Effects of experimental drying intensity and duration on respiration and methane production recovery in fen peat incubations

Drying and rewetting to a variable extent influence the C gas exchange between peat soils and the atmosphere. We incubated a decomposed and compacted fen peat and investigated in two experiments 1) the vertical distribution of CO2 and CH4 production rates and their response to drying and 2) the effects of temperature, drying intensity and duration on CO2 production rates and on CH4 production recovery after rewetting. Surface peat down to 5 cm contributed up to 67% (CO2) and above 80% (CH4) of the depth-aggregated (50 cm) production. As CO2 production sharply decreased with depth water table fluctuations in deeper peat layers are thus not expected to cause a substantial increase in soil respiration in this site. Compared to anaerobic water saturated conditions drying increased peat CO2 production by a factor between 1.4 and 2.1. Regarding the effects of the studied factors, warmer conditions increased and prolonged drying duration decreased CO2 production whereas the soil moisture level had little influence. No significant interactions among factors were found. Short dry events under warmer conditions are likely to result in greatest peaks of CO2 production rates. Upon rewetting, CH4 production was monitored over time and the recovery was standardized to pre-drying levels to compare the treatment effects. Methane production increased non-linearly over time and all factors (temperature, drying intensity and duration) influenced the pattern of post-drying CH4 production. Peat undergoing more intense and longer drying events required a longer lag time before substantial CH4 production occurred and warmer conditions appeared to speed up the process. (C) 2011 Elsevier Ltd. All rights reserved.