Linking stem rehydration kinetics to hydraulic traits using a novel method and mechanistic model.

BACKGROUND:Despite the recognized importance of hydraulic capacitance as a mechanism used by plants to maintain hydraulic functioning during high transpiration, characterizing the dynamics of capacitance remains a challenge. METHODS:We used a novel 'two-balance method' to investigate relationships between stem rehydration kinetics and other hydraulic traits in multiple tree species, and we developed a model to explore stem rehydration kinetics further. KEY RESULTS:We found that: (1) rehydration time constants and the amount of water uptake occurring during rehydration differed significantly across species; (2) time constants did not change with declining water potential (Ψ), while water uptake increased at lower Ψ in some species; (3) longer time constants were associated with lower wood density, higher capacitance and less negative stem pressures causing 50 % loss of hydraulic conductivity (P50); (4) greater water uptake occurred in stems with lower wood density and less negative P50 values; and (5) the model could estimate the total hydraulic resistance of the rehydration path, which cannot be measured directly. CONCLUSIONS:Overall, the two-balance method can be used to examine rehydration dynamics quickly and thoroughly in detached woody stems. This method has the potential to improve our understanding of how capacitance functions across tree species, which is an often-overlooked component of whole-plant hydraulics.