Effects Of Nitrogen Addition On Volatile Organic Compounds Emission And Microbial Community Of The Two Leaf Litter Species

Biogenic volatile organic compounds（BVOCs）which exists widely in the atmosphere are involved in photochemical reactions,secondary organic aerosol formation and global carbon cycle processes,and have a critical impact on climate change and the global carbon cycle.The studies on BVOCs emission from forest ecosystems mainly focuses on the forest canopy,but the types and amounts of BVOCs released from leaf litter,which are the main source of surface BVOCs,cannot be ignored.Currently,Nitrogen（N）deposition is increasingly aggravating.Nitrogen addition affects composition of microbial community during decomposition of litter,which might further affects the BVOCs emission,but there is lack of studies on how N addition affects the types and quantities of BVOCs emission during decomposition of leaf litter.Exploring the effect of nitrogen addition on BVOCs emission and microbial changes of leaf litter can provide support for the construction and improvement of BVOCs emission from forest surface.In this study,forest leaf litter of Schima superba Gardn.et Champ.（S.superba）and Cunninghamia lanceolata（Lamb.）Hook（C.lanceolata）,two common subtropical tree species,were selected as research objects.Two different nitrogen levels,control（CK）and nitrogen addition（AN）,were set up for each leaf litter with ammonium nitrate as the nitrogen source,to investigate the effects of N addition,leaf litter species and their interaction on the types and amounts of BVOCs released from leaf litter,microbial diversity and community composition and elements and characteristics of leaf litter,and to explore the relationship between the BVOCs emission and microbial community and elements and characteristics of leaf litter.The main findings as follows:1.The leaf litter species significantly affected the flux and accumulative amount of total BVOCs emission.The accumulative amount of total BVOCs emission of S.superba leaf litter was 18.04%higher than that of C.lanceolata leaf litter.While the accumulative amount of total BVOCs emission of S.superba leaf litter was 25.41%higher than that of C.lanceolata leaf litter under N addition treatments.The accumulative amount of aldehydes,ketones,halohydrocarbons,and benzenoids emission of S.superba leaf litter was significantly higher than that of C.lanceolata leaf litter.In addition,N addition significantly inhibited the flux and accumulative amount of total BVOCs emission.Compared to the control,N addition significantly decreased the accumulative amount of total BVOCs emission of S.superba and C.lanceolata leaf litter by 33.16%and 37.09%,respectively.N addition significantly inhibited the accumulative amount of aldehydes,ketones,benzenoids,alkanes,and terpenoids emission from the two leaf litter species.The accumulative carbon amount of total BVOCs emission in S.superba and C.lanceolata leaf litter accounted for 0.34%and 0.47%of the accumulative carbon amount of CO₂emission,respectively.However,under the N addition condition,the accumulative carbon amount of total BVOCs emission in S.superba and C.lanceolata leaf litter accounted for0.19%and 0.20%of the accumulative carbon amount of CO₂emission,respectively.2.Nitrogen addition did not significantly affect bacterial and fungal diversity of the two leaf litter species.The Observed OTUs index,Chao1index and Shannon index of bacteria and fungi involved in the decomposition of S.superba leaf litter were significantly lower than those of C.lanceolata leaf litter.Leaf litter species significantly influenced the composition of bacterial and fungal communities.The relative abundance of Proteobacteria of S.superba leaf litter was significantly higher than that of C.lanceolata leaf litter,while the relative abundance of Actinomycetes and Bacteroidetes of S.superba leaf litter were lower than that of C.lanceolata leaf litter.The relative abundance of Ascomycetes was significantly higher and the abundance of Basidiomycota was significantly lower of S.superba leaf litter compared with that of C.lanceolata leaf litter.Leaf litter species significantly influenced the relative abundances of Penicillium,Lophiostoma,and beltraniella.In addition,N addition significantly affected the composition of bacterial and fungal communities,but did not affect the major bacterial and fungal phyla and genera in the early period of decomposition of the two leaf litter species.Proteobacteria was the main dominant bacterial phylum in the decomposition process of two leaf litter species.As the decomposition time of leaf litter increased,Proteobacteria was gradually replaced by Actinobacteria.3.Nitrogen addition significantly increased the TN contents and ¹⁵N,and decreased C/N of the two leaf litter species.Compared to the control,the differences in TN contents,TOC contents,¹⁵N,and C/N of S.superba and C.lanceolata leaf litter under N addition conditions were more obvious.Correlation analysis showed that total BVOCs and several types of BVOCs emission were negatively correlated with ¹⁵N at different period of leaf litter decomposition.Fungal and bacterial diversity were positively correlated with ¹⁵N at different time of leaf litter decomposition.Various types of BVOCs flux were negatively correlated with bacterial and fungal diversity and communities at different period of leaf litter decomposition.Overall,N addition significantly inhibited BVOCs emission of the two leaf litter species.N addition also significantly affected the composition of bacterial and fungal communities.N addition significantly increased the TN contents and ¹⁵N,and decreased C/N of the two leaf litter species.These results indicates that N addition may affect elements and characteristics of leaf litter,further affect the BVOCs emission.