Translocation and turnover of rhizodeposit carbon within soil microbial communities of an extensive grassland ecosystem
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Background and Aims
A substantial amount of photosynthesized plant-C is allocated belowground in grassland ecosystems where it influences the structure and function of the soil microbial community with potential implications for C cycling and storage. We applied stable isotope probing of microbial PLFAs and repeated soil sampling in a grassland over a period of 1 year to assess the role of microbial communities in the cycling of rhizodeposit-C.
Pulse-labeling with 13CO2 was performed in a grassland site near Gent (Belgium). Soil samples were taken 24 h, 1 week, 1 month, 4 months, 9 months and 1 year following labeling and analyzed for 13C in soil, roots and microbial PLFAs.
C enrichment of PLFAs occurred rapidly (within 24 h) but temporally varied across microbial groups. PLFAs indicative for fungi and gram-negative bacteria showed a faster 13C uptake compared to gram-positive bacteria and actinomycetes. However, the relative 13C concentrations of the latter communities increased after 1 week, while those of fungi decreased and those of gram-negative bacteria remained constant. PLFA 13C mean residence times were much shorter for fungi compared to bacteria and actinomycetes.
Our results indicate temporally varying rhizodeposit-C uptake by different microbial groups, and faster turnover rates of mycorrhizal versus saprotrophic fungi and fungi versus bacteria. Fungi appeared to play a major role in the initial processing and possible rapid channeling of rhizodeposit-C into the soil microbial community. Actinomycetes and gram-positive bacteria appeared to have a delayed utilization of rhizodeposit-C or to prefer other C sources upon rhizodeposition.
Keywords13C Pulse-labeling Rhizodeposition Soil microbial community structure SIP-PLFA Microbial carbon turnover
Phospholipid fatty acid
Fatty acid methyl ester
Stable isotope probing
Gas chromatography combustion isotope ratio mass spectrometry
Mean residence time
The authors wish to thank Dries Roobroeck, Davy Loete, Katja Van Nieuland and Jan Vermeulen for assistance with pulse-labeling, sample collection and laboratory analyses. This study was funded by the special research fund (BOF) of Ghent University. Dries Huygens is a postdoctoral fellow of the Fund for Scientific Research—Flanders (FWO).
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