Effects of additives on compost quality and cbbL-containing autotrophic microbial community of watermelon straw composting

The amount of CO2 emission reflects the microbial activity in compost, but excessive emission can reduce humification degree of compost. Therefore, this study assessed the effects of superphosphate (SSP) and dicyandiamide (DCD) on CO2 emission, compost quality, and cbbL-containing autotrophic microbes (CCAM) community of watermelon straw composting. Results revealed that SSP and DCD promoted the compost maturity, but the DCD alone did not significant effect of the compost. Single DCD (T1) reduced CO2 emission by 7.02 % and increased humic acid content by 3.09 %. DCD+SSP (T2) resulted in a 15.26 % reduction in CO2 emission, a 9.13 % increase in humic acid content, and a significant increase in compost humification level. Furthermore, DCD+SSP improved the abundance and diversity of the CCAM (mainly Proteobacteria and Actinobacteria), improved the compost microenvironment and reduced carbon loss by 6.89 %. Redundancy analysis (RDA) showed that CCAM community had strong correlations with TOC (84.8 %). This study results provided theoretical and practical support for further exploring the carbon emission reduction in composting and promoting sustainable agricultural development.