Fungal endophytes influence soil organic carbon and nitrogen fractions promoting carbon sequestration and improving grain yield in soybean.

Fungal endophyte inoculants present a promising avenue for enhancing carbon sequestration in agricultural systems. These endophytes can significantly influence soil organic carbon (SOC) and nitrogen (N) fractions by modulating root exudation, soil aggregation, and organic matter decomposition. We investigated the effectiveness of commercial-stage fungal endophyte seed inoculants in an Australian soybean field trial to increase yield, total SOC, stable SOC fractions, and soil N. After one growing season, specific inoculants (Thozetella sp. and Leptodontidium sp.) and dosages increased soybean grain yield and stocks of soil organic matter (SOM) as aggregate occluded particulate organic matter (oPOM) C and N, and mineral-associated organic matter (MAOM) C and N in the topsoil layer (0-15 cm). Furthermore, positive correlations were established between grain yield and the stocks of oPOM (C and N) and MAOM (C and N) in the topsoil layer (0-15 cm). Importantly, increasing grain yield was significantly and positively associated with the proportion of oPOM-C and N stocks to total SOM stock, providing evidence of significant carbon sequestration in oPOM. However, the proportion of MAOM-C and N stock to total SOM stock decreased significantly with increasing grain yield, indicating higher proportion of MAOM is being turned over relative to other SOM fractions although the absolute amounts of MAOM-C and N remained stable. These findings suggest that fungal endophytes and dosages may have variable but potentially beneficial impacts on crop growth, yield and play a crucial role in altering SOM fractions. This alteration potentially leads to changed carbon sequestration strategies, emphasising the need for further research into fungal endophyte-mediated carbon sequestration mechanisms.