Productivity and water use efficiency of Pinus tabulaeformis responses to climate change in the temperate monsoon region

As one of the main afforestation species, Pinus tabulaeformis is an important carbon sink in China. We developed tree-ring chronologies of Pinus tabulaeformis at five plantation sites (Lingkong Mountain (LKM), Fujia (FJ), Heishui (HS), Caijiachuan (CJC) and Jiufeng (JF)), and measured the delta 13C values of tree rings using the stable carbon isotope method to calculate intrinsic water use efficiency (iWUE). The responses of net primary pro-ductivity (NPP) and iWUE to climatic variables were explored. The annual variation in both NPP and iWUE had increasing trends, with lower iWUE increasing rate at LKM site in comparison with those at other 4 sites. iWUE of the young stand was higher than that of the old stand. Annual patterns of the delta 13C values showed significant decreasing trends in LKM and CJC but a rising trend in HS. The growth of Pinus tabulaeformis was more sensitive to temperatures, and temperatures exerted positive effects on NPP and iWUE. At the old stands, both NPP and iWUE had closer relationships with temperatures. On the annual scale, precipitation had little effect on NPP and iWUE. Annual mean standardized precipitation evaporation index had a significant influence on iWUE at the young stand. Resistance was positively correlated with recovery, resilience and iWUE, but negatively correlated with NPP. Pinus tabulaeformis at CJC site had the stronger resistance to drought events in comparison with that at LKM and FJ sites. This study provides insight into the responses of Pinus tabulaeformis productivity and water use to climate change, and helps evaluate carbon sink and water-carbon trade-off of plantations.