Water use efficiency and its influencing factors following plantations restoration with Caragana korshinskii and Robinia pseudoacacia in the loess hilly region

Abstract

Water use efficiency (WUE) as an indicator reflecting plant drought resistance, is crucial for plant survival adaptation and forestland sustainability especially in water scarce areas during revegetation. The understanding of WUE characteristics of major tree species at different ages and the key factors influencing WUE in the loess hilly region is currently lacking. The study selected Caragana korshinskii (CK) and Robinia pseudoacacia (RP) plantations, two species widely planted in different plantation ages (16, 30, and 47 years), in the loess hilly region. The instantaneous water use efficiency (WUEt) and short-term water use efficiency (WUEs) of these plantations were calculated to investigate the factors influencing both WUEt and WUEs. The results showed that the WUEt and WUEs of CK plantations showed an increasing trend with increasing plantation age, while the RP plantations was lowest at 30 years. The soil water content (SWC) in CK and RP plantations demonstrated an upward trend as the age of the plantations increased, while the pH showed a decreasing trend. Older CK plantations had high porosity of soil (Ps) and saturated hydraulic conductivity (Ks), coupled with a low bulk density (BD). Unlike CK plantations, the maximum value of Ps in RP plantations was observed at 30 years. The soil organic carbon (SOC), dissolved organic carbon (DOC), total nitrogen (TN), and dissolved organic nitrogen (DON) contents of RP and CK plantations increased with the increase of restoration years. Except for net photosynthetic rate (An), the 16-year RP and CK showed strong photosynthesis. During the revegetation process, soil and leaf factors explained 85.31% and 90.52% of the differences in WUEt and WUEs under plantations at different stand ages. Among them, DON and intercellular CO2 concentration (Ci) were the most sensitive factors to WUE in soil physicochemical and leaf physiological properties, respectively. The interaction between soil physicochemical and leaf physiological properties significantly influences variations in WUEt and WUEs. These variations were primarily constrained by the synergistic effects of DON, SWC and, Ci. In conclusion, our study underscores the importance of soil and leaf factors in affecting WUE, contributing to improved understanding of water utilization capacity and stand growth strategies during vegetation restoration.