Microbial Necromass Carbon Distribution Differs Between Four Soil Types After Long-Term Straw Return

Abstract

Microbial necromass carbon (MNC) is an important fraction of soil organic carbon (SOC) as it contributes to the long-term stable SOC pool. However, the effect of long-term straw return on MNC and its contribution to SOC accumulation across different soil types and soil depths remains insufficiently understood in agricultural ecosystems. By conducting a decadal scale field experiment across four soil types, long-term straw return was shown to increase SOC by 6%–109% and MNC by 3%–173% (except for the top 20 cm of Chernozem). MNC significantly increased only in the 0–40 cm of Phaeozem and 0–80 cm of Arenosol. The contribution of MNC to SOC increased significantly in the 0–40 cm layer of Phaeozem but remained almost unchanged in Chernozem, Lixisol, and Arenosol. Fungal necromass C (FNC) contributed significantly more to MNC accumulation than bacterial necromass C (BNC), comprising over 70% of MNC across all four soils. Mantel and Random Forest analyses revealed that microbial and soil properties positively influence MNC accumulation, with higher fungal phospholipid fatty acid (PLFA) levels strongly linked to increased MNC content. The results indicate that edaphic variables regulate MNC through FNC. Our study demonstrates the changes in profile distribution of MNC following long-term straw return across four soil types and explores the divergent regulatory pathways of edaphic factors on MNC via FNC and BNC, which could contribute to the regulation of SOC accumulation in cropping soils.