Effects Of Atmospheric Aerosols On The Ecosystem Productivity Of Poplar Plantation In North China

Atmospheric aerosol can influence the total amount of solar radiation reaching the ground and the ratio of its components,thus having important effects on plant photosynthesis,ecosystem productivity and regional carbon balance.However,the mechanisms of aerosol regulation on ecosystem productivity are not clear at present.Therefore,an in-depth investigation of the effects of aerosol on ecosystems can not only provide a comprehensive understanding of the ecological effects of atmospheric aerosol,but also facilitate an accurate assessment of ecosystem productivity and regional carbon sink capacity in the context of climate change.In this study,long-term localized observations of carbon and water fluxes in poplar(Populus euramericana)plantation ecosystems in northern China were conducted in Daxing(2006-2009)and Shunyi(2014-2017),Beijing,using eddy correlation techniques and microclimate observations,and combined with atmospheric aerosol observation data in Beijing to investigate the effects of atmospheric aerosols on poplar plantation forest The direct and indirect effects of various biophysical factors,including atmospheric aerosols,on ecosystem productivity were quantified,the fertilization effects of aerosols under different moisture conditions were compared,and a neural network model was used to predict future aerosol impacts on the ecosystem.(1)Atmospheric aerosols not only change the total amount of radiation reaching the ground and its components,but also have significant effects on environmental factors such as temperature and humidity.At midday,heavy aerosol pollution(AOD=2.5)can lead to a 29% decrease in total radiation,while scattered radiation increases by 40% and saturated water vapor pressure difference decreases by 40% in Beijing.On the daily scale,heavy aerosol pollution(AOD=3)can lead to a 43% decrease of total radiation and more than 1 times increase of scattered radiation in Beijing,while it will make the daily temperature difference increase.(2)Atmospheric aerosol has a significant effect on the productivity of poplar plantation forest ecosystem.Ecosystem productivity increases exponentially with the increase of aerosol photochemical thickness(AOD),but when the aerosol photochemical thickness exceeds 1,the ecosystem productivity is not sensitive to the change of atmospheric aerosol.(3)Under different moisture conditions,aerosols have different effects on ecosystem productivity.Under moisture deficit conditions,aerosols have no significant effect on ecosystem productivity of poplar plantations;when moisture is sufficient,ecosystem productivity increases first and then decreases with increasing aerosol concentration.(4)Aerosol affects ecosystem productivity mainly through the fertilization effect of scattered radiation and the perturbation of environmental factors,and the fertilization effect of scattered radiation and the perturbation of environmental factors cannot be completely separated,and scattered radiation is the dominant factor of ecosystem productivity in poplar plantation forests,and the apparent photosynthetic quantum efficiency of scattered radiation is 2.55 times higher than that of direct radiation.(5)Although both soil moisture and scattered radiation ratio can affect photosynthesis in poplar plantation forest ecosystem by influencing apparent photosynthetic quantum efficiency,maximum net photosynthetic exchange rate,and stomatal conductance,the effect of soil moisture is more obvious.(6)With the management of atmospheric environment,the concentration of atmospheric aerosol will be reduced continuously.Ecosystem productivity will not be significantly reduced until the aerosol concentration is reduced to 1.