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1. Stronger increase of methane emissions from coastal wetlands by non‐native Spartina alterniflora than non‐native Phragmites australis

   https://doi.org/10.1002/ppp3.10578  

   Fuchs, Andrea ; Davidson, Ian C ; Megonigal, J Patrick ; Devaney, John L ; Simkanin, Christina ; Noyce, Genevieve L ; Lu, Meng ; Cott, Grace M ( January 2025 , PLANTS, PEOPLE, PLANET)

   The invasive speciesS. alternifloraandP. australisare fast growing coastal wetland plants sequestering large amounts of carbon in the soil and protect coastlines against erosion and storm surges. In this global analysis, we found thatSpartinaandPhragmitesincrease methane but not nitrous oxide emissions, withPhragmiteshaving a lesser effect. The impact of the invasive species on emissions differed greatly among different types of native plant groups, providing valuable information to managers and policymakers during coastal wetland planning and restoration efforts. Further, our estimated net emissions per wetland plant group facilitate regional and national blue carbon estimates.

   Globally,Spartina alternifloraandPhragmites australisare among the most pervasive invasive plants in coastal wetland ecosystems. Both species sequester large amounts of atmospheric carbon dioxide (CO₂) and biogenic carbon in soils but also support production and emission of methane (CH₄). In this study, we investigated the magnitude of their net greenhouse gas (GHG) release from invaded and non‐invaded habitats.

   We conducted a meta‐analysis of GHG fluxes associated with these two species and related soil carbon content and plant biomass in invaded coastal wetlands.

   Our results show that both invasive species increase CH₄fluxes compared to uninvaded coastal wetlands, but they do not significantly affect CO₂and N₂O fluxes. The magnitude of emissions fromSpartinaandPhragmitesdiffers among native habitats. GHG fluxes, soil carbon and plant biomass ofSpartina‐invaded habitats were highest compared to uninvaded mudflats and succulent forb‐dominated wetlands, while being lower compared to uninvaded mangroves (except for CH₄).

   This meta‐analysis highlights the important role of individual plant traits as drivers of change by invasive species on plant‐mediated carbon cycles.

    

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2. Soil depth and grassland origin cooperatively shape microbial community co‐occurrence and function

   https://doi.org/10.1002/ecs2.2973  

   Upton, Racheal N. ; Checinska Sielaff, Aleksandra ; Hofmockel, Kirsten S. ; Xu, Xia ; Polley, H. Wayne ; Wilsey, Brian J. ( January 2020 , Ecosphere)

   Many soils are deep, yet soil below 20 cm remains largely unexplored. Exotic plants can have shallower roots than native species, so their impact on microorganisms is anticipated to change with depth. Using environmentalDNAand extracellular enzymatic activities, we studied fungal and bacterial community composition, diversity, function, and co‐occurrence networks between native and exotic grasslands at soil depths up to 1 m. We hypothesized (1) the composition and network structure of both fungal and bacterial communities will change with increasing depth, and diversity and enzymatic function will decrease; (2) microbial enzymatic function and network connectedness will be lower in exotic grasslands; and (3) irrigation will alter microbial networks, increasing the overall connectedness. Microbial diversity decreased with depth, and community composition wasdistinctly differentbetween shallow and deeper soil depths with higher numbers of unknown taxa in lower soil depths. Fungal communities differed between native and exotic plant communities. Microbial community networks were strongly shaped by biotic and abiotic factors concurrently and were the only microbial measurement affected by irrigation. In general, fungal communities were more connected in native plant communities than exotic, especially below 10 cm. Fungal networks were also more connected at lower soil depths albeit with fewer nodes. Bacterial communities demonstrated higher complexity, and greater connectedness and nodes, at lower soil depths for native plant communities. Exotic plant communities’ bacterial network connectedness altered at lower soil depths dependent on irrigation treatments. Microbial extracellular enzyme activity for carbon cycling enzymes significantly declined with soil depth, but enzymes associated with nitrogen and phosphorus cycling continued to have similar activities up to 1 m deep. Our results indicate that native and exotic grasslands have significantly different fungal communities in depths up to 1 m and that both fungal and bacterial networks are strongly shaped jointly by plant communities and abiotic factors. Soil depth is independently a major determinant of both fungal and bacterial community structures, functions, and co‐occurrence networks and demonstrates further the importance of including soil itself when investigating plant–microbe interactions.

    

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3. Data for: Drainage impacts on the productivity of wetland species Spartina alterniflora and Salicornia pacifica

   https://doi.org/10.5061/dryad.5qfttdzc1  

   Watson, Elizabeth ; Chernesky, Kylie ; Njie, Daouda ; Champlin, Lena ; Swenson Perger, Darci ; University, Drexel ( January 2023 , Dryad)

   Coastal wetlands display ecohydrological zonation such that vertical differences of plant zones are driven by varying groundwater levels over tidal cycles. It is unclear how variable levels of tidal drainage directly impact biotic and abiotic factors in coastal wetland ecosystems. To determine the impacts of drainage levels, simulated tides in mesocosms with varying degrees of drainage were created with Spartina alterniflora, the salt marsh coastal ecosystem dominant species on the United States Atlantic Coast, and Salicornia pacifica, the Pacific Coast dominant. We measured biomass production and photosynthesis as indicators of plant health, and we also measured soil and porewater characteristics to help interpret patterns of productivity. These measures included above and belowground biomass, porewater pH, salinity, ammonium concentration, sulfide concentration, soil redox potential, net ecosystem exchange, photosynthesis rate, respiration rate, and methane flux. We found the greatest plant production in soils with intermediate drainage levels, with production values that were 13.7% higher for S. alterniflora and 57.7% higher for S. pacifica in the intermediate flooding levels than found in more inundated and more drained conditions. Understanding how drainage impacts plant species is important for predicting wetland resilience to sea level rise, as increasing water levels alter ecohydrological zonation. 

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4. Year-around survey and manipulation experiments reveal differential sensitivities of soil prokaryotic and fungal communities to saltwater intrusion in Florida Everglades wetlands

   https://doi.org/10.1016/j.scitotenv.2022.159865  

   Zhao, Jun ; Chakrabarti, Seemanti ; Chambers, Randolph ; Weisenhorn, Pamela ; Travieso, Rafael ; Stumpf, Sandro ; Standen, Emily ; Briceno, Henry ; Troxler, Tiffany ; Gaiser, Evelyn ; et al ( February 2023 , Science of The Total Environment)

   Global sea-level rise is transforming coastal ecosystems, especially freshwater wetlands, in part due to increased episodic or chronic saltwater exposure, leading to shifts in biogeochemistry, plant- and microbial communities, as well as ecological services. Yet, it is still difficult to predict how soil microbial communities respond to the saltwater exposure because of poorly understood microbial sensitivity within complex wetland soil microbial communities, as well as the high spatial and temporal heterogeneity of wetland soils and saltwater exposure. To address this, we first conducted a two-year survey of microbial community structure and bottom water chemistry in submerged surface soils from 14 wetland sites across the Florida Everglades. We identified ecosystem-specific microbial biomarker taxa primarily associated with variation in salinity. Bacterial, archaeal and fungal community composition differed between freshwater, mangrove, and marine seagrass meadow sites, irrespective of soil type or season. Especially, methanogens, putative denitrifying methanotrophs and sulfate reducers shifted in relative abundance and/or composition between wetland types. Methanogens and putative denitrifying methanotrophs declined in relative abundance from freshwater to marine wetlands, whereas sulfate reducers showed the opposite trend. A four-year experimental simulation of saltwater intrusion in a pristine freshwater site and a previously saltwater-impacted site corroborated the highest sensitivity and relative increase of sulfate reducers, as well as taxon-specific sensitivity of methanogens, in response to continuously pulsing of saltwater treatment. Collectively, these results suggest that besides increased salinity, saltwater-mediated increased sulfate availability leads to displacement of methanogens by sulfate reducers even at low or temporal salt exposure. These changes of microbial composition could affect organic matter degradation pathways in coastal freshwater wetlands exposed to sea-level rise, with potential consequences, such as loss of stored soil organic carbon. 

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5. Functional effects of subsidies and stressors on benthic microbial communities along freshwater to marine gradients

   https://doi.org/10.1002/ecy.4427  

   Anderson, Kenneth J ; Kominoski, John S ; Choi, Chang Jae ; Stingl, Ulrich ( October 2024 , Ecology)

   Leaf litter in coastal wetlands lays the foundation for carbon storage, and the creation of coastal wetland soils. As climate change alters the biogeochemical conditions and macrophyte composition of coastal wetlands, a better understanding of the interactions between microbial communities, changing chemistry, and leaf litter is required to understand the dynamics of coastal litter breakdown in changing wetlands. Coastal wetlands are dynamic systems with shifting biogeochemical conditions, with both tidal and seasonal redox fluctuations, and marine subsidies to inland habitats. Here, we investigated gene expression associated with various microbial redox pathways to understand how changing conditions are affecting the benthic microbial communities responsible for litter breakdown in coastal wetlands. We performed a reciprocal transplant of leaf litter from four distinct plant species along freshwater‐to‐marine gradients in the Florida Coastal Everglades, tracking changes in environmental and litter biogeochemistry, as well as benthic microbial gene expression associated with varying redox conditions, carbon degradation, and phosphorus acquisition. Early litter breakdown varied primarily by species, with highest breakdown in coastal species, regardless of the site they were at during breakdown, while microbial gene expression showed a strong seasonal relationship between sulfate cycling and salinity, and was not correlated with breakdown rates. The effect of salinity is likely a combination of direct effects, and indirect effects from associated marine subsidies. We found a positive correlation between sulfate uptake and salinity during January with higher freshwater inputs to coastal areas. However, we found a peak of dissimilatory sulfate reduction at intermediate salinity during April when freshwater inputs to coastal sites are lower. The combination of these two results suggests that sulfate acquisition is limiting to microbes when freshwater inputs are high, but that when marine influence increases and sulfate becomes more available, dissimilatory sulfate reduction becomes a key microbial process. As marine influence in coastal wetlands increases with climate change, our study suggests that sulfate dynamics will become increasingly important to microbial communities colonizing decomposing leaf litter.

    

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