Effects Of Nitrogen Levels On Seed Yield Formation And Physiological Characteristics Of Leymus Chinensis In Horqin Sandy Land

From 2018 to 2019,in the Agricultural Science and Technology Park of Inner Mongolia University for Nationalities in Tongliao City,Inner Mongolia Autonomous Region,in order to determine the appropriate nitrogen application rate for the formation of Leymus chinensis seed production in the Horqin Sandy land,it was proposed that topdressing nitrogen fertilizer promotes the photosynthetic characteristics,fluorescence characteristics,and fluorescence characteristics of Leymus chinensis seed production.Physiological mechanism of nitrogen metabolism.The artificially established Leymus chinensis grassland in 2015 was treated with different nitrogen application rates for two consecutive years,and five nitrogen application levels were set at 0,100,200,300,and400 kg·hm^-2.（Respectively denoted by N₀,N₁,N₂,N₃,N₄）,the artificial nitrogen fertilizer is applied on April 20（tillering period）and July 20（fruit setting period）of each year,To study the effects of topdressing nitrogen fertilizer on seed yield and seed yield component factors,photosynthetic characteristics,chlorophyll fluorescence characteristics,key enzyme activities of nitrogen metabolism,and accumulation and distribution of dry matter and nitrogen content in different organs,and determine suitable Leymus chinensis seeds by statistical methods The nitrogen level formed by yield and the physiological and growth mechanism for increasing seed yield are expected to provide theoretical and practical basis for seed production of Leymus chinensis.The main research results are as follows:In 2018 and 2019,two consecutive years of different nitrogen application levels had a significant impact on the seed yield of Leymus chinensis.With the increase of nitrogen application,the seed yield and yield components first increased and then decreased;The seed yield reached the maximum when the nitrogen application rate was 200 kg·hm^-2,which were 212.5 kg·hm^-2and 236.2 kg·hm^-2respectively,which were significantly higher than the control,so the nitrogen application rate was 200 kg·hm^-2o’clock is beneficial to the formation of Leymus chinensis seed yield,The seed yield of Leymus chinensis was positively correlated with the number of grains per ear,thousand-grain weight,number of spikelets,and ear length（2018,P<0.05）and extremely significant（2019,P<0.01）;The plant height,stem thickness and leaf area of Leymus chinensis increased significantly with the increase of nitrogen application rate,thereby increasing the dry matter accumulation of Leymus chinensis.The seed yield and reproductive branch height,stem thickness and leaf area of Leymus chinensis were significant（2018,P<0.05）or extremely significant（P<0.01in 2019）positive correlation,indicating that the seed yield of Leymus chinensis is affected by yield traits such as ear length,number of spikelets,number of grains per ear,and thousand-grain weight.Chlorophyll content,stomatal conductance（Gs）,transpiration rate（Tr）,net photosynthetic rate（Pn）,and minimum fluorescence intensity（F0）of the upper leaves（flag leaves and first two leaves）and lower leaves（first three leaves）of Leymus chinensis,The maximum fluorescence（Fm）and the maximum light energy conversion efficiency（Fv/m）of PSII reach the maximum when the nitrogen application rate is 300 kg·hm^-2,so the photosynthesis capacity increases first with the increase of the nitrogen application rate However,the non-photochemical quenching coefficient（NPQ）and intercellular CO₂concentration（Ci）show a trend of first decreasing and then increasing with the increase of nitrogen application rate,so too high nitrogen content will affect the normal leaf The photosynthetic rate.Leymus chinensis leaves glutamate pyruvate transaminase（GPT）,glutamate oxaloacetate transaminase（GOT）,glutamine synthetase（GS）,nitrate reductase（NR）activity and free amino acid（AA）,soluble protein content（SP）and significantly increased.When the nitrogen application rate is 300 kg·hm^-2,the enzyme activities of GPT,GOT,NR and GS are the strongest,which is conducive to the nitrogen metabolism of Leymus chinensis;however,the content of Leymus chinensis soluble protein（SP）and The content of free amino acids（AA）reached the maximum when the nitrogen application rate was200 kg·hm^-2.The distribution ratio of dry matter accumulation in each organ of Leymus chinensis is stem>leaf>ear,and the fresh weight,dry weight and dry-to-fresh ratio of different organs reach the maximum when the nitrogen application rate is 200 kg·hm^-2.Leymus chinensis has the best dry matter accumulation.Nitrogen accumulation in different organs of Leymus chinensis first increased and then decreased with the increase in nitrogen application rate,but the distribution ratio of nitrogen accumulation in different organs was leaf>ear>stem,when the nitrogen application rate was 200 kg·hm^-2,The accumulation of nitrogen in different organs of Leymus chinensis reaches its maximum value.At this time,Leymus chinensis has the fullest utilization of nitrogen fertilizer and the highest efficiency.