| Forest is an important component of the terrestrial ecosystem and its soil is the significant sink of atmospheric methane.Therefore,the accurate estimation of methane flux in forest soil can help to further predict global climate change.In recent years,human activities have led to the environmental deterioration and the intensification of extreme weather,and among these issues,intensifying typhoon disturbance has made the canopy gaps of tropical forests gradually increase.The impact of canopy gap formation on soil methane has become a hot issue in the field of forest methane flux estimation and global climate change ecology.At the same time,the topic of soil non-microbial methane emission is the leading edge of carbon cycle research,and ignoring its impact may increase the uncertainty of methane flux estimation.Based on above,this study took the Jianfengling tropical montane rainforest as the object,carried out a two-year field positioning observation experiment of methane flux,and discussed the influence of canopy gaps on soil methane flux and its regularity.Furthermore,the potential of non-microbial methane emission from tropical forest soil and its influencing mechanism were studied by laboratory simulation.The main research results are as follows:1.The effects of canopy gaps on soil methane emission were elucidated.The tropical montane rainforest of Jianfengling shows soil methane absorption,and the average annual methane flux inside and outside the canopy gaps are-0.62±0.43 nmol·m-2·s-1 and-0.63±0.43nmol·m-2·s-1 respectively.The monthly change of soil methane flux inside and outside the canopy gaps generally shows a cyclic trend of first decrease and then increase,but the difference is not significant(P>0.05).Its seasonal characteristics are more obvious,showing the characteristics of dry season and low rainy season.The results show that the 6 canopy gaps formed by the typhoon have no significant effect on soil methane flux in the short term(6-7 years).2.The main factors affecting soil methane flux inside and outside the canopy gaps were identified.Pearson correlation analysis showed that soil moisture,soil ammonium nitrogen,soil total nitrogen,soil urease,and soil sucrase of inside and outside the canopy gaps and soil organic of outside the canopy gaps were extremely significantly correlated with soil methane flux(P<0.01).Moreover,soil temperature were significantly correlated with soil methane flux of inside and outside the canopy gaps(P<0.05).The statistical analysis of the differences shows that soil temperature in the rainy season and whole year,soil total phosphorus in the dry season and whole year,soil ammonium nitrogen in the whole year,soil sucrase in both seasons and whole year,soil urease in the rainy season and whole year have extremely significant differences inside and outside the canopy gaps(P<0.01),and total phosphorus in the rainy season,ammonium nitrogen in both seasons,and pH in the rainy season have significant differences inside and outside the canopy gaps(P<0.05).The optimal structure model of soil methane flux indicates that soil water content is the most important factor affecting soil methane flux.3.The distribution of soil methanogens inside and outside the canopy gaps was revealed.The formation of canopy gaps has no significant effect on the species abundance of soil methanogens and it even increased the diversity of the microbial community to a certain extent,but the difference was not significant(P>0.05).On the phylum classification level,the main archaea groups inside and outside the canopy gaps of Jianfengling tropical montane rainforest are Thaumarchaeota,Euryarchaeota,and Crenarchaeota.Through analysis,a total of 571 OTU species of soil methanogens were found,including 2 classes,3 phylums,4families and 5 genera.4.The potential and mechanism of non-microbial methane emissions from tropical forest soil were discussed.High temperature and high hydrogen peroxide content can significantly promote the emissions of soil non-microbial methane,indicating that there are at least two mechanisms of non-microbial methane emissions(thermal degradation and free radical mechanism)in tropical forest soil.The suitable soil water content(0-100%)and organic carbon content had very significant positive correlation with methane emission rate(P<0.01).The methane emission rate of non-microbial methane under aerobic condition was significantly higher than that under anaerobic condition.This means that soil moisture content,soil organic carbon content and oxygen conditions can all affect the emission rate of soil non-microbial methane.In this study,the maximum potential of soil non-microbial methane emissions of the per gram of dry soil in Jianfengling tropical montane rainforest was calculated,which is 212.45 ng/g. |
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