Diurnal variations and gap effects of soil CO2, N2O and CH4 fluxes in a typical tropical montane rainforest in Hainan Island, China

Abstract

AbstractAccurate estimations of soil greenhouse gas (GHG) fluxes in tropical montane rainforests are critical for assessing the role of tropical forests in influencing global climate change. This research aimed to determine the diurnal variation in soil GHG fluxes and understand the effects of forest canopy gaps on GHG fluxes, and their major controlling factors. The diurnal fluxes of soil carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4) inside and outside three forest canopy gaps in a tropical montane rainforest were measured with a closed static chamber system in June 2015. The main results are as follows. (1) There was an obvious single‐peak daily variation of soil GHG fluxes. (2) The averaged soil CO2, N2O and CH4 fluxes of the whole day were closest to the daily average emission fluxes at 9:00 and 12:00 for CO2, 6:00 and 9:00 for N2O, and 9:00 and 12:00 for CH4, respectively. (3) Soil CO2 and N2O emissions (positive values) and CH4 uptake (negative values) were higher inside gaps than outside. (4) There were stronger exponential relationships between soil CO2 and N2O emissions and temperature inside gaps than outside, and there was a stronger quadratic relationship between CH4 uptake and temperature outside gaps than inside. However, significant relationships between soil CO2 (or CH4) and soil moisture only occurred inside gaps (P < 0.01). There were clear diurnal variations and significant effects of gaps on soil CO2, N2O and CH4 fluxes. Our study indicated that understanding the different diurnal variations of soil CO2, N2O and CH4 fluxes inside and outside canopy gaps could improve the accurate evaluation of soil GHG fluxes in tropical montane rainforests under a changing climate.