Studies On The Emission Characteristics Of CH₄ And N₂O From Mangrove Plants And Their Influencing Mechanism

In recent years,increasing evidences have shown that the stems and leaves of trees can release or consume methane(CH4)and nitrous oxide(N2O),which are important sources and sinks of CH4 and N2O in forest ecosystems.Mangrove ecosystems are coastal wetlands composed of woody plant communities in intertidal zone of tropical and subtropical region and mangrove plants are the core of mangrove ecosystem.The contribution of mangrove plants to the CH4 and N2O fluxes at the ecosystem level is still unclear.In particular,the main factors affecting the CH4 and N2O fluxes of mangrove plants require more in-depth research.Therefore,this study takes mangrove plants as the core of our research.We set two sample sites(S1 and S2)to measure CH4 and N2O fluxes from mangrove plants(Kandelia obovata,Avicennia marina,Aegiceras corniculatum)in the Zhangjiang Estuary National Mangrove Nature Reserve through field observation.Based on the survey results,we next analyzed the contribution of endophytic and epiphytic bacterial to CH4 and N2O fluxes of mangrove plants in the field environment.What’s more we collected leaf litter of different mangrove species for incubation to study the effects of litter decomposition on soil CH4 and N2O production.The main results of this study are as follows:1.The CH4 and N2O fluxes measured on the stem and leaf surface of mangrove plants Kandelia obovata,Avicennia marina and Aegiceras corniculatum have a significant impact on the CH4 and N2O budget of the mangrove ecosystem.Mangrove plants in S1(Kandelia obovata and Avicennia marina)was the net sink of CH4,and the CH4 fluxes of leaves and stems were-39.06 g ha-1 d-1 and-5.23 g ha-1 d-1 respectively.Leaves were the main CH4 consumption sites of mangrove plants.The CH4 flux of mangrove leaves and stems in S2(Kandelia obovata and Aegiceras corniculatum)was35.3 and 34.41 g ha-1 d-1 respectively.The mangrove leaves in S1 and S2 were an important source of N2O,and the N2O fluxes of mangrove leaves were-1.38 and 0.83 g ha-1 d-1 respectively.Stem N2O fluxes were smaller than that of leaves.2.Mangrove soils were the source of CH4 and N2O in this study.The CH4 and N2O flux in S1 was 121.10 and 4.87 g ha-1 d-1 respectively,while that of S2 was 244.58 and 9.40 g ha-1 d-1 respectively.The analysis results of soil physical and chemical properties at a depth of 0-20 cm show that the soil salinity(S),extractable carbon content and microbial biomass carbon content(MC)of S1 and S2 were significantly different(p<0.05),which were the main factors affecting soil CH4 and N2O fluxes.3.Mangrove plants(Kandelia obovata and Avicennia marina)in S1 were net sinks of CH4,which could consume 38.19%of soil CH4 emission,and mangrove leaves were the main part of CH4 consumption,which could consume 32.25%of soil CH4 emission;The CH4 fluxes of mangrove(Kandelia obovata and Aegiceras corniculatum)leaves and stems in S2 could offset each other.Mangrove plants were important sources of N2O.The leaves and stems of mangrove plants in S1 contributed 40.62%and 13.17%of the ecosystem N2O budget,respectively;In S2,mangrove leaves and stems contributed 18.65%and 4.84%of the ecosystem N2O flux,respectively.4.By studied the effects of Endophytes and epiphytes of mangrove plant Kandelia obovata on the CH4 and N2O dynamic in the incubation system.We found that leaves,stems and roots of Kandelia obovata can’t release CH4,and can consume CH4 in high CH4 concentration incubation system.The consumption of CH4 by Kandelia obovata tissue is mainly caused by the CH4 oxidizing bacteria in the epiphytes.What’s more,stable N2O consumption was detected in leaves,stems and roots of Kandelia obovata in high N2O concentration incubation system.Under the condition of low N2O concentration in incubation system,tissues of Kandelia obovata could release a small amount of N2O.High abundance of denitrifying bacteria and functional genes of nitrous oxide reductase(nosZ)were mainly detected in endophytes of Kandelia obovata.The endophyte and epiphyte communities in different tissues of Ko were affected by plant tissues,seawater and soil.5.The total production of CH4 and N2O from our incubation system have significantly different between of mangrove soils treated by leaf litter of mangrove plants(Kandelia obovata,Avicennia marina and Aegiceras corniculatum)and Spartina alterniflora.And the most important factor affecting CH4 and N2O production was the content of phenolic substances in litters through correlation analysis and redundancy analysis(RDA).The abundance of mcrA and norB gene in soils decreased with the increase of litter phenolic substance content.And then the CH4 and N2O production in soils.In addition,the production of CH4 and N2O during the decomposition of litter is also affected by the content of carbon and nitrogen in the soil,as well as the soil NH4+,NO3-,and NO2-content.