土壤微生物在灌丛化草原植物-土壤反馈中的生态学机制研究

Over the last century, shrub encroachment occurred widely in global drylands，and has the significant influence on community structure and biogeochemical cycles of the grassland ecosystem. At present, the relative research mainly in northern America, and focus on vegetation composition and the changes of soil carbon and nitrogen pools. However, there are lacking the studies on the relationship between above and below ground ecological process, and the mechanism explanations of these phenomena. Previous studies suggested the plant growth and soil biogeochemical cycles was regulated by plant–soil feedback, and the soil microbial play key roles in this process, but the relative studies are surprisingly lacking in shrub encroached grassland. Based on large-scale field survey of shrub encroachment in Inner Mongolia, we plant to select 3 typical regions, in each region we set 12 study sites with different shrub cover. Through comparing the plant-soil-microbial interactions with different encroachment level and climate, vegetation and soil conditions, we try to answer these questions: (1) How about the plant–soil feedback in shrub encroached grassland with different encroachment level, and what the difference in different environmental conditions? (2) How microbial affect the plant–soil feedback in shrub encroached grassland? Moreover, this study tries to provide insight for a deeper understanding of the mechanism of nutrient cycling with the shrub encroachment development in grassland, and provided basically information for grassland protection and utilization.

上个世纪以来，草原灌丛化在全球范围内广泛发生，对草原生态系统的群落结构和养分循环产生了显著影响。目前，草原灌丛化的研究主要集中在北美地区，重点关注植被组成与土壤碳、氮库的变化，缺乏将地上-地下过程相关联的研究，以及对这些现象的机理性解释。研究显示，植物和土壤之间通过反馈作用来调控植物生长和土壤养分循环，而土壤微生物群落在此过程中起着关键作用。但是，灌丛化草原中的相关研究还比较匮乏。为此，本项目拟在内蒙古灌丛化草原样带调查的基础上，选择 3 个典型区域，每个区域设置12个不同盖度的灌丛化草原样地，通过分析不同气候、植被和土壤条件下，不同程度灌丛化草原的植物-土壤-微生物的相互作用关系，试图揭示：（1）不同程度灌丛化草原中植物-土壤反馈作用如何，在不同环境下有何差异？（2）微生物在植物-土壤反馈中有何作用？以期揭示灌丛化草原发生发展过程中养分循环的可能机制，并为草地的保护和利用提供理论基础。

草原灌丛化现象在干旱、半干旱区域的广泛发生并对生态系统结构和功能产生了显著影响，因此，草原灌丛化对植被、土壤养分循环及其微生物调控机制成为了当前全球变化研究中的热点问题。然而，以往的研究主要关注草原灌丛化对植被组成以及养分含量的影响，对其内部机制以及微生物的调控作用及其与植被、土壤的反馈机制关注较少；并且，尚不清楚存在哪些区域差异。本项目拟以内蒙古温带灌丛化草原为研究对象，调查典型草原、荒漠草原区域内不同程度灌丛化草原的植被组成、土壤养分以及微生物群落结构，阐明灌丛化草原植物和土壤之间的反馈作用以及土壤微生物在此过程中起着关键作用。研究发现：灌丛化草原中，灌木下土壤中有机碳、可溶性氮等土壤养分显著高于灌木外，并且随着灌木盖度的增加，土壤养分增加的量也随之上升，而这与木本植物生物量的输入以及相关微生物群落结构的改变显著相关，尤其是与氮元素和碳元素代谢相关的微生物群落存在显著差异。本项目证实了不同程度灌丛化草原中植物-土壤反馈作用以及微生物的重要作用，有助于加深学术界对灌丛化草原的发生发展中养分循环机制的认识。