内蒙古草原灌丛化对土壤有机碳的影响及其驱动机制

Shrub encroachment in arid and semiarid grasslands has been widely reported, and could substantially affect ecosystem structure and function. However, the impacts of shrub encroachment on soil organic carbon (SOC) storage and its underlying mechanisms still remain unclear. There are only few studies from field observations, and most of the evidences are limited in shallow soil layers within 1m, and little evidence is available from deeper soil layers. Shrub plants usually have deep root than grass. Shrub encroachment into grassland are expected to not only change SOC in shallow soil, but also to affect the SOC in deep soil, which is controlled by several factors, such as shrub species, degree of shrub encroachment, soil environment and climate etc. In this proposal, we try to provide first attempt to examine the impacts of shrub encroachment on SOC in deep soil, and their driving mechanism in Inner-Mongolian grasslands. By using field observation, biogeochemical and molecular microbial ecological methods, we are to 1) investigate the SOC both in shallow and deep soil under conditions with different shrub species and different degree of shrub encroachment; 2) clarify the effect of shrub encroachment on soil physicochemical characteristics and microbial community structure, and the relationship between these changes and SOC storage and its vertical distribution; then 3) indicate the impacts of shrub encroachment on SOC distribution and storage, and their underlying mechanisms. This study will provide scientific insight and basic information for predicting the soil carbon effect of shrub encroachment, and conserving ecosystem function in arid and semiarid grasslands.

草原灌丛化在干旱半干旱地区普遍发生，给生态系统结构和功能产生深刻影响。然而，草原灌丛化如何改变土壤有机碳含量一直在争论之中，野外观测证据有限而且绝大多数仅仅局限于浅层土壤，对驱动机制的研究也十分缺乏。灌木的深根性不仅显著影响浅层土壤也会深刻改变深层土壤的有机碳，而且灌丛化对土壤有机碳的影响受灌木种类、灌丛化程度、土壤环境和气候条件等多种因素的控制。本项目拟以内蒙古典型灌丛化草原为研究对象，采用有机地球化学、生物标志物及微生物分子生态学等分析方法，研究不同种类灌木及不同程度的灌丛化对表层及深层土壤有机碳的影响，阐明土壤有机碳的垂直分布与土壤理化性质和微生物群落组成等的关系，揭示灌丛化对草原生态系统土壤有机碳分布、储量的影响以及驱动机制。本项目的研究结果为正确评估草原灌丛化的土壤碳源汇效应，保护干旱半干旱地区草原的生态功能提供必要的科学依据。

草原灌丛化在干旱半干旱地区普遍发生，给生态系统结构和功能产生深刻影响。然而，草原灌丛化如何改变土壤有机碳含量一直在争论之中，野外观测证据有限而且绝大多数仅仅局限于浅层土壤，对驱动机制的研究也十分缺乏。本项目以内蒙古典型灌丛化草原为研究对象，采集了5m深度土壤样品和群落优势植物样品，采用有机地球化学、生物标志物及微生物分子生态学等方法，分析了草原灌丛化对土壤有机碳的影响，阐明了植被、气候、土壤等因素对灌丛化效应的调控作用，揭示了灌丛化对土壤碳源汇效应的可能机制。结果表明：内蒙古草原灌丛化显著增加土壤有机碳密度，平均5m深度土壤有机碳密度增加量为2.95 kg C m-2，而且这种效应在30 ~ 300 cm 土壤深度中更显著。灌丛化对土壤有机碳密度的影响受气候、植被、土壤等多因素的调控作用，土壤有机碳的变化量与气温、土壤pH显著负相关，而与降水和植被生物量显著正相关；而且在浅层土壤中主要受气候影响，在深层土壤中主要受土壤因素影响。灌丛化主要通过改变植物碳输入的数量和质量、土壤微生物群落组成和生物量、以及土壤团聚体结构及其有机碳含量，进而改变土壤有机碳的组成、分解及稳定性。这些结果为正确评估草原灌丛化的土壤碳源汇效应，保护干旱半干旱地区草原的生态功能提供了重要的科学依据。. 通过项目的实施，共发表SCI论文8篇，培养了1名博士后和2名博士生。