[Seasonal Variation and Differences in Microbial Biomass Carbon in Yellow Soil Under Different Long-term Crop...

Studying the seasonal variation characteristics and main driving factors of soil microbial biomass carbon （MBC） in yellow soil under long-term crop rotation could provide a theoretical basis for formulating reasonable crop rotation systems and improving soil fertility in the region. Based on a long-term positioning experiment of 26-year rotation in yellow soil, three rotation modes were selected： maize monoculture （MM）, rapeseed-maize rotation （RMR）, and wheat-green manure-maize rotation （WMR）. The seasonal variation characteristics of soil MBC content, carbon conversion enzyme activity, and soil respiration rate （Rs） under different rotation patterns were analyzed, and the annual turnover amount and turnover time of MBC were calculated. The main driving factors were also analyzed. The results showed that, compared with those in the MM treatment, the annual average MBC content, β-1, 4-glucosidase （BG） activity, cellobiohydrolase （CBH） activity, BG+CBH activity, and Rs increased significantly by 18.9%-34.0%, 40.0%-60.2%, 36.8%-57.1%, 39.1%-59.2%, and 47.0%-58.1%, respectively. In addition, the rotation treatments increased the annual turnover amount of MBC by 34.5%-42.0% and shortened the turnover time of MBC by 0.07-0.15 a. There was a highly significant linear positive correlation between soil MBC content, BG activity, and CBH activity in different crop growth seasons, but there was a highly significant linear negative correlation between MBC variation （ΔMBC） and CBH variation （ΔCBH）. Soil total organic carbon and total nitrogen were significantly positively correlated with MBC content, Rs, MBC annual assimilation amount, and MBC annual turnover amount, while C/P was significantly positively correlated with BG activity, CBH activity, and MBC annual mineralization amount. In summary, MBC could reflect the carbon fertility of yellow soil, and long-term crop rotation could increase soil MBC content, carbon conversion enzyme activity, and soil respiration rate； promote MBC turnover； and enhance soil microbial carbon sequestration and supply capacity. Among different crop rotation patterns, WMR had the best effect.