Effect Of Vegetation On Greenhouse Gases Emission In Estuarine Wetland And Its Response To Global Change

Estuarine wetlands,working as the buffer zone between the terrestrial ecosystem and aquatic ecosystem,play an important role in the global carbon and nitrogen cycle,and have been long recognized as a critical greenhouse gases?GHGs?source.Vast amounts of research have proved that the process of carbon and nitrogen cycle in wet-lands is particularly complex for being regulated by various environmental factors.Among those,the widely distributed plants in wetland can affect the production,con-sumption and transportation of GHGs to a large extent and determine the role of a wet-land as source or sink of GHGs.As a consequence of the severer global climate change,estuarine wetlands will be undoubtedly influenced by rising temperature,elevated sea level,salt water intrusion and bio-invasion.Thus,the response of the function and bio-genic cycle in plant community become a hot spot in estuarine wetland study.This paper was supported by the project of "The effect and mechanism of vegeta-tion on methane and nitrous oxide emission in estuarine wetland",funded by National Nature Science Foundation.Chongming Dongtan wetland in the Yangtze River estuary was chosen as the research object.CH₄,CO₂ and N2O fluxes in the Phrgmites australis and Spartina alterniflora community were monitored across the whole growth stage.In addition,a brackish mesocosm was established to assess the response of physiolog-ical parameter and GHGs emission of wetland plant to multiple global climate-driven changes.The main conclusion of the research were as followed:?1?The CH₄ fluxes in phragmites marsh during the growth period ranged from 16.55?351.93?mol·m^-2·h^-1,which acts as a net source of atmospheric CH₄.The CH₄ emission fluxes between day time and night exhibited constant change from the sink to source with the range of 1.61?2.77mmol·m^-2·h^-1.The N2O emission fluxes in phrag-mites marsh ranged from-0.18?0.36?mol·m^-2·h^-1.The P.australis communities and S.alterniflora communities in the mesocosms both act as CH₄ source and CO₂ sink with the average CH₄ fluxes reaching 141.03?mol·m^-2·h^-1 and 502.84?mol·m^-2·h^-1,the av-erage CO₂ fluxes reaching-5.22mmol·m^-2·h^-1 and 4.42mmol·m^-2·h^-1,respectively.The N2O fluxes of two communities revealed that the S.alrniflora communities acts as a constant N2O source though the P.australis communities exhibits obvious transfor-mation between the sink and source during the vigorously growing season.The CH₄ and CO₂ emissions of two communities showed distinct diel variations.The CH₄ emis-sion fluxes reached to the peak value in the day time with obviously declining during the night.Due to the photosynthesis,the CO₂ emission fluxes showed that both com-munities absorb CO₂ during the day and release it at night.The difference of N2O emis-sion fluxes among diel range was not significant.?2?The vegetation in the community has a remarkable effect on production and transportation of greenhouse gases.By Pearson correlation and regression analysis,CH₄ fluxes have a significant positive correlation with both biomass of P.australis communities and living shoot density.However,they present a negative correlation with CO₂ fluxes.P.australis community plays a great role of greenhouse transportation.The results of the clipping treatment showed that the stalk of P.australis is critical to gase transportation and the stimulating function varied among different growth stage.The monitoring results of leaves fluxes revealed that the photosynthesis of phragmites leaves is the main factors to influence the exchange fluxes of CO₂,but with less contri-bution to CH₄ and N2O transportation.?3?Different physiological properties between P.australis and S.alterniflora com-munity lead to a significant difference of greenhouse gases emission fluxes.The equiv-alent emission?e-emission?of CO₂ reaching^-14.38 mg CO₂-C·m^-2·h^-1 showed that the phragmites community inhibit the global warming effect.However,the spartina alterni-flora community promote the effect of global warning with e-emission fluxes reaching 117.09 mg CO₂-C·m^-2·h^-1.?4?The rising temperature greatly influences the physiological status and biochem-ical of vegetation communities.Under the condition of the average temperature rising of 5 degrees,the biomass of P.australis community significantly declined but non-significant difference happened in S.alterniflora community.The CH₄ emission in P.australis and S.alterniflora communities was accelarated by 130.32%and 73.02%,re-spectively,in the warmer mesocoms.The plant communities witnessed a larger amount of CO₂ uptake in warmer condition in the early growth stage,but emitted more gases during summer time.Change in temperature didn't have significant effect on N20 emission from both species.?5?The physiology parameters of P.australis and S.alterniflora were not found significantly different in the high water level plot,which showed that both type species have good adaptive capacity to an increasing water supply.The rising water table could tremendously promoted CH₄ emission by altering the sediment to a more anaerobic environment.The P.australis and S.alterniflora in high water level plots emitted 2.87 and 6.49 times of CH₄ than they do in the low water level plots,respectively.The CO₂ influxes in both species were diminished in low water level plots.The N2O emission didn't show significant response to the water level change.?6?The response of the plants' physiology parameter showed a significant differ-ence from two vegetation type.The growth of P.australis was suppressed by the in-creasing salinity.The biomass of P.australis in 30‰ plot was only 2.96%of that in 5‰plot,but S.alterniflora was less affected by its better capacity of salt elimination.The CH₄ fluxes from both vegetation type were peaked in 5‰ plot and bottomed in 30‰.The influxes of P.australis community showed a negatively response to salinity rise that the CO₂ uptake decreased by 65.31%from 5‰ to 30‰,whereas its S.alterniflora counterpart didn't show distinct variation within all salinity level.?7?The interactive effect of global change factors on plant marshes are particularly complex.The CH₄ fluxes of the plant community demonstrated a positive response to rising temperature in low water table level,and the sensitivity to the temperature,along with the CH₄ fluxes,became much greater when the water table was raised.The CO₂ influxes of two type of plants increased with intermediate rise of temperature and sa-linity,and could be rather stimulated at a higher water table level.?8?The result of multi-regression model analysis showed that the change on plant biomass could be well predicted by global change factors,however,the change on CH₄ and CO₂ fluxes were poorly correlated with environmental parameters' change.This result,once again,showed that the response of biogenic cycle in estuarine plant com-munities to global change is extremely sophisticated.