Ectomycorrhizal fungi: mediators of plant-microbial interactions and terrestrial biogeochemistry

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

New Orleans, LA

Congreso; American Geophysical Union (AGU) meeting 2021; 2021

AGU

Ectomycorrhizal fungi (EMF) that are symbiotic with tree roots can shape forest biogeochemical cycling by mining soil for nitrogen (N), increasing plant carbon (C) allocation belowground, and interacting with free-living saprotrophic (SAP) microbes that decompose soil C. We aimed to test the hypothesis that EMF slow decomposition and reduce soil CO2 release by competing with SAPs for access to N in soil organic matter (i.e. the Gadgil effect) and that these processes would be exacerbated under high plant C availability to EMF, but suppressed under high soil N. To test this hypothesis, we performed a series of greenhouse-based synthetic ecosystem experiment using Pinus taeda seedlings with and without their EMF symbiont (Suillus cothurnatus) under high and low levels of soil carbon (C), soil nitrogen (N), and plant C (ambient vs. elevated carbon dioxide (CO2)). We found that EMF primed decay of soil organic matter under low soil C, increasing expression of genes involved in fermentation and soil C and N depolymerization by both SAPs and EMF. By contrast, EMF slowed decay under high soil C and elevated soil N suppressed the EMF effect on soil C-derived CO2 losses. Elevated CO2 reversed these trends: EMF suppressed soil CO2 release under low soil C but had no effect under high soil C. Together, these results suggest that the direction of EMF-SAP interactions is highly dependent on soil C availability to SAPs and might reverse according to plant C allocation belowground to access soil N.