模拟冻融环境下亚高山森林凋落物分解速率及有机碳动态

Abstract

森林凋落物分解是森林生态系统物质循环的重要环节，季节性冻融交替是影响凋落物分解的重要环境因素之一，但不同林型的凋落物对冻融响应的差异性很少被量化。为了解冻融环境对森林凋落物分解进程的影响，以川西亚高山森林地区阔叶林、针叶林和针阔混交林3种典型林型的凋落物为实验材料，从凋落物基质质量、冻融环境等影响凋落分解的因素着手，采用模拟冻融循环过程（-5-5℃），研究了冻融循环中3种林型凋落物分解速率和有机碳含量的动态变化。结果发现，3中典型林型凋落物经过不同冻融处理后，其质量损失、质量损失速率均存在显著差异（P<0.05）。混交林凋落物和针叶林凋落物的分解速率呈慢-快-慢的趋势，而阔叶林凋落物的分解速率逐渐减小。在冻融循环处理下，3种林型的凋落物碳绝对含量呈波动下降的趋势，说明微生物固定外源碳和凋落物释放碳间存在动态平衡。相同林型的凋落物在不同冻融处理下，有机碳释放有显著差异（P<0.05）。其中，冻融环境显著（P<0.05）促进了混交林凋落物和针叶林凋落物有机碳的释放，但是对阔叶林凋落物有机碳的释放没有起到促进作用。这表明全球气候变暖情景下，亚高山森林土壤冻融事件频发将加快凋落物的分解，但变化程度受到凋落物质量控制。;In this study, we address the effects of freeze-thaw cycles on the process of litter decomposition in subalpine forests. In a microcosm experiment, we measured the dynamics of litter moss loss rates and organic carbon by controlling the freeze-thaw environment (-5-5℃) in three typical forests in the sub-alpine region in western Sichuan. The three forest types including coniferous, coniferous-broadleaf, and broadleaf forest were selected for our experiment design based on the criteria of their abundance in the study area. Our results showed that clear and significant differences (P<0.05) in all measured litter types were all observed due to the freeze-thaw treatments. Specially, the mass loss rate of litter in both coniferous-broadleaf and coniferous forests showed a slow-fast-slow trend. In contrast, in the broadleaf forests, the mass loss rates exhibited a gradual decrease trend. This fluctuation phenomenon implies that there is a balance between microbial-fixed exogenous carbon and substrate-released carbon. In conclusion, the increase of globally average temperature would accelerate the freeze-thaw cycles and thus significantly change the process of mass loss and nutrient cycles in the subalpine forests, but both the magnitude and direction of the freeze-thaw effects varied with initial litter quality.