Hydroscapes, hydroscape plasticity and relationships to functional traits and mesophyll photosynthetic sensitivity to leaf water potential in Eucalyptus species

The isohydric-anisohydric continuum describes the relative stringency of stomatal control of leaf water potential (psi(leaf)) during drought. Hydroscape area (HA)-the water potential landscape over which stomata regulate psi(leaf)-has emerged as a useful metric of the iso/anisohydric continuum because it is strongly linked to several hydraulic, photosynthetic and structural traits. Previous research on HA focused on broad ecological patterns involving several plant clades. Here we investigate the relationships between HA and climatic conditions and functional traits across ecologically diverse but closely related species while accounting for phylogeny. Across a macroclimatic moisture gradient, defined by the ratio of mean annual precipitation to mean annual pan evaporation (P/E-p), HA decreased with increased P/E-p across 10 Eucalyptus species. Greater anisohydry reflects lower turgor loss points and greater hydraulic safety, mirroring global patterns. Larger HA coincides with mesophyll photosynthetic capacity that is more sensitive to psi(leaf). Hydroscapes exhibit little plasticity in response to variation in water supply, and the extent of plasticity does not vary with P/E-p of native habitats. These findings strengthen the case that HA is a useful metric for characterizing drought tolerance and water-status regulation.