典型草原风吹凋落物迁移特征与截存机制研究

Wind-blown litter movement is a universal ecological phenomenon in steppe regions. However, there is a lack of studies on the process, capture mechanism and potential ecological significance of wind-blown litter movement. We select Inner Mongolia’s typical steppes as a case study and conduct comprehensive experimental investigations, applying various methods like position observation, manipulation experiments, wind tunnel simulation and laboratory analysis, to analyze litter biomass, composition and seasonal dynamics of the steppe communities, and clarify its formation mechanism based on different plant communities and different grazing intensities. The mechanism of different types of wind-driven litter’s movement is determined, and the blowing litter’s flux characteristics for different steppe communities (blowing litter’s flux at different heights from the ground and litter component) are clarified. The relationship between blowing litter’s movement flux and vegetative cover as well as wind condition are analyzed to estimate the amount of blowing litter and calculate amount of associated nutrients. Different vegetative cover (vegetation patches) conditions’ effect on capturing wind-blown litter is also determined. We are focused on clarifying the mutual feedback mechanism between vegetative cover (vegetation patches) and capturing wind-blown litter, and determining the grassland-use intensity (vegetative cover threshold) threshold based on the capturing litter. The project will provide the basis for protection, rational use and management of grassland.

风吹凋落物迁移在典型草原区是一个具有普遍性的生态现象，但对其迁移过程、截存机制等尚缺少系统的研究。本项目以内蒙古典型草原为研究对象，通过野外定位观测、控制实验、风洞模拟及室内分析相结合，分析草原群落凋落物现存量、组成和季节动态，从植物群落类型及放牧利用强度上阐明其形成机制；揭示不同类型凋落物在风力作用下起动与迁移的影响机制，阐明风力驱动下不同草原群落的凋落物迁移通量特征（距地面不同高度的迁移通量及凋落物组分）；综合分析地表覆盖状况、风速等主要影响因素与凋落物迁移通量之间的关系，实现草原风吹凋落物及其养分迁移量估算；揭示不同植被覆盖条件（群落斑块）对风吹凋落物的截存作用机制，重点阐明植被覆盖变化与风吹凋落物截存的互馈机制，从凋落物截存角度确定草原利用强度的临界阈值（植被覆盖阈值），为草原保护、合理利用及管理提供科学依据。

针对风吹凋落物迁移这一重要生态过程研究的不足，以内蒙古典型草原为研究对象，通过野外定位观测、控制实验及室内分析相结合，对风力驱动下凋落物迁移通量特征、流失速率、截存累积特征及其生态学意义等方面开展研究。结果表明：风力驱动下的枯落物迁移主要发生在非生长季，每年每1米宽横截面（2m高度范围内）风吹凋落物迁移量可达2843g，且95%以上为风滚植物，主要发生在近地面0-30cm范围内；不同植被斑块截获风吹凋落物的能力存在显著差异，具有植被覆盖的斑块能够明显增加凋落物累积同时减少凋落物流失速率；不同类型凋落物对风的敏感性存在差异，在供试的6种凋落物中，糙隐子草具有最小的起动风速和最大的流失速率，相同植物，其叶凋落物相对于其茎凋落物更容易被吹蚀。风力驱动的凋落物在裸地、大针茅群落及灌丛斑块景观格局中的再分配在景观尺度上影响着资源空间异质性；另外发现风滚植物枯落物在灌丛内聚集是灌丛化草原的普遍现象，经对锡林浩特与西乌旗境内10个小叶锦鸡儿灌丛化草地研究点的调查发现，灌丛内聚集的风滚植物枯落物平均可达到92.3gm-2，是对照草地枯落物聚集量的30倍以上。风滚植物的供应是灌丛斑块捕获风吹凋落物量的最强预测因子，这表明风滚植物的捕获是源限制而不是汇限制。在温带草原上，风滚植物糙隐子草是次优势种或优势种，其优势度在放牧干扰下呈增加趋势，风吹凋落物累积为灌丛斑块提供了大量的有机物输入，这可能是蒙古高原东部小叶锦鸡儿灌丛肥岛形成及自我强化的重要机制。