Stratification ratio of rhizosphere soil microbial index as an indicator of soil microbial activity over conversion of cropland to forest
2020
Qu, Qing | Xu, Hongwei | Xue, Sha | Liu, Guobin
Studying soil microbial activity is important for evaluating soil microbial conditions and soil nutrient cycling. This study examined how the conversion of cropland to forest affects soil microbial activity and stratification ratios of the rhizosphere soil microbial index (RSMI), as well as to clarify the relationship between the stratification ratios of RSMI and soil microbial activity. Soils beneath two typical vegetation types of shrubland (Caragana korshinskii and Hippophae rhamnoides) and forestland (Robinia pseudoacacia) in the Loess Hilly region of China that had recovered for up to 47 and 56 years, respectively, were evaluated at four soil depths (0–10, 10–20, 20–30, and 30–50 cm). Our findings showed that the conversion of cropland to forest mainly affected soil microbial activity in the surface layer (0–10 cm), in which microbial biomass, enzyme activity (saccharase, urease, and phosphatase), and RSMI increased over time, whereas the microbial metabolic quotient decreased. After the conversion from cropland, recovery time (years) caused an increase in the SRR₁ (the RSMI ratio in 0–10 cm versus 10–20 cm layer) of shrubland (by 40.56–108.14%, compared to 0 year) and forestland (by 18.48–79.71%, compared to 0 year). Overall, SRR₁ was positively correlated with RSMI in both conversion types. In conclusion, the stratification ratios of the rhizosphere soil microbial index of SRR₁ provided good indicators of soil microbial activity and were significantly enhanced by the process of the conversion from cropland to forest.
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