[Niche of main populations and environmental interpretation in grassland of Loess Plateau hilly region, China].

Focused on different rehabilitation ages grassland in Wuqi County in loess hilly region, the present study aimed to explore niche characteristics of populations and their influence factors. The results showed that the dominant species were Artemisia sacrorum, A. leucophylla, A. scoparia, Lespedeza daurica and Poa sphondylodes, and the dominant species varied along with the rehabilitation age. The niche breadth of dominant populations increased with increasing rehabilitation age from 5 to 10 years, indicating enhanced adaptability to the environment. The niche breadth indices of the populations decreased from 10 to 20 years, and then increased from 20 to 25 years. After 25 years, the niche breadth of the grassland narrowed gradually, indicating weakened adaptability. The niche breadth indices of most populations peaked at 10 and 25 years, respectively. There was no li-near relationship between synthetic dominance index and niche breadth in different grass communities. With the increasing rehabilitation age, the niche overlap indices were highest at 15 years with a single hump pattern, indicating that the interspecific competition increased to the highest at 15 years and then decreased. It was shown that attitude, soil water content (SWC) and soil organic matter content (SOM) were the main factors affecting the niche breadth, while soil total nitrogen content (STN), attitude and SWC were the main factors affecting the niche overlap. There was no linear relationship between niche breadth and niche overlap of tested species in different rehabilitation ages due to resource spatial heterogeneity and growth stages of grass species. These findings indicated that with the increasing rehabilitation age, the population adaptability to the environment are generally enhanced and the resource competition among populations increases and then decreases. It was concluded that attitude, SWC and STN were the key environmental factors that affect population adaptability and interspecific relationship in natural grassland of loess hilly region.