Combined Use of Biochar and Microbial Agents Can Promote Lignocellulosic Degradation Microbial Community Optimization during Composting of Submerged Plants

Aerobic composting is one of the methods for the resource utilization of submerged plant residues. This study investigated the effects of biochar, wetland sediments and microbial agents added individually or combined on the humification process, lignocellulose degradation and microbial communities during Ceratophyllum demersum and Potamogeton wrightii composting. The results showed that the addition of wetland sediment and biochar was found to significantly elevate the composting temperature and humification of compost products. The average content of lignin in wetland sediment and/or biochar treatments was 12.2–13.5%, which was higher than the control group (10.9–11.45%). Compared with the organic matter (19.4%) and total nitrogen concentration (35.3%) of compost treated with complex microbial agent treatments, the homemade microbial agents significantly increased the values by 22.1% and 41.0%, respectively. By comparing the differences in microbial communities among different treatments, the sediments and homemade agents demonstrated greater increases in activity and diversity of lignocellulose degradation-related microbes, especially for Truepera and Actinomarinale. Humus component and temperature were the most critical parameters influencing the changes in the bacterial community. Based on these results, a combination of biochar and homemade agents was a promising additive for an effective composting strategy, and sediment was identified as a potential control of bacterial diversity in wetland plant compost.