Xylem traits and water-use efficiency of woody species co-occurring in the Ti Tree Basin arid zone

摘要

The hydraulic niche separation theory proposes that species co-exist by having a range of traits to allow differential access to resources within heterogeneous environments. Here, we examined variation in branch xylem anatomy and foliar carbon stable isotopes (delta C-13) as a measure of water-use efficiency (WUE) in seven co-occurring species, Acacia aneura, Acacia bivenosa, Corymbia opaca, Eucalyptus camaldulensis, Erythrina vespertilio, Hakea sp., and Psydrax latifolia, in an arid zone open Corymbia savanna on the Ti Tree Basin, Northern Territory, Australia. We test the following hypotheses: (1) Species with large conductive areas exhibit a low density of intact branches, while species with small conductive areas have a significantly higher density of intact branches. (2) Species with smaller conductive areas exhibit more enriched values of delta C-13 and therefore have larger WUE than those with larger conductive areas and (3) there is an inverse correlation between theoretical sapwood hydraulic conductivity and vessel implosion resistance. The results of this study demonstrated significant variation in density of intact branches, ranging from 0.38 to 0.80 g cm(-3) and this variation was largely explained by variation in sapwood conductive area. Species with low conductive areas (P. latifolia, Hakea sp. and Acacia species) exhibited large values of WUE (r(2) = 0.62, p < 0.05). These species are likely to be less vulnerable to cavitation by having small conductive areas and thicker fibre walls. We demonstrated a significant (r(2) = 0.83, p = 0.004) negative correlation between theoretical sapwood hydraulic conductivity and vessel implosion resistance. These results are discussed in relation to hydraulic niche separation.