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

POLICELLI, NAHUEL; AVERILL, COLIN; BRZOSTEK, EDWARD; LIAO, HUI-LING; WANG, HAIHUA; 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-; 2022

US Department of Energy

Ectomycorrhizal fungi (EMF) are the main tree roots symbionts in temperate and boreal forests and can mine soil for nitrogen (N), increase trees carbon (C) allocation belowground, and interact with free-living saprotrophic microbes (SAPs) that decompose soil C. We hypothesized that plant-EMF-SAP interactions and their controls over ecosystem biogeochemistry are context-dependent but predictable, based on resource (C and N) availability to both SAPs and EMF. In a greenhouse-based synthetic ecosystem experiment, we grew Pinus taeda seedlings with and without a highly specific EMF symbiont (Suillus cothurnatus), under high and low levels of soil C, soil N, and plant C (ambient vs. elevated carbon dioxide -CO2). To assess soil microbial activity, we measured soil CO2 release under the different conditions. We also measured plant biomass and EMF root colonization. We found that when more plant C was available, EMF suppressed soil CO2 release under low soil C but had no effect under high soil C. By contrast, when less plant C was available, EMF promoted CO2 release under high soil C conditions. Elevated soil N had a tendency to suppress the EMF effect on soil C-derived CO2 release, although the result was not significant. Biomass was higher for those plants growing with EMF, regardless of soil C. Plants inoculated with EMF doubled the biomass of non-inoculated plants under high CO2 conditions. EMF root colonization of inoculated plants was similar between treatments. Together, our results show that the direction of EMF-SAP interactions depends on soil C availability, potentially reversing according to plant C allocation belowground.