摘要:半干旱黄土丘陵区土壤水分亏缺引起人工苜蓿草地退化会显著影响其他草本植物的分布及多样性，然而地形驱动下的苜蓿草地退化及植被群落多样性响应还尚不清楚。以典型半干旱黄土丘陵区龙滩小流域为研究区，对不同地形条件下退化苜蓿草地地上生物量、草本多样性及生长季内0-200 cm土壤水分进行了定位监测，利用方差分析、相关分析和典范对应分析（CCA）明确坡面地形、苜蓿生长状况和土壤水分与其他草本植物分布及多样性之间的关系。结果表明：（1）地形显著影响植被群落特征，西坡、东坡和北坡样带苜蓿地上生物量明显不同，西坡和东坡样带中、下坡位苜蓿地上生物量明显高于上坡位，而其他草本的生物量、物种丰富度和多样性指数的变化趋势则与苜蓿相反；（2）苜蓿地上生物量与80-200 cm土壤水分显著正相关，而与0-20 cm和20-80 cm土壤水分的相关性较小；（3）地形特征、不同深度土壤水分和苜蓿地上生物量解释了退化苜蓿草地其他草本群落变异的87.8%，其中坡向、苜蓿地上生物量、0-20 cm和20-80 cm土壤水分4个因子解释了79.3%的群落变异。研究认为，半干旱黄土丘陵区不同地形条件引起坡面土壤水分变化，进而影响退化苜蓿草地地上生物量，使得苜蓿退化程度不同，而苜蓿退化程度和0-80 cm土壤水分决定了不同部位草本分布及多样性。



Abstract:The degeneration of alfalfa (Medicago sativa L.) caused by soil desiccation can significantly affect the distribution and diversity of the herbage community in the semi-arid Loess Plateau. However, the mechanism by which soil moisture redistribution caused by topographic features at the hillslope scale influences the degradation of alfalfa and the distribution of other herbage has received limited attention. In this study, the Longtan watershed was selected as the study area. The above-ground biomass of alfalfa and diversity of herbage were investigated, and soil moisture content at a depth of 0-200 cm under different topographic conditions was monitored. The relationships between topographic features, above-ground biomass of alfalfa, soil moisture content, and herbage distribution and diversity were quantitatively analyzed by using ANOVA, Pearson's correlation analysis, and CCA. The following results were obtained:(1) Topographical features significantly affected vegetation community characteristics. Significant differences in the above-ground biomass of alfalfa were found between different slope aspects and slope positions. The biomass of alfalfa on the middle-hillslope and foot-hillslope positions was significantly higher than that on the upper-hillslope in west-and east-facing hillslopes. However, the spatial variability of the biomass of other herbage, species richness, and diversity indices differed with the spatial variation characteristics of biomass. (2) The above-ground biomass of alfalfa was significantly positively correlated with soil moisture content at a depth of 80-200 cm, whereas the correlations between biomass and soil moisture content at a depth of 0-20 cm and 20-80 cm were not significant. (3) The topographical features, soil moisture content at different depths, and biomass of alfalfa explained 87.8% of the variation of other herbage in the alfalfa degeneration communities. Furthermore, the total variation of the slope aspect, biomass of alfalfa, soil moisture content at 0-20 cm, and soil moisture content at 20-80 cm explained 79.3% of the variation in plant communities. The topographical factors caused the spatial and temporal variation in soil moisture content, which affected the degree of alfalfa degeneration through the variation in alfalfa's above-ground biomass in the semi-arid loess hilly watershed. The distribution and diversity of herbage were determined by the degree of alfalfa degeneration and the soil moisture content at 0-80 cm under different topographic conditions.





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