Isometric partitioning of hydraulic conductance between leaves and stems: balancing safety and efficiency in different growth forms and habitats

Recent advances in modelling the architecture and function of the plant hydraulic network have led to improvements in predicting and interpreting the consequences of functional trait variation on CO2 uptake and water loss. We build upon one such model to make novel predictions for scaling of the total specific hydraulic conductance of leaves and shoots (k(L) and k(SH), respectively) and variation in the partitioning of hydraulic conductance. Consistent with theory, we observed isometric (slope=1) scaling between k(L) and k(SH) across several independently collected datasets and a lower ratio of k(L) and k(SH), termed the leaf-to-shoot conductance ratio (C-LSCR), in arid environments and in woody species. Isometric scaling of k(L) and k(SH) supports the concept that hydraulic design is coordinated across the plant. We propose that C-LSCR is an important adaptive trait that represents the trade-off between efficiency and safety at the scale of the whole plant. Plant hydraulic network models have improved our ability to predict and interpret the consequences of functional trait variation. We build upon one such model to make novel predictions for scaling of the total specific hydraulic conductance of leaves and shoots and variation in the partitioning of hydraulic conductance between plant components. We observed coordinated design of the stem and leaf hydraulic network and partitioning of less hydraulic conductance to leaves of woody perennial plants and in arid environments. From these observations it is proposed that the partitioning of hydraulic conductance between stems and leaves represents a trade-off between efficiency and safety at the scale of the whole plant.