Effects Of Soil Warming And Nitrogen Deposition On The Fluxes And Composition Of Root Exudates In Cunninghamia Lanceolata Seedlings

According to the fifth assessment report of the International Commission on Climate Change(IPCC),the global warming of the earth s surface is expected to increase by 0.3-4.8℃ at the end of this century.The impact of global warming on the aboveground and underground processes of forest ecosystems cannot be ignored.With the increase in population,the burning of fossil fuels,and the use of chemical fertilizers,the nitrogen compounds released into the atmosphere continue to rise.It is expected that by the end of the 21st century,the global rate of nitrogen deposition will increase by 2～3 times.The study considers that the subtropical region of China is a region with severe nitrogen deposition.Therefore,it is of great significance to study the effects of soil warming and nitrogen deposition on forest ecosystems in maintaining ecosystem productivity and carbon sinks in forest ecosystems.To reveal the quantitative and chemical composition of Cunninghamia lanceolata fine root exudates in response to global warming and nitrogen deposition and factors affecting the rate of fine root exudation.In this study,two-factor experiments of soil temperature increase and nitrogen deposition of Cunninghamia lanceolata seedlings were carried out at Chenda observation site of the Sanming Forest Ecosystem and Global Change Research Station in Fujian Province,including control(CT),soil warming(W,4℃),and nitrogen deposition(N,40 kg N hm-2·a-1)and soil temperature increase+nitrogen deposition(WN)treatments.The in situ collection method was used to study the effects of different treatments on the exudation rate,annual flux and secretion metabolomics of Cunninghamia lanceolata,and analyzed from the aspects of soil nutrients,fine root physio-ecological characteristics,growth of Cunninghamia lanceolata,and physiological and ecological characteristics of leaves.Fine root exudation rate influencing factors.The results show:(1)Increasing temperature significantly reduced root exudation rates I(μg C g-1 root biomass h-1),Ⅱ(μg C cm-1root length h-1)Ⅲ(μg C cm-2 root area h-1).Total root exudation were also decreased significantly in warming treatments.The root exudation rate was higher in July and August,but the lowest concentration was in February and March.In winter and spring,the secretion rates Ⅰ,Ⅱ and Ⅲ were significantly lower than those in summer and autumn.Nitrogen deposition,interaction of warming and nitrogen deposition treatments all significantly reduced root excretion rate.Compared with CT,the annual fluxes of the secretions of W treatment and N treatment were significantly reduced.(2)Analysis of the metabolic components of fine root exudates,compared with controls,warming causes amino acids such as L-theanine in root exudates to increase significantly.Some phenols and flavonoids also increased significantly after warming.Compared with the control,nitrogen deposition treatment of Chinese fir root secretions of fatty acids and their derivatives increased significantly.The lipid content in the warming treatment was significantly increased.This may be due to the decreased water availability of the fine roots at increased temperature and the secretion of more lipids to withstand the arid environment.Nitrogen deposition treatment has a significant increase in organic acids such as malic acid compared to control,warming treatments because in the nitrogen settling process,roots secrete organic acids to activate more phosphorus.Compared with the control,the argininosuccinic acid decreased in warming treatment and nitrogen deposition treatment.Compared with the control,the phenol and flavonoids content of nitrogen deposition treatment and interaction of warming and nitrogen deposition treatment,and nitrogen deposition increased significantly,such as sidaryl alcohol,which was related to the production of phenols in Chinese fir and its adjacent plants.(3)Warming,the interaction of warming and nitrogen deposition can significantly increase the tree height.In summer and autumn,the tree height grows slower than in spring.Overall,it is the longest and fastest in spring.(4)Warming had significant effects on N,P,C/N and N/P of Chinese fir leaves.Warming treatment and interaction of warming and nitrogen deposition treatment had significant effects on the N content and N/P of Chinese fir leaves in winter and spring.(5)The mixed linear analysis model showed that there was a significant negative correlation between N content and root exudation rate in Chinese fir leaves,which may be related to the increase of soil N availability and the decrease of C distribution to root exudates.There was also a significant negative correlation between tree height and root exudation rate,which may be related to the relative increase in C aboveground distribution due to increased ground growth.There was a significant positive correlation between root length and root exudation rate,indicating that fine root morphological changes also regulate the secretion of root exudates.Warming and nitrogen deposition reduced the exudation rate of fine roots and the annual flux of secretions.Warming and nitrogen deposition had a significant interaction with the fine root exudation rate and the annual flux of secretions.The chemical composition of fine root exudates such as fatty acids and their derivatives,increased sugars are conducive to fine root absorption of nutrients;increased temperature and nitrogen concentration of fine roots,free nitrogen is stored as amino acids,the amino acids in fine roots increase;Roots in order to compete for nutrients secrete flavonoids for the production of neighboring plants;after nitrogen application,fine roots secrete organic acids to activate more phosphorus.There was a significant negative correlation between N content,tree height growth and fine root exudation rate of Cunninghamia lanceolata leaves,and there was a significant positive correlation between root length and fine root exudation rate.In the subtropics,conducted warming experiments to study the quantity and chemical composition of fine root exudates of Chinese fir,in order to gain a deeper understanding of the contribution of fine root exudates to subsurface carbon input and soil carbon and nitrogen cycling in the context of global warming,and climate-carbon cycle feedback has important scientific value.