Changes in soil microbial biomasses and their quotients over the succession of karst rocky desertification

To evaluate soil fertility of karst land undergoing rocky desertification (RD), the changing trend of soil microbial biomass properties over the succession of RD were studied by investigating the stands and analyzing the soil samples with four different RD grades in the northwestern Hunan province, China. The results showed that the changing trend of microbial biomass C (MBC), microbial biomass N (MBN), microbial biomass P (MBP), and the microbial biomass quotients including the ratio of MBC to total organic C (MBC/TOC), the ratio of MBN to total N (MBN/TN), and the ratio of MBP to TP (MBP/TP) was: potential RD > light RD > moderate RD > intensive RD, whereas the changing trend of microbial communities was not entirely consistent with the succession of RD. The increased grade of RD was significantly and negatively correlated to the increased contents of MBC (r = -0.86), MBN (r = -0.85), MBP (r = -0.73), MBC/TOC (r = -0.81), MBN/TN (r = -0.64), and MBP/TP (r = -0.72). The values of microbial biomass quotients were influenced by the content of organic matter inputting to soil. Therefore, microbial biomass C, N, P and microbial biomass quotients might be sensitive indicators to reflect the strength of soil fertility in the degraded karst regions.