Succession of fungal community and enzyme activity during the co-decomposition process of rice (Oryza sativa L.) straw and milk vetch (Astragalus sinicus L.).

The co-incorporation of rice straw (RS) and milk vetch (MV) into paddy fields has been increasingly applied as a sustainable farming practice in southern China. Our previous study revealed the contribution of bacteria to the co-decomposition of the RS and MV mixture, although additional underlying factors driving the co-decomposition process need to be clarified. The present study further determined the succession of fungal communities and enzyme activity in the co-decomposition process of the RS and MV mixture. The results showed that non-additive synergistic effects on biomass loss were observed in 55.6% of the sampled RS and MV mixture during the co-decomposition process, stimulating mixture decomposition. Overall fungal abundance was 19.6-30.6% higher in the RS and MV mixture throughout the study than in the single residue. Fungal diversity and community structure were mainly affected by the sampling date rather than the type of residue. Specifically, mixing RS and MV significantly increased the abundance of Peziza sp. and Reticulascus tulasneorum (lignocellulose- and lignin-decomposing fungi) and exhibited higher activities of C- and N-related hydrolases than monospecific residues. Random forest (RF) models showed that bacteria contributed more to the residue decomposition and activities of C-related hydrolases, N-related hydrolases, and oxidases than fungi. However, both RF and partial least squares path models revealed that fungal abundance and community structure directly or indirectly affected the residue decomposition rate. These findings showed that mixing RS and MV could stimulate their decomposition by enhancing C-related hydrolase activity and Peziza sp. and Reticulascus tulasneorum abundance.