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1.  Modelling leaf photosynthetic and transpiration temperature-dependent responses in Vitis vinifera cv. Semillon grapevines growing in hot, irrigated vineyard conditions 
AoB Plants  2012;2012:pls009.
Grapevines growing in Australia suffer from high temperatures which have major effects on photosynthesis and transpiration. To learn more, gas exchange was measured over several seasons and then modelled across temperatures from 20 to 45°C and validated with independent data.
Background and aims
Grapevines growing in Australia are often exposed to very high temperatures and the question of how the gas exchange processes adjust to these conditions is not well understood. The aim was to develop a model of photosynthesis and transpiration in relation to temperature to quantify the impact of the growing conditions on vine performance.
Leaf gas exchange was measured along the grapevine shoots in accordance with their growth and development over several growing seasons. Using a general linear statistical modelling approach, photosynthesis and transpiration were modelled against leaf temperature separated into bands and the model parameters and coefficients applied to independent datasets to validate the model.
Principal results
Photosynthesis, transpiration and stomatal conductance varied along the shoot, with early emerging leaves having the highest rates, but these declined as later emerging leaves increased their gas exchange capacities in accordance with development. The general linear modelling approach applied to these data revealed that photosynthesis at each temperature was additively dependent on stomatal conductance, internal CO2 concentration and photon flux density. The temperature-dependent coefficients for these parameters applied to other datasets gave a predicted rate of photosynthesis that was linearly related to the measured rates, with a 1 : 1 slope. Temperature-dependent transpiration was multiplicatively related to stomatal conductance and the leaf to air vapour pressure deficit and applying the coefficients also showed a highly linear relationship, with a 1 : 1 slope between measured and modelled rates, when applied to independent datasets.
The models developed for the grapevines were relatively simple but accounted for much of the seasonal variation in photosynthesis and transpiration. The goodness of fit in each case demonstrated that explicitly selecting leaf temperature as a model parameter, rather than including temperature intrinsically as is usually done in more complex models, was warranted.
PMCID: PMC3345123  PMID: 22567220
2.  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 
AoB Plants  2011;2011:plr023.
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.
Background and aims
Covering whole vines with shade cloth is used to protect the vines from heat stress, but may have costs on vine productivity through reduced light availability. Our aim was to assess the carbon balance of vines growing with and without shade to quantify the impact of the covering.
Whole vines were covered with 70 % shade cloth, and shoot leaf area and leaf, stem and bunch growth were followed over two growing seasons. Photosynthesis was measured in situ in all leaves along selected shoots over the growing season. A carbon balance was constructed from the difference in acquisition of carbon and the sequestration of carbon as biomass across the growing seasons.
Principal results
Shade covering had no initial impact on shoot growth but later reduced leaf growth and later still bunch growth. Stem growth was unaffected. Photosynthetic properties were characteristic of shade leaves, with lower rates and lower light saturation compared with well-exposed leaves. Overall, net photosynthesis was reduced by 40 % by the shade covering and was attributed to the reduced photon flux densities. From the carbon balance, vines were reliant on carbon reserves over 6 weeks after budbreak until current photosynthate increased sufficiently to supply the growth. Shade covering impacted most on biomass accumulation to leaves and bunches at the stage when the vines became autotrophic, consistent with the reduction in carbon acquisition. The markedly high carbon demand by bunches caused a mid-season negative carbon balance, implying that shoots had to draw further on reserves to supply the carbon.
Shade covering over whole grapevines exacerbated the imbalance between the supply of and demand for carbon and greatly reduced vine biomass, especially reproductive allocation. Covering vines with shade cloth to protect the vines from heat events, therefore, had major costs in the carbon economy.
PMCID: PMC3176522  PMID: 22476493

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