Soil microbial community responses to forage grass cultivation in degraded karst soils, Southwest China

Abstract Variation of soil microbial community abundance and structure has great implications for soil fertility and nutrient cycling. A better understanding of soil microbial community dynamics under different land use types is undoubtedly needed in order to develop sustainable land use schemes. The current study aimed to assess how soil microbial community changed after replacement of maize–soybean crop by sugarcane, mulberry, or forage grass crop in a karst area of Southwest China. Mature forests were included for comparison. Phospholipid fatty acid (PLFA) method was used to characterize soil microbial community abundance and structure. The abundances of total PLFAs and PLFAs of bacteria, fungi, actinomycetes, and arbuscular mycorrhizal fungi were significantly increased in the forage grass field but not in the sugarcane and mulberry fields relative to the maize–soybean field. Total PLFAs' abundance in the forage grass field was increased by 81% compared with that in the maize–soybean field but was about 52% lower than that in the forest. The microbial community structure was not distinguished as much as the microbial abundance among the five land use types. Soil organic carbon (SOC) was identified as the primary factor affecting both soil microbial abundance and structure. Soil microbial community abundance was positively correlated with SOC, but the ratios of fungal to bacterial PLFAs and Gram‐positive to Gram‐negative bacterial PLFAs were negatively correlated with SOC. Our findings suggest that the replacement of the maize–soybean rotation system by forage grass cultivation has the potential to improve soil fertility in the karst region, Southwest China.