Abstract
Forest soil processes carried out by microorganisms are critical for the global carbon (C) cycle and climate. Characterizing the utilization of differently recalcitrant C sources is an important step towards understanding the ecosystem-level function of microorganisms in temperate forest soils.
Here, using stable-isotope probing (SIP), we tracked C incorporation into bacterial and fungal biomass by quantifying (13)C incorporation into phospholipid fatty acids (PLFA-SIP), its respiration (i.e., content in the produced CO2) and C accumulation by individual microbial taxa (DNA-SIP), following the addition of (13)C-labelled substrates of different recalcitrance (citric acid, glucose, chitin, cellulose, hemicellulose, and plant biomass) in microcosms. The highest (13)C respiration was observed after the addition of the low-molecular-mass substrates citric acid and glucose, while the highest (13)C incorporation into microbial biomass was observed during growth on chitin.
Communities of fungi and bacteria that incorporated (13)C of various origins into their biomass differed from the original soil communities, as well as between treatments. The most distinct microbial community was observed in microcosms containing (13)C-chitin, indicating its utilization by both fungi and bacteria.
Bacterial taxa were more often versatile, incorporating C of various origins, while there was a higher share of fungi that were specialists. Together, our results show that low -molecular-mass compounds that belong to typical root exudates are more readily respired, while the C from biopolymers studied was relatively more incorporated into microbial biomass.
Various C sources are targeted by distinct microbial communities, although their composition partly overlaps due to the existence of generalist bacteria and fungi that are capable of utilizing various C sources.