Abstract: Understanding the relationship between soil moisture and species diversity and biomass has great significance for exploring plant community characteristics and distribution. We examined the effects of soil water gradient on the diversity and biomass of naturally restored plant communities in Wuqi, Mizhi, Fugu and Dingbian which are located in typical loess hilly region in Northern Shaanxi. The aim of this study was to provide scientific basis for vegetation restoration and biodiversity management in loess hilly area. The results showed that soil water content exhibited a decline trend with the decrease of precipitation from southeast to northwest. The average soil water contents in Wuqi, Mizhi, Fugu and Dingbian were 9.77%, 9.40%, 7.91% and 6.40%, respectively. A total of 71 species, belonging to 56 genera and 24 families were recorded in the study sites. Among all those species, species from Gramineae, Asteraceae and Leguminosae were dominated and herb species accounted for the large proportion. With the decreasing soil water content, plant community composition had low similarity among the four study sites, indicating that species composition changed with soil water content. Meanwhile, community biomass, Margalef index, Shannon index and Pielou index all showed a decreasing trend with decreasing soil water content. Additionally, community biomass, Margalef index and Shannon index had significant positive correlation with water content of shallow soil. Our results indicated that soil water had an important effect on plant community species composition, diversity, and biomass, and that soil water carrying capacity should be considered in vegetation restoration and construction in this area.

Key words: northern Shannxi Province, species diversity, productivity, soil moisture, vegetation restoration.