黄土丘陵区人工林刺槐和油松凋落叶在不同降雨时期的分解特征

凋落物分解是维持生态系统养分循环和能量流动的关键过程，但在雨热同期的黄土丘陵区，不同降雨时期凋落物基质质量动态对该区不同树种凋落物分解速率的影响还不清楚。采用凋落物分解袋法，基于野外原位分解实验分析黄土丘陵区主要人工林刺槐（Robinia pseudoacacia Linn.）和油松（Pinus tabulaeformis Carr.）凋落叶在不同降雨时期的分解特征和分解过程中凋落叶基质质量的变化与分解速率之间的关系。研究结果发现：（1）经过391 d的分解，刺槐凋落叶的平均质量损失速率为（51.0±8.44）mg/d，显著地高于油松凋落叶（36.7±4.83）mg/d；雨季期间两树种凋落叶的质量损失速率均显著地高于旱季，其中夏季多雨期间凋落叶的质量损失速率最高，冬季微量降雨期间质量损失速率最低。（2）在整个分解过程中两树种凋落叶C和N含量都表现为净释放且主要发生在雨季，P含量表现为释放与富集交替进行；刺槐凋落叶C/N比、C/P比和N/P比呈波动的趋势，油松凋落叶C/N比则显著地增加且在夏季多雨期出现峰值，C/P比呈波动的状态，N/P比变化较小。（3）不同降雨时期刺槐凋落叶的质量损失速率与凋落叶P含量动态显著正相关，与C含量、C/P比和N/P比动态显著负相关。油松凋落叶质量损失速率与C/N比动态显著正相关，与C、N含量动态显著负相关，与N/P比动态呈负二次函数的关系。这些结果说明黄土丘陵区刺槐和油松凋落叶在不同降雨时期分解速率之间的差异显著且两树种凋落叶的分解都集中在雨季期间；此外凋落叶分解主要受到凋落叶N含量和N/P比动态变化的制约，与刺槐凋落叶相比，N含量与N/P比对油松凋落叶的限制作用更强。

Leaf-litter decomposition of Robinia pseudoacacia and Pinus tabulaeformis planted forests at different rainy periods in the loess hilly region

Litter decomposition is a key process to maintain nutrient circulation and energy flow in the ecosystem. However, in the loess hilly region where rain and heat happen in the same period, it remains unclear how the litter quality during different rainfall periods affects litter decomposition rate. In order to better understand the leaf-litter decomposition characteristics during different rainfall periods and the relationships between the dynamic in substrate mass and decomposition rate during decomposition, a field litter bag experiment was conducted in two types of planted forest of Robinia pseudoacacia and Pinus tabulaeformis in the loess hilly region. The results revealed that: (1) after 391 days of decomposition, the average leaf-litter mass loss rate of R. pseudoacacia was (51.0±8.44) mg/d, significantly higher than that of P. tabulaeformis (36.7±4.83) mg/d. The leaf-litter mass loss rate of both species during rainy season was significantly higher than those during dry season. (2) During decomposition, C and N content in the leaf-litter of two studied species showed a net release, mainly occurring in the summer rainy season. The dynamic of P content showed a release and enrichment alternately. The leaf-litter C/N, C/P and N/P ratios of R. pseudoacacia showed a fluctuant trend, while the C/N ratio of P. tabulaeformis increased significantly over time and peaked in summer rainy season, the C/P ratio had a trend of fluctuation but the N/P ratio did not significantly change. (3) The leaf-litter mass loss rate of R. pseudoacacia was significantly and positively correlated with leaf-litter P content dynamic, negatively correlated with C content, C/P ratio and N/P ratio. However, the leaf-litter mass loss rate of P. tabulaeformis was positively correlated with C/N ratio and negatively with C and N content and N/P ratio, and showed negative quadratic function with N/P ratio. These results indicated that the leaf-litter decomposition of R. pseudoacacia and P. tabulaeformis in loess hilly region tended to significantly differ in different rainfall periods and mainly occur in rainy season. And the leaf-litter decomposition was mainly restricted by leaf-litter N content and N/P ratio, the leaf-litter decomposition of P. tabulaeformi was more restricted by N content and N/P ratio than that of R. pseudoacacia.