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Clarifying the changing trends and driving factors of soil respiration in fragile habitats under the background of climate change is of great significance for understanding the regional carbon cycle and the conversion of ecosystem carbon source and sink functions. This research focused on grasslands that had been naturally abandoned and restored for 12 years in the loess hilly region of northern Shaanxi, using an open top chamber (OTC) and artificially increased natural rainfall to simulate climate warming and precipitation increase and their interaction. Furthermore, we used a combination of field monitoring and indoor analysis to explore soil water content, temperature, and nutrient characteristics and the response characteristics of soil respiration rate to warming and increased precipitation and further analyzed the key factors driving changes in soil respiration. The results showed that:① warming (W) significantly increased the 5 cm soil temperature, with an average increase of 1.34℃ throughout the sampling year, whereas the increased precipitation (P50%) treatment significantly reduced the 5 cm soil temperature, reducing the average 5 cm soil temperature during the entire sampling year by 0.88℃ and increasing the soil water content (SWC) at the same time. The SWC was 13.12% and 16.45% higher than that in the control (CK), respectively. In addition, compared with that in the CK, the treatment of warming and increased precipitation (WP50%) not only increased soil temperature but also increased SWC; in general, the increase in temperature and precipitation played an antagonistic effect on the influence of soil temperature and humidity. ② P50% significantly increased the content of soil organic carbon, dissolved organic carbon, and labile organic carbon, causing changes in the soil stoichiometric ratio and the distribution characteristics of labile-recalcitrant carbon components, whereas W did not have a significant impact on organic carbon. In addition, soil total nitrogen and phosphorus and available nitrogen and phosphorus nutrients were not significantly different between treatments. ③ P50% significantly increased the

The trends of and relationships among the plant community, soil nutrients, and four soil enzymes were investigated after being abandoned for 10, 15, 20, 30, and 45 years to reveal the soil properties during the restoration in the Loess Hilly Region. The results indicate the following ranking of dominant plant community species

We investigated the species composition and diversity of four grassland communities with different slope aspects in the loess hilly area of China. The power law was used to analyze spatial heterogeneity of the community and spatial pattern of the population. The results showed that Artemisia sacrorum was the dominant species and occurred in each site. Other species had different status and contributed differently to the spatial pattern of communities. Moreover, the spatial patterns of communities responded differently to various slope aspects, with the degree of aggregation ranked as sunnyhalf-sunnyhalf-shadyshady. The spatial heterogeneity index of community was positively correlated with the Simpson diversity index, but was negatively correlated with Margalef richness, Shannon diversity and Pielou evenness. The relative spatial heterogeneity index of the dominant species (A. sacrorum), sub-dominant species (Lespedeza dahurica and Stipa bungeana), and a few associated species (Artemisia scoparia, Melica scabrosa) were larger than that of the community, which resulted in cluster distribution. However, the relative spatial heterogeneity index of most associated species (Phragmites communis, Sonchus arvensis, and Bothriochloa flaccidum) showed the similar trends with the distribution of the community. In contrast, the relative spatial heterogeneity index of Cephalanoplos segetum, Gueldenstaedtia multiflora and Artemisia giraldii was lower than that of the community. These differences reduced the aggregation degree of the community. In summary, the aggregation degree of community was determined by dominant species, sub-dominant species and occasional species. Specifically, the dominant species, sub-dominant species and some associated species could promote the aggregation of the community, but occasional species would reduce the cluster distribution.本研究以黄土丘陵沟壑区4种不同坡向的草地植物群落为研究对象,探讨其物种组成和多样性特征,并运用幂乘方法则分析了群落的空间异质性和种群空间格局.结果表明: 铁杆蒿在不同坡向均有分布,为群落优势种;其他物种在不同坡向群落中的地位及对群落空间格局的贡献不同.不同坡向植物群落的空间分布格局均为集群分布,且聚集程度大小为阳坡＞半阳坡＞半阴坡＞阴坡.群落空间异质性指数与Simpson多样性指数呈显著正相关,与Margalef丰富度指数、Shannon多样性指数和Pielou均匀度指数呈显著负相关.优势种铁杆蒿、亚优势种达乌里胡枝子和长芒草,以及少数伴生种如猪毛蒿、臭草的相对空间异质性指数大于群落整体空间异质性指数,使群落趋于集群分布;多数伴生种如芦苇、苦荬菜、白羊草的相对空间异质性指数与群落整体空间异质性指数相近,它们与群落自身分布状态一致;刺儿菜、米口袋、茭蒿等偶见种的相对空间异质性指数小于群落整体空间异质性指数,降低了群落的聚集程度.综上,群落的聚集程度主要由优势种、亚优势种和偶见种共同决定,其中优势种、亚优势种和部分伴生种促使群落呈聚集分布,偶见种则降低了群落的集群分布.