  Compost is used worldwide as a soil conditioner for crops, but its functions
have still been explored. Here, the omics profiles of carrots were
investigated, as a root vegetable plant model, in a field amended with compost
fermented with thermophilic Bacillaceae for growth and quality indices.
Exposure to compost significantly increased the productivity, antioxidant
activity, red color, and taste of the carrot root and altered the soil
bacterial composition with the levels of characteristic metabolites of the
leaf, root, and soil. Based on the data, structural equation modeling (SEM)
estimated that L-2-aminoadipate, phenylalanine, flavonoids and / or carotenoids
in plants were optimally linked by exposure to compost. The SEM of the soil
estimated that the genus Paenibacillus, L-2-aminoadipate and nicotinamide, and
S-methyl L-cysteine were optimally involved during exposure. These estimates
did not show a contradiction between the whole genomic analysis of
compost-derived Paenibacillus isolates and the bioactivity data, inferring the
presence of a complex cascade of plant growth-promoting effects and modulation
of the nitrogen cycle by compost itself. These observations have provided
information on the qualitative indicators of compost in complex soil-plant
interactions and offer a new perspective for chemically independent sustainable
agriculture through the efficient use of natural nitrogen.
