Plant hydraulic traits regulating productivity and drought resistance in boreal crops

Abstract. Crop hydraulics play a critical role in coordinating crop photosynthesis and hydraulic safety when facing water scarcity. Boreal crop hydraulic traits and their relevance to productivity and drought resistance, however, remain poorly researched. In this study, we leveraged multi-year carbon and water flux measurements from a perennial forage grass and an annual cereal (oat) field in Finland using a novel process-based model with fully-coupled plant photosynthesis, hydraulics, and soil moisture to decipher the apparent hydraulic traits of the crops and their association with crop performances under varying drought conditions. It is found that both crops exhibited remarkably low hydraulic conductance, which plays a pivotal role in preventing soil water depletion and thereby ensures a high hydraulic safety margin and productivity under drought conditions. Both crops also showed higher susceptibility to atmospheric dryness than to soil drought, likely due to their anisohydric ("risky") stomatal behaviour. The remaining discrepancy between our model-inferred hydraulic traits and available empirical data for temperate crops highlights the need for more measurements of boreal crop hydraulic traits. Our findings underscore the importance of incorporating crop hydraulic processes in process-based crop models to gain physiological insights for crop performance and to enhance their accuracy and predictive power in both current and future climates.