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

Abstract

Abstract. Salt marshes play an important role in the global carbon (C) cycle due to the large amount of C stored in their soils. Soil C input in these coastal wetland ecosystems is strongly controlled by the 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 °C and +3.0 °C) across whole-soil profiles (0–60 cm soil depth) and the entire flooding gradient ranging from pioneer zone via low marsh to high marsh. We used standardized plant materials, following the Tea Bag Index approach, to assess the initial decomposition rate of (k) and the stabilization factor (S) of labile organic matter (OM) inputs to the soil system. While k describes the initial pace at which labile (= hydrolyzable) OM 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 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.

Warming experiment indicates that increasing global temperatures may not affect windows of opportunity for salt marsh seedlings

“…Domes for aboveground warming are covered with foil from March to September. More details on the experimental design can be found in Tang et al (2023) and will be described by R. Rich et al (unpubl.). In 2019, soil warming was switched‐on on March 14th, treatment levels were overall reached on March 22nd after some initial technical issues.…”

Interplay of soil characteristics and arbuscular mycorrhizal fungi diversity in alpine wetland restoration and carbon stabilization

“…The TBI protocol, as described by Keuskamp et al (2013), was employed to provide a standardized measure of decomposition. Commercial green tea (EAN: 8714100770542; Lipton, Unilever) and rooibos tea (EAN: 8722700188438; Lipton, Unilever) were utilized, chosen for the well-documented decomposition characteristics reported by Tang et al (2021Tang et al ( , 2023. Green tea, known for its relatively high nitrogen content and rapid decomposition rate, contrasts with rooibos tea, which decomposes more slowly due to its lower nitrogen content and higher lignin composition.…”

“…The k and S values of the tea material were calculated according to the methodology outlined by Mueller et al (2018), involving W r (t), the post-incubation weight of the rooibos tea (t in days), a r for the labile fraction of the rooibos tea, and 1-a r for its recalcitrant fraction. a g represents the labile fraction of the green tea, while H g and H r , as reported by Tang et al (2023), represent the labile fractions of the green and rooibos teas, respectively.…”

Minerogenic salt marshes can function as important inorganic carbon stores

“…2) was driven by differences in inorganic carbon in deep soil layers, where conditions are frequently or permanently anoxic and support anaerobic microbial metabolism (Fig. 4; Tang et al 2022).…”