LAUSR

The differential stomatal regulation of transpiration among plant species in response to water deficit is not fully understood, although several hydraulic traits have been reported to influence it. This knowledge gap is partly due to a lack of direct and concomitant experimental data of transpiration, stomatal conductance and hydraulic traits. We measured sap flux density (Js), stomatal conductance (gs) and different hydraulic traits in five crop species. We aim to contribute to establish the causal relationship between water consumption and its regulation using a hydraulic trait-based approach. The results showed that the species-specific regulation of Js by gs was overall coordinated with the functional hydraulic traits analyzed. Especially relevant was the negative and significant relationship found between the Huber value (Hv) and its functional analogue ratio between maximum Js and gs (Jsmax/gsmax) which can be understood as a compensation to maintain the hydraulic supply to the leaves. Hv was also significantly related to the slope of the relationship between gs and Js response to vapor pressure deficit and explained most of its variability, adding up to evidence recognizing Hv as a major trait in plant water relations. Thus, hydraulic basis for the regulation of tree water use should be considered.