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1. Plant functional types and tissue stoichiometry explain nutrient transfer in common arbuscular mycorrhizal networks of temperate grasslands

   https://doi.org/10.1111/1365-2435.14634  

   Dawson, Hilary Rose; Shek, Katherine L; Maxwell, Toby M; Reed, Paul B; Bomfim, Barbara; Bridgham, Scott D; Bohannan, Brendan_J M; Silva, Lucas_C R (October 2024, Functional Ecology)

   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. 

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2. Herbarium specimens reveal that mycorrhizal type does not mediate declining temperate tree nitrogen status over a century of environmental change

   https://doi.org/10.1111/nph.19452  

   Michaud, Talia J; Cline, Lauren C; Hobbie, Erik A; Gutknecht, Jessica_L M; Kennedy, Peter G (May 2024, New Phytologist)

   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. 

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3. Inorganic nitrogen and organic matter jointly regulate ectomycorrhizal fungi‐mediated iron acquisition

   https://doi.org/10.1111/nph.20394  

   Wang, Haihua; Zhang, Kaile; Tappero, Ryan; Victor, Tiffany W; Bhatnagar, Jennifer M; Vilgalys, Rytas; Liao, Hui‐Ling (January 2025, New Phytologist)

   Summary Ectomycorrhizal fungi (EMF) play a crucial role in facilitating plant nutrient uptake from the soil although inorganic nitrogen (N) can potentially diminish this role. However, the effect of inorganic N availability and organic matter on shaping EMF‐mediated plant iron (Fe) uptake remains unclear.To explore this, we performed a microcosm study onPinus taedaroots inoculated withSuillus cothurnatustreated with +/−Fe‐coated sand, +/−organic matter, and a gradient of NH₄NO₃concentrations.Mycorrhiza formation was most favorable under conditions with organic matter, without inorganic N. Synchrotron X‐ray microfluorescence imaging on ectomycorrhizal cross‐sections suggested that the effect of inorganic N on mycorrhizal Fe acquisition largely depended on organic matter supply. With organic matter, mycorrhizal Fe concentration was significantly decreased as inorganic N levels increased. Conversely, an opposite trend was observed when organic matter was absent. Spatial distribution analysis showed that Fe, zinc, calcium, and copper predominantly accumulated in the fungal mantle across all conditions, highlighting the mantle's critical role in nutrient accumulation and regulation of nutrient transfer to internal compartments.Our work illustrated that the liberation of soil mineral Fe and the EMF‐mediated plant Fe acquisition are jointly regulated by inorganic N and organic matter in the soil. 

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4. Symbiotic nitrogen fixation reduces belowground biomass carbon costs of nitrogen acquisition under low, but not high, nitrogen availability

   https://doi.org/10.1093/aobpla/plae051  

   Perkowski, Evan A; Terrones, Joseph; German, Hannah L; Smith, Nicholas G (October 2024, AoB PLANTS)

   Kalcsits, Lee (Ed.)

   Abstract Many plant species form symbiotic associations with nitrogen-fixing bacteria. Through this symbiosis, plants allocate photosynthate belowground to the bacteria in exchange for nitrogen fixed from the atmosphere. This symbiosis forms an important link between carbon and nitrogen cycles in many ecosystems. However, the economics of this relationship under soil nitrogen availability gradients is not well understood, as plant investment toward symbiotic nitrogen fixation tends to decrease with increasing soil nitrogen availability. Here, we used a manipulation experiment to examine how costs of nitrogen acquisition vary under a factorial combination of soil nitrogen availability and inoculation with Bradyrhizobium japonicum in Glycine max L. (Merr.). We found that inoculation decreased belowground biomass carbon costs to acquire nitrogen and increased total leaf area and total biomass, but these patterns were only observed under low fertilization and were the result of increased plant nitrogen uptake and no change in belowground carbon allocation. These results suggest that symbioses with nitrogen-fixing bacteria reduce carbon costs of nitrogen acquisition by increasing plant nitrogen uptake, but only when soil nitrogen is low, allowing individuals to increase nitrogen allocation to structures that support aboveground growth. This pattern may help explain the prevalence of plants capable of forming these associations in less fertile soils and provides useful insight into understanding the role of nutrient acquisition strategy on plant nitrogen uptake across nitrogen availability gradients. 

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5. Global imprint of mycorrhizal fungi on whole-plant nutrient economics

   https://doi.org/10.1073/pnas.1906655116  

   Averill, Colin; Bhatnagar, Jennifer M.; Dietze, Michael C.; Pearse, William D.; Kivlin, Stephanie N. (November 2019, Proceedings of the National Academy of Sciences)

   Mycorrhizal fungi are critical members of the plant microbiome, forming a symbiosis with the roots of most plants on Earth. Most plant species partner with either arbuscular or ectomycorrhizal fungi, and these symbioses are thought to represent plant adaptations to fast and slow soil nutrient cycling rates. This generates a second hypothesis, that arbuscular and ectomycorrhizal plant species traits complement and reinforce these fungal strategies, resulting in nutrient acquisitive vs. conservative plant trait profiles. Here we analyzed 17,764 species level trait observations from 2,940 woody plant species to show that mycorrhizal plants differ systematically in nitrogen and phosphorus economic traits. Differences were clearest in temperate latitudes, where ectomycorrhizal plant species are more nitrogen use- and phosphorus use-conservative than arbuscular mycorrhizal species. This difference is reflected in both aboveground and belowground plant traits and is robust to controlling for evolutionary history, nitrogen fixation ability, deciduousness, latitude, and species climate niche. Furthermore, mycorrhizal effects are large and frequently similar to or greater in magnitude than the influence of plant nitrogen fixation ability or deciduous vs. evergreen leaf habit. Ectomycorrhizal plants are also more nitrogen conservative than arbuscular plants in boreal and tropical ecosystems, although differences in phosphorus use are less apparent outside temperate latitudes. Our findings bolster current theories of ecosystems rooted in mycorrhizal ecology and support the hypothesis that plant mycorrhizal association is linked to the evolution of plant nutrient economic strategies. 

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