101-14 Mgt: Climatic profiles and vine physiological status

Agricultural and Forest Meteorology 228–229 (2016) 104–119

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Vineyard row orientation of Vitis vinifera L. cv. Shiraz/101-14 Mgt: Climatic profiles and vine physiological status J.J Hunter a,∗ , C.G. Volschenk a , R. Zorer b a

Dept. of Viticulture, ARC Infruitec-Nietvoorbij, Private Bag X5026, 7599 Stellenbosch, South Africa Biodiversity and Molecular Ecology Department, Research and Innovation Centre, Fondazione Edmund Mach, Via E. Mach 1, 38010 San Michele all’Adige, TN, Italy b

a r t i c l e

i n f o

Article history: Received 27 January 2016 Received in revised form 13 June 2016 Accepted 20 June 2016 Available online 16 July 2016 Keywords: Grapevine row orientation Macroclimate Vineyard mesoclimate Canopy microclimate Photosynthesis Water potential

a b s t r a c t Establishment of vineyards is often forced towards geo-morphologically complex terroir where aspect, slope, relief and erosion are determining factors in orientation of rows. In this novel study, changes in primarily microclimate profiles and vine physiological behaviour with different row orientations were studied on a flat terrain in a semi-arid environment with the purpose of aiding vineyard management decisions and practices for production of grapes and wine. Effects of grapevine row orientation (NS, EW, NE-SW, NW-SE) of vertically trellised and shoot positioned Vitis vinifera L. Shiraz/101-14 Mgt on vineyard meso- and microclimate as well as vine physiological status, within the context of regional macroclimate, were investigated under field conditions over many seasons. Novel wind velocity and direction profiles in vineyard rows showed velocity in work rows paralleling ambient prevailing wind and direction flow patterns being affected by canopy development and row orientation; NW-SE and EW orientated rows maintained higher wind velocity in work rows than NS and NE-SW rows. Mesoclimatic photosynthetic active radiation was in line with macroclimate radiation. Microclimatically, EW orientated rows maintained lowest interior canopy light interception, NS orientation displayed highest values, peaking in morning and afternoon, whereas NE-SW and NW-SE orientations peaked primarily in afternoon and morning, respectively. The EW orientated rows captured largest portion of total radiation in the bunch zone from soil reflected radiation. Canopy interior temperature differences were likely masked by air temperature. Basal leaf water potential was relatively unaffected by row side; results point to internal regulation of whole plant water status. Leaf temperature showed minor differences. Relative humidity followed opposite trends to those of air- and leaf temperature. Leaves of EW orientated vines had highest average photosynthesis, corresponding to stomatal conductance and transpiration. Most uniform canopy photosynthesis occurred for NS and NW-SE orientations. Photosynthesis trends practically demonstrated mirror diurnal images for canopy sides of each orientation. Row orientation significantly affected mesoand microclimate, radiation in particular directly affecting energy/heat balances and concomitant canopy physiological processes. The study provided new insights into: vine physiological response to row orientation, the role of row orientation as viticulture practice; decision-making for establishment; and management of existing vineyards, irrespective of terroir soil and climatic conditions and product objectives. Results are globally relevant, especially within the context of climate change, and provide first comprehensive climatic/grapevine physiological evidence on the impact of grapevine row orientation as viticulture practice. © 2016 Elsevier B.V. All rights reserved.

1. Introduction Valley climatic conditions, such as temperature, wind and humidity, and valley floor/edaphic conditions, such as soil water availability and drainage, often force establishment of vineyards ∗ Corresponding author. E-mail addresses: [email protected] (J.J Hunter), [email protected] (C.G. Volschenk), [email protected] (R. Zorer). http://dx.doi.org/10.1016/j.agrformet.2016.06.013 0168-1923/© 2016 Elsevier B.V. All rights reserved.

towards geo-morphologically complex terroir where aspect, slope, relief and erosion are determining factors in orientation of rows. Spatial environmental conditions (geo-morphometric and climatic profile) of landscapes [including soil water availability, solar radiation (total light spectrum component and photosynthetically active radiation component), temperature, humidity and air flow dynamics] would naturally superimpose onto suitability of a vineyard row orientation chosen during establishment for purpose of sustainable yields and enhancement of grape and wine quality. On

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complex reliefs, convex and concave row orientation variations, with reference to the ecliptic, would naturally occur and represent multiple row orientations that may lead to a mixture of perpendicular or oblique incident sun rays being absorbed, transmitted and reflected by leaves and grapes. This may result in various levels of sunlight and heat energy distribution and implications to leaf and berry morphology and metabolism. Orientation of canopies and grapes accommodated in vertical planes (e.g. with vertical shoot positioned canopies) on complex reliefs (hilly, mountainous) may thus lead to an array of edaphic and biological effects. In a study on sensitivity of sunlight interception of vine rows to trellis system and soil surface reflection, Pieri and Gaudillère (2003) found the most significant driving parameters to be row spacing, row shape, soil surface reflection and row azimuth; parameters were sensitive to variation in row orientation. Such simulations are useful to evaluate the relationship between soil water balance, transpiration, vegetative growth and harvest potential and could be used to improve crop coefficients. Although decreasing canopy vertical wall height (within limitations of vigour) and increasing row spacing to eliminate interference of adjacent rows would always complement sunlight interception, this is dictated by a broader perspective of sustainability, including optimum physiological function, aboveground and belowground growth, and wine quality (Archer and Strauss, 1985, 1989, 1990; Hunter, 1998a,b). According to a numerical model of Smart (1973), high vertical NS orientated vineyard rows had highest seasonal sunlight interception. Differences in energy interception between NS and EW orientated rows were shown to decrease with closer row spacing. Diurnally, NS orientated rows were advantageous during midmorning and mid-afternoon, during which periods EW orientated rows had lowest sunlight interception in canopies. Irrespective of orientation, slanting canopy walls could increase interception on a surface basis, reducing soil exposure to direct light. The major advantage of slanting canopy walls over vertical canopy walls would be gained over mid-day, vertical canopies increasing sunlight capture away from mid-day and slanting walls increasing sunlight capture towards mid-day. Larger (vertical) walls would increase interception, if illuminated. Photosynthetic activity is high during late morning (Hunter et al., 1994) and capture of high levels of sunlight is therefore preferred during this time. Photosynthetic output of the canopy and general metabolic activity may be further improved by proper canopy management (Kriedemann, 1977; Pandey and Farmahan, 1977; Hunter and Visser, 1988a,b; Hunter et al., 1995, 2004a,b). De Jong and Doyle (1985) found no differences in total amount of light interception between NS and EW pear rows, at 36.4◦ N latitude. According to Zufferey et al. (1999), net diurnal photosynthesis of leaves on S-exposed canopy sides of EW orientated Chasselas rows in Switzerland was highest during the whole growth season. Outer leaves of NS canopies showed highest net photosynthesis until the start of the ripening period, whereas that of outer leaves of EW rows was slightly higher at the end of grape ripening (Champagnol, 1982; Zufferey et al., 1998). In Portugal, Moutinho-Pereira et al. (2003) found higher photosynthetic rates for Touriga Nacional leaves on NE sides of NW-SE orientated rows in the morning, whereas photosynthetic activity of leaves on the SW canopy side is greatly reduced in the afternoon as a result of stomatal and non-stomatal restrictions. In South Africa, Novello and Hunter (2004) found with NS orientated Shiraz that net photosynthetic rates of both primary and secondary leaves in all positions from basal to apical were higher on the canopy side that received maximum irradiance, i.e. eastern side in morning and western side in afternoon, the former tending towards higher total photosynthetic output; differences in water potential were smaller. Overall, rates of leaf net CO2 assimilation on west side in afternoon was 88% of that measured on east canopy side in morning, whereas photosynthetic rate on east side in after-

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noon was 74% of that measured on west side in morning. Since light interception at leaf level on east side in morning was similar to that on west side in afternoon, this reduction in photosynthetic activity was related to a photosynthetic inhibition effect that may have built up during the day and/or other biochemical factors acting at mesophyll level (Chaumont et al., 1994; Düring, 1991; Zang et al., 1991). Clearly, the impact of row orientation on functioning of both leaves and grapes would also depend on other factors, such as dimensions of canopy (density, length and leaf age composition, largely determined by vigour, pruning system, and canopy management practices), developmental stage, time of year, and latitude (Smart, 1973; Hunter, 1999; Intrieri et al., 1999). Intrieri et al. (1998) showed that total canopy assimilation and transpiration of NS and EW canopy orientations of potted and field-grown vines differed, pointing to the impact of growth conditions. It follows logical that terroir per se (e.g. soil fertility, soil reflection coefficient and water holding capacity, evaporative demands, temperature range, prevailing wind, humidity, altitude, aspect and slope), vine and row spacing, and trellis and training system, would also play a critical role in the final effect of row orientation and that row orientation would provide a further dimension to base effects induced by these factors (Bois et al., 2008; Hunter et al., 2010b). In this study, the impact of row orientation, at fixed row and vine spacing, on microclimate of canopy and grapes and physiological status of the grapevine is determined on a flat terrain in a region of South Africa that experiences semi-arid macroclimatic conditions. The role of row orientation in transitions between meso- and microclimate is presented. This extensive study is unique in many ways and provides information on the impact of row orientation on physiological and climatic scales (3-scale climatic approach) that has not been shown before.

2. Materials and methods 2.1. Vineyard Vitis vinifera L. cv. Shiraz (clone SH 9C)/101-14 Mgt was planted during 2003 to four row orientations, i.e. North-South (NS), East-West (EW), North-East-South-West (NE-SW), and NorthWest-South-East (NW-SE), replicated five times. Each replicate is confined to a separate vineyard block with surface area of approximately 800 m2 on a flat site of approximately 3 ha with uniform clayey loam soil at the Robertson Experiment Farm of ARC Infruitec-Nietvoorbij in the Breede River Valley, Robertson (33◦ 49 35S/19◦ 52 53E/153 m a.s.l.), South Africa (See location on map of South Africa, Fig. 1, as well as photos of the experimental vineyard, Fig. 2). The environment and climatic conditions of the region in which the study was done were elaborated in Hunter and Bonnardot (2011). Vines were spaced to a fixed distance of 1.8 × 2.7 m and cordon trained. From the third winter after planting, vines were pruned to two bud spurs, spaced approximately 14 cm apart. Vertical shoot-positioned canopies had approximately four leaf layers (from side to side) and were managed uniformly for the whole duration of the study, i.e. 2006/07–2013/14. Vines were only shoot positioned and topped. Both these actions were performed on average three times per year. A cover crop (Rye) was sowed after harvest and killed before budding. Vines were medium intensity irrigated weekly at a volume of 14 mm during the high season period, due to the region receiving low winter rainfall that averages 150–300 mm per annum. This was based on a crop factor for the region and on experience; initial crop factor-based irrigation was insufficient and had to be adjusted.

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Fig. 1. Location of the Breede River Valley, Robertson, South Africa.

2.2. Macroclimate (regional) environment Hourly climatic data was obtained from an automatic weather station (part of the weather station network of the ARC Institute for Soil, Climate and Water—the South African Weather Service is a member of the World Meteorological Organisation and complies with international meteorological standards), located approximately 200 m from the experimental vineyard at Robertson Experiment Farm. This was used to calculate daily and monthly averages at macro scale. Temperature (◦ C), radiation (MJ/m2 ), rainfall and wind speed/velocity profiles are reported. Average macro temperature climate profiles from October to March (grapevine growth season in the Southern Hemisphere) of the years 2006/07–2010/11 and 2011/12–2013/14 are reported. Periods were split in order to correspond to physiological measurements during the first period and meso- and microclimate measurements during the second period. Grapevine canopies were managed uniformly in all years with minimal seasonal variation (data not shown) 2.3. Mesoclimate (vineyard) measurements Campbell Scientific CR1000 measurement and control systems were used to record hourly data continuously (recording every 10 s, averaged per hour) during the whole growth season (beginning October to end March) (average of 2011/12–2013/14 seasons). Batteries of loggers were charged by means of solar panels installed above logging stations. Ambient photosynthetic active radiation (PAR) (400–700 nm) (␮mole/m2 /s) was recorded in three randomly selected positions in the vineyard by means of LI-COR LI-190 Quan-

tum sensors located approximately 0.5 m on top of vineyard rows. Wind speed/velocity (m/s) (average of 2011/12–2013/14 seasons) and wind direction (in degrees) (average of 2012/13–2013/14 seasons) were recorded by means of RM Young Wind Sentry Sets in the centre of the work row at a height of approximately 1.2 m in one randomly selected position in three replications per treatment and in three randomly selected positions in the whole vineyard at a height of 1 m above the canopy/vineyard row. 2.4. Microclimate (canopy) measurements As for mesoclimate, Campbell Scientific CR1000 measurement and control systems were used to record hourly data continuously during the whole growth season (beginning October to end March for seasons). Average data of the 2011/12–2013/14 seasons are presented. The PAR captured inside the canopy was measured in one randomly selected position in each of three replications per treatment by means of two LI-COR LI-191 Line Quantum sensors fixed in parallel in the bunch zone, one facing up (photo-tropically) and other facing down (geo-tropically) (i.e. canopy filtered radiation was measured 180◦ upwards and soil reflected radiation 180◦ downwards). Ambient temperature (◦ C) and relative humidity (%) were recorded in one randomly selected position in each of three replications per treatment in the bunch zone by means of Vaisala HMP 50 or −60 sensors. 2.5. Canopy physiological measurements All measurements were done approximately six weeks after véraison (berry colouring) (during the last week of February) on all

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Fig. 2. A Complete experiment layout, B: Close-up view at treatment level, and C: Close-up view at canopy level, of the experiment at Robertson Experiment Farm of ARC Infruitec-Nietvoorbij, Breede River Valley, Robertson, South Africa.

treatments and replications. Average data of the 2006/07–2008/09 seasons are presented. The % relative humidity, air temperature (◦ C), leaf temperature (◦ C), photosynthetic photon flux density (PPFD) (␮mole/m2 /s), transpiration (mmole/m2 /s), stomatal conductance (mmole/m2 /s), internal CO2 concentration, and photosynthetic activity (␮mole/m2 /s) (Pn ) of two basal (bunch zone) primary shoot leaves on each side of the canopy was measured during mid-morning (10:00), mid-day (13:00) and afternoon (16:00) using an open system ADC portable photosynthesis meter (The Analytical Development Co., Ltd., England), as specified in Hunter and Visser (1988b, 1989). Leaf water potential (–kPa) (L ) measurements were done similarly to Pn measurements, using two equally calibrated (1000 kPa/30 s) Scholander pressure chambers (Scholander et al., 1965).

Macroclimate profiles of growth seasons were divided into two periods in order to correspond with measurements taken during these periods (average of 2006/07–2010/11 and 2011/12–2013/14, respectively). Meso- and microclimate profiling was done for three consecutive seasons (average of 2011/12–2013/14 data) (except for wind direction, being averaged for 2012/13–2013/14). Canopy physiological measurements were also done for three consecutive seasons (average of 2006/07–2008/09 data). Analysis of variance was performed using SAS version 9.2 (SAS, 2012). The Shapiro-Wilk test was performed to test for non-normality (Shapiro and Wilk, 1965). Student’s t-Least Significant Difference was calculated at 5% significance level to compare treatment means (Ott, 1998).

3. Results and discussion 2.6. Statistics

3.1. Macroclimate

The experiment comprised a randomized design with four vineyard row orientations and five replicates per orientation.

The Breede River Valley experiences semi-arid conditions (Preston-White and Tyson, 1988; Hunter et al., 2010a; Hunter and

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Bonnardot, 2011) and is situated on the edge of the southern temperate zone. The region constitutes a climatic transition between the winter rainfall area to the west, semi-arid southern interior to the northeast and evenly distributed rainfall area towards the east. Mountains situated to the west and south of the Robertson region are barriers to westerly cyclonic rainfalls (See also Fig. 1). They cause a real “rain shadow” in the region. Average annual rainfall is low (<300 mm) and drought is experienced for approximately seven months (September to March). Annual mean temperature is 17.8 ◦ C. Winters are mild, but cool at night (mean max. and min. July temperatures are 18.8 ◦ C and 5.2 ◦ C, respectively). Frost can occur. The pre-véraison period (green berry growth stages up to berry colouring/véraison – more or less from September/October up to first half of January) is warm (max. temperature 27–30 ◦ C) and ripening period (from after berry colouring – more or less from middle January to end of March) hot (max. temperature >30 ◦ C). Average macro temperature climate profiles of 2006/07–2010/11 and 2011/12–2013/14 seasons obtained from the weather station located at Robertson Experiment Farm are displayed in Figs. 3 and 4. Average temperatures increased from approximately mid-December (around pea berry size) and maximum temperatures frequently reached more than 30 ◦ C from there on. These temperatures would seem to be slightly higher than long term average profiles reported for the region (Hunter and Bonnardot, 2011) and appear to be in line with observations that the region is experiencing a change in climate (Hunter et al., 2010a). The latter is also in agreement with a recent report on global atmospheric changes stating, amongst others, increasing greenhouse gas concentrations, positive radiative forcing and warming in the atmosphere (IPCC, 2013). Radiation seemed higher during the second climatic profile period and seemed more or less in line with average air temperature. In general, it seemed to pick up from the beginning to the middle of the growth season/beginning of berry ripening (January—corresponding to véraison), where after it decreased towards the end of March. The wind speed averages per day showed little variation, but highlighted the active vegetative/flowering phase (November) as a period of stronger winds and the last month of the grape ripening phase (March) as a period in which the wind velocity decreased. Low precipitation occurred in summer and comprised inconsistent events with occasional higher precipitation that would nevertheless be quickly evaporated under high evaporation demand caused by the relatively high air temperatures. A river based water resource is available in this region and vines in this study were irrigated from a river/canal/reservoir system. In general, high temperatures are not favourable for optimal photosynthetic activity (25–30 ◦ C—adapted from Kriedemann, 1968, 1977) and supply of precursors for various compounds associated with quality grape and wine composition; risk for organic acid respiration, high pH, and poor colour and flavour development and maintenance would be high (Lakso and Kliewer, 1978; De Freitas et al., 2000; Hunter, 2001; Rodriquez Montealegre et al., 2006; Pastor del Rio and Kennedy, 2006; Hunter and Bonnardot, 2011). Such secondary compounds would include terpenoids (e.g. monoterpene flavour compounds and carotenoids), flavonoids, and non-flavonoids [e.g. phenolic acids, polymeric flavan-3-ols (condensed tannins), flavonols and colour (anthocyanin) compounds]. In a recent study on implications of within-vineyard variation (focused on soil properties and topography) on presence of rotundone (peppery aroma of Shiraz, chemically characterised as an oxygenated bicyclic sesquiterpene—Wood et al., 2008), it was also suggested that further research should target the role of temperature and radiation on presence of this compound (Scarlett et al., 2014), implicating that it may also be prone to change when exposed to varying levels of these factors.

During pre- and post-véraison periods climatic conditions and vineyard practices should favour maintenance and formation of compounds in berries. High photosynthetic activity (sucrose availability) during the pre-véraison period would contribute to primary and secondary compound pools available in berries at the start of ripening, whereas it would largely buffer a decrease in organic acid and an increase in pH during the post-véraison period (by preventing excessive amounts of potassium as osmotic agent in the phloem) and promote further development of secondary compound pools required for quality grape composition and wine (Iland, 1987; Patrick, 1997; Riou, 1998; Hunter, 2000; Ojeda et al., 2002; Hunter et al., 2004a,b). 3.2. Mesoclimate The wind velocity in work rows of different row orientation treatments decreased from October to March, parallel to ambient prevailing wind (Fig. 5). In general, it may be expected that terroir of the vineyard location (altitude, topography, surrounding vegetation) and the vineyard per se (mostly canopy density and height as well as distance between rows) would have a controlling effect on wind velocity prevailing in work rows. Throughout the season, NW-SE and EW orientated rows maintained higher wind velocity in work rows than the other two row orientations, with NS orientated rows having generally lowest diurnal values. Trends of treatments, however, stayed the same, i.e. wind increased in velocity between rows until late afternoon (18:00), where after it sharply decreased. In general, wind velocity in NW-SE work rows seemed slightly higher during the afternoon, whereas that in EW orientated rows seemed highest during the evening, followed by NW-SE, NE-SW and NS. Although it depends on the air mass properties (mainly temperature/water vapor), a higher wind velocity would most likely have a faster cooling and drying effect on grapes and along with a proper canopy microclimate would decrease risk of diseases (such as Botrytis cinerea and Plasmopara viticola) (Stapleton and Grant, 1992; Hunter, 2000), especially after intermittent summer rainfalls; as explained above, it would therefore support development of favourable grape composition in hot and humid terroirs in particular. Consideration should however also be given to physical damage that may be caused by strong winds especially during early growth phases, whereas inflorescence damage is a major concern regarding yields and sustainability. Furthermore, warm winds may lead to berry dehydration and the risk of weight loss (especially in the case of the Shiraz variety—Hunter et al., 2014a,b). Row orientation choices (and canopy management) should therefore be carefully considered in such terroirs in order to obtain favourable compromises between vegetative growth, inflorescence development, berry development, grape exposure and impacting mesoclimatic factors affected by viticulture practices. Prevailing wind direction, measured on top and in work rows, showed a similar profile for the whole growth season (Fig. 6); in the beginning of the season (October–November) wind maintained an S-SE direction during the night, changing progressively to S incoming towards early morning and then to SE incoming from mid-day onwards. After that, night time winds shifted to SE, then to S during mid-morning to mid-day, where after it progressively reverted back to SE. These patterns fit well with the occurrence of alternate valley and mountain breezes and materialises the effect of topography on the onset of a local air circulation. As canopies developed, impact of row orientation on wind flow between rows became clearer (from November). Patterns of diurnal change in direction of wind observed in the beginning of the season stayed more or less the same for the different treatments throughout the season, but wind direction was

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Fig. 3. Macro hourly temperature (min, max, and mean), radiation, rainfall and wind speed at Robertson experiment farm of ARC Infruitec-Nietvoorbij (average of five seasons: 2006/07–2010/11).

clearly different for different row orientations. Diurnally, main wind directions in NS, NW-SE, EW and NE-SW orientated work rows were S incoming; SE incoming changing to S incoming during late season; SE incoming; and E-SE incoming, respectively. Patterns may change under different prevailing wind directions. The impact of row orientation on wind direction patterns together with wind velocity recordings between differently orientated rows are extremely important in decisions regarding vineyard establishment and expectations and interpretation of yields and berry mass, temperature, composition and health under different climatic conditions.

3.3. Microclimate Ambient (mesoclimatic) photosynthetic active radiation measured on top of canopies was highest during November to January (Fig. 7), in line with macroclimate radiation profiles displayed in Figs. 3 & 4. Seasonal patterns of photosynthetic active radiation (PAR received in bunch zones at microclimate level after being filtered by the canopy) showed that EW orientated rows maintained lower interior canopy interception than other row orientations (Fig. 7); it decreased during the season as canopies developed, generally peaking just after mid-day. The NS orienta-

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Fig. 4. Macro hourly temperature (min, max and mean), radiation, rainfall and wind speed at Robertson experiment farm of ARC Infruitec-Nietvoorbij (average of three seasons: 2011/12–2013/14).

tion displayed highest values in the form of two clear peaks in morning and in afternoon, respectively, whereas NE-SW and NWSE orientations showed peaks primarily in afternoon and morning, respectively. Average radiation reflection from soil (measured in the bunch zone) during the grape ripening period showed more or less similar trends, but interception shifted towards afternoon for NS and NE-SW orientations, whereas EW and NW-SE orientations showed uniform trends with optima at mid-day (Fig. 8). Interestingly, in comparison to other orientations, EW orientated

vine rows captured largest portion of total radiation received in the bunch zone from soil reflected radiation. This may change with different soil type (e.g. clay versus calcareous versus stony versus sandy soils) and different soil covers/mulches, affecting colour of the surface. Soil-reflected light contribution to total light component captured in canopies of vines grown in different soil types and with different soil mulching may have significant effects on total light spectrum received by leaves and berries, changing the far-red:red ratio and therefore biochemical and morphologi-

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Fig. 5. Meso hourly mean wind velocity in work rows of Shiraz/101-14 Mgt vineyard planted to four different row orientations at Robertson experiment farm of ARC Infruitec-Nietvoorbij (average of three seasons: 2011/12–2013/14).

cal processes in which the proteinaceous pigment phytochrome (having photochrome characteristics) may play a noticeable role. This pigment has been implicated in control of many critical enzymes involved in primary and secondary metabolism, such as glyceraldehyde-3-P dehydrogenase, phenylalanine ammonia lyase, ribulose-1,5-bisP carboxylase, PEP carboxylase, malate dehydrogenase, amylase, nitrate reductase, invertase, etc. (Mitrakos and Shropshire, 1972; Salisbury and Ross, 1978; Smart, 1985;

Kasperbauer, 1988; Bradburne et al., 1989). Density of the canopy (also affected by soil type) would play a large role in quantity of the Pr component reaching interior leaves and berries (and therefore conversion of inactive Pr pigment to active Pfr form). Furthermore, changes in soil type may result in changes in radiant heat; apart from the fact that this would impact on berry temperature and composition as explained above, humidity in the bunch zone may also increase, especially in regions (such

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Fig. 6. Meso hourly mean wind direction in work rows of Shiraz/101-14 Mgt vineyard planted to four different row orientations at Robertson experiment farm of ARC Infruitec-Nietvoorbij (average of two seasons: 2012/13–2013/14).

as the study area) where frequent irrigation is required during summer. Although quantity (and most likely quality) of light is very different, EW and NS orientations may generally be considered as causing most uniform light distribution in canopies. However, implications for canopy disease occurrence for example may be very different as Dalla Marta et al. (2008) showed an inverse relationship between polyphenolics produced when leaves are exposed and severity of downy mildew; this may equally well apply to grape bunches, in which it was shown that berry phenolic composition reacted positively to sun exposure (Crippen

and Morrison, 1986; Price et al., 1995). Plant phenolics have for a very long time been implicated in defence against invading phyto-pathogens (Walker, 1975; Shirley, 1996). This is a critical aspect during especially pre-véraison canopy development stages of the grapevine when pathogen infection of the canopy should be prevented in order to secure a healthy, efficient and sufficient canopy during grape ripening. Row orientation may therefore be a natural way to enhance defence mechanisms against fungal diseases. Significance of different light distribution patterns and quantities for physiological performance is discussed later.

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Fig. 7. Micro hourly mean photosynthetic active radiation of Shiraz/101-14 Mgt vineyard planted to four different row orientations at Robertson experiment farm of ARC Infruitec-Nietvoorbij (average of three seasons: 2011/12–2013/14).

Despite higher wind velocity in work rows (Fig. 5), canopyinteriors of EW orientated rows tended to have higher relative humidity during morning periods (Fig. 9). High humidity is commonly associated with high risk of Plasmopara viticola (Dalla Marta et al., 2008) and Botrytis cinerea (Thomas et al., 1988) development; wind velocity and low relative humidity had a greater effect than temperature on evaporative potential of ambient air and therefore control of pathogens (Thomas et al., 1988). Too dense canopies are associated with high incidence and severity of grape rot (Volschenk and Hunter, 2001) and EW orientated canopies in particular would therefore have to be managed judiciously (Stapleton and Grant, 1992; Hunter, 2000) in order not to compromise other positive factors related to this row orientation [Even though VSP vineyards are not common in table grape production and it may be argued that

light microclimate profiles as shown in this study would not have similar impact on grape exposure in larger and more horizontal trellising systems used in table grape production, row orientation would be very important in directing wind velocity and direction in order to dry grapes after morning dew or when high humidity conditions prevail after irrigation; these are critical factors for table grape sanitary status. To accomplish that, rows should therefore rather be orientated towards the incoming prevailing wind direction in such cases; this is plausible as table grapes are mainly produced in flat areas]. Except for generally slightly lower and higher morning temperatures of EW and NS row orientations, respectively, canopy interior temperature profiles did not show marked differences between treatments (Fig. 10). In general, temperatures peaked at approx-

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Fig. 8. Diurnal hourly mean soil-reflected radiation intercepted inside canopies during the ripening period (February) of Shiraz/101-14 Mgt vineyard planted to four different row orientations at Robertson experiment farm of ARC InfruitecNietvoorbij (average of three seasons: 2011/12–2013/14).

imately 30 ◦ C from December onwards at around 15:00–16:00. In January and February canopy temperatures were highest at just over 30 ◦ C. As noticeable differences in wind velocity and wind direction between treatments as discussed above (Figs. 5 & 6) had no apparent impact on respective canopy temperatures, air flow dynamics along, over and through differently orientated rows (canopies) may not have had any major effect on that. Since canopy vegetative characteristics were relatively uniformly controlled for all treatments (data not shown), canopy interior temperature might have been primarily affected by ambient air temperature. Given the vineyard air flow dynamics, results point to a masking effect of ambient air temperature. Nevertheless, flow dynamics must still be linked with efficiency to affect berry temperature in various positions on bunches. 3.4. Canopy physiological measurements Basal (bunch zone) leaf water potential (L ) results are shown in Table 1. In general, L decreased noticeably from morning to midday, after which it more or less stayed constant on either side of the canopy and for all row orientations. Although differences occurred, L did not vary that much between different sides of rows; given differences in light exposure of canopy sides (judged from bunch zone light interception profiles—Figs. 7 & 8), results point to internal regulation of whole plant water status. The EW orientation displayed highest and NW-SE orientation lowest water potential in morning. Despite a further decrease in water status of EW orienta-

tion, higher L was maintained for the remainder of the day. The L of other orientations decreased to similar values. Diurnally, NS, NE-SW and NW-SE orientations therefore displayed lower L than EW orientation. As general viticulture practices and canopy dimensions and exposure were managed similarly between treatments, differences in L seem naturally induced only by change in row orientation. Results of physiological measurements in canopies of different row orientations, done during the ripening period, are given in Table 2. In general, % relative humidity (% RH) followed opposite trends to those of air temperature (Tair ) and leaf temperature (Tleaf ), typically decreasing and increasing, respectively, during the day from morning to afternoon. The E, S, SE, and SW canopy sides had noticeably lower % RH and Tleaf values than other canopy sides (except for NS orientation where E and W side Tleaf was similar), whereas Tair differences were not pronounced, but followed similar trends. Largest differences in Tleaf were found for EW orientation with N side displaying almost 2 ◦ C higher values than S side. On average, Tleaf showed minor differences between row orientations, EW and NW-SE displaying slightly lower values. Leaves on N side of EW orientation had lowest internal CO2 concentration ([i CO2 ]). This corresponded with highest Pn found for leaves on this side of the canopy. Likewise, lowest i CO2 assimilation of leaves on S side of these canopies conformed to lowest Pn . Despite the latter, leaves of EW row orientation still had highest average Pn , in agreement with highest leaf stomatal conductance (Sg ) and transpiration (E). Very low photosynthetic photon flux density (PPFD) values for S side of EW orientated rows were most probably the main reason for low photosynthetic performance of leaves on this side. Most uniform canopy Pn (based on leaves measured in this study) was found for NS and NW-SE orientations. The Pn trends of different canopy sides were parallel to PPFD trends during the day and practically followed sun movement over vineyard rows; with few exceptions, mirror images of these parameters occurred for canopy sides of each orientation during the day. This corresponds to Pn results found for different sides of NS orientated vineyard rows (Novello and Hunter, 2004; Intrieri et al., 1998; Zufferey et al., 1999). Trends of Pn were also in general agreement with those found for E, Sg and Tleaf . In line with that, sides facing W, S, SE and SW displayed lower average Pn and photosynthetic efficiency (Pn :E ratio). Higher overall Pn of EW row orientation also corresponded to higher water retention in the canopy (Table 1). This needs to be judged in view of the fact that these measurements were done during the ripening period when the sun azimuth was already mostly in favour of northerly exposed side of the canopy. Considering the more uniform light interception in the canopy of EW treatment during the season (Figs. 7 & 8), similar Pn for canopy sides may have been expected; however, this was not the case during this period

Table 1 Leaf water potential measured in the bunch zone during grape ripening of Shiraz/101-14 Mgt vineyard planted to four different row orientations at Robertson experiment farm of ARC Infruitec-Nietvoorbij (average of three seasons: 2006/07–2008/09). Leaf water potential (-kPa)

Row orientation

Canopy side

10:00

Avg.

13:00

Avg.

16:00

Avg.

Diurnal Avg.

NS

E W

1441.8 a 1424.2 ab

1433.0 a

1629.3 ab 1654.2 a

1641.8 a

1697.5 ab 1656.7 b

1677.1 a

1583.9 a

EW

N S

1250.0 c 1279.5 bc

1264.8 b

1530.8 bc 1521.8 c

1526.3 b

1545.0 c 1511.7 c

1528.3 b

1439.8 b

NE-SW

NW SE

1455.8 a 1404.8 ab

1430.3 a

1605.8 abc 1646.5 a

1626.2 a

1679.2 ab 1733.3 a

1706.3 a

1587.6 a

NW-SE

NE SW

1466.7 a 1555.0 a

1510.8 a

1604.2 abc 1666.8 a

1635.5 a

1670.0 a 1657.3 a

1663.7 a

1603.3 a

150.8

106.6

1013.7

71.7

75.4

53.3

50.9

LSD (p = 0.05)

LSD applicable to mean values followed by letters within columns.

Table 2 Canopy physiological parameters (Photosynthesis-related) measured in the bunch zone during grape ripening of Shiraz/101-14 Mgt vineyard planted to four different row orientations at Robertson experiment farm of ARC Infruitec-Nietvoorbij (average of three seasons: 2006/07–2008/09). Time

Can RH side (%)

RH (%) Avg. can side

NS

Tair

Avg. can

21.2 fgh 22.0 efg 23.7 def 22.3 b 28.4 b 19.1 hij 13.7 l 20.4 b 21.3 a

10:00 N 13:00 16:00 10:00 S 13:00 16:00

Avg. can side

PPFD

Avg. can

PPFD (␮mole/m2 /s) Avg. can side

Pn

Avg. can

Pn (␮mole/m2 /s) Avg. can side

92.6 g 992.7 e 1577.6 b 1743.4 ab 922.5 e 81.6 g

32.0 a 27.0 bc 24.0 de 25.3 cd 19.6 ghi 16.8 jk

30.6 b 35.8 a 27.7 a 36.0 a 34.1 ab 30.5 b 35.8 a 20.6 b 24.1 a 36.0 a 34.1 ab 34.1 a

1377.7 cd 1777.3 a 1365.3 d 141.8 g 164.7 g 192.4 fg

8.03 ab 8.47 a 1506.8 a 6.53 cde 2.77 gh 2.34 hi 166.3 e 836.5 a 1.86 hi

NE-SW 10:00 NW 21.9 efg 23.1 def 13:00 16:00 21.9 efg 10:00 SE 27.5 bc 17.8 ijk 13:00 16:00 16.3 kl

30.6 b 35.9 a 22.3 b 36.2 a 34.2 a 30.9 b 35.8 a 20.5 b 21.4 a 36.1 a 34.2 a 34.2 a

242.6 fg 1671.3 ab 1674.2 ab 1563.0 bc 218.7 fg 88.0 g

2.02 hi 6.16 de 1196.0 b 6.09 de 4.76 bc 6.96 bcde 2.62 gh 623.2 d 909.6 a 1.44 hi 3.67 cd 4.21 b

887.6 c

915.8 c

1.89 hi 4.32 f 6.27 de 4.16 bc 7.42 abcd 3.91 fg 901.7 a 1.18 i 4.17 bc 4.16 b

7.68 a

2.32 e

E

Avg. can

30.7 b 35.9 a 36.1 a 34.3 a 30.7 b 35.9 a 35.9 a 34.2 a 34.2 a

EW

10:00 W 13:00 16:00 10:00 E 13:00 16:00

Tair (◦ C)

3.24 kl 4.43 cdef 4.94 bc 4.34 cdefg 3.93 fghij 2.83 l

4.87 bc 5.52 a 5.03 ab 3.83 ghij 3.94 fghi 5.00 a 3.44 hijk 3.36 jkl 4.74 bcd 4.57 bcde 4.26 defg 3.63 hijk 3.38 ijkl

E Sg (mmole/m2 /s)

Sg (mmole/m2 /s)

Avg. can side

Avg. can side

Avg. can

Tleaf

Avg. can

Avg. can side

111.7 de 104.6 defg 4.20 b 112.9 de 138.9 b 85.9 ghi 3.70 b 3.95 a 60.3 j

29.5 f 35.7 bc 109.75 b 36.7 ab 31.9 e 35.8 bc 95.06 b 102.41 a 34.8 cd

172.8 a 131.6 bc 5.14 a 116.9 cd 140.7 b 94.8 efghi 3.74 b 4.44 a 76.4 ij

30.9 e 36.5 ab 140.43 a 36.2 ab 29.1 f 34.4 d 103.95 b 122.19 a 34.9 cd

115.4 cd 104.7 defg 4.22 b 94.2 efghi 141.0 b 88.4 fghi 3.76 b 3.99 a 77.1 ij

29.6 f 36.7 ab 104.76 b 37.2 a 31.7 e 34.6 d 102.16 b 103.46 a 34.8 cd

NW-SE 10:00 NE 13:00 16:00 10:00 SW 13:00 16:00

28.2 b 22.5 ef 16.7 jk 22.5 b 20.9 fgh 17.3 ijk 19.6 ghi 19.2 b 20.9 a

30.7 b 35.6 a 35.8 a 34.0 b 30.4 b 35.6 a 35.9 a 34.0 b 34.0 a

1702.5 ab 1626.5 ab 105.2 g 109.3 g 374.6 f 1189.8 d

7.86 abc 5.82 e 1144.7 b 1.70 hi 2.20 hi 2.52 hi 557.9 d 851.3 a 4.14 f

4.30 defg 4.55 bcde 5.13 b 3.47 hijk 3.13 kl 3.45 hijk 2.95 de 4.04 b 4.01 efgh

137.8 b 103.0 defgh 4.11 b 79.0 ij 106.57 b 105.9 def 78.9 ij 3.53 b 3.82 a 85.2 hi 89.99 b 98.28 a

31.8 e 36.5 ab 34.5 d 29.3 f 34.8 cd 36.3 ab

LSD (p = 0.05)

2.7

1.0

195.1

127.8

1.10

0.80

1.1

3.9

4.2

0.3

0.3

73.3

1.40

0.70

0.60

0.80

19.3

28.30

29.70

Tleaf (◦ C)

[iCO2 ] Avg. can

Avg. can side

34.1 a

328.2 a 266.9 ef 235.7 jkl 257.7 ghij 261.3 fg 317.9 ab

33.7 a

260.4 fgh 223.8 l 241.9 hijkl 323.7 ab 310.8 ab 306.0 c

34.1 a

322.6 ab 236.6 jkl 226.1 kl 250.4 fghij 284.5 d 314.9 ab

33.4 d

33.8 a

239.0 ijkl 243.4 ghij 310.0 ab 324.2 ab 290.9 cd 259.9 fgh

0.5

0.5

19.2

34.0 bc

34.2 ab

34.5 a

32.8 e

34.5 abc

33.7 cd

34.3 ab

[iCO2 ]

Pn:E ratio Avg. can

276.9 bc

279.0 bc 277.9 a

Avg. can side 0.72 klmn 1.17 fgh 1.41 cdef 1.81 ab 1.22 efgh 0.49 n

277.8 a

1.77 ab 1.63 bc 1.39 cdefg 0.85 jkl 0.71 klmn 0.67 lmn

272.5 a

0.76 klm 1.45 cde 1.48 cd 1.85 ab 1.03 hij 0.55 mn

291.6 b

278.0 a

1.94 a 1.36 defg 0.63 lmn 0.79 jklm 0.92 ijk 1.15 ghi

15.2

13.1

0.24

242.0 e

313.5 a

261.8 d

283.3 b

264.3 cd

Pn:E ratio

Avg. can

1.10 cd

1.13 bc 1.12 a

1.59 a

0.74 e

1.17 a

1.23 bc

1.14 c

1.19 a

1.31 b

0.95 d

1.13 a

0.15

0.11

J.J Hunter et al. / Agricultural and Forest Meteorology 228–229 (2016) 104–119

Row orien

Row orien = row orientation; Can side = canopy side; % RH =% relative humidity; Tair = air temperature; PPFD = photosynthetic photon flux density; Pn = photosynthesis; E = transpiration; Sg = stomatal conductance; Tleaf = leaf temperature; iCO2 = internal CO2 concentration. LSD applicable to mean values followed by letters within columns.

115

116

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Fig. 9. Micro hourly mean relative humidity of Shiraz/101-14 Mgt vineyard planted to four different row orientations at Robertson experiment farm of ARC InfruitecNietvoorbij (average of three seasons: 2011/12–2013/14).

of measurement and N and S canopy sides in fact showed most different values of all treatments. In view of this, canopy density of EW orientated rows would be critical during the entire season and should be well managed in order to favour Pn and other viticulturally important factors, such as bud fertility, shoot lignification and grape ripening (Hunter, 2000; Hunter et al., 2004a,b). In a preliminary study, row orientations studied here also showed an impact on orientation of leaves in a horizontal plane, with a significant change in direction of primary leaf dorsal surface exposure from an early to late ripening stage (Pisciotta et al., 2011). Specific leaf weight was also affected.

Results point to differences in energy balances and seasonal dynamics of physiological parameters, such as carbon assimilation and water status, which may be induced by row orientation in the grapevine canopy. Results showed the necessity of creating a well-accommodated and microclimatic-efficient canopy to maintain capacity to supply primary compounds and hormones to bunches and reserve compartments as well as to protect bunches from extreme environmental/climatic events that may be physically and physiologically detrimental. Sucrose and water transport to grapes seems to be regulated by a combination of environmental and physiological factors, i.e. photosynthetic activity,

J.J Hunter et al. / Agricultural and Forest Meteorology 228–229 (2016) 104–119

117

Fig. 10. Micro hourly mean canopy temperature of Shiraz/101-14 Mgt vineyard planted to four different row orientations at Robertson experiment farm of ARC InfruitecNietvoorbij (average of three seasons: 2011/12–2013/14).

canopy and berry microclimate, osmotically driven transport, berry evapotranspiration, sucrolytic enzyme activity, membrane degeneration/permeability and a change in ratio of xylem:phloem import after véraison (Lang and Düring, 1991; Greenspan et al., 1994; Hunter et al., 1994; Rebucci et al., 1997; Dreier et al., 1998; Dreier et al., 2000; Hunter and Ruffner, 2001; Hunter et al., 2004a,b; Greer and Rogiers, 2009; Hunter et al., 2010b; Hunter et al., 2014a, 2014b). Clearly, orientation of grapevine rows may have a large impact on the value of each of these factors in seasonal behaviour of vines and eventual effect on grape composition and wine quality/style. As the physiological measurements were not continuously moni-

tored during the season, results represent a temporal status during the time period of measurement. The level of reaction to the climatic profiles may change according to e.g. time of season/canopy age/grape development and the intensity level of meteorological impact. Light exposure and ambient temperature have differential effects that are not easily separated under field conditions. Nevertheless, given data in this study on light distribution in the canopy, row orientation can be crucial in determination of microclimatic conditions under which the grape berry grows and ripen. As berry sunlight exposure and temperature are well-known regu-

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lating drivers of modification of whole plant and berry size (along with water availability) and the wide variety of biochemical and physiological processes taking place pre- and post-véraison in both canopy and grapes, oenological quality potential of grapes is largely determined by these two environmental factors; it has already been linked to the matrix of sugar accumulation, anthocyanin formation, flavonol and tannin contents, and terpene, carotenoid and methoxypyrazine synthesis and maintenance in both red and white grapes (Coombe, 1987, 1989, 1992; Smart et al., 1990; Hunter et al., 1991a,b, 2010b; Allen and Lacey, 1993; Marais et al., 1999; Spayd et al., 2002; Pereira et al., 2006; Tarara et al., 2008, and references therein; Hunter and Bonnardot, 2011). Row orientation as viticulture practice is therefore of critical importance in the quest for grape and wine quality/style.

4. Conclusions The study provides novel knowledge on the effect of row orientation of vertically trellised vines on vineyard meso- and microclimate and vine physiological status, within context of regional macroclimate characterised by low winter rainfall, relatively high summer temperatures and the necessity of intensive irrigation of vineyards. The global climate change scenario made this a suitable environment in which to study the impact of row orientation as viticulture practice on climatic and physiological parameters. Although latitude would impact on solar incidence angles, results have global relevance from a vineyard decisionmaking and management perspective. Climatic profiles of different vertically trellised row orientations are extremely important in expectations and interpretation of vine physiological and morphological behaviour, especially at levels of leaf function, yield, berry development, berry temperature, berry composition and whole plant health under different climatic conditions. Differences in energy balances and seasonal dynamics of physiological parameters, such as carbon assimilation and water status, may be induced by grapevine row orientation. Irrespective of row orientation, canopy density is re-confirmed as an important factor in composition of the climatic environment to which leaves and grapes are subjected during growth. Judicious vineyard management during both pre- and post-véraison periods is required to buffer environmental extremes and would largely contribute to an efficient, sufficient and healthy canopy that satisfies anticipated viticulturally important outcomes, such as berry and shoot growth, bud fertility, shoot lignification, yields, and a grape composition that would support wine quality objectives; this would also minimise interference of other biotic and abiotic factors on the role and contribution of row orientation as viticulture practice. Comprehensive results in this study provide novel insights on the role of row orientation in vineyard- and canopy climatic profiles and its complex relationship with some important physiological processes. These results are critical for new establishments and management of existing vineyards, irrespective of prevailing environmental/climatic conditions and product objectives.

Acknowledgements We would like to thank the Agricultural Research Council and South African Wine Industry (through Winetech) for funding. Our gratitude goes to personnel of the Viticulture Department (especially G.W. Fouché, A. Marais, C. Paulse and V. Jones) and farm personnel at Robertson Experiment Farm of ARC InfruitecNietvoorbij for their diligence and devotion. We would also like to extend our sincerest gratefulness to many international and local collaborators and specialists for their assistance and contributions

in many ways. Special thanks also to M. Booyse of the Biometry Department of ARC.

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