Water cycling and partitioning through the soil–plant–atmosphere continuum in a subtropical, urban woodland inferred by water stable isotopes

Abstract

AbstractFor many urban woodlands, knowledge of how water is cycled and partitioned by plants is important for improving water management strategies, particularly during warm and wet periods with heavy, convective events in subtropical monsoon regions which are characterized by hot and humid summers. Still, most studies on these processes have been conducted in rural, none subtropical areas. Useful tools for tracing water movement during different precipitation events are stable water isotopes. So far, very few studies have been carried out in urbanized woodlands where the natural hydrological cycle is affected by strong anthropogenic influences. We conducted an intense spatio‐temporal sampling campaign of water isotopes, combined with relevant atmospheric parameters, climatic and hydrometric data across an evergreen broad‐leaved woodland near Chengdu, SW China, to assess event‐based changes in water cycling and partitioning during the warm and wet summer of 2020. Based on event‐scale precipitation samples, soil and plant water samples, we found similar temporal variations in the water isotopes of precipitation, soil, and plants, with a gradual enrichment in the order of precipitation – soil water – plant water. However, the responses of soil and plant water to precipitation were delayed. From the dynamics of soil water content and soil water isotopes, evaporative fractionation and precipitation signatures were determined as the critical factors in influencing water storage and compositions through the soil profile. Only precipitation events >5 mm recharged the soil profile, with a ~ 24 h time lag in the response time of soil water (0–50 cm) to effective events. The water isotopes in the branches and leaves of the plants reflected their water sources primarily from 0 to 50 cm soil layers and water losses through evapotranspiration, respectively. These isotopic signals described the transfer and exchange of water in the soil–plant‐atmosphere continuum and therefore improved our understanding of water cycling and partitioning in an urban woodland in a subtropical monsoon humid region, which may have important implications for urban green space and ecosystem services in other regions.