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1. Warming alters cascading effects of a dominant arthropod predator on fungal community composition in the Arctic

   https://doi.org/10.1128/mbio.00590-24  

   Koltz, Amanda M; Koyama, Akihiro; Wallenstein, Matthew (July 2024, mBio)

   Giovannoni, Stephen J; Weedon, James (Ed.)

   ABSTRACT Rapid climate change in the Arctic is altering microbial structure and function, with important consequences for the global ecosystem. Emerging evidence suggests organisms in higher trophic levels may also influence microbial communities, but whether warming alters these effects is unclear. Wolf spiders are dominant Arctic predators whose densities are expected to increase with warming. These predators have temperature-dependent effects on decomposition via their consumption of fungal-feeding detritivores, suggesting they may indirectly affect the microbial structure as well. To address this, we used a fully factorial mesocosm experiment to test the effects of wolf spider density and warming on litter microbial structure in Arctic tundra. We deployed replicate litter bags at the surface and belowground in the organic soil profile and analyzed the litter for bacterial and fungal community structure, mass loss, and nutrient characteristics after 2 and 14 months. We found there were significant interactive effects of wolf spider density and warming on fungal but not bacterial communities. Specifically, higher wolf spider densities caused greater fungal diversity under ambient temperature but lower fungal diversity under warming at the soil surface. We also observed interactive treatment effects on fungal composition belowground. Wolf spider density influenced surface bacterial composition, but the effects did not change with warming. These findings suggest a widespread predator can have indirect, cascading effects on litter microbes and that effects on fungi specifically shift under future expected levels of warming. Overall, our study highlights that trophic interactions may play important, albeit overlooked, roles in driving microbial responses to warming in Arctic terrestrial ecosystems. IMPORTANCEThe Arctic contains nearly half of the global pool of soil organic carbon and is one of the fastest warming regions on the planet. Accelerated decomposition of soil organic carbon due to warming could cause positive feedbacks to climate change through increased greenhouse gas emissions; thus, changes in ecological dynamics in this region are of global relevance. Microbial structure is an important driver of decomposition and is affected by both abiotic and biotic conditions. Yet how activities of soil-dwelling organisms in higher trophic levels influence microbial structure and function is unclear. In this study, we demonstrate that predicted changes in abundances of a dominant predator and warming interactively affect the structure of litter-dwelling fungal communities in the Arctic. These findings suggest predators may have widespread, indirect cascading effects on microbial communities, which could influence ecosystem responses to future climate change. 

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2. Direct and indirect interactions among warming, water, and growing condition slow decomposition rates of temperate-boreal tree litter

   https://doi.org/10.32942/X26Q0Q  

   King, Rachel; Reed, Samuel; Flores-Moreno, Habacuc; Bermudez_Villanueva, Raimundo; Stefanski, Artur; Williams, Laura; Hobbie, Sarah; Kennedy, Peter; Reich, Peter (May 2025, EcoEvorxiv)

   Plant litter decomposition is a primary control on carbon fluxes in terrestrial ecosystems around the world. Individually, the key mediators of decomposition rates—litter traits, temperature, and moisture—are relatively well understood. However, our understanding of how combined drivers influence decomposition remains limited. To test how multiple, interactive climate change factors directly alter decomposition rates and indirectly influence leaf litter decomposition rates by altering substrate chemistry, we conducted two decomposition experiments within the Boreal Forest Warming at an Ecotone in Danger (B4WarmED) study in Minnesota, USA. Our first experiment decomposed ambient-grown leaf litter from eight common tree species under a factorial combination of warming and rainfall reduction treatments. We found that the direct effects of combined warming and rainfall reduction increased litter half-life by 42% ± 11% in comparison to ambient plots with no warming or rainfall reduction. In contrast, only rainfall reduction influenced litter mean residence time, which increased by 37% ± 18% in comparison to ambient rainfall plots. Our second experiment decomposed ambient- and warm-grown leaf litter from the same eight species under ambient and warmed conditions. We found that warming slowed decomposition of both litter types, but warm-grown litter had a 22% ± 6.5% shorter half-life than ambient-grown leaf tissue under ambient environmental conditions. Warm grown litter half-life then increased by 36% ± 11% with warmed environmental conditions. Our results highlight that climate change could slow carbon and nutrient cycling in systems where moisture becomes a limiting factor. In addition, our study demonstrates that there may be an overlooked relationship between the growth conditions of plants and the temperature of decomposition. This nuanced understanding of decomposition can then support carbon cycling models and more effective nature-based climate mitigation efforts. 

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3. Experimental warming accelerates positive soil priming in a temperate grassland ecosystem

   https://doi.org/10.1038/s41467-024-45277-0  

   Tao, Xuanyu; Yang, Zhifeng; Feng, Jiajie; Jian, Siyang; Yang, Yunfeng; Bates, Colin T; Wang, Gangsheng; Guo, Xue; Ning, Daliang; Kempher, Megan L; et al (December 2024, Nature Communications)

   Abstract Unravelling biosphere feedback mechanisms is crucial for predicting the impacts of global warming. Soil priming, an effect of fresh plant-derived carbon (C) on native soil organic carbon (SOC) decomposition, is a key feedback mechanism that could release large amounts of soil C into the atmosphere. However, the impacts of climate warming on soil priming remain elusive. Here, we show that experimental warming accelerates soil priming by 12.7% in a temperate grassland. Warming alters bacterial communities, with 38% of unique active phylotypes detected under warming. The functional genes essential for soil C decomposition are also stimulated, which could be linked to priming effects. We incorporate lab-derived information into an ecosystem model showing that model parameter uncertainty can be reduced by 32–37%. Model simulations from 2010 to 2016 indicate an increase in soil C decomposition under warming, with a 9.1% rise in priming-induced CO₂emissions. If our findings can be generalized to other ecosystems over an extended period of time, soil priming could play an important role in terrestrial C cycle feedbacks and climate change. 

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4. Fast-decaying plant litter enhances soil carbon in temperate forests but not through microbial physiological traits

   https://doi.org/10.1038/s41467-022-28715-9  

   Craig, Matthew E.; Geyer, Kevin M.; Beidler, Katilyn V.; Brzostek, Edward R.; Frey, Serita D.; Stuart Grandy, A.; Liang, Chao; Phillips, Richard P. (December 2022, Nature Communications)

   Abstract Conceptual and empirical advances in soil biogeochemistry have challenged long-held assumptions about the role of soil micro-organisms in soil organic carbon (SOC) dynamics; yet, rigorous tests of emerging concepts remain sparse. Recent hypotheses suggest that microbial necromass production links plant inputs to SOC accumulation, with high-quality (i.e., rapidly decomposing) plant litter promoting microbial carbon use efficiency, growth, and turnover leading to more mineral stabilization of necromass. We test this hypothesis experimentally and with observations across six eastern US forests, using stable isotopes to measure microbial traits and SOC dynamics. Here we show, in both studies, that microbial growth, efficiency, and turnover are negatively (not positively) related to mineral-associated SOC. In the experiment, stimulation of microbial growth by high-quality litter enhances SOC decomposition, offsetting the positive effect of litter quality on SOC stabilization. We suggest that microbial necromass production is not the primary driver of SOC persistence in temperate forests. Factors such as microbial necromass origin, alternative SOC formation pathways, priming effects, and soil abiotic properties can strongly decouple microbial growth, efficiency, and turnover from mineral-associated SOC. 

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5. Small spaces have large impacts: Microsites determine plant litter decomposition rates in drylands

   https://doi.org/10.1073/pnas.2503852122  

   Throop, Heather L; de_Graaff, Marie-Anne; Belnap, Jayne (November 2025, Proceedings of the National Academy of Sciences)

   Our understanding of carbon and nutrient dynamics in globally vast and socioeconomically critical dryland ecosystems lags behind mesic systems. Litter decomposition models consistently underestimate measured decomposition in these regions. Both models and measurements largely represent spatially dominant intercanopy areas; however, little litter resides in these interspaces as transport vectors move litter to other microsites such as beneath plant canopies and buried in soil. Abiotic and biotic conditions differ among microsites, but few studies have characterized microsite impacts on decomposition. We collated data on microsites where litter accumulates. In microsites with sufficient available data, we used meta-analysis to test hypotheses on decomposition relative to litter in intercanopy spaces. Decomposition was lower under woody plant canopies than in intercanopy spaces. Buried litter decomposed faster than surface litter. There was no difference in decomposition between surface litter and litter suspended aboveground to simulate standing dead. All microsite contrasts had exceptions, suggesting that site-specific characteristics influence microclimate and subsequent decomposition. Extrapolation of decomposition rates to the landscape-level (using estimates of microsite-specific decomposition rates multiplied by litter pools), suggests that decomposition estimates based on intercanopy data alone underrepresent landscape-level decomposition. Thus, despite advances in the understanding of mechanistic decomposition drivers in drylands advancing, most studies are spatially unrepresentative analyses in intercanopy areas and this will underestimate decomposition at the landscape level. Expanding the ecological relevance of decomposition processes to be useful for predicting larger-scale carbon and nutrient dynamics requires improved characterization of dryland litter distribution, coupled with a mechanistic understanding of decomposition in microsites where litter accumulates. 

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