Design and Assessment of a Novel Approach for Ecosystem Warming Experiments in High‐Energy Tidal Wetlands

Rich, Roy L.; Mueller, Peter; Fuß, Miriam; Gonçalves, Salomé; Ostertag, Eva; Reents, Svenja; Tang, Hao; Tashjian, Allegra; Thomsen, Simon; Kutzbach, Lars; Jensen, Kai; Nolte, Stefanie

doi:10.1029/2023jg007550

Cited by 3 publications

(1 citation statement)

References 30 publications

(75 reference statements)

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“…Our study system was a salt marsh on the European Wadden Sea coast. Here, soil redox potentials are predominantly hydrology-driven and vary along an elevation gradient, representing a flooding-frequency gradient, and in relation to soil depth (Rich et al, 2023;Tang et al, 2023). Wadden Sea salt marshes typically show a distinct vegetation zonation along the elevation gradient.…”

Section: Introductionmentioning

confidence: 99%

Wetland roots as soil reducers – Insights from a Wadden Sea salt-marsh study

Mittmann-Goetsch,

Wilson,

Jensen

et al. 2024

Preprint

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The redox potential in wetland soils exerts strong control over microbial decomposition and consequently carbon cycling. Wetland plants influence redox by supplying both terminal electron acceptors (i.e. oxygen) and electron donors (i.e. organic matter) to the soil. However, quantitative insight into plant effects on wetland soil redox are scarce. We investigated plant effects on soil reduction using IRIS (Indicator of Reduction in Soils) sticks. Vegetated and unvegetated treatments were created along salt-marsh flooding gradients both in a mesocosm facility and in situ. We show that the presence of plants resulted in both increased and decreased soil reduction compared to non-vegetated controls in the mesocosm study and that the direction of the plant effect (i.e. reducing versus oxidizing) depended on the background redox conditions observed in non-vegetated controls. When background soil reduction was high, plants tended to act as net oxidizers, whereas under more oxidizing conditions plants acted as net reducers of the soil. High-resolution oxygen profiling via planar optode imaging further supported these findings. Plant effects on soil reduction in the field study were negative across all elevational zones. We attribute this effect to the comparably well aerated soils of Wadden Sea salt marshes. Reduction correlated positively with belowground biomass, indicating that a higher availability of plant-derived electron donors increased soil reduction. Challenging the dominant paradigm that wetland plants primarily act as soil oxidizers, our study reveals their potential to exert a net reducing effect.

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Section: Introductionmentioning

confidence: 99%

Wetland roots as soil reducers – Insights from a Wadden Sea salt-marsh study

Mittmann-Goetsch,

Wilson,

Jensen

et al. 2024

Preprint

Self Cite

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Root-Driven Soil Reduction in Wadden Sea Salt Marshes

Mittmann-Goetsch,

Wilson,

Jensen

et al. 2024

Wetlands

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The soil redox potential in wetlands such as peatlands or salt marshes exerts a strong control over microbial decomposition processes and consequently soil carbon cycling. Wetland plants can influence redox by supplying both terminal electron acceptors (i.e. oxygen) and electron donors (i.e. organic matter) to the soil system. However, quantitative insight into the importance of plant effects on wetland soil redox and associated plant traits are scarce. In a combined mesocosm and field study we investigated the impact of plants on soil reduction using IRIS (Indicator of Reduction in Soils) sticks. Vegetated plots were compared to non-vegetated plots along an elevational gradient in a salt marsh of the Wadden Sea and along an artificially created gradient in a tidal tank mesocosm experiment. Our findings from the mesocosm experiment demonstrated that vegetation both enhanced and suppressed soil reduction relative to non-vegetated control pots. The direction of the plant effect (i.e., net oxidizing or net reducing) was inversely correlated with background redox conditions. Insights from high-resolution oxygen profiling via planar optode imaging corroborated these findings. In the field study, vegetation consistently reduced the comparatively well-aerated Wadden Sea salt marsh soil. Reduction correlated positively with soil organic matter content and belowground biomass, indicating that greater availability of plant-derived electron donors, in the form of organic matter, increased soil reduction. Challenging the dominant paradigm that wetland plants primarily act as soil oxidizers, our study reveals their potential to exert a net reducing effect. The documented impact of these plant-induced changes in soil redox conditions suggests a previously overlooked role in shaping the stability of soil organic carbon stocks in wetland ecosystems with variable water tables.

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Warming accelerates belowground litter turnover in salt marshes – insights from a Tea Bag Index study

Tang¹,

Nolte²,

Jensen³

et al. 2023

Biogeosciences

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Abstract. Salt marshes play an important role in the global carbon cycle due to the large amount of organic carbon stored in their soils. Soil organic carbon formation in these coastal wetland ecosystems is strongly controlled by the plant primary production and initial decomposition rates of plant belowground biomass and litter. This study used a field warming experiment to investigate the response of belowground litter breakdown to rising temperature (+1.5 and +3.0 ∘C) across whole-soil profiles (0–60 cm soil depth) and the entire intertidal flooding gradient ranging from the pioneer zone via the low marsh to high marsh. We used standardized plant materials, following the Tea Bag Index approach, to assess the initial decomposition rate (k) and the stabilization factor (S) of labile organic matter inputs to the soil system. While k describes the initial pace at which labile (= hydrolyzable) organic matter decomposes, S describes the part of the labile fraction that does not decompose during deployment in the soil system and stabilizes due to biochemical transformation. We show that warming strongly increased k consistently throughout the entire soil profile and across the entire flooding gradient, suggesting that warming effects on the initial decomposition rate of labile plant materials are independent of the soil aeration (i.e., redox) status. By contrast, negative effects on litter stabilization were less consistent. Specifically, warming effects on S were restricted to the aerated topsoil in the frequently flooded pioneer zone, while the soil depth to which stabilization responded increased across the marsh elevation gradient via the low to high marsh. These findings suggest that reducing soil conditions can suppress the response of belowground litter stabilization to rising temperature. In conclusion, our study demonstrates marked differences in the response of initial decomposition rate vs. stabilization of labile plant litter to rising temperature in salt marshes. We argue that these differences are strongly mediated by the soil redox status along flooding and soil-depth gradients.

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Design and Assessment of a Novel Approach for Ecosystem Warming Experiments in High‐Energy Tidal Wetlands

Cited by 3 publications

References 30 publications

Wetland roots as soil reducers – Insights from a Wadden Sea salt-marsh study

Wetland roots as soil reducers – Insights from a Wadden Sea salt-marsh study

Root-Driven Soil Reduction in Wadden Sea Salt Marshes

Warming accelerates belowground litter turnover in salt marshes – insights from a Tea Bag Index study

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