Linking soil microbial community traits and organic carbon accumulation rate under long-term conservation tillage practices

Conservation tillage practices may stimulate soil organic carbon (SOC) storage in croplands by reducing soil disturbance and increasing inputs of crop residue. Although the effect of tillage practices on soil C dynamics is mediated by soil microbes, the relation between microbial community traits and SOC accumulation rate (SAR) remains unclear. In this study, we investigated the effect of tillage management on soil properties and microbial community traits (i.e. diversity, composition and keystone taxa) in a long-term (17 years) field experiment. Our experiment was located in a spring maize field with a sandy loam soil (Calcaric-Fluvic Cambisol) in northwest China and included three tillage practices: 1) CT-RR, conventional tillage with residue removed; 2) RT-RI, reduced tillage with residue incorporated; and 3) NT-RM, no-tillage with residue mulched. We sampled soil at 0-10 cm and 10-25 cm to assess the relation between bacterial and fungal community traits and SAR. We found that the initial and current of average SOC stocks was 19 and 28 Mg ha-1 at 0-25 cm, respectively. RT-RI and NTRM increased SOC accumulation at 0-10 cm by 116% and 131% compared with CT-RR, respectively, and RT-RI increased SOC accumulation at 10-25 cm by 159%. Changes in co-occurrence network analysis revealed that NTRM resulted in a stable bacterial network, whereas both RT-RI and NT-RM produced a stable fungal network relative to CT-RR. Microbial diversity and keystone taxa correlated positively with SAR under conservation tillage practices. Using a Zi-Pi plot, we identified several keystone OTUs, five of which (i.e. Cytophagales, JG30KF-CM45, Sphingobacteriales, Thelephorales and Pleosporales) showed a positive correlation with SAR. Our results suggest a strong link between microbial community traits and SOC accumulation rate under conservation tillage practices, and provide insights into the contribution of microbial traits to the sustainability of agroecosystems.