Monoculture and improper management may reduce soil fertility and deteriorate soil structure in Black soils (Mollisols) of Northeast China. The experiment was carried out from 2015 to 2016 in Black Soils comprising five cropping systems: continuous corn (CC), soybean-corn rotation (SC), corn-soybean rotation (CS), fallow-corn (FC), and fallow-soybean (FS). Our results showed that CS and FS treatments significantly increased mean weight diameter (MWD) and fractal dimension (D) in mechanical stability aggregates (MSAs), and increased MWD and geometric mean diameter (GMD) in water-stable aggregates (WSAs) compared with CC treatment. These two treatments were also significantly increased water-stable aggregates stability rate (WSAR), but decreased percentage of aggregates destruction (PAD) than CC treatment. Meanwhile, CS and FS treatments exhibited a higher carbon accumulation than CC treatment in bulk soils. Soil organic carbon (SOC) concentration in WSA_0.106-0.25,WSA_{2-5 mm}and WSA_{0.5-1 mm}had a dominant effect on aggregate stability. Simutaneously, SOC in WSA_{>5 mm}affected SOC concentration in bulk soils. As a whole, the CS and FS treatments can increase the percentage of macro-aggregates, enhance aggregate stability, as well as increase SOC concentration in bulk soils and all soil aggregate sizes.

Background: Microbial contributions to soil organic carbon formation have received increasing attention, and microbial carbon use efficiency is positively correlated with soil organic carbon storage. Mainbody: This work reviews the impact on microbial carbon use efficiency from six constraints, including plant community composition and diversity, soil pH, substrate quality, nutrient availability and stoichiometric ratios, soil texture and aggregates, water and thermal constraints, and external nutrient inputs. In general, the response of microbial carbon use efficiency showed large uncertainty to above constraints, including positive-, negative-, or non-correlation. However, some factors are biased, more likely to promote or inhibit carbon use efficiency. For example, external nutrient input (N, P, K, Ca) tended to promote carbon use efficiency, while climate warming showed more negative influence. Conclusion: Further, overwhelming works focused on single constraint, we suggest the importance to consider the synergistic influence of multiple environmental variables on microbial carbon use efficiency, special for the regulation mechanism of biological-environmental interactions.