Water-use efficiency of a mallee eucalypt growing naturally and in short-rotation coppice cultivation

Abstract

This study compared mature Eucalyptus kochii subsp. plenissima trees in inner regions or edges of natural bushland to young trees belt-planted through cleared agricultural land as uncut saplings or regenerating coppice over 2.7 years at Kalannie, Western Australia (320 mm annual rainfall). We assessed the ability of the species to alter its gas exchange characteristics, leaf physical attributes, and water-use efficiency of foliar carbon assimilation (WUE i) or of total dry matter production (WUE DM). Stomatal conductance (g s) varied five-fold between treatment means, with coppices exhibiting greatest values and mature bush least. Photosynthetic rates followed this trend. Leaf photosynthetic capacity estimated by chlorophyll content varied 1.3-fold parallel with variations in leaf thickness, with coppices rating lowest and mature edge trees most highly. WUE i varied 1.5-fold between treatments and was greatest in mature inner-bush and edge trees. Leaf photosynthetic capacity and g s were both correlated with WUE i. Carbon isotope composition (δ13C values) of new shoot dry matter produced early in a seasonal flush were similar to those of root starch but when averaged over the whole season correlated well with WUE i and gas exchange characteristics of trees of each treatment. Coppices showed poorest WUE i and most negative shoot tip δ13C but their WUE DM was high. This discrepancy was suggested to relate to carbon allocation strategies in coppices favouring fast growth of replacement shoots but not of roots. Physiology of coppice growth of E. kochii is usefully geared towards both rapid and water-use efficient production of woody biomass in water limited environments.