Canopy physiological changes of differently orientated vertically trellised Shiraz grapevines (NS, EW, NE-SW and NW-SE rows) were investigated.

 

Introduction

Within a specific terroir, the effect of grapevine row orientation on the functioning of both leaves and grapes would depend on factors such as dimensions of the canopy (density, length, leaf age composition – largely determined by vigour, pruning method and system, and canopy management practices), developmental stage, time during the season, and latitude. Terroir per se (e g soil fertility, soil reflection coefficient and water holding capacity, evaporative demands, ambient temperature range, prevailing wind, relative humidity, altitude, aspect, slope and erosion potential), vine and row spacing, and trellis and training, would also play a critical role in the final outcomes of row orientation.

 

Vineyard and measurements

The effect of row orientation [North-South (NS); East-West (EW); North-East-South-West (NE-SW); North-West-South-East (NW-SE), each replicated five times on a flat site of approximately 3 ha] at fixed row (2.7 m) and vine (1.8 m) spacing, on canopy physiological status of spur pruned (two buds) vertically trellised Shiraz/101-14 Mgt, was determined at the Robertson Experiment Farm of ARC Infruitec-Nietvoorbij in the Breede River Valley, a region that experiences semi-arid macroclimatic conditions. Vines were medium intensity irrigated weekly at a volume of 14 mm during the high season period. A cover crop (rye) was sowed after harvest and killed before budding. Vines were only vertically shoot positioned and topped and both actions were performed on average three times per year. Physiological measurements were done during three consecutive seasons approximately six weeks after véraison (during the last week of February) on all treatments and replications. Average data of mid-morning (10:00), mid-day (13:00) and afternoon (16:00) leaf water potential and photosynthesis are presented.

 

 

 

PHOTO 1. Close-up views at canopy level of the experiment at Robertson Experiment Farm of ARC Infruitec-Nietvoorbij, Breede River Valley, Robertson, South Africa.

 

 

 

Results

 

Macroclimate

The temperature, radiation and wind macroclimate of the Breede River Valley was discussed in the companion articles on the effect of row orientation on canopy light, temperature, wind and humidity profiles. According to the weather station data, the pre-véraison period is warm (maximum temperature 27 – 30°C) and the ripening period hot (maximum temperature >30°C). Radiation seems to pick up from the beginning to the middle of the growth season/beginning of berry ripening, whereafter it decreased towards the end of March. In general, high temperatures are not favourable for optimal photosynthetic activity (25 – 30°C under field conditions) and supply of precursors for various compounds associated with quality grape and wine composition. Under high temperature conditions (especially >35°C), the risk for organic acid respiration, high pH, poor colour and flavour development and maintenance, would be high. High photosynthetic activity (thus sucrose availability for transport to the grapes) during the pre-véraison period would contribute to primary and secondary compound pools present in berries at the start of ripening, whereas it would largely restrict a decrease in organic acid and an increase in pH during ripening.

 

Canopy physiology

Basal (bunch zone) leaf water potential, measured during the grape ripening period, generally decreased noticeably from morning to mid-day, after which it more or less stayed constant on either side of the canopy and for all row orientations (Table 1). Although differences occurred, water potential did not vary that much between different sides of the rows (irrespective of the differences in light exposure of canopy sides as shown in the companion article). The EW orientation displayed highest and NW-SE orientation lowest water potential in the morning. Despite a further decrease in water status of EW orientation, higher water retention was maintained for the remainder of the day. The water potential of other orientations decreased to similar values. Diurnally, NS, NE-SW and NW-SE orientations therefore displayed lower water potential than the EW orientation. Since general viticulture practices and canopy dimensions and exposure were managed similarly between treatments, differences seemed naturally induced only by the change in row orientation.

 

 

Photosynthesis and related parameters of canopies of different row orientations were measured during the grape ripening period (Table 2). In general, leaf temperature increased along with air temperature from the morning to the afternoon. The E, S, SE and SW canopy sides had noticeably lower leaf temperature values than other canopy sides (except for NS orientation where E and W sides showed similar values). The N side of the EW orientation displayed almost 2°C higher values than the S side, which corresponded with highest photosynthesis of leaves on this side of the canopy. Very low light conditions on the S side of EW-orientated rows were most probably the main reason for low photosynthetic activity of leaves on this side of the canopy. On average, leaf temperature showed minor differences between row orientations, with the EW and NW-SE displaying slightly lower values. The EW row orientation still had highest average photosynthesis, in agreement with high stomatal conductance and transpiration. Most uniform canopy photosynthesis (based on leaves measured in this study) was found for NS and NW-SE orientations. The photosynthesis trends of different canopy sides paralleled the light profile trends during the day and practically followed the sun movement over vineyard rows. Sides facing W, S, SE and SW displayed lower average photosynthesis and photosynthetic efficiency (photosynthesis:transpiration ratio/carbon assimilated per water loss). Higher overall photosynthesis of the EW row orientation also corresponded to higher water retention in the canopy (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 the northerly exposed side of the canopy). Considering the seasonal sun path, canopy density of EW-orientated rows would be critical during the entire season and should be managed well in order to favour photosynthesis and other viticulturally important factors, such as bud fertility, shoot lignification and grape ripening.

 

 

Results showed the necessity of creating a well-accommodated and microclimatic-efficient canopy to maintain the capacity to supply primary compounds (sucrose, amino acids, minerals, etc) and hormones to bunches and reserve compartments (roots, trunk, cordon and shoots/canes) of the vine, as well as to protect bunches from extreme environmental/climatic events that may be physically and physiologically detrimental. Clearly, orientation of grapevine rows may have a large impact on the value of each of these abiotic factors in seasonal behaviour of vines and eventual effect on grape composition and wine quality/style. As the physiological measurements were not continuously monitored during the season, results represent a temporal status at the time of measurement. The level of reaction of the vine to the climatic profiles may change according to, e g time of season/canopy age/grape development and meteorological intensity. The complex interplay between microclimatic parameters, water potential and photosynthetic activity leads to an array of physiological trigger and homeostatic mechanisms that require careful interpretation under challenging environmental conditions.

 

Conclusions

  • Differences in carbon assimilation and distribution, as well as water status, are induced by grapevine row orientation and reaction of the vine largely reflected the sun path over the canopy.
  • Row orientation is crucial in determining canopy microclimate, physical grape protection, and the metabolic activity of both leaves and berries, essential to drive sustainable yields and a grape composition suitable for high quality wine.
  • Information contributes to understanding vineyard behaviour and outcomes and is valuable for decisions regarding new establishments.

 

Summary

Vine carbon assimilation and water status responses largely reflected the sun path over the differently orientated canopies. The E, S, SE and SW canopy sides had lower leaf temperatures; E and W sides were similar. Average leaf temperature differed only slightly amongst row orientations. The EW row orientations had highest average stomatal conductance, transpiration and photosynthesis. Most uniform canopy photosynthesis was found for NS and NW-SE orientations. Sides facing W, S, SE and SW displayed lower average photosynthesis and photosynthetic efficiency (carbon assimilated/water loss). The EW rows showed higher water retention. Considering the sun path, canopy density of EW rows must be well-managed to favour photosynthesis and other important factors (bud fertility, shoot lignification and grape ripening). Information contributes to understanding vineyard behaviour and outcomes under varying and challenging terroir conditions.

 

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 L. Adams) and farm personnel at Robertson Experiment Farm of ARC Infruitec-Nietvoorbij 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. Details of this popular script can be found in the following scientific article (and the references therein):

 

Reference

Hunter, J.J., Volschenk, C.G. & Zorer, R., 2016. Vineyard row orientation of Vitis vinifera L. cv. Shiraz/101-14 Mgt: Climatic profiles and vine physiological status. Agricultural and Forest Meteorology 228, 104 – 119.

 

– For more information, contact Kobus Hunter at hunterk@arc.agric.za.

 

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