喀斯特地区坡耕地与退耕地土壤有机碳空间异质性及其影响因素

利用网格采样(10 m×10 m),对比分析了典型喀斯特坡耕地(长期耕作)和退耕地(自然恢复)表层(0—15 cm)土壤有机碳(SOC)的空间变异特征,以期探究退耕恢复20a后SOC的空间异质性及其主要影响因素的变化。结果表明退耕地SOC含量(75.5 g/kg)显著高于坡耕地(15.1 g/kg),为坡耕地的5.0倍,说明自然恢复能显著提高SOC累积量;半变异函数分析结果表明退耕地基台值(521.7)为坡耕地(25.7)的14.9倍,说明退耕地SOC空间异质性远大于坡耕地。坡耕地和退耕地SOC的主要影响因子存在较大差异,土地覆盖类型、坡位、岩石出露率以及三者的交互作用显著控制着坡耕地SOC的空间格局,其贡献率分别为9.1%、6.3%、4.6%以及17.0%;土壤水分、坡度、岩石出露率以及三者的交互作用显著控制退耕地SOC的空间格局,其贡献率分别为26.0%、10.7%、7.2%以及3.6%;尽管岩石出露率对坡耕地和退耕地SOC的空间格局均有显著影响,但坡耕地SOC的主要控制因子为土地覆盖类型以及各因子的交互作用,而退耕地的主要控制因子为土壤水分。以上研究表明随着植被恢复和物种多样性增加,喀斯特坡地SOC的累积量和空间异质性增强,自然因素对SOC空间格局影响凸显,而岩石出露率始终控制SOC空间格局。

Spatial variability of surface soil organic carbon and its influencing factors in cultivated slopes and abandoned lands in a Karst peak-cluster depression area

Soil organic carbon (SOC) content and its spatial heterogeneity are important components of regional and global carbon sequestration. However, the spatial variability of SOC in karst areas is poorly understood, especially in southwest China in areas of severe land degradation. In the present study, we selected isolated areas in the closest possible proximity to cultivated slopes in order to ensure similar soil and microclimate conditions. The spatial heterogeneity of cultivated slopes under long-term cultivation and abandoned lands under natural restoration in a karst peak-cluster depression area were analyzed by using the grid sampling method at 10 m × 10 m. A total of 230 soil samples were collected, including 123 from the cultivated slopes and 107 from abandoned lands. We used a one-way analysis of variance (ANOVA) to evaluate the differences between the plots. The results showed that the average SOC content in the abandoned lands was ~5 times greater than that in the cultivated slopes, which indicates that vegetation recovery significantly improved the SOC content. The estimate of the spatial pattern and scaling of the studied SOC was performed by geostatistical analyses using semivariograms to determine the average variance between samples collected at increasing distances. The results showed that all semivariograms of the two plots were fitted to an exponential model. The sill values of the semivariogram functions for the abandoned lands were about 15 times greater those of the cultivated slopes, which indicates that the spatial variation of SOC in the abandoned lands was higher than that in the cultivated slopes. Stepwise regression and redundancy analysis showed that factors influencing the spatial distributions of SOC in the cultivated slopes and abandoned lands were different. In particular, land cover type, slope position, rock ratio, and their interaction explained 9.1%, 6.3%, 4.6%, and 17.0% of the total variance of SOC in the cultivated slopes, respectively. Soil water content, slope gradient, rock ratio, and their interaction explained 26.0%, 10.7%, 7.2%, and 3.6% of the total variance of SOC in the abandoned lands, respectively. We conclude that land abandonment increased both the SOC content and its spatial heterogeneity in karst areas in southwest China. In addition, the degree of human disturbance and soil water content are the primary factors in determining the spatial variation of SOC in the cultivated slopes and abandoned lands, respectively. Moreover, the rock ratio is an important factor for controlling the spatial variation of SOC in both the cultivated slopes and abandoned lands. Our findings can provide a better understanding of the relationships between ecosystem restoration and SOC recovery and can give scientific basis for karst ecosystem restoration.