Synergistically promoting humification and polluting gas reduction in cherry tomato straw composting via carbon bioavailability management

The synergistic control of composting humification level and polluting gas emission reduction is a persisting challenge in aerobic composting. Numerous previous studies reported that the effects of various carbon source types or the total C/N ratios on the compost humification; However, only a few explored the role of carbon composition, particularly from a bioavailable quantization perspective. This study aimed to clarify the synergistic impact of bioavailable carbon composition and systematically accessed the interaction mechanisms that drove the composting. Six composting experiments with different content of bioavailable carbon were conducted and analyzed from four aspects, polluting gas emissions, compost characteristics, humification, and microbial community structure. The results indicated that a higher proportion of bioavailable carbon enhanced the transformation of organic matter, total nutrient, and available nutrient, accompanied by enhanced humification level of the compost. A slight increase in bioavailable carbon led to higher gas emissions (CO₂ equivalent emissions) to some extent. Only when the proportion of available carbon proportion I (ACC1) exceeded 60.31% (threshold value, T5 treatment) did the compost humification level and gas emission-reduction effect improve simultaneously. Under the T5 treatment, the nitrous oxide reduction rate reached 76.98% with its contribution to global warming potential decreasing to 21.0%.In this study, labile carbon component directly participated in the humification process and also indirectly enhanced the humification of compost and reduced pollutant gas emissions through the mediation of microbial communities. Overall, this study presented a comprehensive correlation network that links multiple composting parameters and identified the LCP1 was the key carbon component of carbon bioavailability. The findings offer a theoretical basis and empirical support for integrated improvement of compost humification efficiency, compost quality, and gas emission reduction in practical applications.