| In order to study the nitrogen management rule of greenhouse tomato under high temperature stress,a comprehensive experiment of high temperature and nitrogen application rate was conducted in the Venlo greenhouse of NUIST.Four temperature levels(T1(25?/15?,CK),T2(30? /20?),T3(35? /25?)and T4(40? /30?)were set up,namely,no nitrogen N1,0.5 times recommended fertilization N2(1.3 g·plant-1),0.75 times recommended fertilization N3(1.95 g·plant-1),normal recommended fertilization N4(2.6g·plant-1,CK),1.25 times recommended fertilization N5(3.75 g·plant-1).After the potted tomato plants began to absorb fertilizer,the high temperature test was carried out in the climate box with different temperature treatment.After 7 days of high temperature treatment,the tomato plants were moved to the Venlo type experimental greenhouse at normal temperature for continuous cultivation.From the second day,the plant biomass and nitrogen content of each organ were systematically measured by periodic destructive sampling.In this study,we systematically investigated the photosynthetic characteristics,growth characteristics,nitrogen absorption and metabolism characteristics of tomato plants under different high temperature/nitrogen application rates,and established the critical nitrogen concentration dilution model and nitrogen nutrition diagnosis model under different temperature treatments.The results are as follows:(1)With the increase of high temperature stress,the fluorescence value,fluorescence parameters and PSII reaction center activity parameters of tomato leaves gradually decreased,and the nitrogen demand of tomato plants gradually decreased.The variable fluorescence FV and the maximum photochemical efficiency Fv/FM of tomato leaves showed a law of first increasing and then decreasing with the increase of nitrogen application rate.The ASC/RC value,ETO/RC value and DIO/RC value of N1 treatment were gradually higher than those of other 4 treatments nitrogen treatments.(2)With the increase of high temperature stress,the changes of plant height and stem diameter were similar,and gradually decreased,and the change range of stem diameter was smaller than that of plant height;the demand of nitrogen for tomato plants decreased,the dry matter accumulation decreased,and the accumulation rate became slower,and the dry matter accumulation under low nitrogen treatment was higher than that under high nitrogen treatment;the dry matter distribution proportion of leaves decreased,and the dry matter proportion of stems increased,The difference of dry matter accumulation and dry matter distribution ratio among different nitrogen treatments decreased.In T1 and T2 treatments,the root activity of tomato increased with the increase of nitrogen application rate,while in T3 and T4 treatments,the root activity of tomato increased first and then decreased with the increase of nitrogen application rate.(3)With the growth of tomato plants,the nitrogen content of all treatments decreased gradually,reflecting the phenomenon of nitrogen dilution.In a certain temperature range,increasing temperature can increase the soluble protein content of tomato leaves,thus promoting the nitrogen metabolism of tomato plants.Under high temperature stress,with the increase of high temperature stress,the soluble protein content of tomato leaves under five nitrogen treatments decreased significantly,which indicated that the nitrogen metabolism level of tomato plants was seriously inhibited under severe high temperature stress.With the increase of sampling days,the activities of NR,GS and GOGAT increased in all treatments.Under normal temperature treatment T1 and mild high temperature treatment T2,NR,GS and GOGAT activities increased with the increase of nitrogen application.Under moderate high temperature stress T3 and severe high temperature stress T4,the nitrogen demand of tomato plants decreased.Excessive nitrogen application would significantly reduce NR,GS and GOGAT activities.(4)The relationship between critical nitrogen concentration and aboveground biomass of greenhouse tomato was in accordance with power exponent,that is: Nc=a·DM-b,where T1:Nc= 4.167DM-0.252;T2:Nc= 4.689DM-0.375;T3:Nc= 3.287DM-0.353;T4:Nc=3.812DM-0.403.With the aggravation of high temperature stress,the critical nitrogen concentration of tomato first increased and then decreased;with the increase of nitrogen application rate,the plant nutrition index(NNI)increased under each temperature treatment,and with the extension of treatment time,the plant nutrition index generally decreased.In conclusion,with the aggravation of high temperature stress,the amount of nitrogen applied to tomato plants gradually decreased.Appropriate nitrogen application can alleviate the damage of high temperature stress on tomato plants and enhance the stress resistance of tomato plants.Excessive nitrogen application will aggravate the damage of tomato plants.The results showed that the suitable nitrogen application rates of treatment T1-T4 were 2.6,2.6,1.95 and 1.3 g · plant-1,respectively. |
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