Impacts of Land Use Intensification Level on Fluvo-aquic Cropland Soil Microbial Community Abundance and Necromass Accumulation in North China

Abstract

Despite the essential role of soil microorganisms in nutrient turnover in soil ecological systems and the recognized paramount significance of microbial necromass to soil organic carbon accumulation, how microbial community abundance and necromass respond to land use intensification level regulation remains poorly understood. To address this knowledge gap, based on the land use intensification level, three treatments were set up[annual wheat-maize rotation (CC), alternating temporary grassland with wheat planting (TG), and perennial grassland (PG)], and a long-term fixed filed experiment was established to investigate the influences of the regulation of land use intensification level on bacterial and fungal community abundances; the accumulation of bacterial, fungal, and total microbial necromass; and their contributions to SOC sequestration using droplet digital PCR and amino sugar detection technologies. We further sought to determine the key factors driving the bacterial, fungal, and total microbial necromass C accumulation. Our results demonstrated that fungal community abundance was strongly affected by land use intensification level regulation compared to that of the bacterial community, which increased with decreasing land use intensification level. The total microbial necromass C predominated the SOC accumulation across all three land use intensification levels, which contributed 52.78%, 58.36%, and 68.87% to SOC, respectively, exhibiting an increasing trend with the decline in land use intensification level. Fungal necromass C accounted for more than 80% of the total microbial necromass C, indicating its predominance in the accumulation of the total microbial necromass C and active variation via the reduction in land use intensification level. There was no significant difference in bacterial necromass C (MurA) content, with the trend of CC<PG<TG, whereas fungal necromass C (GluN) was observed to be significantly shifted by the modulation of land use intensification level, with contents in the TG and PG treatments being higher than that in the CC treatment, especially for the PG treatment (with an increase of 66.10%). The increase in bacterial necromass C accumulation was associated with microbial demand for N and was affected by the balance between soil C and N; however, the accumulation of fungal necromass C was jointly manipulated by a wide variety of biotic and abiotic factors. Altogether, our work provides evidence that agricultural land use intensification level regulation can enhance soil extracellular enzyme activity and accelerate nutrient transformation through changing edaphic properties, thus improving fungal amount and necromass C accumulation, with active contribution to total microbial necromass C and even SOC.