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1. Experimental warming alters free‐living nitrogen fixation in a humid tropical forest

   https://doi.org/10.1111/nph.70592  

   Bartz, Parker M; Grullón‐Penkova, Iana F; Cavaleri, Molly A; Reed, Sasha C; Shahid, Saima; Wood, Tana E; Bachelot, Benedicte (October 2025, New Phytologist)

   Summary Microbial nitrogen (N) fixation accounts forc. 97% of natural N inputs to terrestrial ecosystems. These microbes can be free‐living in the soil and leaf litter (asymbiotic) or in symbiosis with plants. Warming is expected to increase N‐fixation rates because warmer temperatures favor the growth and activity of N‐fixing microbes.We investigated the effects of warming on asymbiotic components of N fixation at a field warming experiment in Puerto Rico. We analyzed the function and composition of bacterial communities from surface soil and leaf litter samples.Warming significantly increased asymbiotic N‐fixation rates in soil by 55% (to 0.002 kg ha⁻¹ yr⁻¹) and by 525% in leaf litter (to 14.518 kg ha⁻¹ yr⁻¹). This increase in N fixation was associated with changes in the N‐fixing bacterial community composition and soil nutrients.Our findings suggest that warming increases the natural N inputs from the atmosphere into this tropical forest due to changes in microbial function and composition, especially in the leaf litter. Given the importance of leaf litter in nutrient cycling, future research should investigate other aspects of N cycles in the leaf litter under warming conditions. 

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2. Arbuscular Mycorrhizal Tree Communities Have Greater Soil Fungal Diversity and Relative Abundances of Saprotrophs and Pathogens than Ectomycorrhizal Tree Communities

   https://doi.org/10.1128/AEM.01782-21  

   Eagar, Andrew C.; Mushinski, Ryan M.; Horning, Amber L.; Smemo, Kurt A.; Phillips, Richard P.; Blackwood, Christopher B. (January 2022, Applied and Environmental Microbiology)

   Druzhinina, Irina S. (Ed.)

   ABSTRACT Trees associating with different mycorrhizas often differ in their effects on litter decomposition, nutrient cycling, soil organic matter (SOM) dynamics, and plant-soil interactions. For example, due to differences between arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) tree leaf and root traits, ECM-associated soil has lower rates of C and N cycling and lower N availability than AM-associated soil. These observations suggest that many groups of nonmycorrhizal fungi should be affected by the mycorrhizal associations of dominant trees through controls on nutrient availability. To test this overarching hypothesis, we explored the influence of predominant forest mycorrhizal type and mineral N availability on soil fungal communities using next-generation amplicon sequencing. Soils from four temperate hardwood forests in southern Indiana, United States, were studied; three forests formed a natural gradient of mycorrhizal dominance (100% AM tree basal area to 100% ECM basal area), while the fourth forest contained a factorial experiment testing long-term N addition in both dominant mycorrhizal types. We found that overall fungal diversity, as well as the diversity and relative abundance of plant pathogenic and saprotrophic fungi, increased with greater AM tree dominance. Additionally, tree community mycorrhizal associations explained more variation in fungal community composition than abiotic variables, including soil depth, SOM content, nitrification rate, and mineral N availability. Our findings suggest that tree mycorrhizal associations may be good predictors of the diversity, composition, and functional potential of soil fungal communities in temperate hardwood forests. These observations help explain differing biogeochemistry and community dynamics found in forest stands dominated by differing mycorrhizal types. IMPORTANCE Our work explores how differing mycorrhizal associations of temperate hardwood trees (i.e., arbuscular [AM] versus ectomycorrhizal [ECM] associations) affect soil fungal communities by altering the diversity and relative abundance of saprotrophic and plant-pathogenic fungi along natural gradients of mycorrhizal dominance. Because temperate hardwood forests are predicted to become more AM dominant with climate change, studies examining soil communities along mycorrhizal gradients are necessary to understand how these global changes may alter future soil fungal communities and their functional potential. Ours, along with other recent studies, identify possible global trends in the frequency of specific fungal functional groups responsible for nutrient cycling and plant-soil interactions as they relate to mycorrhizal associations. 

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3. Foliar pathogen epidemic slows decomposition of invasive plant litter

   https://doi.org/10.1002/ecy.70374  

   Lane, Brett R; Wojan, Chris; Meehan, Carlie; Kendig, Amy E; Holt, Robert D; Harmon, Philip F; Clay, Keith; Flory, S Luke; Goss, Erica M (April 2026, Ecology)

   Abstract Decomposition of plant litter, facilitated primarily by microbial decomposers, plays a critical role in biogeochemical cycling and ecosystem function. The rate of litter decomposition can determine its environmental impact, where accelerated decomposition alters the timing and rate of nutrient release and may promote nutrient leaching, whereas slowed decomposition can result in litter accumulation, which impacts seedling recruitment, fire regimes, perennation of microbial communities, and slows nutrient release. Mutualistic endophytes are known to slow litter decomposition, but less is known about the impact that plant pathogens, present in diseased litter, have on decomposition rates. We compared litter decomposition of the invasive annual grassMicrostegium vimineumwith Bipolaris leaf spot symptoms, a fungal disease, to litter without symptoms of the disease in a year‐long common garden experiment. We found leaf tissue with disease symptoms decomposed later in the year compared to litter without symptoms. By summer, 54% of leaf tissue from healthy sites remained compared to 80% of leaf material from diseased litter. Fungal infection did not impact the lignin or C:N content of the litter. There were significant differences in fungal community composition between infected and healthy litter at the start of the experiment that persisted until the end of summer. Disease epidemics prior to senescence contributed to the persistence of infected tissue, which could slow the return of nutrients to the environmental pool and promote the survival and dispersal of pathogen inoculum the following season. 

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4. Well-Aerated Southern Appalachian Forest Soils Demonstrate Significant Potential for Gaseous Nitrogen Loss

   https://doi.org/10.3390/f10121155  

   Baas, Peter; Knoepp, Jennifer D.; Mohan, Jacqueline E. (December 2019, Forests)

   null (Ed.)

   Understanding the dominant soil nitrogen (N) cycling processes in southern Appalachian forests is crucial for predicting ecosystem responses to changing N deposition and climate. The role of anaerobic nitrogen cycling processes in well-aerated soils has long been questioned, and recent N cycling research suggests it needs to be re-evaluated. We assessed gross and potential rates of soil N cycling processes, including mineralization, nitrification, denitrification, nitrifier denitrification, and dissimilatory nitrate reduction to ammonium (DNRA) in sites representing a vegetation and elevation gradient in the U.S. Department of Agriculture (USDA) Forest Service Experimental Forest, Coweeta Hydrologic Laboratory in southwestern North Carolina, USA. N cycling processes varied among sites, with gross mineralization and nitrification being greatest in high-elevation northern hardwood forests. Gaseous N losses via nitrifier denitrification were common in all ecosystems but were greatest in northern hardwood. Ecosystem N retention via DNRA (nitrification-produced NO3 reduced to NH4) ranged from 2% to 20% of the total nitrification and was highest in the mixed-oak forest. Our results suggest the potential for gaseous N losses through anaerobic processes (nitrifier denitrification) are prevalent in well-aerated forest soils and may play a key role in ecosystem N cycling. 

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5. Soil microbial community response to ectomycorrhizal dominance in diverse neotropical montane forests

   https://doi.org/10.1007/s00572-023-01134-4  

   Edwards, Joseph D; Krichels, Alexander H; Seyfried, Georgia S; Dalling, James; Kent, Angela D; Yang, Wendy H (April 2024, Mycorrhiza)

   Abstract Ectomycorrhizal (EM) associations can promote the dominance of tree species in otherwise diverse tropical forests. These EM associations between trees and their fungal mutualists have important consequences for soil organic matter cycling, yet the influence of these EM-associated effects on surrounding microbial communities is not well known, particularly in neotropical forests. We examined fungal and prokaryotic community composition in surface soil samples from mixed arbuscular mycorrhizal (AM) and ectomycorrhizal (EM) stands as well as stands dominated by EM-associatedOreomunnea mexicana(Juglandaceae) in four watersheds differing in soil fertility in the Fortuna Forest Reserve, Panama. We hypothesized that EM-dominated stands would support distinct microbial community assemblages relative to the mixed AM-EM stands due to differences in carbon and nitrogen cycling associated with the dominance of EM trees. We expected that this microbiome selection in EM-dominated stands would lead to lower overall microbial community diversity and turnover, with tighter correspondence between general fungal and prokaryotic communities. We measured fungal and prokaryotic community composition via high-throughput Illumina sequencing of theITS2(fungi) and16SrRNA (prokaryotic) gene regions. We analyzed differences in alpha and beta diversity between forest stands associated with different mycorrhizal types, as well as the relative abundance of fungal functional groups and various microbial taxa. We found that fungal and prokaryotic community composition differed based on stand mycorrhizal type. There was lower prokaryotic diversity and lower relative abundance of fungal saprotrophs and pathogens in EM-dominated than AM-EM mixed stands. However, contrary to our prediction, there was lower homogeneity for fungal communities in EM-dominated stands compared to mixed AM-EM stands. Overall, we demonstrate that EM-dominated tropical forest stands have distinct soil microbiomes relative to surrounding diverse forests, suggesting that EM fungi may filter microbial functional groups in ways that could potentially influence plant performance or ecosystem function. 

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