Temporary carbon capture potential of winter fallow weeds and their effects on topsoil organic carbon and bacterial communities in rice cropping systems

Winter fallow weeds, which experience minimal human disturbance, may provide important ecological services, including carbon (C) capture and sequestration, as well as influencing soil bacterial communities. Despite their potential, research on these functions remains limited. This study evaluated the temporary C capture potential of winter fallow weeds—defined as biomass C retained before decomposition—and their effects on topsoil (0–20 cm) organic carbon (OC) content and bacterial communities in rice-based cropping systems. On-farm investigations were conducted in Hunan Province, China, at 27 sites in 2022 and 32 sites in 2023, complemented by a field experiment from 2020 to 2024. The field experiment included two weed incorporation rates—0 (W0) and 500 g m -2 yr -1 (W1, equivalent to 210 g C m –2 yr –1 )—combined with three nitrogen (N) application rates for rice: 0 (N0), 150 (N1), and 225 kg ha –1 yr –1 (N2). On-farm results indicated that winter fallow weeds produced average biomasses of 519 g m –2 in 2022 and 580 g m –2 in 2023, corresponding to temporary C captures of 209 and 247 g m –2 , respectively. In the field experiment, W1 significantly increased soil OC content by 7%, the relative abundance of the phylum Proteobacteria by 16%, and the abundance of the genus Sideroxydans within Proteobacteria by 37% compared with W0, averaged across N rates. W1 also significantly increased the relative abundance of the phylum Desulfobacterota by 13% under N0, whereas no significant differences were observed under N1 and N2. These results demonstrate that winter fallow weeds have substantial temporary C capture potential due to their high biomass and that their incorporation into rice fields can enhance topsoil OC and modify topsoil bacterial communities. • The temporary C capture potential of winter fallow weeds exceeded 200 g m –2 . • Incorporation of winter fallow weeds increased topsoil organic C content. • Incorporation of winter fallow weeds altered topsoil bacterial communities.