混合放牧对草地枯落物分解的影响及其作用机制研究

Plant litter plays an important role in regulating process and functioning, and litter decomposition is a key step of nutrient cycling in grassland ecosystem. Grazing is widely used in grassland management and exerts great influence on litter decomposition. However, there is litter attention paid on the effects and mechanisms of mixed grazing on litter accumulation and decomposition. Therefore, we apply this project, with controlled grazing experiments and litter decompostion trials, to investigate the impacts of different grazing types (cattle grazing, sheep grazing and mixed grazing) on litter nutrient content (nitrogen, phosphorus, lignin,fibrin and tannin), species composition, as well as mass loss and nutrient release rate (nitrogen and phosphorus) during decomposition, and the effects of selecting forage, trampling, urine and feces deposition on litter quality and environmental conditions (soil temperature, moisture and light), and consequently on litter decomposition. Structural equation model (SEM) will be used to figure out the pathway and mechanism how mixed grazing affects litter accumulation and decomposition through the effects of selecting forage, trampling and excreta on litter quality and environmental factors. The novelty of this project: it will reveal the mechanism how mixed grazing influences litter decomposition throght the influence of herbivore forage behaviour on environmental conditions, litter quality and decomposition. This work will improve our knowledge of maintenance mechanism of the process and function in grassland ecosystem, and provide scientific guideline to grassland management.

枯落物在调节草地生态系统过程及功能中发挥重要作用，枯落物的分解是营养循环的关键环节。放牧是草地最广泛的利用方式，能够影响草地枯落物的积累和分解，而混合放牧对枯落物分解的作用规律及其机制缺少研究。因此，本项目以温带草甸草原为对象，通过受控放牧实验和枯落物分解实验，研究不同放牧方式（牛单牧、羊单牧和牛羊混合放牧）对草地枯落物质量(养分含量、物种组成)、环境条件（土壤温度、湿度、养分和光照）和枯落物分解过程中质量损失和养分释放速率的影响，以及动物采食行为（选择性采食、践踏和排泄物）对枯落物分解的作用效果，并采用结构方程模型分析混合放牧过程中动物采食行为通过改变枯落物质量和环境条件影响枯落物分解的作用途径。特色与创新：通过比较动物采食行为对环境条件、枯落物质量和分解的作用，揭示混合放牧影响枯落物分解的内在机制。本研究能够加深对草地生态系统过程及功能维持机理的理解，并为草地的科学管理提供理论指导。

放牧能够通过改变植物组成、枯落物质量和土壤理化性质调节枯落物分解，本项目以温带草甸草原为对象，通过受控放牧实验和枯落物分解实验，研究不同放牧方式（牛单牧、羊单牧和牛羊混合放牧）对草地枯落物分解速率的影响，并采用结构方程模型分析混合放牧通过改变枯落物质量和环境条件影响枯落物分解的作用途径，揭示混合放牧影响枯落物分解的内在机制。研究发现，羊单牧能够增加返青期枯落物积累量，而牛羊单牧和混合放牧能够减少雪后枯落物倒伏量；羊单牧和混牧能够显著增加枯落物中羊草和其他禾本科植物的比例，牛单牧能够显著降低枯落物氮含量而提高枯落物碳氮比；放牧能够提高枯落物分解速率，并且羊单牧对枯落物分解的抑制作用更强；枯落物返还率与羊草和禾本科植物的比例显著负相关，而枯落物分解速率与土壤湿度和碳氮比显著负相关；结构方程模型结果表明，放牧能够通过增加土壤容重、降低土壤含水量，增加枯落物质量存留时间，降低枯落物分解速率；另一方面，放牧能够通过增加土壤碳氮比，减少枯落物质量存留时间，进而提高枯落物分解速率，而第二种途径放牧对枯落物分解速率的作用更强，所以放牧能够抑制枯落物分解。本项目明晰了混合放牧对草地枯落物分解的作用规律，揭示了混合放牧通过改变枯落物营养含量、物种组成以及环境条件影响枯落物分解的内在机制，能够加深对草地生态系统过程及功能维持机理的理解，并为草地的科学管理提供理论指导。