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Creators/Authors contains: "Hutchings, Jack A."

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  1. Abstract

    Climate‐driven thawing of Arctic permafrost renders its vast carbon reserves susceptible to microbial degradation, serving as a potentially potent positive feedback hidden within the climate system. While seemingly intuitive, the relationship between thermally driven permafrost losses and organic carbon (OC) export remains largely unexplored in natural settings. Filling this knowledge gap, we present down‐core bulk and compound‐specific radiocarbon records of permafrost change from a sediment core taken within the Alaskan Colville River delta spanning the lastc. 2,700 years. Fingerprinted by significantly older radiocarbon ages of bulk OC and long‐chain fatty acids, these data expose a thermally driven increase in permafrost OC export and/or deepening of mobilizable permafrost layers over the lastc. 160 years after the Little Ice Age. Comparison of OC content and radiocarbon data between recent and Roman warming episodes likely implies that the rate of warming, alongside the prevailing boundary conditions, may dictate the ultimate fate of the Arctic's permafrost inventory. Our findings highlight the importance of leveraging geological records as archives of Arctic permafrost mobilization dynamics with temperature change.

     
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  2. Abstract

    Despite the large contribution of rangeland and pasture to global soil organic carbon (SOC) stocks, there is considerable uncertainty about the impact of large herbivore grazing onSOC, especially for understudied subtropical grazing lands. It is well known that root system inputs are the source of most grasslandSOC, but the impact of grazing on partitioning of carbon allocation to root tissue production compared to fine root exudation is unclear. Given that different forms of root C have differing implications forSOCsynthesis and decomposition, this represents a significant gap in knowledge. Root exudates should contribute toSOCprimarily after microbial assimilation, and thus promote microbial contributions toSOCbased on stabilization of microbial necromass, whereas root litter deposition contributes directly as plant‐derivedSOCfollowing microbial decomposition. Here, we used in situ isotope pulse‐chase methodology paired with plant and soil sampling to link plant carbon allocation patterns withSOCpools in replicated long‐term grazing exclosures in subtropical pasture in Florida,USA. We quantified allocation of carbon to root tissue and measured root exudation across grazed and ungrazed plots and quantified lignin phenols to assess the relative contribution of microbial vs. plant products to totalSOC. We found that grazing exclusion was associated with dramatically less overall belowground allocation, with lower root biomass, fine root exudates, and microbial biomass. Concurrently, grazed pasture contained greater totalSOC, and a larger fraction ofSOCthat originated from plant tissue deposition, suggesting that higher root litter deposition under grazing promotes greaterSOC. We conclude that grazing effects onSOCdepend on root system biomass, a pattern that may generalize to other C4‐dominated grasslands, especially in the subtropics. Improved understanding of ecological factors underlying root system biomass may be the key to forecastingSOCand optimizing grazing management to enhanceSOCaccumulation.

     
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