Characteristics And Pattern Of Biogenic Volatile Organic Compounds (BVOCs) Emission For Common Deciduous Fruit Trees In China

Biogenic volatile organic compounds?BVOCs?are the most significant component of VOCs.Besides promoting plant against external biotic and abiotic stresses,BVOCs are wildely involved in the generation of surface layer ozone?O₃?,secondary organic aerosol?SOA?and other secondary pollutants,which have an important impact on regional atmospheric environmental quality and even global climate change.At present,only a few studies have been investigated BVOCs emmision in agro-forest complex ecosystems,but BVOCs from fruit trees in periurban areas has not been considered.In this study,we analyzed the inventory and characteristics of biogenic volatile organic compounds?BVOCs?for 12 deciduous fruit trees by a combined dynamic sampling and sorbent tube techniques.Samples were conducted in field and analysed with a thermal desorption system equipped with a gas chromatography-mass spectrometry?GC/MS?from July to September 2018.Moreover,the possible characterization index of plant BVOCs emission rate and the periodic change of BVOCs typical substances were investigated in this study.The main results and conclusions are summarized as follow:1.Three fruit trees speies,such as peach tree,were high emitter,and the remaining 9species,such as Persimmon tree,were medium emitter.The emission rates of total BVOCs?including isoprene,monoterpenes and sesquiterpenes?in different fruit trees were ranged from?2.6±0.1?to?14±0.8??g.?g.h?^-1.Analyses on BVOCs in different families and plant life-form indicated isoprene emission rate were significantly higher in woody fruit trees[?4.2±1.4??g.?g.h?^-1]than that in vine fruit trees[?0.6±0.2??g.?g.h?^-1,P=0.03],whereas there was no significant difference between family or genus,thus suggesting that the emission level of BVOCs from fruit trees cannot be classified at different family and genera presently.2.Monoterpenes?MTs?emited from fruit trees were different from those in conifers species,which have been extensively studied,?-myrcene,D-limonene and?-terpinene,which with floral or resinous aromas,were found as the main monoterpenes for fruit trees.The emission rate of?-myrcene is the highest,accounting for 59.3%of total monoterpene emisions.In addition,BVOCs emission from fruit trees contained 9 kinds of other compounds such as hydrocarbons,alcohols,aldehydes and so on,among them,the content of hydrocarbon was highest?accounting for about 39.0%?,Besides,fruit trees may emit other 8 fragrant VOCs,which are listed as hazardous air pollutants?HAPs?,such as fluorene,phenanthrene,naphthalene and so on.3.Intercellular CO₂ concentration?Ci?was the only leaf gas exchange parameter which may reflect the characters of BVOCs in fruit trees.According to analyzing the correlation between BVOCs components and gas exchange parameters parameters or leaf traits,a significant negative linear correlation was found between Ci and both isoprene?r=-0.742,P<0.01?and total BVOCs?r=-0.927,P<0.01?emission rate,while Ci was weakly correlated with monoterpenes?r=-0.495?.Furthermore,there were no obvious correlations between other gas exchange parameters and the emission rate of each BVOCs component,thus indicating that other parameters cannot manifest the difference in BVOCs emission rate among fruit trees species,except for Ci.4.The total BVOCs emissions from fruit trees displayed obvious diurnal variations,with the lower emisions in the morning and afternoon,reaching peak emissions atnoon?13:00 pm?,although at this moment the photosynthesis of persimmon trees and pear trees were inhibited,MTs emission rates of two fruit trees were?5.2±0.3??g.?g.h?^-1and?2.1±0.3??g.?g.h?^-1respectively.It is speculated that the replacement of carbon sources for plant BVOCs synthesis under thermal stress was a potential cause of this phenomenon.In addition,the changes in MTs was higher from persimmon trees than from pear trees when environmental?light and temperature?sensitivity was considered.5.The type of BVOCs were basically unchanged at diffrernt growth stages of permission fruit,while the composition of BVOCs varied greatly.The leaf mass per area?LMA?could be a possible index,which can reflect the emission ability of BVOCs at each stage.Taking alkene as an example,the dominant substances?contents?from fruit setting stages to fruit swelling and finally ripening stages were?-pinene?7.86%?,1-dodecene?3.29%?,and tetradecene?7.76%?,respectively.Moreover,the emission rate in the fruit swelling[?5.7±0.2??g.?g.h?^-1]and ripening stages[?5.6±1.7??g.?g.h?^-1]were significant higher than in fruit setting stages[?2.1 0.3??g.?g.h?^-1,P<0.05]when the total BVOCs emission were concerned.A strong positive correlation between the emission rate of BVOCs and LMA?r=0.660,P<0.01?was observed for both growth stages.Thus suggesting LMA,as an external indicator parameter,has the potential capacity to judge BVOCs emission rate from different phenological periods for persimmon.