Mark M. Weedon

Modelling photosynthetic responses to temperature of grapevine (Vitis vinifera cv. Semillon) leaves on vines grown in a hot climate

Field measurements of photosynthesis of Vitis vinifera cv. Semillon leaves in relation to a hot climate, and responses to photon flux densities (PFDs) and internal CO(2) concentrations (c(i) ) at leaf temperatures from 20 to 40 °C were undertaken. Average rates of photosynthesis measured in situ decreased with increasing temperature and were 60% inhibited at 45 °C compared with 25 °C. This reduction in photosynthesis was attributed to 15-30% stomatal closure. Light response curves at different temperatures revealed light-saturated photosynthesis optimal at 30 °C but also PFDs saturating photosynthesis increased from 550 to 1200 µmol (photons) m(-2)s(-1) as temperatures increased. Photosynthesis under saturating CO(2) concentrations was optimal at 36 °C while maximum rates of ribulose 1,5-bisphosphate (RuBP) carboxylation (V(cmax)) and potential maximum electron transport rates (J(max)) were also optimal at 39 and 36 °C, respectively. Furthermore, the high temperature-induced reduction in photosynthesis at ambient CO(2) was largely eliminated. The chloroplast CO(2) concentration at the transition from RuBP regeneration to RuBP carboxylation-limited assimilation increased steeply with an increase in leaf temperature. Semillon assimilation in situ was limited by RuBP regeneration below 30 °C and above limited by RuBP carboxylation, suggesting high temperatures are detrimental to carbon fixation in this species.

The impact of high temperatures on Vitis vinifera cv. Semillon grapevine performance and berry ripening

The heat event that occurred in many parts of Australia in 2009 was the worst on record for the past decade, with air temperatures exceeding 40°C for 14 days. Our aim was to assess the impacts of this heat event on vine performance, including ripening, yield, and gas exchange of Vitis vinifera cv. Semillon grown in a Riverina vineyard. To assess the affect of high temperatures on Semillon grapevines, the vines were covered with a protective layer to reduce radiant heating and were compared with vines exposed to ambient conditions. The heat event had major effects on ripening; reducing the rate of ripening by 50% and delaying harvest ripeness and causing a high incidence of berry shrivel and sunburn. Yield was not affected. Photosynthesis was reduced 35% by the heat event while transpiration increased nearly threefold and was accounted for by increased stomatal conductance. The conclusion of this study was that heat events delayed ripening in Semillon berries and caused a significant reduction in berry quality. Strategies to minimize the radiant load during heat events are required and this study has confirmed a protective layer can reduce canopy temperatures and enhance berry quality.

Reductions in biomass accumulation, photosynthesis in situ and net carbon balance are the costs of protecting Vitis vinifera ‘Semillon’ grapevines from heat stress with shade covering

Shade cloth can be used to protect grapevines from high temperatures. However, the resulting low light intensity is shown to reduce photosynthesis, leading to lower carbon allocation to vegetative growth and sugar accumulation. Protection from heat by shading is, therefore, costly for the carbon economy of the vines.

Shoot architecture, growth and development dynamics of Vitis vinifera cv. Semillon vines grown in an irrigated vineyard with and without shade covering

Covering vines with shade cloth has been proposed as a means of reducing canopy temperatures to reduce heat impacts. Because shade cloth concomitantly reduces irradiance, the objective of the study was to assess the effects of shade covering on growth and development of Semillon (Vitis vinifera L.) vines in vineyard conditions over three growing seasons. Air and canopy temperatures were measured throughout. Stem extension and leaf areas were measured on selected shoots throughout the season and at harvest, all shoots were destructively harvested and internode lengths, leaf areas and stem lengths were measured and leaves, stems and bunches dried to the determine the dry matter of each shoot. Results showed shoot growth, architecture and development were all affected by the shade. Total shoot biomass was reduced by 20%, although shoot biomass allocation was not affected. The distribution of different shoot types, based on numbers of nodes and stem lengths, was shifted in favour of medium length shoots at the expense of long shoots under the shade, consistent with decreased apical meristem activity in shade conditions. Shade also caused a major impediment to leaf development, with individual leaves delayed in expansion by 10–25 days compared with leaves on exposed vines at comparable stages of development. However, the delay in development was offset by expansion; shaded leaves expanding to a larger size than for exposed leaves. The difference in leaf size may be a strategy to compensate for the slower development in the shade conditions.

Temperature-dependent responses of the berry developmental processes of three grapevine (Vitis vinifera) cultivars

The intrinsic relationship between grape berry ripening and temperature is not well understood. The aim was to compare ripening in three cultivars—Vitis vinifera L. cv. Chardonnay, cv. Merlot and cv. Semillon—in response to temperature. In the post-veraison period (soluble solids 8–12 oBrix), whole vines were exposed to five controlled temperature regimes, with the day temperature ranging from 20–40 °C, and the berry attributes and the ripening processes followed. Temperature had little effect on the berry expansion process in all cultivars. However, there were marked effects of temperature on the accumulation of both dry matter and sugar in all varieties. The rate of ripening in all three cultivars was a curvilinear function of temperature. Rate of ripening of Chardonnay berries was highest at 25 °C and for Semillon and Merlot at 35 °C and 40 °C, respectively. Application of the temperature response to field-grown Semillon vines accurately predicted the seasonal progression of ripening.

Does the hydrocooling of Vitis vinifera cv. Semillon vines protect the vegetative and reproductive growth processes and vine performance against high summer temperatures

A hydrocooling system applied to Semillon (Vitis vinifera L.) grapevines as a means of protecting the vines from recurrent high temperatures. This system was assessed for impacts on vegetative and reproductive growth and development as well as for carbon economy of vines growing in vineyard conditions. The system maintained canopy temperatures at 35°C over the growing season. Leaf and bunch biomass and yield were all higher in the hydrocooled compared with control vines: the major effect was on dynamics of leaf and berry expansion. Leaf expansion was delayed and occurred over a longer duration whereas berry expansion was advanced and occurred over a longer duration than in control vines. Berry ripening was also faster in the hydrocooled vines and berries had accumulated more sugar at harvest. Leaf photosynthesis along the shoot was also higher in hydrocooled than control vines and there was a significant effect of leaf position on rates of photosynthesis of the hydrocooled vines but not with control vines. However, no differences were observed in the net shoot carbon budget. Lowered canopy temperatures were beneficial for yield and berry composition and, therefore, the cooling system warrants adoption in vineyards at risk from high temperature events during the growing season.

Establishing the temperature dependency of vegetative and reproductive growth processes and their threshold temperatures of vineyard-grown Vitis vinifera cv. Semillon vines across the growing season

A hydrocooling system provided canopy temperature control of Vitis vinifera L. cv. Semillon vines at set points of 30, 35 and 40°C. The impacts on vegetative and reproductive growth over the growing season were assessed. Dynamics and rates of leaf expansion, bunch biomass and sugar accumulation were strongly affected by canopy temperatures - being highest at 30°C and lowest at 40°C. Leaf and stem biomass accumulation at 40°C was detrimentally affected but was otherwise little affected by temperature. Leaf expansion was earliest, leaf sizes greatest and rates of expansion all optimal at 30°C and all were strongly temperature dependent. Bunch biomass accumulation was earliest at 35°C but amount of biomass in bunches and rates were both highly temperature dependent and optimal at 30°C. Rates of sugar accumulation and total amounts accumulated at harvest were both highly temperature-dependent processes: fastest and greatest at 30°C. Many of the temperature-dependent processes decreased in rates and amounts linearly between 30 and 40°C. Despite the effects of temperature on bunch and berry growth, there were no treatment effects on the yield per vine. The study confirms that the threshold temperature for most processes was 35°C, where some depreciation in dry matter and sugar accumulation occurred, whereas 40°C was detrimental to all growth processes.

Can a small differential in canopy temperature influence performance of Semillon in a vineyard

ABSTRACT Vegetative and reproductive growth responses of vineyard-grown Vitis vinifera cv. Semillon vines to canopy temperatures were followed. Canopies were controlled at means of 29.8°C, 31.5°C and 32.7°C. Stem and leaf growth were affected; length and canopy leaf area was maximal in the warmest treatment and smallest in the coolest treatment. Accumulation of biomass of leaves, stems and bunches was highest in the coolest treatment and lowest in warm conditions. Berry expansion was affected by treatment temperatures but most reduced in the warm treatment, whereas accumulation of sugar in the berries was highest in the coolest treatment. There were treatment differences in yield, with a marked reduction in the warm treatment. Clearly, there were detrimental growth responses to the higher temperatures. The temperature differential between treatments of 3°C was comparable with what might occur with climate change and the study shows such a difference can be detrimental to vine growth and development.