黄土丘陵沟壑区地形变化对土壤微生物群落功能多样性的影响

Impact of terrain changes on the functional diversity of soil microbial community in the loess hilly-gully region of China

研究黄土高原丘陵沟壑区破碎地形对土壤微生物功能多样性的影响,对于理解复杂地形区生态过程与系统功能的空间变化具有重要意义。选择陕西省安塞县陈家洼为研究区,依据坡面地形变化选择不同坡位土壤,采用Biolog微平板培养法探究地形变化对土壤微生物群落功能多样性的影响。实验发现,土壤微生物群落培养的平均颜色变化率(AWCD)增长曲线总的呈现出坡下部>坡中部>坡上部的规律,且坡下部AWCD值与坡中部、坡上部间差异显著(P<0.05);坡下部土壤微生物群落功能多样性显著高于坡中部和坡上部,但不同土层深度(0—10 cm、10—20 cm)间无显著性差异(P>0.05);对土壤微生物群落功能多样性差异贡献较大的碳源是糖类、羧酸类和多酚化合物类碳源;土壤含水率高低是不同坡位土壤微生物群落功能多样性差异显著的主要原因;微生物群落丰富度(H)和均一度(D)与土壤全氮含量正相关,优势度(U)反之,土壤全碳、全磷和p H对土壤微生物群落结构和功能多样性差异作用不显著。

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.