Microbial utilization of photosynthesized carbon depends on land-use

The release of organic compounds from plant roots (rhizodeposits) and their subsequent utilization by soil microbial communities is a key process linking atmospheric and terrestrial carbon (C) and nutrient cycling. However, the effects of land-use types on rhizodeposit-mediated alteration of microbial community structure and its consequences for soil C cycle are still, largely, unknown. Therefore, we used 13C-PLFA-SIP to evaluate the rhizosphere C fluxes to microorganisms in a monoculture crop (oilseed rape, Brassica napus L.), a mixed grassland (dominated by Lolium perenne L. mixed with clover Trifolium repens L.), and a tree (willow, Salix schwerinii E.L. Wolf and Salix viminalis L.) within an agroforestry system. Though harboring similar total microbial biomass, less 13C was recovered in microorganisms in soil under willow (0.017 % of 13C input) after 14 days as compared to rape (0.03 %) and grassland (0.09 %). Across three land use types, gram negative bacteria incorporated most of the 13C (28–42 % of total 13C labeled PLFAs), followed by fungi and gram positive bacteria (12–18 %) and less abundance groups (e.g. actinomycetes, <5 %). The arbuscular mycorrhizal fungal biomarker 16:1ω5c was enriched with 13C in soil under grassland (8 % of total 13C labeled PLFAs). The 13C incorporation into gram positive bacteria was higher in soil under willow than under grassland and rape. By contrast, 42 % of total 13C labeled PLFAs were attributed to gram negative bacteria in soil under rape. Overall, our results demonstrated that pronounced differences in microbial community structure and subsequent microbial C utilization between land-use types could affect soil C cycles and storage.