LEAF MORPHOLOGY AND LIFE FORM INFLUENCE WATER RELATIONS OF HAKEA SPECIES ON DIFFERENT SOIL SUBSTRATES WITHIN SOUTHWESTERN AUSTRALIA

Water relations (xylem pressure potential (XPP), transpiration, stomat al conductance) and leaf specific resistivity (LSR) of our co-occurrin g Hakea species at each of four sires (two sites on rocky laterite, tw o sites on deep sand) were investigated under moist spring and summer drought conditions. Hakea species can be classified as possessing broa d or terete (needle-like) leaves, and either die or resprout in respon se to fire. Species representing each oi these four morphological grou ps were examined at all sires. The eight species inhabiting the lateri tic sites were more stressed (more negative XPP) in summer than the ri ght species on sandy soils, with lower conductances and higher LSR in both seasons. Broad-leaved species had higher transpiration rates and LSR, and more negative XPP in both seasons, but lower conductances in spring, than tel cte-leaved species. Non-sprouters had lower XPP in su mmer, and lower transpiration rates and conductances in both seasons, than resprouters. Among interaction effects, non-sprouters on lateriti c sites had the lowest water relations values in summer (drought toler ators) with no consistent trends in spring. There was a tendency for b road-leaved resprouters on sandy soils to have higher summer water rel ations values (drought avoiders). Broad-leaved non-sprouters on lateri tic soils could be considered the most water stressed group, with subs tantial plant death during the summer period. Terete-leaved species on sandy soils had the highest XPP in both seasons. Thus the relative ec ophysiology of co-occurring species varying in leaf morphology and lif e form may be site dependent, with differences between morphological g roups most prominent during summer.