As a child, I spent much time playing in the farmland, watching my parents sow, irrigate, weed, and harvest. I was convinced there was 'something' in the soil, a mysterious force that guided a seed's journey to becoming a fruit-bearing plant. After earning my PhD in Soil Science from the Chinese Academy of Science, I discovered that this 'magic something' was 'soil organic matter', the brown and black matter in the soil. This revelation marked the beginning of my professional journey, exploring the formation of soil organic matter and investigating ways to manage it to increase crop yield. 

The croplands of Northeast China are the nation's primary crop production bases, significantly influencing regional and national food security. However, studies suggest that the soil organic matter content in this region has declined due to long-term cultivation of crops. Therefore, it is crucial to understand what controls the formation and turnover of soil organic matter to halt this decreasing trend. 

To bridge this knowledge gap, my collaborators and I conducted a regional soil survey at 468 sites in Liaoning province, China, including two major crop types: maize and rice. With increasing evidence suggesting that microorganisms can moderate soil organic matter through their metabolic processes, our focus was on the relationship between 'microbial life cycles' (from growth to death) and soil organic matter content. We measured soil organic carbon content, microbial composition, and microbial death residual materials. 

The location and sampling sites in Liaoning province, China.

Our study revealed a significant difference in soil organic carbon content between rice and maize sites. Interestingly, the contribution of microbial residues to soil organic carbon was higher in maize than in rice, suggesting that microbial death may play a more crucial role in regulating soil organic carbon in maize. Furthermore, microbial diversity and inter-species connections strongly correlated with soil organic carbon, indicating that these tiny organisms might influence soil carbon formation and stabilization through their life cycles. To further understand these relationships, we built two models exploring the linkages between microbial processes and soil organic carbon for maize and rice, which may assist in managing carbon in cropland. 

In conclusion, our work provides empirical evidence that microorganisms mediate soil carbon matter in cropland and could significantly contribute to carbon accumulation. This insight suggests that if we aim to reverse the declining trend in cropland soil organic carbon, we should consider creating a healthy environment for microorganisms, enabling them to effectively moderate soil organic carbon cycling.