Climate Drivers of Crop Carbon Gain and Water Use in Apple Between Western and Eastern States

Apple is cultivated under various climatic conditions in many parts of the world. Better understanding of how climate factors affect crop growth and productivity at different locations will improve our ability to optimize crop selection, management strategies, and resource use. The objective of this work was to apply a process-based apple canopy model 1) to identify what and how climatic factors limit crop biomass accumulation and water use at multiple locations in the states of Washington, California, and West Virginia, and 2) to evaluate how these climate factors influence crop radiation use efficiency (RUE) and water use efficiency (WUE) in apple. Our results indicate that temperature is a dominant factor limiting biomass gain when compared across the locations while VPD was predominantly dictating crop water use during the growing season. Crop RUE and WUE were strongly correlated with each other while VPD showed highly negative correlation with both RUE and WUE across all locations examined. Locations in western WA were found to have both higher RUE and WUE than other locations examined in this study. Locations with higher diffuse light fraction (e.g., WV and western WA) tended to have greater RUE than other locations but its positive effects on RUE and WUE were negated by low total radiation and high temperatures in WV. Our results provide effective means and useful insights to disentangle the complex relationships between canopy carbon gain, water use, and climate factors that are site-specific.