Protaetia brevitarsis larvae frass affects substrate microecological systems via two suggestive pathways to enhance cherry tomato growth

BACKGROUND: The identification and development of high-quality humus sources to enhance the productivity and performance of substrate-based vegetable cultivation systems remains a significant challenge in sustainable agriculture. Protaetia brevitarsis larvae (PBL) exhibit exceptional efficiency in decomposing decaying crop straw and produce nutrient-rich frass with high humic acid content and a complex microbial community. However, its impacts on substrate microecological systems and the underlying functional mechanisms remain unclear, limiting its rational application in substrate cultivation. This study aimed to investigate the effects of PBL frass on substrate microecology and elucidate the associated mechanisms using cherry tomato (Lycopersicon esculentum Mill. var. cerasiforme Alef) pot experiments. RESULTS: Incorporation of 2% or 4% (w/w) PBL frass into cherry tomato cultivation substrates significantly promoted plant growth, characterized by reduced plant height (indicating more robust, dwarf-type growth) and increased aboveground (stem) and belowground (root) biomass. Furthermore, PBL frass application enhanced substrate microbial diversity through two distinct, complementary pathways: (ⅰ) Frass-derived microbes, which possess specific colonization capabilities, directly augmented microbial communities in both the rhizoplane and bulk substrate; and (ⅱ) Organic compounds in PBL frass may have activated a broad range of microbes, enriching the rhizosphere microbiome. This enhanced microbial diversity was associated with an increased abundance of plant-beneficial taxa, which likely contributed to growth promotion and substrate health maintenance. CONCLUSIONS: This study uncovers the multifaceted contributions of PBL frass to substrate microbial ecology and reveals its two suggestive regulatory pathways. These results provide a theoretical basis for the sustainable utilization of PBL frass and advance the development of eco-friendly amendments for modern vegetable production.