Intercropping increases soil macroaggregate carbon through root traits induced microbial necromass accumulation

Microbial necromass, as part of persistent soil organic matter, plays a significant role in maintaining soil fertility and sustainability of agroecosystems. Intercropping, planting multiple crop species in the same field at approximately the same time, has been demonstrated to increase soil organic matter through enhanced biomass input. Nonetheless, little is known as to how intercropping affects microbial necromass accumulation in soils and the underlying microbiological mechanisms, particularly about microbial life strategies and network stability. Here, we investigated the carbon (C) accumulation mechanism of microbe-aggregate interactions using aggregate fractionation combined with microbial biomarkers as well as high-throughput sequencing in an 11-year maize/peanut intercropping field experiment. We found that intercropping increased soil organic carbon (SOC) and microbial necromass C in macroaggregates (>250 μm) compared with sole crops, and it was mostly accounted for by fungal necromass C. Within small macroaggregates (250–2000 μm), bacterial necromass C was positively correlated with r-strategy bacteria, and fungal necromass C was positively correlated with K-strategy fungi. Microbial inter-kingdom co-occurrence network analysis showed higher proportions of positive links in intercropping system than in sole crops, and the proportions of positive links positively correlated with fungal necromass C in macroaggregates (>250 μm). Path analysis revealed that intercropping increased SOC mainly through root traits induced microbial life strategies and microbial network stability, resulting in increased microbial necromass. In conclusion, crop diversity-driven changes in root traits induced microbial traits promote microbial necromass accumulation. A new mechanism elucidating the positive crop diversity effect on soil C sequestration is proposed.