Insect addition in post-compost products offers a novel approach for straw utilization, while its effect on nutrient availability remains unclear. This study introduced black soldier fly larvae (BSFL), yellow mealworm larvae (YML), and Protaetia brevitarsis larva (PBL) into rice straw compost to investigate nutrient transformation and explore biological mechanisms using high-throughput sequencing, metagenomics, and metabolomics. Adding insects significantly increased the levels of available nitrogen and phosphorus in the composts, with the most pronounced effect in BSFL. The abundances of key functional genes involved in organic nitrogen degradation (e.g., glsA , gdh ) were elevated in insect frass, which promoted the degradation of various organic nitrogen (e.g., choline, C16 sphingosine) and amino acid metabolites (e.g., L -arginine, D -proline). Compared to PBL and YML, BSFL treatment increased dissimilatory nitrate reduction but decreased denitrification, leading to the higher levels of available nitrogen and NH 4 + -N. The increase in available phosphorus in PBL and YML frass primarily depended on mineralization of organic phosphorus and activation of inorganic phosphorus, respectively; while BSFL treatment simultaneously enhanced both metabolic processes. Organic phosphorus compounds containing lipids and nucleotide analogues were mineralized by microbial functional genes including opd , ugpQ , aphA , and phoC . Activation of inorganic phosphorus relied on various organic acids, with key regulatory genes belonging to the pst and phn gene cluster. These metabolic processes should be carried out by the bacterial phyla Bacteroidota and Actinomycecota . Therefore, applying insects improved the quality of compost by promoting nitrogen and phosphorus transformation, but the effectiveness varied among insects due to differences in metabolic pathways. • Adding insects increased available nitrogen and phosphorus in the straw composts. • BSFL frass showed the higher available nitrogen and phosphorus than YML and PBL. • BSFL increased dissimilatory nitrate reduction but decreased denitrification. • Degradation of organic nitrogen and amino acid metabolites was promoted in frass. • BSFL simultaneously enhanced organic P mineralization and inorganic P activation.
Zhou et al. (Tue,) studied this question.