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1. Seagrass Abundance Predicts Surficial Soil Organic Carbon Stocks Across the Range of Thalassia testudinum in the Western North Atlantic

   https://doi.org/10.1007/s12237-023-01210-0  

   Fourqurean, James W.; Campbell, Justin E.; Rhoades, O. Kennedy; Munson, Calvin J.; Krause, Johannes R.; Altieri, Andrew H.; Douglass, James G.; Heck, Kenneth L.; Paul, Valerie J.; Armitage, Anna R.; et al (May 2023, Estuaries and Coasts)

   The organic carbon (Corg) stored in seagrass meadows is globally significant and could be relevant in strategies to mitigate increasing CO2 concentration in the atmosphere. Most of that stored Corg is in the soils that underlie the seagrasses. We explored how seagrass and soil characteristics vary among seagrass meadows across the geographic range of turtlegrass (Thalassia testudinum) with a goal of illuminating the processes controlling soil organic carbon (Corg) storage spanning 23° of latitude. Seagrass abundance (percent cover, biomass, and canopy height) varied by over an order of magnitude across sites, and we found high variability in soil characteristics, with Corg ranging from 0.08 to 12.59% dry weight. Seagrass abundance was a good predictor of the Corg stocks in surficial soils, and the relative importance of seagrass-derived soil Corg increased as abundance increased. These relationships suggest that first-order estimates of surficial soil Corg stocks can be made by measuring seagrass abundance and applying a linear transfer function. The relative availability of the nutrients N and P to support plant growth was also correlated with soil Corg stocks. Stocks were lower at N-limited sites than at P-limited ones, but the importance of seagrass-derived organic matter to soil Corg stocks was not a function of nutrient limitation status. This finding seemed at odds with our observation that labile standard substrates decomposed more slowly at N-limited than at P-limited sites, since even though decomposition rates were 55% lower at N-limited sites, less Corg was accumulating in the soils. The dependence of Corg stocks and decomposition rates on nutrient availability suggests that eutrophication is likely to exert a strong influence on carbon storage in seagrass meadows. 

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2. Global seagrass carbon stock variability and emissions from seagrass loss

   https://doi.org/10.1038/s41467-025-59204-4  

   Krause, Johannes R; Cameron, Clint; Arias-Ortiz, Ariane; Cifuentes-Jara, Miguel; Crooks, Steve; Dahl, Martin; Friess, Daniel A; Kennedy, Hilary; Lim, Kiah Eng; Lovelock, Catherine E; et al (December 2025, Nature Communications)

   Seagrass ecosystems are recognized for their capacity to sequester and store organic carbon, but there is large variability in soil organic carbon stocks associated with plant traits and environmental conditions, making the quantification and scaling of carbon storage and fluxes needed to contribute to climate change mitigation highly challenging. Here, we provide estimates of carbon stocks associated with seagrass systems (biomass and soil) through analyses of a comprehensive global database including 2700+ seagrass soil cores. The median global soil Corg stock estimate is 24.2 (12.4 – 44.9) Mg Corg ha−1 in the top 30 cm of soil, 27% lower than estimates from previous global syntheses, refining the IPCC Tier 1 soil Corg stock currently used for carbon accounting in places without local data. We estimate that seagrass carbon stocks at risk of degradation could emit 1,154 Tg (665 – 1699) CO2 with a social cost of $213 billion (2020 US dollars), if no action is taken to conserve these habitats. 

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3. Climate oscillations drive nutrient availability and seagrass abundance at a regional scale

   https://doi.org/10.1002/lno.12787  

   Krause, Johannes R; Roden, Ana; Briceño, Henry; Fourqurean, James W (March 2025, Limnology and Oceanography)

   Abstract Seagrasses are increasingly recognized for their ecosystem functions and services. However, both natural and anthropogenic stressors impact seagrass functional traits, for example by altering nutrient regimes. Here, we synthesize 27 yr of data from regional, long‐term seagrass and water quality monitoring programs of south Florida to investigate the impacts of relative nutrient availability on seagrass abundance (as expressed by percent cover) across an oligotrophic seascape. We employ linear mixed‐effect models and generalized additive models to show that seagrass abundance is driven by interannual variations in nutrient concentrations, which are ultimately controlled by climate oscillations (El Niño Southern Oscillation Atlantic Multidecadal Oscillation) via regional rainfall‐runoff relationships. Our study suggests that climate oscillations drive interannual variations in seagrass cover on a regional scale, with high‐rainfall years leading to increased nitrogen availability and higher seagrass abundance in typically nitrogen‐limited backreef meadows. Conversely, these periods are associated with reduced seagrass cover at the more P‐limited inshore sites and in Florida Bay, with yet unknown consequences for the provision of seagrass ecosystem services. We show that nutrient delivery from runoff can have diverging impacts on benthic communities, depending on spatial patterns of relative nutrient limitation, with some N‐limited seagrass meadows showing resilience to periodic nutrient enrichment. 

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4. Shifting Fungal Guild Abundances are Associated with Altered Temperate Forest Soil Carbon Stocks

   https://doi.org/10.1007/s10021-024-0093 4-9  

   DeLancey, L; Maillard, F; Hobbie, SE; Kennedy, PG (October 2024, Ecosystems)

   Despite the importance of fungi to forest carbon (C) cycling and increasing calls to include microbial interactions in ecosystem models, how shifting fungal guild abundances impact soil C stocks re- mains poorly quantified, particularly in mineral soils where most C is stored. Additionally, a greater understanding of how fungal interguild interac- tions affect belowground litter decomposition is needed to more fully characterize soil C dynamics. To address these knowledge gaps, we conducted a multi-year soil trenching experiment in two tem- perate Pinus strobus stands in Minnesota, USA. We found that after two years, trenching increased ectomycorrhizal fungal relative abundance while decreasing saprotrophic fungal relative abundance (decreased ectomycorrhizal/saprotrophic ratio) and concurrently decreased soil C stocks by 10%. The decreased C stocks were primarily due to changes in particulate organic matter and were largely constrained to the top 5 cm of the soil. Trenching also stimulated both root and fungal litter decom- position in surface soils. Together, these results support the often proposed but rarely tested hypothesis that shifting fungal guild abundances promote soil C accumulation. However, they also suggest this effect may be most relevant for short- term C storage in upper soil layers. 

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5. Seagrass Recovery Following Marine Heat Wave Influences Sediment Carbon Stocks

   https://doi.org/10.3389/fmars.2020.576784  

   Aoki, Lillian R.; McGlathery, Karen J.; Wiberg, Patricia L.; Oreska, Matthew P.; Berger, Amelie C.; Berg, Peter; Orth, Robert J. (January 2021, Frontiers in Marine Science)

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   Worldwide, seagrass meadows accumulate significant stocks of organic carbon (C), known as “blue” carbon, which can remain buried for decades to centuries. However, when seagrass meadows are disturbed, these C stocks may be remineralized, leading to significant CO 2 emissions. Increasing ocean temperatures, and increasing frequency and severity of heat waves, threaten seagrass meadows and their sediment blue C. To date, no study has directly measured the impact of seagrass declines from high temperatures on sediment C stocks. Here, we use a long-term record of sediment C stocks from a 7-km 2 , restored eelgrass ( Zostera marina ) meadow to show that seagrass dieback following a single marine heat wave (MHW) led to significant losses of sediment C. Patterns of sediment C loss and re-accumulation lagged patterns of seagrass recovery. Sediment C losses were concentrated within the central area of the meadow, where sites experienced extreme shoot density declines of 90% during the MHW and net losses of 20% of sediment C over the following 3 years. However, this effect was not uniform; outer meadow sites showed little evidence of shoot declines during the MHW and had net increases of 60% of sediment C over the following 3 years. Overall, sites with higher seagrass recovery maintained 1.7x as much C compared to sites with lower recovery. Our study demonstrates that while seagrass blue C is vulnerable to MHWs, localization of seagrass loss can prevent meadow-wide C losses. Long-term (decadal and beyond) stability of seagrass blue C depends on seagrass resilience to short-term disturbance events. 

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