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1. Soil nutrient amendment increases the potential for inter-kingdom resource competition among foliar endophytes

   https://doi.org/10.1093/ismeco/ycae130  

   Hansen, Zoe A; Fulcher, Michael R; Wornson, Nicholas; Spawn-Lee, Seth A; Johnson, Mitch; Song, Zewei; Michalska-Smith, Matthew; May, Georgiana; Seabloom, Eric W; Borer, Elizabeth T; et al (January 2024, ISME Communications)

   Abstract Foliar endophytes play crucial roles in large-scale ecosystem functions such as plant productivity, decomposition, and nutrient cycling. While the possible effects of environmental nutrient supply on the growth and carbon use of endophytic microbes have critical implications for these processes, these impacts are not fully understood. Here, we examined the effects of long-term elevated nitrogen, phosphorus, potassium, and micronutrient (NPKμ) supply on culturable bacterial and fungal foliar endophytes inhabiting the prairie grass Andropogon gerardii. We hypothesized that elevated soil nutrients alter the taxonomic composition and carbon use phenotypes of foliar endophytes and significantly shift the potential for resource competition among microbes within leaves. We observed changes in taxonomic composition and carbon use patterns of fungal, but not bacterial, endophytes of A. gerardii growing in NPKμ-amended versus ambient conditions. Fungal endophytes from NPKμ-amended plants had distinct carbon use profiles and demonstrated greater specialization across carbon sources compared to control plots. Resource niche overlap between bacterial and fungal endophytes also increased with plot nutrient supply, suggesting enhanced potential for inter-kingdom competition. Collectively, this work suggests that soil nutrient enrichment alters how fungal endophyte communities exist in the foliar environment, with potentially significant implications for broad-scale ecosystem function. 

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2. Coupled Shifts in Ectomycorrhizal Communities and Plant Uptake of Organic Nitrogen Along a Soil Gradient: An Isotopic Perspective

   https://doi.org/doi.org/10.1007/s10021-021-00628-6  

   Pellitier, P.T. D.R. (April 2021, Ecosystems)

   null (Ed.)

   Abstract Plants associating with mutualistic ectomycorrhizal (ECM) fungi may directly obtain nitrogen (N) bound in soil organic matter (N-SOM). However, the contribution of N-SOM to plant growth under field conditions remains poorly constrained. We tested the hypothesis that turnover in ECM communities along soil inorganic N gradients mediates a functional transition from plant reliance on N-SOM in low inorganic N soils, to primarily inorganic N uptake in inorganic N-rich condition soils. We quantified the δ 15 N of Q. rubra foliage and roots, organic and inorganic soil N pools, and used molecular sequencing to characterize ECM communities, morpho-traits associated with N-foraging, and a community aggregated sporocarp δ 15 N. In support of our hypothesis, we document the progressive enrichment of root and foliar δ 15 N with increasing soil inorganic N supply; green leaves ranged from − 5.95 to 0.16‰ as the supply of inorganic N increased. ECM communities inhabiting low inorganic N soils were dominated by the genus Cortinarius, and other fungi forming hyphal morphologies putatively involved in N-SOM acquisition; sporocarp estimates from these communities were enriched (+ 4‰), further supporting fungal N-SOM acquisition. In contrast, trees occurring in high inorganic N soils hosted distinct communities with morpho-traits associated with inorganic N acquisition and depleted sporocarps (+ 0.5‰). Together, our results are consistent with apparent tradeoffs in the foraging cost and contribution of N-SOM to plant growth and demonstrate linkages between ECM community composition, fungal N-foraging potential and foliar δ 15 N. The functional characteristics of ECM communities represent a mechanistic basis for flexibility in plant nutrient foraging strategies. We conclude that the contribution of N-SOM to plant growth is likely contingent on ECM community composition and local soil nutrient availability. 

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3. Efficacy of Spent Lime as a Soil Amendment for Nutrient Retention in Bioretention Green Stormwater Infrastructure

   https://doi.org/https://doi.org/10.3390/w11081575  

   Shrestha, P.; Salzl, M.; Jimenez, I.; Pradhan, N.; Hay, M.; Wallace, H.; Abrahamson, J.; Small, G. (January 2019, Water)

   The composition of bioretention soil media (BSM) is among the most critical design attributes contributing to the water quality performance of bioretention systems, as various amendments may increase the capacity for chemical sorption of certain nutrient pollutants. We investigated the spent lime (a calcium-based water treatment residual) as BSM amendments for nutrient retention. The study was conducted in two parts: the first was a field-based mesocosm experiment in which we assessed the effect of spent lime amendments on leachate nutrient concentration for treatments receiving different levels of phosphorus and nitrogen loading (simulated by different levels of compost added to the substrate). The second was a laboratory study comparing various levels of spent lime and coir on leachate nutrient concentration at two different simulated loading rates. Effluent water was collected and analyzed for PO43−, NH4+ and NO3− concentrations in the field and lab. Spent lime significantly reduced leachate PO43− concentrations (upwards of 50%) in both the field and lab mesocosm studies compared to treatments without spent lime. Reductions in NH4+ concentrations were also observed due to spent lime but with variable significance across the different compost levels, whereas NO3− concentrations were higher in plots with spent lime than plots without spent lime. In the lab, columns with coir had significantly higher leachate PO43− concentrations compared to spent lime-treated columns, however, leachate NH4+ and NO3− concentrations did not significantly differ between treatments at the same compost levels. This study shows that spent lime, which is a waste product, is effective in significantly reducing leachate PO43− concentrations from BSM, while be a cost-effective substitute to engineered proprietary media that is expensive to acquire; however, future studies must also evaluate its potential for clogging. 

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4. Warming Disrupts Plant–Fungal Endophyte Symbiosis More Severely in Leaves Than Roots

   https://doi.org/10.1111/gcb.70207  

   Edwards, Joseph D; Kazenel, Melanie R; Luo, Yiqi; Lynn, Joshua S; McCulley, Rebecca L; Souza, Lara; Young, Carolyn; Rudgers, Jennifer A; Kivlin, Stephanie N (April 2025, Global Change Biology)

   ABSTRACT Disruptions to functionally important symbionts with global change will negatively impact plant fitness, with broader consequences for species' abundances, distribution, and community composition. Fungal endophytes that live inside plant leaves and roots could potentially mitigate plant heat stress from global warming. Conversely, disruptions of these symbioses could exacerbate the negative impacts of warming. To better understand the consistency and strength of warming‐induced changes to fungal endophytes, we examined fungal leaf and root endophytes in three grassland warming experiments in the US ranging from 2 to 25 years and spanning 2000 km, 12°C of mean annual temperature, and 600 mm of precipitation. We found that experimental warming disrupted symbiosis between plants and fungal endophytes. Colonization of plant tissues by septate fungi decreased in response to warming by 90% in plant leaves and 35% in roots. Warming also reduced fungal diversity and changed community composition in plant leaves, but not roots. The strength, but not direction, of warming effects on fungal endophytes varied by up to 75% among warming experiments. Finally, warming decoupled fungal endophytes from host metabolism by decreasing the correlation between endophyte community and host metabolome dissimilarity. These effects were strongest in the shorter‐term experiment, suggesting endophyte‐host metabolome function may acclimate to warming over decades. Overall, warming‐driven disruption of fungal endophyte community structure and function suggests that this symbiosis may not be a reliable mechanism to promote plant resilience and ameliorate stress responses under global change. 

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5. Comparison of nodule endophyte composition, diversity, and gene content between Medicago truncatula genotypes

   https://doi.org/10.1094/PBIOMES-10-20-0077-R  

   Burns, Mannix; Epstein, Brendan; Burghardt, Liana (May 2021, Phytobiomes Journal)

   null (Ed.)

   Leguminous plants form symbiotic relationships with rhizobia. These nitrogen-fixing bacteria live in specialized root organs called nodules. While rhizobia form the most notable host relationship within root nodules, other bacterial endophytes also inhabit these root nodules and can influence host-rhizobia interactions as well as exert effects of their own, whether beneficial or detrimental. In this study, we investigate differences in nodule communities between genotypes (A17 and R108) of a single plant species, the model legume Medicago truncatula. While diversity of endophytes in nodules was similar across hosts, both nodule endophyte composition and gene functional groups differed. In contrast to the significant direct effect of host genotype, neither the presence nor identity of a host in the previous generation (either A17 or R108) had a significant effect on the nodule endophyte diversity or composition. However, whether or not a host was present altered gene functional groups. We conclude that genetic variation within a legume host species can play an important role in the establishment of nodule microbiomes. Further studies, including GWAS and functional assays, can open the door for engineering and optimizing nodule endophyte communities that promote growth or have other beneficial qualities. 

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