Ecosystem respiration in peatlands: a global quantitative review

Abstract:

Since the last glacial maximum, peatlands have sequestered vast amounts of carbon (C) globally. This previously stored C, and peatland capacity to store more in the future, are vulnerable to climate change. For example, warming and drying of northern peatlands is expected to increase C losses from these systems and further feedback into climate warming, but the magnitude and mechanisms of this increased C loss remain uncertain. Over the past several decades, peatland carbon cycling has been studied to estimate rates of production, decomposition and C accumulation. Chamber flux measurements are a common method used to estimate inputs and losses of C. Structural (plant community) and abiotic (moisture and temperature) controls on chamber-based CO₂ flux have also been investigated in disparate studies but have not been compiled to test overarching hypotheses on structure-function linkages. Lastly, it is unclear whether hypotheses about controls on C fluxes are true for a diversity of peatlands globally. We quantitatively synthesize the peatland CO₂ flux body of literature with a focus on ecosystem respiration (ER). In addition to compiling a dataset of published chamber ER from peatlands, we examine the following questions: 1) What is the spatial variability of in situ ER from peatlands? 2) What are the major structural (plant community) and abiotic controls (temperature and moisture) on ER? 3) What are the remaining knowledge gaps regarding ER in northern peatlands and 4) Can lessons learned from northern peatlands be applied to tropical peatlands? We find that ER was highly variable both across (global CV = 73%) and within sites (within-site mean CV = 32%). A range of temperature, moisture, vegetation and other peatland-specific variables, such as peat depth, were significant predictors of ER. Northern peatlands typically had different functional relationships with predictors when compared to tropical peatlands. A global best fit model included mean annual precipitation, incoming shortwave radiation and gross primary productivity and was able to explain up to 40% of the ER variability. Using this review we will provide a peatland ER conceptual framework and dataset, and highlight knowledge gaps; all necessary steps toward understanding and modeling future peatland function and C sequestration or loss.