Effects of long‐term nitrogen addition on water use by Cunninghamia lanceolate in a subtropical plantation

Abstract

AbstractThe deposition of reactive nitrogen (N) has substantially increased in subtropical regions due to human activities. However, the effects of long‐term N addition on the water‐use efficiency of subtropical forests are poorly understood. Here, we conducted an 11‐year experiment in a subtropical Cunninghamia lanceolate plantation with four N‐addition levels: N0, N1, N2, and N3 (equivalent to 0, 6, 12, and 24 g N m−2 year−1, respectively). A thermal dissipation probe system was used to calculate sap flow, and plant biomass carbon was assessed by field investigation. The whole‐plant water use and water‐use efficiency were estimated. In addition, the δ13C of tree rings was used to indicate the plant intrinsic water‐use efficiency. The results showed that N3 treatment significantly increased the annual sap flow velocity, especially in summer and winter. Annual water use, plant growth, and water‐use efficiency did not significantly differ among the N treatments, but water use tended to be higher in N3 treatment than in N0 treatment. Furthermore, the significant reduction of δ13C in N3 treatment than in N0 treatment supported the inference that N addition could increase water use. We conclude that long‐term addition of high levels (but not of low levels) of N increased whole‐plant water use in C. lanceolate plantations. Our findings indicate that N deposition accompanied by high temperature and drought events may negatively affect water balance in subtropical forests.