Leaf water relations during summer water deficit: Differential responses in turgor maintenance and variation in leaf structure among different plant communities in south-western Australia

Abstract

We measured leaf water relations and leaf structural traits of 20 species from three communities growing along a topographical gradient. Our aim was to assess variation in seasonal responses in leaf water status and leaf tissue physiology between sites and among species in response to summer water deficit. Species from a ridge-top heath community showed the greatest reductions in pre-dawn leaf water potentials (Ψleaf) and stomatal conductance during summer; species from a valley-floor woodland and a midslope mallee community showed less reductions in these parameters. Heath species also displayed greater seasonal reduction in turgor-loss point (ΨTLP) than species from woodland or mallee communities. In general, species that had larger reductions in Ψleaf during summer showed significant shifts in either their osmotic potential at full turgor (Ψ π100; osmotic adjustment) or in tissue elasticity (εmax). Ψπ 100 and εmax were negatively correlated, during both spring and summer, suggesting a trade-off between these different mechanisms to cope with water stress. Specific leaf area varied greatly among species, and was significantly correlated with seasonal changes in ΨTLP and pre-dawn Ψleaf. These correlations suggest that leaf structure is a prerequisite for cellular mechanisms to be effective in adjusting to water deficit. © 2008 The Authors.