In the loess hilly-gully region，a fragmented terrain considerably impacts soil physical and chemical properties
and vegetation distribution． Soil microbial community is an important biological component of terrestrial ecosystems，and its
structural and functional diversity directly affects the ecological processes of carbon，nitrogen，and other elements． Exploring
the influence of the terrain changes on soil microbial functional diversity is of great significance in order to better understand
the ecological processes and system functional changes at spatial scales． The objective of the present study is to evaluate the
impact of terrain changes on soil microbial community structures in the loess hilly-gully region and support the vegetation
restoration in this area． We collected soil samples at three different slope positions ( downslope，mid-slope，and upslope)along a slope transect in Chenjiawa，Ansai County of Shaanxi Province． At each sampling site，soil samples were collected
in two vertical layers ( 0—10 cm and 10—20 cm) along soil profile． All soil samples were divided into two parts: one part
was used to measure the physical and chemical properties ( total carbon，total nitrogen，total phosphorus，moisture content，
and pH) and the other part was used to analyze the soil microbial community functional diversity using the Biolog microplate
culture method． We then used the principal component analysis ( PCA) to explore the impact of terrain changes on the
functional diversity of the soil microbial communities． The results showed that the growth curves of the Average Well Color
Development ( AWCD) are higher in the downslope position than that in the mid-slope position，which is higher than that in
upslope position． Meanwhile，the functional diversity of soil microbial community at the downslope position is significantly
higher ( P＜0．05) than that in the mid-slope and upslope positions; however，there are no significant differences ( P＞0．05)
between two soil layers ( 0—10 cm and 10—20 cm) ． The differences in using carbon sources reflect the structure and
function of soil microbial communities． PCA shows that sugar，carboxylic acids，and polyphenol compounds contribute most
to soil microbial community functional diversity． The changes in soil moisture content along slope positions are the main
factors affecting the soil microbial community functional diversity． There was a positive correlation between the microbial
community richness( H) and homogeneous degree( D) and the total nitrogen content，whereas the dominance index ( U) is
negatively correlated with the total nitrogen content． Total carbon content，total phosphorus content，and pH have little
effect on community structure and functional diversity． In the present study，the soil physical and chemical properties
showed no significant differences among the three slope positions，but significant differences did exist in soil microbial
community functional diversity among slope positions． The downslope position had a higher soil microbial community
functional diversity than that in the mid-slope and upslope positions，suggesting that the microbial functional diversity is
more sensitive to environmental changes than soil elements such as carbon and phosphorus，and can better reflect the impact
of terrain changes on ecological processes．
; 李鸣雷1,3; 朱朵菊3; 曾鸿文4; 史海静3
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