Effects Of Elevated CO₂ And Nitrogen Deposition On Gas Exchange Parameters And Monoterpenes Emission Of Pinus Massoniana Lamb And Schima Superba Seedlings

With the rapid development of industrialization,the concentration of CO₂is constantly rising,and nitrogen deposition is greatly intensifying.Biogenic volatile organic compounds?BVOCs?are the main components of volatile organic compounds?VOCs?in the atmosphere and one of the key processes for vegetation to affect environment and climate.The research on BVOCs emission by plants under climate change has become one of the hotspots.In 2017,1-year-old Masson pine seedlings?Pinus massoniana Lamb?were fumigated with four concentrations(1000,750,and 550?mol·mol^-1and ambient air)based on IPCC?Intergovernmental Panel on Climate Change?Fifth Evaluation Report in open-top chambers?OTCs?.In 2018,1-year-old Schima superba were exposed to a factorial combination of four CO₂concentrations and three N deposition in open-top chambers.Gas exchange parameters,leaf photosynthetic pigments,carbon and nitrogen contents,monoterpene emissions of Masson pine and Schima superba were measured to deepening the understanding of the response of plant physiology to CO₂concentration and N deposition.The conclusions of the research were shown as follows:The photosynthetic acclimation to CO₂enrichment of Masson pine seedlings was appeared in long-term CO₂fumigation;When measured in ambient air,the net photosynthetic rate?Pn?of Pinus massoniana seedlings treated in the 60-day CO₂enrichment was significantly lower than that of the control group;The photosynthesis of Schima superba seedlings was enhanced by elevated CO₂and N deposition,and the interaction between CO₂and N had a significant effect on the net photosynthetic rate of Schima superba seedlings.With 120 days'fumigation,the effect of elevated CO₂on the net photosynthetic rate of Schima superba seedlings was not significant in low nitrogen environment.CO₂enrichment significantly reduced the content of chlorophyll in Pinus massoniana seedlings,but had little effect on SPAD value of Schima superba seedlings;Elevated CO₂reduced stomatal conductance?gs?of the two plants seedlings,and improved water use efficiency;nitrogen deposition increased stomatal conductance of Schima superba seedlings.CO₂ enrichment significantly reduced the total nitrogen content and C/N in leaves of Schima superba seedlings,and promoted the accumulation of starch in leaves,while nitrogen deposition effectively alleviated the effects.This may explained that long-term CO₂enrichment at low nitrogen level has no significant effect on net photosynthetic rate of Schima superba seedlings.Elevated CO₂ concentration significantly decreased the emission rate of monoterpenes in Pinus massoniana and Schima superba seedlings.And monoterpenes emission rate was positively correlated with stomatal conductance in both seedlings.The decrease of stomatal conductance caused by elevated CO₂enrichment may be one of the limiting factors of plant monoterpenes release.