Composition of fungal functional guilds explains variance in forest soil nutrient cycling

Soil fungi and bacteria are responsible for soil nutrient cycling, including decomposition, mineralization, immobilization, and transfer of nutrients to tree roots, yet the role of soil community composition in controlling forest nutrient cycling is poorly understood. We aimed to test the hypothesis that incorporating microbial community composition into linear models will increase the variation explained in forest soil N and P cycling relative to models including only plant community and abiotic characteristics. To do this, we designed a forested field system in New England in which variation in microbial community composition was crossed with variation in vegetation composition and soil nutrient content. At six forest sites (three suburban and three rural sites), we sampled soil along a transect from the forest edge to interior from four stand types dominated by trees of varying litter quality: pine-dominated, pure hardwood, hardwood with pines in the understory, and mature mixed pine-hardwood. In each soil sample, we measured inorganic and total nitrogen (N) and phosphorus (P), N and P mineralization rates, and nitrification rates. We also performed high-throughput sequencing of fungal and bacterial rDNA amplicons (16S/ITS) and calculated functional guild abundance for fungi and bacteria in each sample. Excluding microbial factors, N mineralization was best explained in a linear model by pH, soil temperature, soil moisture, % soil organic matter, and the abundance of understory vegetation; nitrification was best explained by pH, the proportion of hardwood litter, the abundance of understory vegetation, and basal area of arbuscular mycorrhizal-associating trees. We found that including the proportion of fungal functional guilds improved linear statistical models explaining variance in rates of N mineralization and nitrification, but not in single point measurements of inorganic N or total P. The proportion of ectomycorrhizal fungi per sample was positively related to N mineralization (p = 7e-05, R2 = 0.128), and including it in the model increased the proportion of variance explained in N mineralization rates by 2.8%. The proportion of saprotrophic fungi per sample was positively related to nitrification (p = 0.001, R2 = 0.083), and including it in the model increased the proportion of variance explained in nitrification rates by 2.0%. These findings suggest that ectomycorrhizal fungi may play a role in N mineralization, while saprotrophs may be more important for nitrification. We are currently building models to explain P mineralization and to improve current models by incorporating bacterial functional guilds.Fil: Vietorisz, Corinne. Boston University; Estados UnidosFil: Policelli, Nahuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Instituto Patagónico para el Estudio de los Ecosistemas Continentales; Argentina. Boston University; Estados UnidosFil: Li, Abigail. Boston University; Estados UnidosFil: Adams, Lindsey. Boston University; Estados UnidosFil: Bhatnagar, Jennifer M.. Boston University; Estados UnidosESA 2023 - Meeting of the Ecological Society of AmericaPortlandEstados UnidosEcological Society of Americ

Does elevated CO2 alter the way microbes behave underground?

Increase in carbon (C) emissions due to human activity is a major cause of global change, but it is unclear how trees obtain soil nutrients to sustain growth under these conditions. To better understand how root symbiotic fungi (ectomycorrhizal fungi, EMF) will react to an increase in atmospheric CO2 we’ve simulated such scenario using synthetic ecosystems where pine trees were planted with and without their EMF (Suillus cothurnatus), nitrogen (N), and soil carbon (C) additions, in elevated vs ambient CO2 growth chambers. By combining biogeochemical analysis with differential isotopic signatures of soil vs plant C, and a series of -omic approaches, we captured changes in soil nutrients, soil respiration, and microbial composition and activity. We found that elevated CO2 did not lead to a change in free living fungal community composition compared to ambient CO2. However, under elevated CO2, more gene modules of S. cothurnatus involved in C-N degradation pathways were impacted by soil C and N additions. In turn, under elevated CO2 and when the EMF was present, we found high enrichment of non-targeted metabolites. The release of CO2 from soil was highly dependent on soil C and N availability and shifted depending on plant C availability. Our results inform ecosystem models by showing that interactions between free living fungi and EMF are an important mechanism for determining ecosystem responses to elevated CO2. In turn, our results challenge the classic perspective that EMF solely absorb nutrients and water and give them to plants.Fil: Policelli, Nahuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Instituto Patagónico para el Estudio de los Ecosistemas Continentales; Argentina. Boston University; Estados UnidosFil: Averill, Colin. Eidgenossische Technische Hochschule zurich (eth Zurich);Fil: Brzostek, Edward. West Virginia University; Estados UnidosFil: Wang, Haihua. University of Florida; Estados UnidosFil: Liao, Hui-Ling. University of Florida; Estados UnidosFil: Verma, Vijay. University of Florida; Estados UnidosFil: Tappero, Ryan. Brookhaven National Laboratory; Estados UnidosFil: Vietorisz, Corinne. Boston University; Estados UnidosFil: Nash, Jake. University of Duke; Estados UnidosFil: Vilgalys, Rytas. University of Duke; Estados UnidosFil: Bhatnagar, Jennifer M.. Boston University; Estados UnidosESA 2023 - Meeting of the Ecological Society of AmericaPortlandEstados UnidosEcological Society of Americ