Effects Of Nitrogen Application On Tea Plant-Pest-Natural Enemy

Nitrogen is one of important and necessary nutritional elements for growth and development of tea plants and arthropods.The excessive application of nitrogen fertilizer was considered as one of key factors of rampancy of pest herbivores.But little was known about the effects of nitrogen aplication on herbivores.In this thesis, the effects of different rates of nitrogen application on growth,productivity and physiology of Oolong tea plant Camellia sinensis,ecological fitness of green leafhopper Empoasca vitis Gothe and tea aphid Toxoptera aurantii Boyer,as well as predation of Erigonidium graminicolum Sundevall werestudied.The experiment was conducted in a greenhouse with daily mean temperature of 25℃,70-80%RH and L:D=12:12,at Fujian Agriculture and Forestry University,by varying nitrogen application rates(0.00,0.50,1.00,1.50,2.00,and 2.50 g N·pot^-1).1.Productivity and physiologcal responses of tea plants to different rates of nitrogen applicationThe biomass of young shoots,biomass of roots,total biomass and yield of young tea plants decreased significantly with nitrogen application rate increasing,indicating that the young plants require lower intake and application of nitrogen.The contents of tissue nitrogen,total free amino acids,tea polyphenols,caffeine and Chlorophyll of young shoots increased significantly as the rate of nitrogen application increased.The contents of total free amino acids,caffeine and Chlorophyll of young shoots increased significantly with tissue nitrogen concentration increasing, but the content of total sugars reduced with excessive nitrogen application or high tissue nitrogen concentration of young shoots.These results might result from that more carbon resources were allocated to nitrogen metabolism with increasing nitrogen application,promoting the accumulations of free amino acids,caffeine and Chlorophyll and reducing the accumulation of carbohydrate.The biomass of young shoots was significantly,negatively correlated with the contents of nitrate nitrogen of roots and total free amino acids of young shoots.The biomass of roots was significantly,negatively correlated with the ratio of carbon to nitrogen of roots and caffeine concentration of young shoots.Shoot biomass and total biomass of tea plant were significantly,positively correlated with tissue nitrogen concentration of roots,but were negatively correlated with nitrate nitrogen concentration of roots and the content of total free amino acids of young shoots.The results suggested that the productivity reduction of tea plants with excessive nitrogen application might result from increased total free amino metabolism and decreased carbon-compounds(e.g.,total sugar).2.Ecological fitness of green leafhopper and tea aphid against the rate of nitrogen applicationAdult leafhopper preferred moderate nitrogen fertilized host,but the nymphae were unable to distinguish different tissue N concents of young shoots.There was a significantly difference among leafhopper feeding positions,usually they feeding on 3rd to 6th leaves.Adult oviposition were also unable to distinguish different tissue N concents.Nitrogen application could prolong the egg period of leafhopper;different nitrogen application rates had strong effects on 2^nd- and 3^rd-instar nymph period of leafhopper,and then impacted the whole nymph period.Based on laboratory population life table of leafhopper against the rates of nitrogen application,we found that,except 1.50 g/pot nitrogen application,net reproduction rate(R₀)of leafhopper was the lowest;the R₀ trend increased at first and subsequently decreased as the rate nitrogen application increased.In reverse,average generation period(T)decreased and then increased.Innate capacity of increase(r_m)and finite rate of natural increase(λ) had no obvious difference between 0.14-0.20 and 1.15-1.22,respectively.Green leafhopper had high death rate in nymphae stage,its survival curves was C style.The effects of different rates of nitrogen applications on the nymph state, fecundity,surival rate and weight of each of 3 continuous generations of tea aphid were different.The life time of adult aphid enhanced with nitrogen application increased.The survival curve of tea aphid was B style,survival rates increased with nitrogen application.Based on the laboratory population life table of tea aphid against the rates of nitrogen application,we found that R₀ and T generally increased with nitrogen application increasing,r_m andλtrends also increased at first and subsequently decreased as S style curve with nitrogen application increasing;I of all 3 generation was more than 1,then the population of aphid obviously increased.Partial correlation analysis between physiological factors of tea plants and the characteristics(including growth,development and survival)of Empoasca vitis and Toxoptera aurantii indicated that nitrogen played a significant part in physiological characteristics of tea plants.But,it also showed that it was difficult to assess the effects of nitrogen to the two pests with a few physiologica indexes of tea plants. Biological and ecological changes of pests induced by host quality were a complex process.3.Spider predation against the rates of nitrogen applicationAverage predation rate of spider Erigonidium graminicolum Sundevall to green leafhopper had no relation to the rate of nitrogen application;but to tea aphid,it had a quadratic relation to the rate of nitrogen application.The most predation to tea aphids occured on tea plant with moderate nitrogen application,excessive nitrogen application decreased spider predation to tea aphids.