Deciphering the bioavailability of dissolved organic matter in thermophilic compost and vermicompost at the molecular level

Studies on compost dissolved organic matter (DOM) previously focus on its composition and humification, without considering DOM bioavailability to understand compost fertility. To decipher the fertility basis of compost, DOM bioavailability in thermophilic compost (TC) and vermicompost (VC) was investigated and linked with its molecular composition. Results showed that DOM bioavailability of VC (36 % BDOC) was generally higher than that of TC (22 % BDOC) due to containing more tannin-like substances. Inversely, only lipid -/car-bohydrate-/protein-like substances contributed to DOM bioavailability in TC. Moreover, these differences of bioavailability expanded with C/N decreased in composting materials. Specifically, the %BDOC of VC with N -rich materials (C/N < 25) was 2.1-3.0 times higher than that in TC, while it was only 1.2-1.4 times for C-rich materials (C/N < 25), because N-surplus facilitated the formation of O-/N-containing aromatics (e.g., CHON and tannin) in VC, but inhibited the decomposition of organic materials into small bioactive molecules in TC.

Automated summary

Previous studies on compost dissolved organic matter (DOM) have mainly focused on its composition and humification, neglecting the importance of DOM bioavailability in understanding compost fertility. This study investigated the bioavailability of DOM in thermophilic compost (TC) and vermicompost (VC), and linked it to its molecular composition. It was found that the bioavailability of VC DOM (36% BDOC) was generally higher than that of TC (22% BDOC) due to higher content of tannin-like substances. Furthermore, the differences in bioavailability between VC and TC increased as the C/N ratio decreased in the composting materials.