Variations of water use efficiency, C, N concentration in Chinese fir under climate change based on carbon stable isotope analysis

Abstract

Water use efficiency (WUEi) can strongly influence the growth of individual tree diameter, and drought caused by increasing temperatures can profoundly affect the water use strategy of red-heart Chinese fir. The differences in WUE of red-heart Chinese fir juveniles under different ages and meteorological conditions have not been studied yet. Here, the standardized precipitation evapotranspiration index (SPEI) was calculated to determine the extent of drought and studied the relationship between WUEi and other ecological factors through path analysis. Compared with 1981–2020, the mean monthly temperature and annual total precipitation in 2015–2020 increased by 0.7 ° C and 177mm, respectively. Significant differences in WUEi at different leaf and branch ages. WUEi and N concentration decreased with the age increase, but C concentration increased. Carbon isotope increased with the increase of relative tree height. N concentration and C/N did not change significantly with the increase in relative tree height. There were significant differences in WUEi under different SPEI. In 2020 (SPEI = 0.12), the WUEi of branches and leaves was the highest, which were 92.7% and 88.4%, respectively. WUEi and C concentration have a significant negative relationship (-0.516). Tree basic area increment (BAI) was significantly negatively correlated with precipitation (-0.777) and relative humidity (-0.488) and significantly positively correlated with temperature (0.871). Our results show that red-heart Chinese fir has a high demand for water and nutrients in the juvenile stage, which could further provide a theoretical basis for the directed cultivation and sustainable management of red-heart Chinese fir.