Effects of simulated nitrogen deposition and precipitation changes on litter decomposition in an evergreen broad-leaved forest in the rainy area of western China
Nitrogen deposition and changes in precipitation patterns are two primary effects of global climate change. In order to understand the effects of both nitrogen deposition and precipitation changes,and their interaction on litter decomposition,in an evergreen broad-leaved forest,from November 2013 to May 2015,an experiment was conducted in situ in the rainy area of western China. The study included six treatments: control (CK),nitrogen deposition (N),water reduction (R),water addition (A),nitrogen deposition * water reduction (NR),and nitrogen deposition * water addition (NA). The results revealed that the leaf decomposition rate was higher than the twig decomposition rate,and litter decomposition was faster in summer than in other seasons. After decomposition for 18 months,the leaf and twig residual rates were 45.86% and 86.67%,respectively. It took 1.42 years for 50% of the leaf litter mass to decompose,which was 6.19 years shorter than that for twigs. The decomposition coefficient of each treatment was as follows: k(A) > k(CK) > k (NA) >k(N) > k(R) > k(NR),and the residual rate of twig decomposition was N>NR>R>NA>CK>A. The simulated nitrogen deposition,water reduction,and water addition treatments,which were performed to decompose 50% of the leaf litter mass,took 1.79,1.94,and 1.36 a,respectively; and 8.84,8.63,and 6.47 a,respectively,to decompose 50% of the litter mass. Each treatment performed to decompose 95% of the leaf litter required 5.3711.33 a,while decomposition of 95% of the twig litter required 27.4133.84 a. Under the same nitrogen deposition conditions,water addition treatment promoted the decomposition of leaf litter,while water reduction treatment reduced the decomposition of leaf litter. Under the same precipitation conditions,nitrogen deposition reduced the decomposition of leaf litter. Thus,nitrogen deposition and precipitation changes had a significant effect on litter decomposition,and their interaction effect was not significant (P > 0.05). Considering that nitrogen deposition increases continuously and that global climate change is occurring,water addition treatment promoted the decomposition of litter,and nitrogen deposition and water reduction treatment reduced the decomposition of litter in an evergreen broad-leaved forest in the rainy area of western China. Therefore,the interaction between nitrogen deposition and precipitation changes did not have a significant effect on litter decomposition in this forest ecosystem.