Response Mechanisms Of The Two Gramineous Forage Grasses Living In The Songnen Plain To Low Nitrogen Stresses

Nitrogen is the most important mineral element in the processes of plant growth,development and reproduction.It is a major constituent of many important compounds,such as amino acids and proteins,nucleotides,nucleic acids,chlorophyll and phytohormones.These compounds are structural or functional components that plant cells depend on for survival.It is generally believed that the nitrogen content in soil is an important factor in determining plant growth and crop yield.In order to increase crop yield,a large amount of nitrogen fertilizer has been applied to the land,causing many environmental problems.Excessive nitrogen application not only increases the global nitrogen deposition,but also increases agricultural input.Therefore,improving the nitrogen use efficiency(NUE)of crops under low nitrogen conditions and developing crop varieties with high nitrogen use efficiency have important practical significance for the sustainable development of ecology and agriculture.In order to improve the nitrogen absorption and utilization efficiency of crops,a more in-depth understanding of the response mechanism of crops to different nitrogen conditions must be deeply understood.Common reed and Chinese leymus,as the two main pastures on Songnen Plain,have been growing in poor soil environment for a long time.They may evolve a unique barren mechanism,especially the mechanism of low nitrogen tolerance.Accordingly,we selected the two species of herbage as experimental materials to study the physiological and biochemical mechanisms of their resistance to low nitrogen conditions.The study on the low nitrogen tolerance mechanism of common reed and Chinese leymus may provide some inspiration for improving the nitrogen use efficiency of crops.In this study,different nitrogen conditions were used to treat common reed and Chinese leymus seedlings under low nitrogen stress through greenhouse control experiments.Several physiological and metabolic parameters were detected,including morphology,growth,photosynthesis,enzyme activities related to nitrogen metabolism,metabonomics and mineral nutrient accumulation.Our results showed that the adaptation mechanisms of common reed and Chinese leymus to low nitrogen conditions were both common and species specific,and the main conclusions were as follows:(1)The characteristics of growth and morphology.Under the low nitrogen condition,the leaf and stem morphology of reed were changed,the growth was inhibited and the biomass decreased significantly.In order to obtain more nutrients,the reed allocated more biomass to the underground part,and the root and crown ratio of reeds increased significantly under low nitrogen conditions.As a nutritive storage organ and an asexual reproductive organ,the rhizome increases the biomass,although it becomes shorter and finer under the low nitrogen condition.However,although the root biomass increased,but the low nitrogen conditions still significantly inhibited the reed asexual reproduction(number).Under the low nitrogen condition,the morphological changes of Chinese leymus were not changed,only the plant diameter changed.However,the biomass allocation of different organs of Chinese leymus has changed significantly,and more biomass is allocated to the underground part to absorb more nutrients.n spite of the increase in rhizome biomass,the low nitrogen condition still significantly inhibited the asexual reproduction of reed.(2)The results of metabonomics.Low nitrogen stress causes the change of leaf metabolism in reed,producing 12 different metabolites,which is of great significance to the adaptation of reed to low nitrogen conditions.(3)The response of carbon and nitrogen metabolism.Under low nitrogen stress,chlorophyll content in leaves of common reed and Chinese leymus decreased,but net photosynthetic rate and chlorophyll fluorescence parameters of Phragmites communis did not change.Net photosynthetic rate of Chinese leymus decreased significantly,indicating that common reed had strong ability of low nitrogen tolerance.Chinese leymus adopted the strategy of maintaining light and area to cope with low nitrogen stress for the decrease of photosynthesis.Under low nitrogen stress,the carbon and nitrogen metabolism of reed and Chinese leymus changed obviously,and the carbon and nitrogen elements were redistributed among the organs.The nitrogen metabolites of reed decreased and carbon metabolites increased.The carbon and nitrogen metabolites of Chinese leymus decreased significantly.In response to low nitrogen stress,reeds and Chinese leymus have different metabolic response mechanisms.(4)Mineral nutrition accumulation.Under low nitrogen stress,the mineral nutrient content of reed and Chinese leymus all changed,and the trend in response to low nitrogen stress was the same.The nitrogen uptake rate of single plant decreased and the nitrogen use efficiency increased greatly.These results prove that all two plants are highly resistant to low nitrogen.The change of mineral nutrition balance may be an important response mechanism for these two species to adapt to low nitrogen conditions.