic (initial and maintenance costs) and environmental
11
issues may limit the widespread diffusion of these greening systems. Mosses can be a low-cost and
12
low-maintenance alternative green envelope for large-scale application on existing urban and
13
industrial buildings thanks to their low requirements in terms of growing substrates, low amount of
14
water and nutrients needed, and high desiccation tolerance. The study assesses the’ growing ability
15
of mosses on building materials and low-cost materials, by means of growing tests performed under
16
controlled environmental conditions on horizontal and vertical surfaces. Moss growth depends
17
mainly on the physical characteristics of the materials, although an acidic moss mixture improves
18
species richness. Results show different surface coverage: capillary matting > cement plaster > lime
19
plaster > terracotta brick > slate > quartzite. The water retention capacity and its homogeneous
20
distribution on the growing surface are the limiting factors for moss growth.
21 22
1. Introduction
23
Urban areas pose significant environmental issues that have to be addressed, i.e. poor air quality
24
with high levels of PMx, NO2, O3 (European Environment Agency, 2018), the Urban Heat Island
25
phenomenon (Nakamatsu and Tsutsumi, 2002), the extreme alteration of urban surfaces (waterproof
26
artificial surfaces with low albedo) and water resources and the deterioration of the urban ecosystem
27
(Rees, 1997).
28
Urban greening is able to mitigate Urban Heat Island phenomenon (Alexandri et al., 2008; Armson
29
et al., 2012; Onishi et al., 2010), collect fine dusts and mitigate the vertical dispersion of gaseous
30
pollutants in urban canyons, with a consequent improvement in air, water and soil quality (Dover,
31
2018a; Perini and Roccotiello, 2018). Moreover, plants contribute to decrease the superficial water
32
flow (Livesley et al., 2014) and remove water pollutants (Jackson and Boutle, 2008), to improve
33
human wellbeing (Fjeld et al., 1998; Grahn and Stigsdotter, 2003; Ulrich, 1984) and support
34
biodiversity on an urban scale (Atkins, 2018).
35
Vertical greening systems and green roofs can provide ecosystem services within densely built
36
fabrics, to address a range of challenges facing urban areas (Dover, 2018b; Manso and Castro-
37
Gomes, 2015a). In addition, green envelopes work as thermal (Sadineni et al., 2011) and acoustic
38
protection (Wong et al., 2010) and as passive systems for energy savings (Coma et al., 2017; Pérez
39
et al., 2014a), contributing to building sustainability performances (Eumorfopoulou and Kontoleon,
40
2009; Ottelé et al., 2011). However, installation and maintenance costs of green infrastructure
41
systems, specifically vertical greening systems, are not always balanced within their life span by the
42
(economic) benefits provided (Ottelé et al., 2011; Pérez et al., 2014b; Perini and Rosasco, 2013;
43
Rosasco and Perini, 2019).
44 45
Table 1: Main characteristics of green roofs and vertical greening systems (Bellomo, 2003; Fernández-
46
Cañero et al., 2018; Manso and Castro-Gomes, 2015b; Medl et al., 2017; Ottelé et al., 2011; Pérez and
47
Coma, 2018; Perini and Rosasco, 2016*, 2013; Rosasco, 2018**)
48 49 50 51 52
Green roofs Extensive
Vertical greening systems
Semi-intensive
Intensive
Direct green façade
Indirect green façade – Ground based
Indirect green façade – Wall based
Living Wall Boxes
Living Wall Felt
Depends on plant species
Depends on plant species and supporting material
Depends on planter boxes size, plant species and supporting materials
94 kg/m² + plant species
13 kg/m² + plant species
Creepers planted in the ground and cling directly to the wall
Light support structures for creepers of stainless steel or similar (cables, nets, trellis)
Planter boxes at different heights connected by means of light supporting structures for creepers
Container elements (galvanized steel, polyethylene, or recycled plastic) with organic substrate
Textile or nonwoven felt with pockets. Hydroponics.
-
-
-
-
Scheme/sk etch
Weight
Layers / materials / supportin g structure
2
50-150 Kg/m
Vegetation, substrate (thickness 6-20 cm), filter, drainage, root barrier, protection and water retention layers. Only accessible for maintenance (slope < 100%)
2
120-350 Kg/m
2
>350 Kg/m
Vegetation, substrate Vegetation, substrate (thickness 10-25 (thickness > 25 cm), cm), filter, drainage, filter, drainage, root root barrier, barrier, protection protection and water and water retention retention layers. layers. Pedestrian areas but with a moderate use (slope < 20%)
Pedestrian / recreation areas (slope < 5%)
Succulent, herbaceous and grasses
Herbaceous, grasses and shrubs, perennials
Herbaceous, grasses, shrubs and trees, perennials
Growing speed
Fast
Fast
Medium
Slow
Medium-slow
Medium-fast
Maintena nce
Low
Moderate
High
Low (2-5 €/m²/year)
Low (2-5 €/m²/year)
Low (5-7,5 €/m²/year)
Irrigation
Never or periodically
Periodically
Regularly
Use
Plant characteri stics
Costs
140-250 €/m² *
Mostly climbing and hanging plants
Periodically depending on plants and climate
22-39 €/m² **
127-270 €/m² **
190-365 €/m² (depending on system conception and material) **
Epiphytic, lithophytic and Bromeliads, ferns, succulent, herbaceous, small shrubs, climbers and even vegetables Fast Medium-high (40-100 €/m²/year)
High (40-100 €/m²/year)
Computerized irrigation (1-5 l/m2/day)
210-590 €/m² (depending on system conception and material) **
53
Among the systems available on the market (Table 1), living wall systems can support a wide
54
variety of plant species. An automated irrigation system covering the entire surface provides water
55
and nutrients, according to the position and requirements of each plant species (Fernández-Cañero
56
et al., 2018). Green façades based on climbers are generally cheaper and easy to maintain
57
(Fernández-Cañero et al., 2018; Perini and Rosasco, 2013), but it is worth mentioning that, although
58
the growing speed depends on several parameters (e.g., climate conditions, plant health, amount of
59
soil available and species), it can range from 50 to 200 cm/year (Bellomo, 2003). Therefore
60
climbers planted on the ground in front of a building can take few years to cover the whole
61
buildings’ surface.
62
Currently, few studies have been carried out on overcoming the economic limitations of vertical
63
greening systems, including the development of a new living concrete material, which allows plants
64
to grow directly on it, resulting in a 50% reduction in installation costs, compared to living wall
65
systems, and a reduction in costs of maintenance (Riley et al., 2019).
66
Since the effect of vegetation in cities is more important the more widespread it is, research is
67
needed to find low-cost and low maintenance green envelopes for large-scale application in
68
existing urban (e.g. social housing) or industrial buildings, where environmental and architectural
69
regeneration interventions are often requested.
70
Although mosses can cover and, in some cases, damage buildings, recent studies highlighted their
71
potential use to protect buildings and other urban surfaces (Kaufman, 2016; Park and Murase,
72
2008). Studies on insertion of mosses onto green roofs demonstrate good stormwater management
73
of some moss species (Anderson et al., 2010; Brandão et al., 2017), the ability to decrease surface
74
temperatures (Aisar et al., 2017), contribution to the mitigation of the UHI phenomenon (Khalid et
75
al., 2017) and the feature of being more durable, resistant, light-weight and easy to maintain than
76
vascular plants (Burszta-Adamiak et al., 2019).
77
Mosses are the second most species-rich group of plants, after the enormously richer Angiosperms.
78
a distinct lineage of Bryophytes that consist in about 12,750 recognized species worldwide (Crosby
79
et al., 1999). Mosses have a mop-like structure, dominance of vegetative reproduction and thin
80
“false” roots (rhizoids) that adhere to building surfaces (Aleffi and Tacchi, 2008). Mosses are an
81
almost perfect sink for some elements, being able to tolerate high levels of salinity (salt crusts),
82
metals (e.g., copper mosses) and air pollutants (ability to accumulate PMx), for this reason some
83
taxa are commonly used as bioindicators for air quality monitoring (Aleffi and Tacchi, 2008;
84
Szczepaniak and Biziuk, 2003).
85
Higher plants have several useful characteristics, already extensively listed above, that cannot be
86
found in mosses. However, mosses can survive in unfavourable environmental conditions because
87
of their ecological needs in terms of growing substrates, low amount of water and nutrients
88
required, ability to absorb liquids up to 20 times their weight and vegetative desiccation tolerance
89
(Wood, 2007). Research is needed to clarify the possible use of mosses as green envelopes of
90
building, growing directly on building materials, and to find the most performing species able to
91
sustain stressful conditions such as those found on building surfaces (e.g., wind, solar radiation, air
92
pollution, etc.).
93 94
1.1 Aim of the study
95
The aim of the study is to evaluate whether mosses could be suitable as a green envelope system,
96
i.e. able to grow under limited water requirements and to cover horizontal/vertical surfaces, and
97
under which environmental conditions. Spontaneous growth of mosses on buildings under certain
98
microclimatic conditions is quite common, but research is needed to develop a promising new
99
building coverage system and material.
100
This research assesses the growing ability of mosses directly on building commonly used materials
101
and low-cost materials, with different physical characteristics (structure and porosity). Tests were
102
performed under controlled environmental conditions on horizontal and vertical surfaces to evaluate
103
moss growth rate and homogeneity, level of maintenance required (water needs, physical and
104
chemical influence of moss mixture- i.e., neutro-acidic for buttermilk moss-mixture, pH 5, or
105
alkaline for water-moss mixture, pH 8), moss mixture performance with respect to biomass
106
production. Verifying the growing capacity of mosses on such materials represents the first step for
107
the evaluation of potential uses and performances of mosses as green envelopes.
108 109
2. Materials and Methods
110
The most promising moss taxa were selected by means of field sampling and literature screening.
111
Five building materials were chosen for the subsequent experiments, allowing the identification of
112
the characteristics needed for the mosses to grow. The study includes two experiments, on both
113
horizontal and vertical surfaces, implemented in a growth chamber, described below. 2.1 Moss sampling
114 115
Several taxa were collected in October-November 2018 from different edaphic conditions (e.g.,
116
from soil to plaster, from low to high water availability, from shadow to full sunlight) at 350 m a.s.l.
117
Details on the sampled mosses and related conditions are summarized in table 2. The pHs of the
118
different substrates were also evaluated. Taxa were identified according to Cortini Pedrotti (Cortini
119
Pedrotti, 2001). In moss sampling, it is not possible to count the number of individuals precisely,
120
due to their small size. For this reason 10x10 cm moss samples were collected (Eldridge et al.,
121
2003).
122 123
Table 2: Determination of the sampled plant taxa and their respective habitats (Cortini Pedrotti, 2001).
124 Taxon
Family
Geographical coordinates
Sampling habitat
Common habitat
Isothecium myosuroides Brid.
Brachytheciaceae
44°29’06.28’’ N 8°50’15.18’’E
Soil, shady rocks, under shrubs. Dry stone wall mortar, sunny position.
Barbula unguiculata Hedw.
Pottiaceae
44°29’15.63’’ N 8°50’21.10’’E
Rhynchostegium confertum (Dicks.) Schimp.
Brachytheciaceae
44°29’14.45’’ N 8°50’20.77’’E
Hypnum jutlandicum Holmen & Warncke
Hypnaceae
44°29’16.64’’ N 8°50’21.29’’E
Hypnum sp.
Hypnaceae
44°29’16.19’’ N 8°50’21.15’’E
Rock, sunny position.
Brachythecium salebrosum (Hoffm. ex F. Weber & D. Mohr) Schimp.
Brachytheciaceae
44°29’13.43’’ N 8°50’19.55’’E
Isothecium alopecuroides (Lam. ex Dubois) Isov.
Brachytheciaceae
44°29’11.23’’ N 8°50’18.29’’E
Wood, shaded position in the undergrow th, wet environme nt. Concrete wall, sunny position.
Dry stone wall shaded by brambles and creepers. Rock, semishaded position.
Soil, base of trees, shady rocks, acid environments; from the plain to the mountain. Neutral or baserich, disturbed and open habitats such as the edges of paths, gardens, fields and old walls. Stones, rocks, walls, old stumps, damp, and shaded environments, both basic and acid. Soil, rocks, tree base, rotting wood, edge of marshes, dry or wet environments, exposed or shaded. Wide variety of habitats and climatic zones. It typically grows on tree trunks, logs, walls, rocks and other surfaces. It prefers acidic environments and is quite tolerant of pollution (Vujičić et al. 2011). Soil, rocks, stumps, base trees, humus forests, shaded environments, acids.
Base of trees, stumps and damp rocks, shady forests, along streams of water, rarely on stony ground.
125 126
2.2 Selection of plant taxa
127
Among the sampled species, a screening was carried out to evaluate the greatest resistance to
128
climatic conditions based on the ecological characteristics of each taxa as a discriminating factor.
129
Basing on literature and ecological requirements (wide species distribution, low water requirements,
130
good coverage, high adaptability to different temperatures), Barbula unguiculata was the species
131
chosen for subsequent growing experiment due to its ability to be more resistant than other sampled
132
taxa with respect to high light radiation level and strong dehydration, and to be able to grow on
133
walls and rocks with alkaline pHs (Segal, 2013). 2.3 Selection of building materials
134 135
Five common (building) materials were selected, considering structure and porosity of the surface
136
(Dassori, 2011). In addition to building materials – i.e. quartzite, plaster, slate, and brick – capillary
137
matting, and gauze were chosen because of their application for floricultural purposes or their
138
previous use to grow mosses (Park and Murase 2008), respectively. As shown in Table 3, the
139
materials selected have different uses (e.g. coating, external and internal flooring, masonry,
140
finishing of exterior and interior walls, growing plants) and physical characteristics. To implement
141
the experiment, quartzite, slate, bricks and plaster were treated with the addition of gauze, as
142
reported in literature (Kaufman, 2016). Lime and cement-based plasters were treated with a trowel
143
to obtain a rougher surface, to allow better adhesion of the moss mixture.
144 145 146 147
Table 3: Materials used for the experiment and related uses, characteristics and eventual surface treatment (Dassori 2011). Photo
Material
Common use
Physical characteristics
Surface treatment waterproof with a structured As is surface
Quartzite plates
coatings
Slate plates
roofing, external and waterproof with a structured As is internal flooring, surface coverings
Full bricks masonry, floors in terracotta coverings
and very porous with a structured As is surface
Lime based finishing of exterior very porous with a structured with a trowel finishing and interior walls surface. Holds moisture to obtain a plaster rougher surface
Finishing finishing of exterior very porous with a structured plaster based and interior walls surface. Holds moisture on white cement
Capillary matting
Gauze
with a trowel to obtain a rougher surface
water irrigation system in fabric, covered with a As is. for indoor plants, seed perforated plastic membrane The capillary trays, greenhouses on both sides, retains moisture matting was tested both by keeping both membranes and by removing one used to support rooting cotton net that promotes As is. of moss rhizoids on a rhizoid attachment and The gauze vertical surface moisture retention was applied (Kaufman, 2016) on half of each traditional building material considered
148 149
2.4 Experimental design and set up
150
Two experiments in growth chamber were set up to establish the response in terms of biomass
151
development on the different building materials used as growing support for the moss mixture,
152
under controlled temperature and light and adequate water supply on horizontal and vertical
153
surfaces. Since water could be a limiting factor in the development of new (vegetative) biomass and
154
water flows easily on vertical surfaces, the experiment on horizontal surface was carried out first.
155
The cultivation methods used direct application of the moss mixture onto the material surfaces.
156
The tests were divided into two experiments (Figure 1): 1) horizontal surface to identify the moss
157
response in terms of growth, with homogeneous water distribution and incident light (i.e. the light
158
that directly falls on the leaf surfaces), and to obtain information on the optimal water supply and
159
better growing support for the moss mixture to develop new biomass and 2) vertical surface to test
160
the same species with different water distribution and mixture response to gravity. The experiment
161
on vertical surface was conducted on the most promising materials obtained after the test on
162
horizontal surface.
163
The experimental design can be applied to other species, adapting the supply of water and light.
164 165 166
167
Figure 1: scheme of the experimental set-up.
168
2.4.1
Test on horizontal surface
169
The moss was cleaned from substrate residues and weighed. Dried B. unguiculata was hydrated
170
with 1:2 (w/v) deionized water. After removing the excess of water, the moss increased by about
171
2/3 its weight.
172
Two types of moss application were prepared.
173
1). Moss: water (1:2) mixture obtained by blending hydrated mosses;
174
2). Moss: water: buttermilk 1:2:0.2 obtained by blending hydrated mosses with the addition
175
of buttermilk.
176
The mixtures of gametophytes of B. unguiculata were placed with a spatula to obtain a spot (about
177
1 mm thick and 5x5 cm wide) on the surfaces on different materials used. Each spot weighs
178
approximately 3.80 g, corresponding to 1.52 kg/m². Half of them were covered with gauze, except
179
for the capillary matting, for each growing surface 8 replicates were done (n=8 each covered
180
material and n=8 each uncovered material, as explained in figure 1).
181
Each application spot was clearly separated from the others, to avoid cross-contamination.
182
The felt was placed in an open Petri dishes (glass-made) with and without its upper semi-waterproof
183
film and submitted to hydration up to 70% WHC.
184
The mosses applications were monitored once a day, for 4 months (i.e. development of new
185
biomass , reached after about 3 months and kept under control for 1 month). Each spot was
186
hydrated by spraying the surface with approximately 4 ml of deionized water for the first 40 days.
187
The capillary matting was imbibed with the same amount of water.
188
Afterwards, the amount of water was increased to 6.5 ml due to the thickening of the moss cushions
189
with the production of new biomass.
190
Each material was moved regularly every 2 days to ensure that each of them received the same
191
amount of light as the others.
192
Gametophytes mixture was incubated in a growth chamber at 18±2°C, 20 µM/m²s light intensity,
193
photoperiod 12/12, 60% of relative humidity.
194
Each spot was photographed once a week to study the evolution of each application.
195
2.4.2
Test on vertical surface
196
Once the most effective materials, in terms of adhesion of the moss mixture and water capacity and
197
distribution, and application techniques, in term of growing capacity and new biomass production,
198
were established with horizontal experimentation, tests began on the vertical surface.
199
The materials were also chosen based on their characteristic surface roughness, to avoid moss
200
washout. The materials (covered and uncovered with gauze) selected for the vertical experiments
201
were: brick, lime-based plaster, cement-based plaster and capillary matting without waterproof
202
membrane. For each material 8 replicates were made. Each replicate consisted of a portion of
203
material approximately 5x5 cm and they were glued in groups of 4 on a 20x20 cm PVC panel.
204
It was decided to adopt the compound consisting of moss and water, based on the results obtained in
205
the previously reported experiment. Application on the materials was performed differently from
206
the tests carried out during the first phase, that is by dipping a brush in the compound and spreading
207
the moss on the different materials.
208
The panels were hung from the grids inside the growth chamber, so that each of them received
209
direct light from the lamps.
210
Each spot was sprayed once a day with 10 ml of deionized water and panels were rotated every 3
211
days and moved off the shelf to partially reproduce less controlled conditions, such as in a natural
212
environment.
213
In addition, a constant daily water supply was provided on capillary matting. Capillary matting
214
strips were applied to transfer water from a beaker to capillary matting samples on 8 replicates.
215
2.4.3
Data acquisition and processing
216
In order to analyse the surface covered by mosses, high resolution photographs were taken for each
217
sample. In order to compare the surface covered by each sample, a portion corresponding to 4 x 4
218
cm was extracted from the photographs and analysed with Adobe Photoshop and ImageJ software.
219
ImageJ (http://imagej.nih.gov/ij/) allowed quantifying the coverage percentage of moss with respect
220
to the whole image.
221
2.4.4
Data analysis
222
One-way ANOVA with Tukey post-hoc test was performed to evaluate significant differences
223
among the selected moss mixture and substrates for the mosses applications on horizontal surface.
224
Results were presented as average (±standard deviations).
225 226
3. Results and Discussion
227
After two months of incubation new moss biomass was produced. The first results show that the
228
growing support is important for its physical characteristics because of its high-water retention and
229
homogeneous water distribution ability. Vertical surfaces have more physical limitations in terms of
230
water distribution and adhesion of moss mixture to the surface.
231
On horizontal surfaces the moss grows with preference: Capillary matting (67%) > cement plaster
232
(56%) > lime plaster (47%) > terracotta brick (35%) > slate (31%) > quartzite (8%).
233
The tests result on horizontal surfaces, under constant light conditions, show that the limiting
234
factors are given by the water distribution and by the physical (i.e., surface roughness and porosity
235
of the substrate that imply a better adhesion of the moss mixture) rather than the chemical (i.e.,
236
buttermilk-moss mixture vs. water-moss mixture) characteristics.
237
The coverage analyses on horizontal surfaces after 4 months show that capillary matting has the
238
highest performances in terms of moss growth, up to a maximum of 72% (samples with buttermilk
239
without waterproofing layer, table 4). The second interesting response is given by finishing cement
240
plaster where moss coverage reaches a maximum of 67% (samples with buttermilk and gauze and
241
water without gauze, table 4). The last potentially useful growing substrate is the finishing lime-
242
based plaster where moss coverage is up to 47% (samples with buttermilk and gauze, table 4). The
243
average moss coverage on terracotta bricks, slate and quartzite is not satisfying (35, 31 and 8%,
244
respectively, table 4).
245 246
Table 4: Binary images of the samples and mosses coverage (horizontal surfaces).
247 248 249
Error! Not a valid link.
250
ability (biomass production) of B. unguiculata (under controlled environmental conditions in a plant
251
growth chamber) on horizontal and vertical surfaces, mainly depends on the moss mixture together
252
with water accumulation and distribution (with and without gauze) and, subsequently, by physical
253
characteristics of the growing support for the moss mixture.
254
The one-way ANOVA (Fig. 2) highlights significant coverage differences among the moss mixtures
255
for different building surfaces. The highest moss coverage is shown on cement plaster, specifically
256
for buttermilk moss mixture and water moss mixture.
This study shows that mosses can grow on common building and low-cost materials. The growing
80
70
Coverage (%)
60
50
40
30
20
10
0 B
BG
W
WG
Moss mixture
257
Quartzite
Slate
Brick
Lime plaster
cement plaster
258 259
Figure 2. One-way ANOVA of moss coverage (%) respect to moss mixture (B: buttermilk mixture; BG:
260
buttermilk mixture with gauze; W: water mixture; WG: water mixture with gauze) on the different building
261
materials used as substrates. n=8 each moss mixture.
262 263 264
However, the qualitative stereomicroscope analysis shows that quartzite, brick, lime and cement
265
plaster seems to favour the almost exclusive presence of B. unguiculata, although a different taxon
266
(pleurocarpous moss, i.e., branched) is quite ubiquitous (with low coverage) in the different
267
substrates and mixtures. On the other hand, capillary matting houses numerous morphologically
268
distinguishable taxa favouring higher biodiversity, especially in the presence of a more acid
269
environment (obtained by adding buttermilk to the moss mixture). They can therefore be more
270
interesting in ecological terms.
271
The tests result on vertical surfaces allow verifying that, in the presence of strong steepness, the
272
water retention and distribution capacity of the substrate represents the major limiting factor for the
273
growth of moss and production of new biomass. On vertical surface, two main problems persist: (1)
274
washing away of the mixture over time on slate, quartzite, plaster and, in part, on brick if they are
275
not covered with a gripping support such as gauze (applied on the surface); (2) water absorption and
276
distribution capacity (key factor more evident than in horizontal tests).
277
Clearly different results were obtained between irrigation once a day (1.5 ml/cm2) with water
278
sprayed on moss spot and capillary water irrigation with no dehydration phase (1.9 ml/cm2), with
279
the same materials: constant irrigation led to the formation of faster biomass (i.e. growth period of 2
280
months vs. 15 days). The coverage analyses on the vertical water capillary matting (water mixture,
281
without waterproofing layer) revealed a low performance of this material when used vertically
282
(10.4%). Capillary matting system has the best overall performance. Even if this is the only material
283
on which moss grew vertically, an adequate irrigation system will help overcome the low coverage
284
on vertical surface linked to unequal water distribution.
285
A possible way to limit the washing away on vertical surfaces could be a mixture added with
286
colloidal substances that allows moss to generate new biomass (especially during the initial
287
adhesion and growth phase). Since the irrigation system remains the focal point for obtaining a
288
functional vertical greening system with low water costs, a little and constant water supply is more
289
efficient, especially during the first biomass production, with a subsequent decrease once the moss
290
cushion is formed (as it can retain moisture more easily).
291
Compared to Kaufman 2016, in which methods were tested to allow moss adhesion to jersey road
292
barriers, the present study highlights that the moss mixture can adhere to porous surfaces and
293
structured verticals - i.e. capillary matting, gauzed surfaces - but needs further study about the
294
smoothest surfaces - i.e. traditional building materials. Moreover, it highlights the need to design a
295
specific water system to guarantee the production of new biomass without the washing away
296
phenomenon, and at the same time to guarantee good evapotranspiration capacity, as indicated in
297
Park and Murase 2008, for lowering superficial temperature of buildings.
298
Mosses may contribute to ecosystem services provision in urban areas (Aisar et al., 2017; Anderson
299
et al., 2010; Brandão et al., 2017; Burszta-Adamiak et al., 2019; Khalid et al., 2017). In particular,
300
B. unguiculata is able to withstand high concentrations of pollutants (e.g., CKD emitted by cement
301
plant contains 40%–50% CaO, 12%–17% SiO2, 6%–9% K2O, 4%–8% SO3, 3%–5% Al2O3, 2%–
302
4% MgO, 2.8%–3.2% Fe2O3, in small amounts Mn, Zn, Cu and B) such as alkaline cement-dust
303
pollution (Paal and Degtjarenko, 2015) and is particularly tolerant to drying (Guo and Zhao, 2017).
304
The tests conducted show that, on horizontal surfaces compared to vertical ones, moss can grow on
305
a greater quantity of materials and it can be hydrated less frequently, since the water does not flow
306
away from the surface. However, it is possible to grow moss even on vertical surfaces by finding
307
the right support material (more porous to prevent the moss from being washed away, like capillary
308
matting) and minimal but constant irrigation, especially during the first phase, in which vegetative
309
reproduction takes place. The search for a suitable moss species (able to withstand variations in
310
light intensity, temperature and humidity), optimal support materials and the type of irrigation are
311
therefore the focal points for the success of the tests.
312
4. Conclusions
313
B. unguiculata can grow on commonly used building materials and alternative low-cost materials.
314
The growing ability (biomass production and surface covered) of the selected species depends on
315
the physical characteristics of the growing support for the moss mixture. The chemical composition
316
of the substrate does not influence moss coverage but the presence of a more acidic environment
317
(obtained with the addition of buttermilk in the moss mixture) increases the species richness. The
318
most influential physical characteristics involve water, in terms of retention capacity and
319
homogeneous distribution.
320
The tests under controlled environmental conditions showed that:
321
-
is capillary matting. On horizontal surfaces,
322 323
-
-
328
on vertical surfaces attention should be paid to water distribution and adhesion of moss mixture to the surface;
326 327
interesting results were also found for cement-based plaster (coverage of 56% on average) and lime-based plaster (coverage of 47% on average);
324 325
the most performing material for the moss growth on both horizontal and vertical surfaces
-
Irrigation system design to allow constant water provision is important for moss growth: low and constant water supply provides faster moss biomass development.
329
The results obtained so far show that the use of mosses in built environments could represent an
330
interesting and affordable solution for both horizontal and vertical surfaces. This type of greening –
331
with a single layer and low-cost materials – could allow overcoming the limits deriving from the
332
installation costs and maintenance needs of many greening systems available on the market (table 1)
333
(Perini and Rosasco, 2013). Although research is needed to quantify the ecosystem services which
334
moss walls and roofs could provide in urban areas (Aisar et al., 2017; Anderson et al., 2010; Heim
335
et al., 2014; Paal and Degtjarenko, 2015), this study shows an interesting potential for the
336
development of a system. This approach could stimulate the greening of existing buildings with low
337
budget availability, such as residential buildings in low income suburbs and neighbourhoods,
338
industrial areas, etc.
339
The tests also highlighted some challenges for the future development of a moss greening system,
340
i.e. water distribution and adhesion of moss mixture. Future research should be oriented on such
341
aspects. The adaptability of mosses to different environmental conditions will also be tested on site
342
and the performances will be evaluated.
343
This interdisciplinary study between plant biology and architecture provides a more comprehensive
344
way to identify new perspectives for greening urban surfaces.
345
346
Acknowledgements
347
The research was supported by PRA 2018 funding (Progetti di Ricerca di Ateneo 2018),
348
provided by the University of Genoa – DAD. Thanks are expressed to Davide Dagnino for
349
his helpful support during mosses identification.
350 351
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Highlights •
Mosses can be a low-cost and low-maintenance alternative to green envelope
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Mosses have high vegetative desiccation tolerance and low growing requirements
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Capillary matting, cement and lime plaster are suitable for horizontal moss growth
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Water distribution limits mosses’ growth on vertical applications
Declaration of interests ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. ☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: