Search for: All records

Summary Unlike most ectomycorrhizal (EM) fungi,Cenococcum geophilumis a prolific producer of sclerotia, which represent a large and persistent, yet rarely quantified pool of EM fungal biomass and carbon in soils. How biomass of these asexual propagules is impacted by global change factors, such as anthropogenic nitrogen (N) deposition, remains unquantified.This study examined the effects of long‐term experimental N fertilization on the standing biomass, abundance, and size ofC. geophilumsclerotia in an oak (Quercusspp.) savanna ecosystem at Cedar Creek Ecosystem Science Reserve in Minnesota, USA.Standing sclerotia biomass in the control treatment averaged 192 g m⁻²(95% CI = 136–267 g m⁻²) and declined sharply under N enrichment, by 44% (95% CI = −53–79%) and 66% (95% CI = 39–82%) in the low N (5.4 g N m⁻² yr⁻¹) and high N (17 g N m⁻² yr⁻¹) treatments, respectively. Sclerotia abundance also declined under both fertilization levels by 58% (95% CI: 8–81%) and 62% (95% CI: 12–84%), while sclerotia diameter was significantly reduced only under high N.Given their high carbon content, melanization, and long persistence, the observed declines inC. geophilumsclerotia (c.84–127 g m⁻²) represent substantial losses from belowground carbon (C) pools. These findings indicate that chronic N deposition suppresses the formation of a functionally important and recalcitrant fungal structure, likely impacting soil C storage and mycorrhizal functional diversity. 

Data include soil and litter measurements for moisture, pH, and carbon-to-nitrogen ratio. Samples were collected from 8 different ecoregions, as determined by NEON, at various NEON/LTER and/or other experimental sites. Soil cores and litter samples were taken in the spring and fall of 2022. 

Despite being present in many North American forest understories, the ectomycorrhizal (ECM) fungal communities associated with Corylus shrubs have received no prior study. To address this knowledge gap, we characterized the ECM fungal communities on roots of Corylus shrubs as well as co-occurring Quercus and Pinus trees in Minnesota, USA. ECM-colonized root tips from pairs of Corylus shrubs and four ECM tree species, Quercus macrocarpa, Quercus ellipsoidalis, Pinus strobus, and Pinus resinosa, growing in close proximity (<1 m), were sampled at the Cedar Creek Ecosystem Science Reserve. ECM fungal communities were assessed using high-throughput sequencing of the ITS2 region. ECM fungal operational taxonomic unit (OTU) richness was equivalent among the two Quercus species and their associated Corylus shrubs, but significantly higher on P. strobus–associated Corylus shrubs compared with P. strobus, P. resinosa, and P. resinosa–associated Corylus shrubs. ECM fungal community composition on Corylus shrubs largely mirrored that on each of the Quercus and Pinus species, although the two Pinus commu- nities were significantly different from each other. Further, the same ECM fungal OTUs were commonly encountered on paired Corylus–tree host samples, suggesting a high potential for co- colonization by the same fungal individuals. Collectively, these results support the growing consensus that woody understory plants often associate with similar ECM fungal communities as co-occurring tree hosts regardless of phylogenetic relatedness 

ABSTRACT Bacteria are major drivers of organic matter decomposition and play crucial roles in global nutrient cycling. Although the degradation of dead fungal biomass (necromass) is increasingly recognized as an important contributor to soil carbon (C) and nitrogen (N) cycling, the genes and metabolic pathways involved in necromass degradation are less characterized. In particular, how bacteria degrade necromass containing different quantities of melanin, which largely control rates of necromass decompositionin situ, is largely unknown. To address this gap, we conducted a multi-timepoint transcriptomic analysis using three Gram-negative, bacterial species grown on low or high melanin necromass ofHyaloscypha bicolor. The bacterial species,Cellvibrio japonicus, Chitinophaga pinensis, andSerratia marcescens, belong to genera known to degrade necromassin situ. We found that while bacterial growth was consistently higher on low than high melanin necromass, the CAZyme-encoding gene expression response of the three species was similar between the two necromass types. Interestingly, this trend was not shared for genes encoding nitrogen utilization, which varied inC. pinensisandS. marcescensduring growth on high vs low melanin necromass. Additionally, this study tested the metabolic capabilities of these bacterial species to grow on a diversity of C and N sources and found that the three bacteria have substantially different utilization patterns. Collectively, our data suggest that as necromass changes chemically over the course of degradation, certain bacterial species are favored based on their differential metabolic capacities.IMPORTANCEFungal necromass is a major component of the carbon (C) in soils as well as an important source of nitrogen (N) for plant and microbial growth. Bacteria associated with necromass represent a distinct subset of the soil microbiome and characterizing their functional capacities is the critical next step toward understanding how they influence necromass turnover. This is particularly important for necromass varying in melanin content, which has been observed to control the rate of necromass decomposition across a variety of ecosystems. Here we assessed the gene expression of three necromass-degrading bacteria grown on low or high melanin necromass and characterized their metabolic capacities to grow on different C and N substrates. These transcriptomic and metabolic studies provide the first steps toward assessing the physiological relevance of up-regulated CAZyme-encoding genes in necromass decomposition and provide foundational data for generating a predictive model of the molecular mechanisms underpinning necromass decomposition by soil bacteria. 

Abstract Mast seeding is a well‐documented phenomenon across diverse forest ecosystems. While its effect on aboveground food webs has been thoroughly studied, how it impacts the soil fungi that drive soil carbon and nutrient cycling has not yet been explored. To evaluate the relationship between mast seeding and fungal resource availability, we paired a Swiss 29‐year fungal sporocarp census with contemporaneous seed production for European beech (Fagus sylvaticaL.). On average, mast seeding was associated with a 55% reduction in sporocarp production and a compositional community shift towards drought‐tolerant taxa across both ectomycorrhizal and saprotrophic guilds. Among ectomycorrhizal fungi, traits associated with carbon cost did not explain species' sensitivity to seed production. Together, our results support a novel hypothesis that mast seeding limits annual resource availability and reproductive investment in soil fungi, creating an ecosystem ‘rhythm’ to forest processes that is synchronized above‐ and belowground. 

Summary Rising atmospheric carbon dioxide concentrations (CO₂) and atmospheric nitrogen (N) deposition have contrasting effects on ectomycorrhizal (EM) and arbuscular mycorrhizal (AM) symbioses, potentially mediating forest responses to environmental change.In this study, we evaluated the cumulative effects of historical environmental change on N concentrations and δ¹⁵N values in AM plants, EM plants, EM fungi, and saprotrophic fungi using herbarium specimens collected in Minnesota, USA from 1871 to 2016. To better understand mycorrhizal mediation of foliar δ¹⁵N, we also analyzed a subset of previously published foliar δ¹⁵N values from across the United States to parse the effects of N deposition and CO₂rise.Over the last century in Minnesota, N concentrations declined among all groups except saprotrophic fungi. δ¹⁵N also declined among all groups of plants and fungi; however, foliar δ¹⁵N declined less in EM plants than in AM plants. In the analysis of previously published foliar δ¹⁵N values, this slope difference between EM and AM plants was better explained by nitrogen deposition than by CO₂rise.Mycorrhizal type did not explain trajectories of plant N concentrations. Instead, plants and EM fungi exhibited similar declines in N concentrations, consistent with declining forest N status despite moderate levels of N deposition.