模拟氮沉降和降雨对华西雨屏区常绿阔叶林凋落物分解的影响

从2013年11月至2015年5月,采用凋落物分解袋法,设置了对照(CK)、氮沉降(N)、减雨(R)、增雨(A)、氮沉降+减雨(NR)、氮沉降+增雨(NA)6个处理水平,研究了模拟氮沉降和降雨对华西雨屏区常绿阔叶林凋落物分解的影响。结果表明:华西雨屏区常绿阔叶林凋落叶分解较快,凋落枝分解较慢;凋落物夏季分解较快,其他季节分解较慢。经过18个月的分解后,凋落叶和枝的质量残留率分别为45.86%和86.67%,凋落叶分解50%需要的时间为1.42 a,比枝短6.19 a。各处理凋落物叶分解系数表现为:k(A)k(CK)k(NA)k(N)k(R)k(NR),凋落枝质量残留率表现为:NNRRNACKA。模拟氮沉降、减雨和增雨处理凋落叶分解50%分别需要1.79、1.94a和1.36a,凋落枝分解50%分别需要8.84、8.63 a和6.47 a。各处理凋落叶分解95%需要5.37—11.33 a,凋落枝分解95%需要27.41—33.84 a。同一氮沉降条件下,增雨处理促进凋落叶分解,减雨处理抑制凋落叶分解;同一降雨条件下,氮沉降抑制凋落叶分解。氮沉降或降雨对凋落物的分解产生显著影响(P0.05),其交互作用影响不显著(P0.05)。可见,在氮沉降持续增加和降雨格局改变的背景下,增雨促进了华西雨屏区天然常绿阔叶林凋落物的分解,氮沉降和减雨抑制了凋落物的分解,模拟氮沉降和降雨对凋落物的分解交互作用表现不明显。

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 5.37-11.33 a, while decomposition of 95% of the twig litter required 27.41-33.84 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.