Global Maps of Canopy Photosynthesis of Grapevines under a Changing Climate

Background and goals Climate change induces shifts in suitable areas for the cultivation and phenology of grapevines, which regulate both complex sunlight patterns within hedgerows and canopy photosynthetic gain (CPG). However, suitability assessments of such areas have focused on climate indices (e.g., growing season temperature) but have ignored canopy photosynthesis, despite its close connection to berry yield and wine quality. Here, we aimed to develop a model of theoretical maxima of grapevine canopy photosynthesis under the clear sky without water- and nutrient-limitations that integrated canopy light interception, leaf thermal balance, and photosynthetic processes. Methods and key findings Maps of CPG during berry development were obtained by running this model with observed hourly meteorological data collected from various sites worldwide and those under future climate with elevated air temperatures and atmospheric carbon dioxide (CO 2 ) concentrations (+2 K warmer, 500 mu mol/mol and +4 K warmer, 850 mu mol/mol). In high-latitude regions expected to become newly suitable in response to the temperature rise, the CPGs were projected to be greater than those in lower latitudes mainly because of higher cumulative light absorption, irrespective of a difference in cultivar-dependent thermal requirements for berry maturation. The higher CO 2 concentrations also increased canopy photosynthesis in these regions. By contrast, at some prestigious sites located at lower latitudes, the projected leaf temperatures exceeded the optimal range for photosynthesis, resulting in reduced gains despite the CO 2 fertilization effect. Conclusions and significance Our results clarify significant spatiotemporal variations in grapevine canopy photosynthesis, with particular emphasis on the north-south gradient, and support the decision-making of grapegrowing stakeholders.