Compost amendment to agricultural soils influences plant growth and soil quality by affecting activity of arbuscular mycorrhizal fungi (AMF) and composition of microbial community. We related the molecular composition of compost of different maturity added to soils to their effects on maize growth, N and P uptake, AMF root colonization and growth, and composition of soil microbial community. The characteristics of compost after different days of maturation (C60, C90, C120) were provided by 13 C-solid state NMR spectroscopy, while neutral (NLFA) and phospholipid (PLFA) fatty acid analyses were used to evaluate the effects of compost on the composition of soil microbial communities. Multivariate elaboration was used to determine the relationships between microbial groups, as identified by PLFA analysis , and molecular properties of composts. Although compost amendments increased soil total C and N, and available P, soil addition of both C60 and C120 compost samples was detrimental to plant and AMF growth. Compost amendments modified the composition of soil microbial communities. The high content of biolabile compounds in C60 and C120 compost samples decreased the C16:1ω5 NLFA that was related to AMF and Gram(+)/Gram(−) and AMF/saprotrophic fungi ratios. A linear correlation was found between the molecular indexes in compost and the microbial groups in soil, thereby suggesting that the molecular composition of compost strictly controls the development and abundance of soil microbial communities. These findings highlight the importance of controlling the molecular quality of recycled biomass added to soil, in order to predict the effect on crop yields and biotic composition of soil

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