Warming accelerates belowground litter turnover in salt marshes – insights from a Tea Bag Index assay
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.
Hao Tang et al.
Status: final response (author comments only)
RC1: 'Comment on bg-2022-189', Md. Golam Rakkibu, 26 Oct 2022
- AC1: 'Reply on RC1', Hao Tang, 06 Jan 2023
RC2: 'Comment on bg-2022-189', Inge Althuizen, 24 Nov 2022
- AC2: 'Reply on RC2', Hao Tang, 06 Jan 2023
RC3: 'Comment on bg-2022-189', Anonymous Referee #3, 07 Dec 2022
- AC3: 'Reply on RC3', Hao Tang, 06 Jan 2023
Hao Tang et al.
Hao Tang et al.
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The paper represents a very important perspective of coastal ecosystem carbon dynamics which is not adequately understood. The findings and arguments of the study are critical and very important for future studies exploring coastal soil carbon dynamics which is susceptible to climate change. The manuscript is very well written, explained and discussed. Data are very well presented and clearly interpreted.
Experimental design and methods used to cover the whole soil profile is the significant development in the study. But the issue of whether TBI materials represent the real world scenario with regard to belowground biomass, litter and organic matter turnover remains critical.
Whether the solid PVC posts and perforated holes in which tea bags were placed had any impact that could lead to different conditions in terms of soil moisture, temperature and microbial activity compared to natural soils around need to be discussed.
Besides mean elevation other edaphic characteristics of the three marsh types could be described under site description to signify the zonations.