Estimation Of Biogenic Volatile Organic Compounds From Dominant Tree Species In The Jing-Jin-Ji Area And Study On The Effects Of Nitrogen And Phosphorus Addition

With the rapid economic development and the acceleration of urbanization,the Jing-Jin-Ji area suffers from severe haze and photochemical pollution all year round,and the air pollution problem needs to be solved urgently.The role of biogenic volatile organic compounds（BVOCs）in the formation of ozone and secondary organic aerosols cannot be ignored,and has adverse effects on the ecological environment and human health.However,as of now,relatively specific regional BVOCs emissions data are scarce.This also limits the realization of air control effects.Therefore,it is very important to estimate the localized BVOCs emission inventory and clarify the BVOCs emission rules from the dominant forest species in the Jing-Jin-Ji area.There are many factors that affect the emission of BVOCs,and the influence of some environmental factors on BVOCs have been fully proved,but the research on the response of plant BVOCs emission rates to nitrogen and phosphorus addition is very limited.In this paper,based on the measured emission rates of forest species,the forest resource survey data and actual field survey,the light and temperature influence model was used to estimate the BVOCs emission of the dominant forest species in the Jing-Jin-Ji area,and analyzed its temporal and spatial distribution characteristics and chemical reaction activity,selected Platycladus orientalis as as the experimental object to explore the effect of nitrogen and phosphorus addition on the emissions of Platycladus orientalis and its mechanism.The results are as follows:The total annual BVOCs emission of the main forest species in the Jing-Jin-Ji area was 70.8 Gg C·a^-1.Isoprene,monoterpenes and other VOCs accounted for 40.5%,36.0%and 23.4%,respectively.From the perspective of monthly and seasonal changes,BVOCs emission peaked in summer（June,July,and August）and reached their lowest in winter（December,January,and February）.In terms of spatial distribution,areas with high BVOCs emissions were mainly distributed in the Taihang Mountains and Yanshan Mountains.Among them,Chengde City has the largest emission,followed by Beijing.Platycladus orientalis,Quercus variabilis,Populus tomentosa,Pinus tabulaeformis and Robinia pseudoacacia were the main contributors to BVOCs emissions and atmospheric reactions.The emission rates of most of the BVOCs components of Platycladus orientalis showed a trend of first decreasing and then increasing with the increase of nitrogen treatment level.The emission rates reached the lowest value under low nitrogen or medium nitrogen treatment level,and reached the highest value under high nitrogen treatment level.The addition of phosphorus promoted this trend.Compared with the control group,the total BVOCs emission rate at low nitrogen levels reduced by about 32.87%.The influence mechanism of nitrogen and phosphorus addition on Platycladus orientalis BVOCs emission is:Low-level nitrogen addition and phosphorus addition promoted the photosynthesis and leaf nitrogen and phosphorus content of Platycladus orientalis.The non-structural carbohydrates are transported for vegetation growth,but less used for the synthesis of BVOCs.There is a threshold for the effect of nitrogen addition on plants.The too much nitrogen affects the nutrient balance in Platycladus orientalis,and the promotion of plant photosynthesis decreases until it is inhibited,plants reduce their demand for nitrogen and phosphorus,and tend to use stored non-structural carbohydrates for the synthesis of BVOCs.