Plant-mycorrhizal-decomposer interactions and their impacts on terrestrial biogeochemistry

POLICELLI, NAHUEL; AVERILL, COLIN; BRZOSTEK, EDWARD; LIAO, HUI-LING; CHEN, KO-HSUAN; TAPPERO, RYAN; CARRARA, JOSEPH; VIETORISZ, CORINNE; NASH, JAKE; VILGALYS, RYTAS; BHATNAGAR, JENNIFER M.

Virtual

Congreso; Department of Energy Biological System Sciences Division Principal Investigators' Virtual Meeting ?Genomic Science Program-; 2021

US Department of Energy

Interactions between soil microbes can drastically alter ecosystem processes both above andbelowground, but the mechanisms by which these microbes interact, and their impacts on soilbiogeochemistry remain elusive and difficult to parameterize in existing ecosystem models. Weaimed to characterize interactions between coniferous plants, their major root fungal symbionts(ectomycorrhizal fungi, EMF), and free-living saprotrophic decomposers (SAPs) in soil. Weperformed a greenhouse-based synthetic ecosystem experiment with Pinus taeda seedlingsgrowing with and without their EMF symbiont (Suillus cothurnatus), under high and low levelsof soil carbon (C), soil nitrogen (N), and plant C (ambient vs. elevated carbon dioxide -CO2). Weexpected that under low soil C, EMF prime decomposer activity and increase the release of soilC as CO2, while under high soil C, EMF slow decomposition and reduce soil CO2 release, withEMF competing with SAPs for access to soil organic matter (i.e. the Gadgil effect). Theseprocesses would be exacerbated under high plant C availability to EMF, but suppressed underhigh soil N. We found that EMF prime decay of soil organic matter under low soil C, but slowdecay under high soil C. Elevated soil N suppressed the EMF effect on soil C-derived CO2losses. Elevated CO₂ might increase plant-EMF uptake of soil N by outcompeting SAPs, buttotal N uptake may depend on soil C availability. Together, our results suggest that the directionof EMF-SAP interactions is highly dependent on soil C and N availability to SAPs and mightchange according to plant C level.