Stand age rather than soil moisture gradient mainly regulates the compromise between plant growth and water use of Eucalyptus urophylla in hilly South China

Abstract

Large-scale cultivation and short-term rotation of Eucalyptus trees for economic reasons have led to excessive consumption of soil water, raising broader ecological, and environmental concerns. Therefore, exploring the balance between water use and plant growth of Eucalyptus trees has become increasingly important but remains understudied. Here, we hypothesized that stand age and soil moisture gradient can both regulate such balance and examined this hypothesis by collecting a field dataset of Eucalyptus urophylla plantations that respectively capture three age categories (i.e., young age of 3–4 years, mature age of 6–7 years, and old age of >25 years) and span three soil moisture gradients along a hilly slope in South China. The datasets collected in Jan/2018–Dec/2019 included (a) continuous measurements of tree sap flow and soil moisture and (b) periodic measurements of leaf water potential (Ψleaf), tree biometric parameters, and stand leaf area index (LAI). With the data, we derived the monthly tree transpiration (EL), annual growth rate, and tree water use efficiency (WUE). Our results showed that stand age importantly regulated plant growth and water use, as old trees transpired more water than young and mature trees, while the young trees have significantly higher WUE due to their relatively higher growth rate and lower water consumption. In contrast, we did not observe significant differences in tree transpiration along with soil moisture gradients at each age level, suggesting stand age rather than soil moisture gradient dominantly regulates the growth versus water-use compromise. Our results also showed that the old trees can maintain a more stable water consumption, suggesting that they are less sensitive to environmental seasonality and thus more stable. Collectively, our study provides important insights into the management and ecosystem stability of Eucalyptus plantation in South China.