Elucidating the impact of mulching film on organic carbon mineralization from the perspective of aggregate level.

Plastic films mulching, a management strategy designed to boost agricultural productivity, significantly impacts soil fertility and the turnover of soil organic carbon (SOC). Aggregates in the soil play a crucial role in this SOC cycling. Yet, the effect of mulching on the changes in organic carbon components and the mineralization at the aggregate scale is still not well understood. We conducted a three-year field experiment to examine the effects of various mulching types (CK: non-mulching, BPM: black polyethylene mulching, CPM: colorless polyethylene mulching, BDM: black degradable mulching, CDM: colorless degradable mulching) on the transformation and mineralization of organic carbon within soil aggregates. Generally, after three years of continuous mulching, compared to CK, soil aggregate stability significantly improved, the content of SOC and HFOC increased by 8-14 % and 12-24 % respectively, while the content of LFOC decreased by 3-51 %. The response mechanisms of organic carbon mineralization in different size aggregates to mulching are different. The change in carbon components is the main factor stimulating the mineralization of organic carbon in >0.25 mm aggregates; microbial diversity is the dominant factor inhibiting the mineralization of organic carbon in 0.053-0.25 mm aggregates; while <0.053 mm aggregates are not significantly affected by mulching. Our findings suggest that plastic mulching reduce the mineralization of SOC and enhances its sequestration by modulating the composition of organic carbon fractions, extracellular enzymes, and microorganisms within soil aggregates of different sizes. This study provides a valuable reference for gaining further insights into the turnover dynamics of soil organic carbon at the aggregate scale.