Abstract
Mechanisms controlling CO2 and CH4 production in wetlands are central to understanding carbon cycling and greenhouse gas exchange. However, the volatility of these respiration products complicates quantifying their rates of production in the field. Attempts to circumvent the challenges through closed system incubations, from which gases cannot escape, have been used to investigate bulk in situ geochemistry. Efforts towards mapping mechanistic linkages between geochemistry and microbiology have raised concern regarding sampling and incubation-induced perturbations. Microorganisms are impacted by oxygen exposure, increased temperatures and accumulation of metabolic products during handling, storage, and incubation. We probed the extent of these perturbations, and their influence on incubation results, using high-resolution geochemical and microbial gene-based community profiling of anaerobically incubated material from three wetland habitats across a permafrost peatland. We compared the original field samples to the material anaerobically incubated over 50 days. Bulk geochemistry and phylum-level microbiota in incubations largely reflected field observations, but divergence between field and incubations occurred in both geochemistry and lineage-level microbial composition when examined at closer resolution. Despite the changes in representative lineages over time, inferred metabolic function with regards to carbon cycling largely reproduced field results suggesting functional consistency. Habitat differences among the source materials remained the largest driver of variation in geochemical and microbial differences among the samples in both incubations and field results. While incubations may have limited usefulness for identifying specific mechanisms, they remain a viable tool for probing bulk-scale questions related to anaerobic C cycling, including CO2 and CH4 dynamics.
Highlights
Wetlands contain enormous reservoirs of carbon (C) [1] and are a significant ecosystem in northern and boreal regions based on large areal extent [2]
This trend in production rates among habitats reflects the trend in CO2 and CH4 emission rates observed in the field across these habitats, and likely results from the inhibition of microbial activity imposed by Sphagnum mosses in the bog, and the fueling of Geochemical processes are maintained during ex situ anaerobic incubation anaerobic decomposition in the fen by the vegetation’s more labile material [30]
We expect the magnitude of production rates in the incubations to be higher than field conditions the preservation of relative production rates among habitats in the incubations suggests that the peat itself exerts a strong control on CO2 and CH4 production which is preserved in the incubations
Summary
Wetlands contain enormous reservoirs of carbon (C) [1] and are a significant ecosystem in northern and boreal regions based on large areal extent [2]. Incubations are a commonly employed method for studying climatically relevant biogeochemical processes in natural ecosystems, peatlands [3,6,7,8,9,10] as they offer several critical advantages over in situ field observations, including control and isolation of variables that fluctuate in complicated and interdependent ways in the field (e.g. temperature, water table depth, etc.), the opportunity for direct manipulation, and the improved potential for detailed measurements. Measurements can be repeated at high resolution over longer timescales in incubations, allowing exploration of kinetic effects [12], mechanisms of C cycling/processing, and the relative impacts of controls on C gas production such as organic matter quality, C and N mineralization potential and C partitioning [3]
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