Temperature responses to infrared-loading and water table manipulations in peatland mesocosms.

We initiated a multi-factor global change experiment to explore the effects of infrared heat loading (HT) and water table level (WL) treatment on soil temperature (T) in bog and fen peatland mesocosms. We found that the temperature varied highly by year, month, peatland type, soil depth, HT and WL manipulations. The highest effect of HT on the temperature at 25 cm depth was found in June for the bog mesocosms (3.34-4.27 degrees C) but in May for the fen mesocosms (2.32-4.33 degrees C) over the 2-year study period. The effects of WL in the bog mesocosms were only found between August and January, with the wet mesocosms warmer than the dry mesocosms by 0.48-2.03 degrees C over the 2-year study period. In contrast, wetter fen mesocosms were generally cooler by 0.16-3.87 degrees C. Seasonal changes of temperatures elevated by the HT also varied by depth and ecosystem type, with temperature differences at 5 cm and 10 cm depth showing smaller seasonal fluctuations than those at 25 cm and 40 cm in the bog mesocosms. However, increased HT did not always lead to warmer soil, especially in the fen mesocosms. Both HT and WL manipulations have also changed the length of the non-frozen season.