Distribution patterns of Batrachium communities in Mediterranean hard waters

Acta Oecologica 52 (2013) 10e14

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Original article

Distribution patterns of Batrachium communities in Mediterranean hard waters Ana Lumbreras*, Cristina Pardo, José A. Molina Departamento de Biología Vegetal II, Universidad Complutense de Madrid, Plaza Ramón y Cajal s/n, 28040 Madrid, Spain

a r t i c l e i n f o

a b s t r a c t

Article history: Received 29 November 2012 Accepted 24 May 2013 Available online 20 July 2013

The greatest number of Batrachium plant-communities is reached in base-poor waters of SW Europe where most Batrachium species develop laminar leaves. In contrast, base-rich waters of the Western Mediterranean are characterized by few Batrachium communities and by the only one Batrachium species present in the area with only dissected leaves. This work focused initially on studying the water ecology of Iberian Batrachium communities’ developing in hard waters in order to seek to what extend the water physicalechemical gradient determines the occurrence of heterophyllous or homophyllous-dissected species. Floristic data and water physicalechemical data were analyzed using multivariate and comparative methods. We found two main types of Batrachium communities: community of Ranunculus trichophyllus e homophyllous and dissected speciese, and community of Ranunculus penicillatus e heterophyllous speciese. Alkalinity degree is the main factor separating both communities. Our results of a tentative survey on Batrachium composition in hard waters in the Eastern Mediterranean showed a wider range of physicalechemical water features as well as a greater number of Batrachium species with only dissected leaves in comparison to Western Mediterranean. We conclude that high alkalinity is related to the occurrence of Batrachium communities characterized by species with only dissected leaves in both the western and eastern parts of Mediterranean Europe. Ó 2013 Elsevier Masson SAS. All rights reserved.

Keywords: Aquatic Ranunculus species Community ecology Freshwater ecology Iberian Peninsula

1. Introduction Aquatic white-flowered ranunculi [Ranunculus subgenus Batrachium (DC.) A. Gray] include heterophyllous species with both laminar and dissected leaves, as well as homophyllous species with only one type of leaf, either laminar or dissected (Cook, 1966). Water crowfoot are mainly found in Eurasia (Cook, 1963; Lumbreras et al., 2011). Batrachium species grow in a wide range of freshwater ecosystems, including different types of water flow and regime (still and flowing waters; permanent and seasonal waters) and nutrient states (Spink et al., 1990; Mony et al., 2006). Water ecology has been widely related with Batrachium distribution-patterns (Géhu and Meriaux, 1983; Boeger, 1992; Spink et al., 1990; Mony et al., 2006). Within water factors, alkalinity has been highlighted as a major factor responsible for distribution in species from different genera such as Isoetes, Potamogeton and Ranunculus (Vestergaard and Sand-Jensen, 2000; Lumbreras et al., 2009). Water alkalinity is closely related to conductivity, the sum of cations,

* Corresponding author. Tel.: þ34 913941770; fax: þ34 913941774. E-mail addresses: [email protected] (A. Lumbreras), [email protected] (C. Pardo), [email protected] (J.A. Molina). 1146-609X/$ e see front matter Ó 2013 Elsevier Masson SAS. All rights reserved. http://dx.doi.org/10.1016/j.actao.2013.05.009

calcium plus magnesium, and hardness in most freshwaters (Stumm and Morgan, 1981) and it is connected with bedrock composition (Margalef, 1981). Terrestrial ecosystems show a positive correlation between species richness and soil pH in floristic regions such as the Mediterranean, which is an evolutionary centre on high pH soils (Pärtel, 2002). However, in aquatic ecosystems, this pattern may not work since water pH influences carbon availability for aquatic plants, and their photosynthetic activity becomes constrained by the increased pH (Bowes, 1987). Moreover, hydrophytes richness has been negatively associated with water conductivity (Herault and Thoen, 2009). Impoverishment in the number of certain aquatic plantcommunities such as Batrachium communities has been described along an increasing alkalinity gradient in freshwater western Mediterranean ecosystems at a local scale (Lumbreras et al., 2009). In SW Europe most Batrachium species consist of laminar-leaved species e e.g. Ranunculus omiophyllus Ten., Ranunculus ololeucos Lloyd, Ranunculus peltatus Schrank, Ranunculus tripartitus DC. e growing in base-poor freshwater habitats (Pizarro, 1995). In contrast, Eastern Europe shows a greater number of water crowfoot species of only dissected leaves occurring in calcareous waters. These include Ranunculus sphaerospermus Boiss. & Blanche, Ranunculus rionii Lagger, Ranunculus circinatus Sibth., and

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Ranunculus trichophyllus Chaix, being the later the only dissectedleaved species found on both sides of Europe (Cook, 1993). Some habitat studies on Batrachium communities have been undertaken in Western Europe (Mony et al., 2006; Lumbreras et al., 2009, 2013). However, there are as yet no specific studies on the distribution patterns of Batrachium communities growing in baserich waters. This work aims to answer the following questions: a) which Batrachium communities do occur in Western Mediterranean base-rich freshwaters? and b) is morphological variation of leaf traits related to water physicalechemical gradient in Batrachium? Answers to these questions are interesting for their application in conservation and restoration of Mediterranean freshwater ecosystems. We also provide arguments to the question of why Western Mediterranean freshwaters has a restricted biodiversity for water crowfoot with only dissected leaves, in comparison with Eastern Mediterranean freshwaters. 2. Material and methods 2.1. Data collection The sampling was focused on Iberian freshwater ecosystems occurring in base-rich lithologies, limestone and marl (IGME-ITGE, 2001), in an area of approximately 92,500 km2 delimited by the grid squares between 2 and 6 300 W and 39 300 - 40 N. A stratified sampling was designed taking into account the representativity of the bioclimatic, lithological and habitat categories present in the territory (Kent and Coker, 1992). 107 localities were previously chosen to visit according to Batrachium bibliographic references and herbarium citations. Batrachium communities were only found in 23 sites which correspond to less than one quarter of the visited localities. In some localities where Batrachium was not found the freshwater ecosystems had disappeared or seriously transformed, in others visible signs of eutrophication were detected. Nevertheless, our sampling covers all the freshwater ecosystem types and bioclimates present in the territory. The sampling was done in the Batrachium’ flowering period ethe moment of optimum development in plant communitiese between March and May 2009. The vegetation relevé was done in visually homogenous plots using the Braun-Blanquet scale of species cover/abundance (Braun-Blanquet, 1979). The plot size was of 4 m2. The water-depth was noted in each site. Six sites from Eastern Europe (four Greek and two Czech) were chosen and studied with the same procedures used in the Iberian localities. Within each of the final locations, we took two samples of water, once; we consider this procedure guarantees the representativity of our data in extensive studies (Lumbreras et al., 2009, 2013). The following water parameters were measured in situ: pH, conductivity, O2, water temperature and water flow. Two aliquots were collected for the physicalechemical analyses: one of one liter and another of half a liter, to which nitric acid was added until a pH of less than 2 was attained, and then kept at 4  C until testing. The following parameters were determined in the laboratory (APHA, 1998): chemical oxygen demand (COD) by oxidability, alkalinity by acidebase evaluation, ammonium, nitrites, nitrates, phosphates by colourimetry, sulphates by turbidimetry, sodium and potassium by flame photometry, and calcium and magnesium by atomic absorption spectrophotometry.

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Multivariate techniques allow identification of important discriminant variables related to the physics and chemistry of the aquatic environment (ter Braak and Verdonschot, 1995; Kowalkowski et al., 2006). Sites were classified based on physicalechemical water features using a space-dilating strategy (McGarigal et al., 2000). We chose the incremental sum of squares as distance-optimizing clustering and Chord distance to compute the distance between each pair of samples. The program used in the classification analysis was Syntax 2000 (Podani, 2001). Two main groups were identified: R. trichophyllus communities, and other Batrachium communities. Water parameters were analyzed separately using Student’s t-test to determine whether the differences between the two main groups in the water classification were significant, using STATGRAPHICS plus 5. The specieseenvironment relationship in R. trichophyllus communities was studied using a direct gradient analysis, since these communities were revealed by previous analysis as being typical of hard waters. An initial detrended correspondence analysis (DCA) was carried out to determine the gradient lengths before deciding on the most appropriate method for analysis. A redundancy analysis (RDA) was carried out to identify the main environmental gradients and the effect of specific environmental variables in R. trichophyllus communities, using the CANOCO program, version 4.5 (ter Braak and Smilauer, 2002). A PCA was carried out with Iberian, Greek and Czech samples based on physicalechemical water data in order to condense the original set of variables into a smaller set of new composite dimensions (McGarigal et al.,2000) by using the Syntax 2000 program (Podani, 2001). 3. Results 3.1. Plant communities Two main Iberian Batrachium communities were identified in hard waters by cluster analysis using floristic data as variables as it can be seen in Fig. 1. Cluster I comprised sites with Ranunculus penicillatus as the dominant species, and one site with Ranunculus aquatilis L.; while cluster II -which includes most of the sites- was composed of R. trichophyllus communities. Cluster II was split in two subgroups. Subgroup IIa included communities with a low abundance of R. trichophyllus, although there was commonly a high abundance of Callitriche brutia Petagna and R. peltatus Schrank. Subgroup IIb is characterized by a high abundance of

2.2. Statistical analysis Classification analysis of the floristic data was performed to determine plant community types using Kendall’s tau as coefficient for an ordinal classification. Mean species richness was calculated for Batrachium communities growing in base-rich water.

Fig. 1. Classification of sites based on floristical data of Batrachium communities developing in the base-rich water bodies on the Iberian Peninsula. Circles ¼ R. trichophyllus communities; triangles ¼ R. trichophyllus and R. peltatus communities; squares ¼ R. penicillatus communities; diamond ¼ R. aquatilis community.

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R. trichophyllus, and an absence of R. peltatus and C. brutia. The richness in Batrachium communities was low (mean richness ¼ 3.6), and ranged from 1 to 8 species. The most frequent accompanying hydrophytes were C. brutia and Potamogeton densus L. The most frequent accompanying helophytes were Glyceria declinata Bréb., Glyceria notata Chevall., Eleocharis palustris (L.) Roem. & Schult., Apium nodiflorum (L.) Lag., and Veronica anagallis-aquatica L. The rest are mainly marginal helophytes from grass on the margins.

3.2. Ecological segregation The dendrogram generated in the classification of the sites based on the physicalechemical data of the water as variables showed two different clusters (Fig. 2). These two clusters each included the same samples as those based on floristic composition. Cluster A comprised the sites without R. trichophyllus (it corresponds to cluster I from floristical classification, Fig. 1), whereas cluster B was composed of sites with R. trichophyllus (it corresponds to cluster II from floristical classification, Fig. 1). Cluster A was characterized by lower values of alkalinity, conductivity, calcium, magnesium and COD, and higher values of flow and phosphates than in cluster B. The Student’s test performed for each parameter corroborates these results (Table 1). Alkalinity and flow were the only parameters for which the ranges did not overlap between clusters. All the sites in cluster A corresponded to flowing waters. The analogies between the classification of the plant communities and the classification of the waters highlight the close relationship between these species and the waters in which they live. A detailed analysis of the water chemistry of R. trichophyllus communities differentiated four situations (Fig. 2, Cluster B). Subgroup B1 included still water bodies with lower values of sulphates, magnesium, alkalinity and pH. This subgroup included the sites of subgroup Ib from the floristic classification. It is worth noting that all of them were found in transitional zones between calcareous and silicate substrates, and could thus be considered ecotones. Subgroup B2 included seasonal streams with high values of nitrates and flow. Subgroup B3 included still-water bodies eshallow seasonal pondse with high values of pH and no flow. Subgroup B4 included rivers, streams and ponds with the highest values of sulphates. Axis 1 of the triplot of the RDA (Fig. 3) separated the sites corresponding to subcluster B1 in the water classification of sites

Fig. 2. Classification of sites based on physicalechemical water features of Batrachium communities growing in base-rich water bodies on the Iberian Peninsula. Symbols correspond to floristical classification (Fig. 1). Equivalences between clusters and color of symbols are as follows: black symbols ¼ cluster A sites; gray symbols ¼ cluster B1 (ecotone); white symbols ¼ clusters B2, B3, and B4.

Table 1 Mean, range, t and p-value of the environmental parameters which show significant differences between the two main clusters obtained from Fig. 2.

Alkalinity (mg CaCO3 L1) Conductivity (mS cm1) Calcium (mg L1) Magnesium (mg L1) COD (mg O2 L1) 1

Flow (m s

Phosphates (mg L1)

)

Cluster

Mean

Range

A B A B A B A B A B A B A

417 2275 331 1179 17.03 81.65 5.40 46.31 6.64 23.50 0.90 0.14 0.16

282e545 1155e6909 105e784 201e3510 0.29e49.94 5.19e225.89 2.33e13.19 3.80e172.92 4.08e8.80 4.80e73.92 0.68e1.21 0e0.58 0.03e0.26

t

p-Value 3.11533

0.0026

2.01474

0.0285

2.37242

0.0273

1.73092

0.0491

1.76833

0.0458

6.81993

4.81  107

1.79108

0.04385

(Fig. 2) on the positive part of the axis from the rest. Axis 2 separated the saline sites from the others. The Monte Carlo test indicated that depth (p ¼ 0.006) and sodium (p ¼ 0.018) were statistically significant and provided a good explanation for differences in floristic composition. The positioning of the environmental variables showed that the first synthetic gradient was strongly positively correlated with depth (ca. 0.667) and pH (ca. 0.565). The second axis was strongly positively correlated with sodium (ca. 0.854) and conductivity (ca. 0.794). Although few aquatic accompanying species have been identified in R. trichophyllus communities, some act as good indicators of certain physicalechemical conditions. For example, in the lower alkalinity habitat, R. trichophyllus co-occurs with Callitriche brutia and R. peltatus. Furthermore, R. trichophyllus communities occurring in water with higher sodium contents include Zannichellia pedunculata Rchb. and Chara vulgaris L. The principal component analysis of the physicalechemical water features including localities outside the Iberian Peninsula

Fig. 3. RDA ordination diagram of Ranunculus trichhophyllus communities. The eigenvalues of axis 1 (horizontally) and axis 2 (vertically) are 0.319 and 0.153, respectively. Species are marked with an “x”, and quantitative environmental variables with arrows. Symbols correspond to the study sites according to their floristical classification (Fig. 1) and colors correspond to physicalechemical water classification (Fig. 2). The species names are abbreviated as follows: Api nod, Apium nodiflorum; Call bru, Callitriche brutia; Cha vul, Chara vulgaris; Ele pal, Eleocharis palustris; Gly dec, Glyceria declinata; Gly not, Glyceria notata; Pot den, Potamogeton densus; Ran pel, Ranunculus peltatus; Ran tri, Ranunculus trichophyllus; Ver ana, Veronica anagallis-aquatica; Zan ped, Zannichellia pedunculata.

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relative abundance of free CO2 in water decreases, whereas the corresponding value for HCO3  increases. High alkalinity buffers pH, maintaining high constant values of pH in a water body. Therefore, alkalinity is a close descriptor of HCO3  concentration (Stumm and Morgan, 1981). The photosynthetic activity of R. trichophyllus leaves shows that the maximum rate at pH 7.5 still remains relatively high at pH 9.5, indicating that R. trichophyllus is a “HCO3  user” which exploits this inorganic carbon form to perform photosynthesis. R. trichophyllus has been shown to possess two different mechanisms for using bicarbonate as a carbon source (Rascio et al., 1999). Our results highlighted some ecological differentiation between Batrachium species with only dissected leaves along a phosphate and sodium gradient in Eastern Mediterranean. The uneven distribution of dissected leaves Batrachium throughout Europe can be explained by the existence of other niches in Eastern Europe which are absent in Western Europe or by the occupation of R. trichophyllus of all the niches in Western Europe than other Batrachium species occupy in eastern Europe. The first explanation is supported by the high variety of carbonated lithologies in Eastern Europe (Zagorchev, 1998). The second explanation is supported by the ecological breadth of R. trichophyllus, along with its high colonization ability (Lacoul and Freedman, 2006).

Fig. 4. Biplot based on a principal components analysis (PCA). The eigenvalues of axis 1 (horizontally) and axis 2 (vertically) are 0.51 and 0.18, respectively. Symbols correspond to floristical classification (Fig. 1) and colors to physicalechemical water classification (Fig. 2) but black circles which correspond to Eastern European sites.

separated the Peloponnesian sites from the rest (Fig. 4). The Peloponnesian group was related to high values of phosphates and sodium. The other Western European samples were located within the Iberian sites.

Acknowledgments We thank the Spanish Ministerio de Ciencia e Innovación for a grant to Ana Lumbreras Corujo (AP2006-01721). Financial support was provided by project A/018321/08 from the Agencia Española de Cooperación Internacional para el Desarrollo (AECID). Appendix A. Supplementary data Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.actao.2013.05.009.

4. Discussion and conclusions References Our results showed that Batrachium vegetation of base-rich Mediterranean water bodies in Iberia consist mainly of two community types segregated along a gradient of alkalinity. R. trichophyllus communities are widespread in very hard waters including a wide range of water salinity and content of nutrients such as nitrates, ammonium and phosphates. R. penicillatus communities are related to phosphate-rich rivers with lower alkalinity. Since R. penicillatus communities are also distributed in non-calcareous zones (Webster, 1988; Lumbreras et al., 2009), their occurrence in calcareous environments, limited to rivers, can be explained by the fact that river-flow washes away substrates, and thus the waters have lower concentrations of calcium and magnesium, showing an inverse relationship between alkalinity and discharge (Piñol and Avila, 1992). This Batrachium communities’ replacement between species with laminar leaves and species with only dissected leaves can be connected with ecophysiological aspects. Growing under water imposes a strong constraint to plant photosynthesis (Santamaría, 2002). Most Iberian Batrachium (e.g. R. penicillatus, R. peltatus, R. aquatilis, R. ololeucos Lloyd) have floating laminar leaves, enabling them to use atmospheric CO2. However, R. trichophyllus is the only species in the Iberian Peninsula with only submersed dissected leaves; therefore the availability of atmospheric CO2 to this species is limited. Batrachium submersed leaves photosynthesize rapidly in water, even at low CO2 concentrations based on HCO3  use, an ability which is lacking in floating laminar leaves (Nielsen and Sand-Jensen, 1993). When water pH increases, the

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