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1. Soil nutrients cause threefold increase in pathogen and herbivore impacts on grassland plant biomass

   https://doi.org/10.1111/1365-2745.14111  

   Zaret, Max; Kinkel, Linda; Borer, Elizabeth T.; Seabloom, Eric W. (August 2023, Journal of Ecology)

   Abstract 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. 

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2. Drivers of soil microbial and detritivore activity across global grasslands

   https://doi.org/10.1038/s42003-023-05607-2  

   Siebert, Julia; Sünnemann, Marie; Hautier, Yann; Risch, Anita C; Bakker, Jonathan D; Biederman, Lori; Blumenthal, Dana M; Borer, Elizabeth T; Bugalho, Miguel N; Broadbent, Arthur_A D; et al (December 2023, Communications Biology)

   Abstract Covering approximately 40% of land surfaces, grasslands provide critical ecosystem services that rely on soil organisms. However, the global determinants of soil biodiversity and functioning remain underexplored. In this study, we investigate the drivers of soil microbial and detritivore activity in grasslands across a wide range of climatic conditions on five continents. We apply standardized treatments of nutrient addition and herbivore reduction, allowing us to disentangle the regional and local drivers of soil organism activity. We use structural equation modeling to assess the direct and indirect effects of local and regional drivers on soil biological activities. Microbial and detritivore activities are positively correlated across global grasslands. These correlations are shaped more by global climatic factors than by local treatments, with annual precipitation and soil water content explaining the majority of the variation. Nutrient addition tends to reduce microbial activity by enhancing plant growth, while herbivore reduction typically increases microbial and detritivore activity through increased soil moisture. Our findings emphasize soil moisture as a key driver of soil biological activity, highlighting the potential impacts of climate change, altered grazing pressure, and eutrophication on nutrient cycling and decomposition within grassland ecosystems. 

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3. Ecosystem feedbacks constrain the effect of day‐to‐day weather variability on land–atmosphere carbon exchange

   https://doi.org/10.1111/gcb.16926  

   Rastetter, Edward B.; Griffin, Kevin L.; Kwiatkowski, Bonnie L.; Kling, George W. (November 2023, Global Change Biology)

   Abstract Whole‐ecosystem interactions and feedbacks constrain ecosystem responses to environmental change. The effects of these constraints on responses to climate trends and extreme weather events have been well studied. Here we examine how these constraints respond to changes in day‐to‐day weather variability without changing the long‐term mean weather. Although environmental variability is recognized as a critical factor affecting ecological function, the effects of climate change on day‐to‐day weather variability and the resultant impacts on ecosystem function are still poorly understood. Changes in weather variability can alter the mean rates of individual ecological processes because many processes respond non‐linearly to environmental drivers. We assessed how these individual‐process responses to changes in day‐to‐day weather variability interact with one another at an ecosystem level. We examine responses of arctic tundra to changes in weather variability using stochastic simulations of daily temperature, precipitation, and light to drive a biogeochemical model. Changes in weather variability altered ecosystem carbon, nitrogen, and phosphorus stocks and cycling rates in our model. However, responses of some processes (e.g., respiration) were inconsistent with expectations because ecosystem feedbacks can moderate, or even reverse, direct process responses to weather variability. More weather variability led to greater carbon losses from land to atmosphere; less variability led to higher carbon sequestration on land. The magnitude of modeled ecosystem response to weather variability was comparable to that predicted for the effects of climate mean trends by the end of the century. 

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4. Long-term climate establishes functional legacies by altering microbial traits

   https://doi.org/10.1093/ismejo/wraf005  

   Broderick, Caitlin M; Benucci, Gian_Maria Niccolò; Bachega, Luciana Ruggiero; Miller, Gabriel D; Evans, Sarah E; Hawkes, Christine V (January 2025, The ISME Journal)

   Abstract Long-term climate history can influence rates of soil carbon cycling but the microbial traits underlying these legacy effects are not well understood. Legacies may result if historical climate differences alter the traits of soil microbial communities, particularly those associated with carbon cycling and stress tolerance. However, it is also possible that contemporary conditions can overcome the influence of historical climate, particularly under extreme conditions. Using shotgun metagenomics, we assessed the composition of soil microbial functional genes across a mean annual precipitation gradient that previously showed evidence of strong climate legacies in soil carbon flux and extracellular enzyme activity. Sampling coincided with recovery from a regional, multi-year severe drought, allowing us to document how the strength of climate legacies varied with contemporary conditions. We found increased investment in genes associated with resource cycling with historically higher precipitation across the gradient, particularly in traits related to resource transport and complex carbon degradation. This legacy effect was strongest in seasons with the lowest soil moisture, suggesting that contemporary conditions—particularly, resource stress under water limitation—influences the strength of legacy effects. In contrast, investment in stress tolerance did not vary with historical precipitation, likely due to frequent periodic drought throughout the gradient. Differences in the relative abundance of functional genes explained over half of variation in microbial functional capacity—potential enzyme activity—more so than historical precipitation or current moisture conditions. Together, these results suggest that long-term climate can alter the functional potential of soil microbial communities, leading to legacies in carbon cycling. 

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5. 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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