Influence Of Nitrogen Fertilizer Application On Foliar Soluble Nutrients And Functional Components Of Tea Seedlings With Tea Aphid Infestation

Tea(Camellia sinensis L.),a woody perennial plant native to China and Southeast Asia,has a 30-50 years’ lifespan.Nitrogen(N)fertilizer is of paramount importance to tea plant growth which directly stimulate the changes in foliar soluble nutrients and functional components,and volatile organic compounds(VOCs)etc.and are used in commercial tea plantations to increase the tea yield.Also,the influence of N-fertilizer application on insect pests and the interactions with their host plants directly stimulate many significant responses upon the physiological and quality parameters of tea plants.The tea aphid,Toxoptera aurantii(Boyer De Fonscolombe)is a polyphagous insect pest predominant in tea orchards and has become the most pernicious pest deteriorating tea quality.In this study,the tea plants(cv.)were applied with normal N-fertilizer(NL)along with reduced N-fertilizers(70% NL and 50% NL)and were inoculated with and without tea aphid,T.aurantii,and we attempted to analyze the effects of N-fertilizer application on tea plant physiological and functional parameters,including key genes involved in the bio-synthetic pathways,and also the tea quality parameters altered by the insect pests’ damage and especially tea aphids’ infestation.The results are given below:ⅰ)The results showed that N-fertilizer application significantly affected plant biomass,root-shoot ratio and photosynthetic indexes(Pn,Gs,Ci & Tr),foliar soluble nutrients(soluble sugars,soluble proteins,free fatty acids)of tea seedlings(P≤0.05).Compared with the normal N-fertilizer level(NL),the reduced N-fertilizer application(70%NL and 50%NL)significantly decreased all the foliar soluble nutrients of tea seedlings without aphid infestation,while concomitantly increased in tea seedlings with aphid infestation.Moreover,the photosynthetic indexes(Pn,Gs,Ci,Tr)were significantly higher in the normal Nfertilizer level than those in the reduced fertilizer level for tea seedlings with and without aphid infestation.The same trend was seen in the biomass of root and shoot.and root-shoot ratio.ⅱ)N-fertilizer application significantly affected foliar functional components(including total polyphenols,catechins,caffeine,essential amino acids and theanine)of tea seedlings(P≤0.001).Compared with the normal N-fertilizer level(NL),the reduced N-fertilizer levels(70%NL and 50%NL)significantly decreased all the foliar functional components of tea seedlings without aphid infestation,while significantly increased in tea seedlings with aphid infestation.Moreover,the transcript expression levels of foliar functional genes(including Cs TCS,Cs TS1,Cs GT1,and Cs MYB75)was significantly higher in the 70%NL,and significantly lower in the 50%NL for tea seedlings with and without aphid infestation,while it showed just the opposite tendency for Cs GT1.ⅲ)N-fertilizer application remarkably affected plant volatile organic compounds(VOCs)of tea seedlings,and the population dynamics of tea aphid,T.aurantii(P≤0.05).Compared with the normal N-fertilizer level(NL),the reduced N-fertilizer levels(70%NLand 50%NL)significantly decreased the percentage concentration of plant VOCs of tea seedlings without aphid infestation,while concomitantly increased in tea seedlings with aphid infestation.Moreover,the population abundance of T.aurantii in the NL treatment was higher than the reduced N-fertilizer levels(50% NL and 70% NL).The results vividly stated that the reduced N-fertilizer application could enhance plant VOCs of tea seedlings especially with T.aurantii infestation and its population dynamics also diminished in the reduced fertilizer levels which can ameliorate pesticide use for control of tea aphid infestation in tea plantations.In conclusion,the results vividly stated that the reduced N-fertilizer application could enhance tea quality parameters of plant chemicals(including foliar soluble nutrients and functional components,and plant VOCs)of tea seedlings especially with T.aurantii infestation,which can relieve soil nitrogen pollution pressure and reduce pesticide use for control of tea aphid infestation in tea plantations.