An official website of the United States government
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.
more »
« less
Nitrogen fertilization reduces the standing biomass, abundance, and size of Cenococcum sclerotia: a ubiquitous but rarely quantified ectomycorrhizal soil carbon pool
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.
more »
« less
- PAR ID:
- 10663850
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- New Phytologist
- Volume:
- 249
- Issue:
- 4
- ISSN:
- 0028-646X
- Page Range / eLocation ID:
- 1709 to 1715
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Ectomycorrhizal (EM) effects on forest ecosystem carbon (C) and nitrogen (N) cycling are highly variable, which may be due to underappreciated functional differences among EM‐associating trees. We hypothesise that differences in functional traits among EM tree genera will correspond to differences in soil organic matter (SOM) dynamics.We explored how differences among three genera of angiosperm EM trees (Quercus,Carya, andTilia) in functional traits associated with leaf litter quality, resource use and allocation patterns, and microbiome assembly related to overall soil biogeochemical properties.We found consistent differences among EM tree genera in functional traits.Quercustrees had lower litter quality, lower δ13C in SOM, higher δ15N in leaf tissues, greater oxidative extracellular enzyme activities, and higher EM fungal diversity thanTiliatrees, whileCaryatrees were often intermediary. These functional traits corresponded to overall SOM‐C and N dynamics and soil fungal and bacterial community composition.Our findings suggest that trait variation among EM‐associating tree species should be an important consideration in assessing plant–soil relationships such that EM trees cannot be categorised as a unified functional guild. Read the freePlain Language Summaryfor this article on the Journal blog.more » « less
-
Abstract Fungal necromass is increasingly recognized as a key component of soil carbon (C) and nitrogen (N) cycling. However, how C and N loss from fungal necromass during decomposition is impacted by global change factors such as anthropogenic N addition and changes to soil C supply (e.g. via changing root exudation and rhizosphere priming) remains unclear and understudied relative to plant tissues.To address these gaps, we conducted a year‐long decomposition experiment with four species of fungal necromass incubated across four forested sites in plots that had received inorganic N and/or labile C fertilization for two decades in Minnesota, USA.We found that necromass chemistry was the primary driver of C and N loss from fungal necromass as well as the response to fertilization. Specifically, N addition suppressed late‐stage decomposition, but this effect was weaker in melanin‐rich necromass, contrary to the hypothesis based on plant litter dynamics that N addition should suppress the decomposition of more complex organic molecules. Labile C addition had no effect on either the early or late stages of necromass decomposition.Nitrogen release from necromass also varied among species, with N‐poor necromass having lower N release after controlling for differences in mass loss via regression. The relatively minor effects of N fertilization on the proportion of initial necromass N released suggest that N demand by decomposers is the primary control on N loss during fungal necromass decomposition.Synthesis. Together, our results stress the importance of the afterlife effects of fungal chemical composition to forest soil C and N cycles. Further, they demonstrate that C and N release from this critical pool can be reduced by ongoing anthropogenic N addition.more » « less
-
Abstract Plants and mycorrhizal fungi form mutualistic relationships that affect how resources flow between organisms and within ecosystems. Common mycorrhizal networks (CMNs) could facilitate preferential transfer of carbon and limiting nutrients, but this remains difficult to predict. Do CMNs favour fungal resource acquisition at the expense of plant resource demands (a fungi‐centric view), or are they passive channels through which plants regulate resource fluxes (a plant‐centric view)?We used stable isotope tracers (13CO2and15NH3), plant traits, and mycorrhizal DNA to quantify above‐ and below‐ground carbon and nitrogen transfer between 18 plant species along a 520‐km latitudinal gradient in the Pacific Northwest, USA.Plant functional type and tissue stoichiometry were the most important predictors of interspecific resource transfer. Of ‘donor’ plants, 98% were13C‐enriched, but we detected transfer in only 2% of ‘receiver’ plants. However, all donors were15N‐enriched and we detected transfer in 81% of receivers. Nitrogen was preferentially transferred to annuals (0.26 ± 0.50 mg N per g leaf mass) compared with perennials (0.13 ± 0.30 mg N per g leaf mass). This corresponded with tissue stoichiometry differences.SynthesisOur findings suggest that plants and fungi that are located closer together in space and with stronger demand for resources over time are more likely to receive larger amounts of those limiting resources. Read the freePlain Language Summaryfor this article on the Journal blog.more » « less
-
Soil nutrients cause threefold increase in pathogen and herbivore impacts on grassland plant biomassAbstract A combination of theory and experiments predicts that increasing soil nutrients will modify herbivore and microbial impacts on ecosystem carbon cycling.However, few studies of herbivores and soil nutrients have measured both ecosystem carbon fluxes and carbon pools. Even more rare are studies manipulating microbes and nutrients that look at ecosystem carbon cycling responses.We added nutrients to a long‐term, experiment manipulating foliar fungi, soil fungi, mammalian herbivores and arthropods in a low fertility grassland. We measured gross primary production (GPP), ecosystem respiration (ER), net ecosystem exchange (NEE) and plant biomass throughout the growing season to determine how nutrients modify consumer impacts on ecosystem carbon cycling.Nutrient addition increased above‐ground biomass and GPP, but not ER, resulting in an increase in ecosystem carbon uptake rate. Reducing foliar fungi and arthropods increased plant biomass. Nutrients amplified consumer effects on plant biomass, such that arthropods and foliar fungi had a threefold larger impact on above‐ground biomass in fertilized plots.Synthesis. Our work demonstrates that throughout the growing season soil resources modify carbon uptake rates as well as animal and fungal impacts on plant biomass production. Taken together, ongoing nutrient pollution may increase ecosystem carbon uptake and drive fungi and herbivores to have larger impacts on plant biomass production.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.1111/nph.70765
