The Dynamic BVOCs Emission Rates Of Tropical Rain Forest Tree Species In Hainan Island And Its Short-term Response To Simulated Nitrogen Deposition

Biogenic volatile organic compounds?BVOCs?are low-boiling,small-molecule secondary metabolites released by plants,and play an important role in the biosphere,such as herbivore deterrence,fungal toxicity,and pollinator attraction.Besides,BVOCs are also important gaseous compounds in the atmosphere,which can react with active free radicals in the atmosphere to form secondary organic aerosols?SOA?and prolongs the life of greenhouse gases such as CH₄ in the atmosphere.Thus,the analysis of the impact of environmental factors on BVOCs emissions is of great significance for scientific understanding of future climate change impacts on atmospheric environmental changes.As we all know,nitrogen is one of the large numbers of nutrients required for plant growth,however,it's increasing in deposition is the main drivers of current global climate change,and the emission of BVOCs in response to elevated N deposition is poorly understood.In this study,Schima superba,Cryptocarya chinensis,and Syzygium araiocladum were chosen as the research objects,which are the tropical rain forest tree species in Hainan Island.A dynamic headspace method was used to collect BVOCs released by the three broad-leaved tree species at low,medium and high altitudes in Bawangling National Forest Park during rainy and dry seasons,and the composition of tree species BVOCs were separated and identified by Gas Chromatography-Mass Spectrometry?GC-MS?.Simultaneously,the short-term effect of nitrogen deposition on the release of BVOCs of three tree species was also simulated through a greenhouse test.The main conclusions are as follows:?1?Under natural conditions,at the same altitude,the rates and compositions of BVOCs released by three broad-leaved tree species showed C.chinensis>S.superba>S.araiocladum.For every tree species,the rates and number of BVOCs released at different altitudes all showed medium>high>low.Among them,16,35 and 19 components of C.chinensis were identified at low,medium and high altitudes respectively,and the average emission rate of Total volatile organic compounds?TVOCs?at three altitudes was 14.59?g/g?h,82.78?g/g?h and 43.85?g/g?h.And the BVOCs of S.superba have identified 4,13,and 9 components at three altitudes,the average emission rate of TVOCs was 50.67?g/g?h and 150.56?g/g?h and 61.09?g/g?h.Besides,20 and 9 kinds of volatile components were released from the leaves of S.araiocladum at middle and high altitudes,respectively,and the average emission rate of TVOCs was 44.40?g/g?h and 32.96?g/g?h.The difference between the three tree species BVOCs components was that S.superba and C.chinensis mainly released monoterpenes,such as?-farnesene and myrcene,while S.araiocladum mainly releases sesquiterpenes,with farnesene and muurolene was the representative.?2?Affected by plant growth and enzyme activity,the seasonal changes in the release rate of BVOCs in S.superba,C.chinensis,and S.araiocladum showed that the rainy season was greater than the dry season.And there were also obvious diurnal changes in the TVOCs emission rate of the three tree species,the emission rate of isoprene,monoterpenes,and sesquiterpenes all changed with time as a single peak,peaking at 11:00-13:00,while the emission rate of other VOCs had no obvious diurnal variation.?3?There was a significant correlation between the BVOCs release rate of different tree species and environmental factors.In general,the emission rates of BVOCs of S.superba,C.chinensis,and S.araiocladum in the rainy season were the most significantly correlated with PAR,followed by temperature.In the dry season,S.superba and C.chinensis were mainly affected by transpiration rate and photosynthetic rate,followed by PAR,temperature and stomatal conductance,while the release of BVOCs from S.araiocladum was the most significantly correlated with PAR,followed by transpiration rate,stomatal conductance,temperature,and photosynthesis rate.Also,soil fertility affected the BVOCs emission,especially TN,TP,and p H,which were strongly correlated with isoprene,monoterpenes,sesquiterpenes,and other VOCs.?4?The effect of simulated nitrogen deposition on the BVOCs release rate was related to the nitrogen application level,nitrogen application method,and the tree species.In general,soil application nitrogen?SN?and foliar application nitrogen?FN?both promoted the release of BVOCs from three plant seedlings,and the emission rates and components of TVOCs increased with the increase of nitrogen concentration.However,the tree seedlings responded to the two nitrogen application methods were different.For the same nitrogen concentration,the effect of FN on the BVOCs release rate was significantly higher than that of SN,and it could cause the change of TVOCs composition.Under FN,the level of nitrogen deposition does not reach the plant's nitrogen-saturated system,and the photosynthetic rate and stomatal conductance were positively correlated with the nitrogen application concentration.Thus,plants released BVOCs to adjust their C balance.While under SN,the nitrogen concentration of plant growth was supersaturated or eutrophic,plants resisted nitrogen stress by reducing the photosynthetic rate and closing stomatal conductance.Besides,in terms of the same nitrogen application method and concentration,the sensitivity of the three plant seedlings to nitrogen deposition was as follows:S.superba>C.chinensis>S.araiocladum.?5?The nitrogen application had a significant effect on plant physiological parameters and soil fertility,and the effect varied with tree species.Among physiological parameters,the net photosynthetic rate was most closely related to the release of BVOCs in seedlings,followed by stomatal conductance.Nitrogen application had a significant effect on soil p H,NH₄⁺-N and NO₃^--N,followed by AP and TP,and the effect of FN was more prominent.Among them,different nitrogen concentrations all caused the p H to decrease,especially high nitrogen concentration.The soil available nitrogen?NH₄⁺-N and NO₃^--N?content increased significantly with the increase of nitrogen level.