Compared with artificial plantation, natural secondary forest has higher function of nutrient cycling, especially carbon source metabolism function. However the reasons for higher nutrient cycling function in natural secondary forest are still not clear. To understand the nutrient cycling function of natural secondary forest, we analyzed the relationship between carbon source metabolism properties of soil microbial communities and the environmental factors in subtropical area, China. From 40 sample plots 40 soil samples at 0-10 cm depth were sampled. The carbon source metabolism capacity of soil microbial communities was analyzed using Biolog method. The soil properties and plant composition of the plots were also surveyed.
Variance partitioning showed that three groups of factors significantly explained 54.4% variation of carbon source utilization by soil microbial communities. Among them, soil chemical characteristics and vegetation factors explained 13.0% (P = 0.001) and 13.4% (P = 0.001) variation, respectively. There existed interaction among three groups of factors. The interaction between soil chemical and physical characteristics explained 13.8% variation, the interaction between vegetation and soil physical characteristics explained 12.9% variation and the interaction of soil chemical factors and vegetation factors explained 1.5% variation of carbon source utilization.
Redundancy analysis (RDA) was used to analyze relationship between carbon source utilization ability and vegetation factors, soil physical characteristics and chemical characteristics respectively. Monte Carlo permutation test (n=999) was used to preselect factors that significantly influenced carbon source utilization of soil microorganisms. RDA showed that among the 7 vegetation factors, tree layer species richness, root biomass and tree biomass significantly influenced carbon source utilization ability of soil microbial communities, which explained 16.7% (P = 0.001), 6.3% (P = 0.017) and 4.6% (P = 0.046) variation of carbon source utilization, respectively. The soil physical characteristics, including soil moisture content, sand content and soil bulk density, also significantly influenced carbon source utilization of soil microbial communities, which explained 10.5% (P = 0.003), 8.8% (P =0.01) and 7.2% variation (P = 0.005) of carbon source utilization. As for the 6 soil chemical characteristics, only soil pH, C∶N ratio and available nitrogen content significantly explained the variation of carbon source utilization by soil microbial communities, which explained 10.5% (P = 0.006), 12.4% (P = 0.002) and 5.2% (P = 0.047) variation of carbon source utilization.
According to the explained variation of carbon source utilization by soil microbial communities, the lower C∶N ratio in soil, higher soil moisture content and soil pH (within the scope of acid soil) were the main factors improving soil carbon source metabolism capacity in natural secondary forest. The higher broad-leafed species ratio also benefit soil carbon source metabolism capacity in natural secondary forest.