51 WETLANDS, Vol. 24, No. 1, March 2004, pp. 51–56  2004, The Society of Wetland Scientists SOIL RESPIRATION RATES OF TROPICAL PEATLANDS IN MICRONESIA AND HAWAII Rodney A. Chimner USDA Forest Service Pacific Southwest Research Station Institute of Pacific Islands Forestry 1151 Punchbowl Street, Room 323 Honolulu, Hawaii, USA, 96813 Present address: Natural Resource Ecology Laboratory Colorado State University Ft. Collins, Colorado, USA 80523 E-mail: rchimner@nrel.colostate.edu Abstract: There are very few published reports of soil respiration rates from tropical peatlands, despite their importance to global carbon cycling. This study quantified in situ soil respiration rates in a suite of tropical peatlands in Micronesia and Hawaii using a soil CO 2 flux chamber connected to a LI-COR 6400 Portable Photosynthesis Infrared Gas Analyzer. Soil respiration rates were higher in the warmer Micronesian peatlands (2.15–2.54 umol m -2 s -1 ) than in the cooler Hawaiian montane peatlands (0.83–1.81 umol m -2 s -1 ). The lone exception was the taro-cultivated peatland in Micronesia that had low soil respiration rates likely due to low amount of litterfall, root biomass, and root production. Deep standing water decreased soil respiration rates, while lowered water levels had mixed effects on soil respiration rates. Surprisingly, mea- sured soil respiration rates were lower than rates measured in temperate and boreal peatlands in the summer. However, soil respiration rates in tropical peatlands are not limited by large diurnal or seasonal changes and can continue respiring at the same rates, resulting in higher annual CO 2 flux rates compared to other non- tropical peatlands. Key Words: peatlands, fens, tropical, soil respiration, CO 2 INTRODUCTION Soil respiration is one of the largest fluxes in the global carbon cycle and is a key component of eco- system carbon balances (Schlesinger and Andrews 2000). Quantifying the temporal and spatial variation in respiration rates is essential to our understanding of the behavior of ecosystems and to our ability to predict the likely consequences of climatic change on carbon cycling. The response of peatlands is of particular con- cern to climate change because of the enormous amount of carbon sequestered as peat (Gorham 1991, Botch et al. 1995, Lappalainen 1996, Clymo et al. 1998). Hydrologic conditions, peat quality, and tempera- ture are the dominant factors controlling soil respira- tion rates. Lower water-table levels have been found to increase soil respiration rates in peatlands (Silvola et al. 1996, Chimner and Cooper 2003a) due to greater oxygen diffusion into unsaturated peat leading to more efficient aerobic respiration and increased transporta- tion of CO 2 through unsaturated peat (Schlesinger 1997). Substrate quality also influences carbon min- eralization rates with greater amounts of recalcitrant material decreasing mineralization rates (Hogg et al. 1992, Updegraff et al. 1995). Warmer temperatures stimulate microbial activity, resulting in greater CO 2 from decomposition in peatlands (Silvola et al. 1996). Soil respiration rates typically increase exponentially with increasing temperatures and are often reported as aQ 10 relationship (magnitude of increase in gas efflux over a 10 °C change). Q 10 values for CO 2 range from 3 to 5 for boreal and subarctic peatlands (Silvola et al. 1996). Given the high temperatures in the tropics, it would be predicted that soil respiration rates should be very high in tropical peatlands compared to non-trop- ical peatlands. There are only a few published reports of soil res- piration rates from tropical peatlands (e.g., Vasander and Jauhiainen 2001, Inubushi et al. 2003). Filling this large gap in our knowledge is vital for quantifying carbon cycling in tropical ecosystems, understanding