Understanding the distribution of gas exchange within a plant is a prerequisite for scaling up from leaves to canopies. We evaluated whether leaf traits were reliable predictors of the effects of leaf ageing and leaf irradiance on leaf photosynthetic capacity (Vcmax, Jmax) in field-grown vines (Vitis vinifera L). Simultaneously, we measured gas exchange, leaf mass per area (LMA) and nitrogen content (Nm) of leaves at different positions within the canopy and at different phenological stages. Daily mean leaf irradiance cumulated over 10 d (PPFD10) was obtained by 3D modelling of the canopy structure. Nm decreased over the season in parallel to leaf ageing while LMA was mainly affected by leaf position. PPFD10 explained 66, 28 and 73% of the variation of LMA, Nm and nitrogen content per area (Na), respectively. Nitrogen content per unit area (Na = LMA ¥ Nm) was the best predictor of the intra-canopy variability of leaf photosynthetic capacity. Finally, we developed a classical photosynthesis-stomatal conductance submodel and by introducing Na as an input, the model accurately simulated the daily pattern of gas exchange for leaves at different positions in the canopy and at different phenological stages during the season.
UMR AGAP Equipe Diversité, adaptation et amélioration de la vigne (DAAV)Background and Aims: Based on 19 nuclear simple sequence repeat markers and parental analysis, we aimed to identify and propose the pedigree of different accessions held at the Estación Experimental Agropecuaria Mendoza of the Instituto Nacional de Tecnología Agropecuaria germplasmcollection. The results were compared with data recorded in large, international databases.Methods and Results: We identified 37 different cultivars, of which 18 were original and not previously identified. The parentage analysis showed that European cultivars, such as Muscat of Alexandria, Muscat à Petits Grains, Listán Prieto, Mollar Cano and Malbec, were involved in natural crossings resulting in different South American cultivars.Conclusions: Many of the cultivars identified here represent unique individuals based on their genotype. The number of cultivars that participated as progenitors in the origin of South American germplasm is higher than previously thought.Significance of the Study: Germplasm collections planted many years ago play a key role in the conservation and characterisation of genotypes that otherwise may have been lost. It is highly probable that there might be other genotypes not identified and mixed in old vineyards. The identification, rescue and conservation of these genotypes are a challenge to preserve the existing genetic variability
Background and Aims Regulated deficit irrigation (RDI) and bunch thinning are two viticultural practices applied worldwide. There is limited knowledge, however, about their combined effects on carbohydrate dynamics and accumulation. We evaluated during year 3 and 4 of the experiment the effect of 4 consecutive years of RDI and bunch thinning on carbohydrate status, vegetative and reproductive variables. Methods and Results From 2006/07 to 2009/10, we imposed four levels of water supply [100, 60, 38 and 25% of reference evapotranspiration (ETo)] and two crop loads (100 and 50% of the bunches). We compared shoot length, flowers per inflorescence and yield in 2009/10. We also measured pruning mass and the concentration of non‐structural carbohydrates in dormant wood in the winters of 2009 and 2010. Starch concentration in the trunk was reduced by severe water deficit (25 and 38% ETo) and improved by bunch thinning. Pruning mass, shoot length, flowers per inflorescence and yield were affected in vines with water applied at 25 and 38% of ETo. Conclusions Severe water stress and high crop load reduced trunk starch concentration with no interaction between both factors, whereas the concentration of total non‐structural carbohydrate was not affected. Vegetative growth and yield were reduced after 4 years of severe water stress. Significance of the Study We provide evidence that starch concentration and carbon partitioning can be manipulated through common viticultural practices, such as irrigation and crop load.
Background and Aims Studies of the interactive effects of drought and high temperature on the physiological responses of grapevines (Vitis spp.) are scarce. We tested whether well‐watered, potted vines were able to avoid heat waves through evaporative cooling in comparison to those suffering from water deficit. Methods and Results A greenhouse experiment was conducted with own‐rooted Malbec grapevines under two water regimes, well‐watered (100% of pot capacity) and water deficit (50% of pot capacity), and two air temperature regimes, high (45/22°C) and Control temperature (35/20°C). Short‐term stomatal and non‐stomatal regulation of photosynthesis was assessed by measuring leaf gas exchange, stomatal conductance (g s) and chlorophyll fluorescence. Whole‐plant transpiration and vegetative growth were also measured. In well‐watered vines, high air temperature increased g s and leaf transpiration (E leaf), which decreased leaf temperature and increased vegetative growth, whole‐vine transpiration and leaf net photosynthesis (P n). Water deficit strongly reduced growth, P n, g s and E leaf. For vines under high temperature, however, reduction in P n, g s and E leaf was smaller than for that under the Control temperature. Conclusions Evaporative cooling may help well‐watered grapevines withstand heat waves and avoid irreversible reduction in gas exchange and chlorophyll fluorescence. Significance of the Study This study improves our understanding of grapevine response to a heat stress and water deficit, which are both predicted to increase with climate change.
Background and Aims Scaling from single-leaf to whole-canopy photosynthesis faces several complexities related to variations in light interception and leaf properties. To evaluate the impact of canopy strucuture on gas exchange, we developed a functional–structural plant model to upscale leaf processes to the whole canopy based on leaf N content. The model integrates different models that calculate intercepted radiation, leaf traits and gas exchange for each leaf in the canopy. Our main objectives were (1) to introduce the gas exchange model developed at the plant level by integrating the leaf-level responses related to canopy structure, (2) to test the model against an independent canopy gas exchange dataset recorded on different plant architectures, and (3) to quantify the impact of intra-canopy N distribution on crop photosynthesis. Methods The model combined a 3D reconstruction of grapevine (Vitis vinifera) canopy architecture, a light interception model, and a coupled photosynthesis and stomatal conductance model that considers light-driven variations in N distribution. A portable chamber device was constructed to measure whole-plant gas exchange to validate the model outputs with data collected on different training systems. Finally, a sensitivity analysis was performed to evaluate the impact on C assimilation of different N content distributions within the canopy. Key Results By considering a non-uniform leaf N distribution within the canopy, our model accurately reproduced the daily pattern of gas exchange of different canopy architectures. The gain in photosynthesis permitted by the non-uniform compared with a theoretical uniform N distribution was about 18 %, thereby contributing to the maximization of C assimilation. By contrast, considering a maximal N content for all leaves in the canopy overestimated net CO2 exchange by 28 % when compared with the non-uniform distribution. Conclusions The model reproduced the gas exchange of plants under different training systems with a low error (10 %). It appears to be a reliable tool to evaluate the impact of a grapevine training system on water use efficiency at the plant level.
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