PNNL

Abstract

Peatlands contain one-third of the world’s soil carbon (C), mostly in the deep permanently saturated anoxic zone (i.e., catotelm)1 where C mineralization rates may be constrained, in part, by low temperatures; yet all soil warming experiments to date have focused on the response of peatland C degradation to surface warming2, 3. If the slow decomposition of deep peat C is due to kinetic constraints, then increasing temperatures at depth should cause parallel increases in carbon dioxide (CO2) and/or methane (CH4) production rates. Increasing CH4 emissions are of particular concern because CH4 has a sustained-flux global warming potential (SGWP) 45-times greater than CO2 over a 100- year timeframe4, creating a significant positive feedback to climate warming. Using a novel whole-ecosystem scale experiment in a regression-based design we show that ecosystem scale warming of deep peat exponentially increased CH4 emissions —but not ecosystem respiration of CO2— in the first year. Multiple lines of evidence, including laboratory incubations and in situ analyses of 14C, dissolved gases, and microbial community metabolic potential, indicate that CH4 emissions increased due to surface processes and not degradation of deep C. Our results indicate that rapid changes to the large bank of deep buried C in temperate peatlands may be minimal under future climatic warming.