| Atmospheric nitrous oxide (N2O) and methane (CH4) are two of the main greenhouse gases,concentrations of those and other greenhouse gases are predicted to cause global warming thatwill have significant impact on the Earth’s environment. The warming potential of N2O isnearly300times greater than that of CO2over a100-year period, and the warming potentialof CH4is nearly25times greater than that of CO2. Tropical rainforest soil is an importantsource of atmospheric nitrous oxide (N2O) and methane (CH4). However, there is stillconsiderable uncertainty about the spatial and temporal variability of N2O, CH4fluxes.Hereafter, detailed measurements of N2O, CH4emission rates from other tropical regionsaround the world, such as Hainan Island, will lead to a better understanding of the globaltropical N2O budget. Hainan Island is the largest island in the tropical region of China, wheretypical rainforests are distributed.To understand these fluxes, we quantified the annual N2O, CH4emissions from threetropical mountain rainforests and respond to nutrients additions (primary mountain rainforest,PMR; secondary mountain rainforest, SMR; and Podocarpus imbricatus plantation, PIP) inthe Jianfengling National Natural Reserve on Hainan Island, China. We quantified the meanN2O, CH4fluxes with the static chamber-gas chromatography method and revealed the keyfactors about N2O, CH4emissions. Then the nutrients addition experimental was conducted tobetter understand the responses of N2O, CH4fluxes to nutrients (N, P) additions in SMR andPMR.We calculated a mean N2O emission rate of2.52±0.33kg N-N2O ha-1yr-1for theJianfengling tropical mountain rainforests that were studied, with the range reported for othertropical rain forests (0.9to5.86kg N-N2O ha-1yr-1). There was no significant differencebetween SMR (3.03±0.64kg N-N2O ha-1yr-1) and PIP (3.49±0.61kg N-N2O ha-1yr-1)(P>0.05), which were both significantly higher than that in PMR (1.53±0.49kg N-N2O ha-1yr-1)(P <0.05for both). N2O emissions exhibited obvious seasonal patterns in the three foresttypes studied. The mean N2O emission rates during the wet season were2times greater than during the dry season. For SMR and PIP, we found a Gaussian relationship between theaverage N2O emission and soil temperature (5cm, R2=0.32, P<0.05, and R2=0.29, P<0.05,respectively;10cm, R2=0.33, P<0.05, and R2=0.29, P<0.05, respectively). There was nosignificant relationship between the average N2O emission and soil temperature in PMR. InSMR and PIP, an exponential relationship was observed between N2O fluxes and WFPS (R2=0.58, P<0.01, and R2=0.25, P<0.01, respectively), but there was no significant relationshipbetween N2O flux and WFPS in PMR (P>0.05). We regarded that denitrification was thedominant process of N2O emission when WFPS was above90%in SMR and PIP.This tropical mountain rainforest region soil was the sink of CH4, and the mean flux wasabout-1.63kg CH4-C ha-1yr-1. There was no significant difference among the three foresttypes (P <0.05for both), the annual mean soil flux in SMR was about-0.5058±0.2026mgCH4m-2d-1,-0.6256±0.1613mg CH4m-2d-1in PIP and the annual mean flux in PMR was-0.6334±0.1968mg CH4m-2d-1. Among the three forest types, there was no significantdifference between the mean CH4emission rates during the wet season and during the dryseason (P>0.05for both). Regression analysis found that there was no significant relationshipbetween CH4flux and soil temperature among the three forest types (P>0.05for both). InSMR and PIP, a linear relationship was observed between CH4fluxes and WFPS (R2=0.24, P<0.01; R2=0.26, P <0.01respectively), but there was no significant relationship betweenN2O flux and WFPS in PMR (P>0.05).There were no significant effect of N, P application on N2O, CH4emission in SMR andPMR (P>0.05for both). |
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