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

We measured leaf water relations and leaf structural traitsof 20 species from three communities growing along atopographical gradient. Our aim was to assess variation inseasonal responses in leaf water status and leaf tissue physiologybetween sites and among species in response tosummer water deficit. Species from a ridge-top heath communityshowed the greatest reductions in pre-dawn leafwater potentials (Yleaf) and stomatal conductance duringsummer; species from a valley-floor woodland and a midslopemallee community showed less reductions in theseparameters. Heath species also displayed greater seasonalreduction in turgor-loss point (YTLP) than species fromwoodland or mallee communities. In general, species thathad larger reductions in Yleaf during summer showed significantshifts in either their osmotic potential at full turgor(Yp 100; osmotic adjustment) or in tissue elasticity (emax).Yp 100 and emax were negatively correlated, during bothspring and summer, suggesting a trade-off between thesedifferent mechanisms to cope with water stress. Specific leafarea varied greatly among species, and was significantlycorrelated with seasonal changes in YTLP and pre-dawnYleaf. These correlations suggest that leaf structure is a prerequisitefor cellular mechanisms to be effective in adjustingto water deficit.