Spatial heterogeneity of soil microbial biomass in Mulun National Nature Reserve in Karst area
木论喀斯特自然保护区土壤微生物生物量的空间格局

Soil microbe is the most important decomposer in forest ecosystems, and plays a key role in material recycling and energy conversion. In this study, the spatial patterns of soil microbial biomass in typical Karst peak-cluster depressions were analyzed through both geo-statistical and traditional statistical methods. The results showed that large variation existed in soil microbial biomass. Soil microbial biomass carbon(Cmic), soil microbial biomass nitrogen(Nmic), and soil microbial biomass phosphorus(Pmic) varied from 44.29-5209.63, 20.91-1894.37, 0.34-77.06 mg/kg, respectively. The Cmic was significantly positively correlated with Nmic. The value of Cmic/Nmic is 4.78, which obviously lower than that in other ecosystems. Semivariance analysis revealed that the Gaussian model fitted best for Cmic and Nmic, the Spherical model fitted best for Pmic, and the Exponential model fitted best for Cmic/Nmic. The SH%(C/(C+C0)×100%) of soil microbial biomass exhibited moderate spatial autocorrelation, ranging from 25% to 75%. Therefore, the spatial patterns were affected by both random and structure factors. The autocorrelation distance of Cmic and Nmic were about 50 m. Moran's I decreased gradually with the increase of separation distance, and showed a statistically negative correlation. Moran's I of Pmic increased when the separation distance was larger than 70 m, which indicated positive correlation. Moran's I of Cmic/Nmic was lower than others, ranging from -0.2 to 0.2 m. The spatial distribution of Cmic and Nmic were similar, and showed a convex-type distribution in which the contents were high in the middle and low on the two sides. In contrast, The Pmic was distributed with a pattern of high in the upper slope and depressions. The content of Cmic/Nmic showed a concave-type distribution with many small patches. We conclude that soil microbes exist in a certain spatial pattern, and that its contents sharply reduced after disturbing. As a result, the protection of Karst primary ecosystems against human disturbing should be strengthened.