半干旱草原植物茎叶凋落物混合分解作用及其对氮沉降的响应机制

Litter decomposition plays an important role in regulating material cycling in grassland ecosystems. At present, there are few studies on mixed decomposition of grassland litters, and most of them are focused on mixed decomposition between different leaves. However, grassland litters are mainly composed of stems and leaves, which is less known about the process of their mixed decomposition and the response of this process to environmental nutrient changes. This project is planned to be carried out in the temperate steppe with long-term simulated nitrogen deposition, in which the dominant plant litters of grasses, legumes and forbs are taken as the research objects. The plant organs are decomposed in a single- and mixed-way. By measuring litter mass and nutrient contents in different decomposition stages, changing characteristics of the mass and nutrients are discussed for the single and mixed litters, and the effects of nitrogen deposition on the decomposition process of different litters are also discussed. The impacts of mixing effects on the mass and nutrient changes in the mixed stems and leaves are quantified, and compared with that in the mixed leaves of two species. Combined with the initial chemical properties of litters, the dominant factors that generating mixing effects are analyzed, which would provide a theoretical basis for in-depth understanding changes of litter decomposition in grassland systems under increasing nitrogen deposition.

凋落物分解是草地生态系统物质循环的重要过程之一。目前关于草地凋落物混合分解的研究较少，且多数是针对于不同物种叶片的混合分解研究。草原地上凋落物主要是由茎秆和叶片器官构成，而我们对于茎叶凋落物混合分解过程及其对环境养分变化的响应尚不清楚。本项目拟依托长期模拟氮沉降实验平台，以禾草、豆科及杂类草植物的茎叶凋落物为研究对象，进行器官单一分解和混合分解。通过测定不同分解时期各类型凋落物的重量和养分含量，探讨凋落物在单一分解和混合分解过程中的重量和养分变化特征，以及氮沉降对不同类型凋落物分解过程的影响；解析茎叶两种不同器官在凋落物分解过程中的混合效应，并量化比较其与不同物种的叶片分解过程中混合效应强度。同时，结合凋落物的初始化学性质，分析混合凋落物在分解过程中产生混合效应的主导因素，从而深入理解氮沉降增加背景下草地生态系统凋落物分解过程的变化。

凋落物分解是草地生态系统重要的碳和养分循环过程之一，草原地上凋落物主要是由茎秆和叶片器官构成，而我们对于茎叶凋落物混合分解过程及其对环境养分变化的响应尚不清楚。本项目依托内蒙古半干旱草原长期氮沉降实验平台，以不同植物功能群的茎叶凋落物为研究对象，进行器官单一分解和混合分解。测定分解后的各类型凋落物的重量和养分含量，结合初始凋落物化学性质，分析凋落物在单一分解和混合分解过程中的重量和养分变化特征，以及氮沉降对不同类型凋落物分解过程的影响。研究发现，不同植物凋落物的重量变化存在显著差异，且叶片凋落物重量损失显著高于茎秆凋落物重量损失，主要是由于叶片凋落物氮含量高于茎凋落物，叶片凋落物的木质素含量、碳氮比以及木质素氮比低于茎秆凋落物，即叶片凋落物质量高于茎秆凋落物质量。氮沉降对茎叶单一凋落物分解过程无显著作用。另外，茎叶混合及不同叶片混合凋落物分解的重量损失和养分释放存在正向混合效应。氮沉降显著提高茎叶混合分解重量变化产生的混合作用，而对不同叶片混合作用无影响。氮沉降对茎叶混合及叶片混合分解释放养分产生的混合作用存在差异。上述成果与结论为后续研究凋落物分解过程提供了新视角，为进一步明确草地生态系统生物地球化学循环过程提供理论支撑。