Trade-offs between water use efficiency and hydraulic conductivity across 52 woody species distributed in three forests along a precipitation gradient

Water use efficiency and hydraulic conductivity are critical determinants of plant growth and adaptive ability. In principle, high hydraulic conductivity could result in low water use efficiency because of the selection between resource acquisition and resource conservation in species. However, there is insufficient evidence on whether a trade-off exists between these two plant hydraulic traits across species. Here, we quantified eight leaf and branch functional traits associated with water use efficiency and hydraulic conductivity across 52 dominant woody species from three forests (i.e. dry forest, DF; semi-wet forest, SWF; wet forest, WF) along a precipitation gradient in China. We found that plant water use efficiency and hydraulic conductivity were significantly and negatively correlated. Principal component analysis revealed that DF, SWF, and WF species were significantly isolated along axis 1. In contrast to species distributed in WF and SWF, DF species had the lowest hydraulic conductivity, stomatal conductance, and leaf/sapwood area ratio but showed the highest intrinsic water-use efficiency, leaf carbon isotope ratio, and wood density. Stomatal conductance to water explained the differences in plant water use efficiency among different sites, whereas leaf maximum carbon assimilation rate did not. Our results suggest a trade-off between hydraulic conductivity and water use efficiency, which influences the vegetation features in different sites.