Combined Effects Of Salt And Nitrogen On The Growth And Reproductive Allocation Of Atriplex Centralasiatica Iljin

At present,the area of saline-alkali land in the world is increasing year by year,especially the salinization of cultivated land is becoming more and more serious.Salt stress has a negative impact on production and makes it difficult to grow sustainably.Our country's attention has been drawn to the problem of soil salinization,as well as the concerns of human society.Nitrogen is the main component of many important organic nitrogen compounds(phospholipids,proteins and nucleic acids)in plants,and it participates in the nutrient accumulation of plants growth and reproduction.A large number of studies have demonstrated that artificial application of nitrogen can effectively regulate plants growth when plants are under stress.Seed polymorphism refers to the production of two or more seeds that differ greatly in morphological structure,physiology and ecological characteristics on the same plant.Atriplex centralasiatica Iljin is a recretohalophyte belong to the Amaranthaceae family,which can excrete excess salt from the body through salt vesicles.Nitrogen and salinity not only affect plants growth,but rising nitrogen deposition and soil salinization have a significant impact on individual plants survival and ecosystem stability.The effects of nitrogen on the physiological,biochemistry,photosynthetic and fruit-set pattern of halophytes with polymorphic seeds are rarely reported.In this study,the differences in physiological,biochemical,photosynthetic capacity,fruit-set pattern and reproductive allocation of plants germinated from seeds of A.centralasiatica with different levels of nitrogen under salt stress(salt-nitrogen interaction)were systematically analyzed,and the differences in dimorphic seeds of A.centralasiatica and the effects of salt-nitrogen interaction on the growth and reproductive allocation of A.centralasiatica were investigated.The results of this paper are as follows:1.Analysis of different morphological characteristics of dimorphic seeds of A.centralasiatica.The seed coat color of brown seeds of A.centralasiatica were yellowish brown,and the seed coat color of black seeds were dark brown.The length,width,two-dimensional area and thousand-grain weight of the black seeds of A.centralasiatica were significantly smaller than the brown seeds.2.Effects of salt-nitrogen interaction on the growth of seedlings germinated from dimorphic seeds of A.centralasiatica.The plant height,dry and fresh weight and other growth indicators of A.centralasiatica were increased when plants treated with 1 mmol/L Na Cl and 8 mmol/L nitrogen,and 200mmol/L Na Cl and 4 mmol/L nitrogen,as well as the increased chlorophyll content(related to photosynthesis),K⁺content and K⁺/Na⁺in the leaves,decreased Na⁺and Cl^-content("K⁺preservation and Na⁺and Cl^-exclusion"to ensure osmotic balance),lower relative conductivity in the leaves and malondialdehyde(MDA)content(less damage to the membrane system),higher proline content(increased plants resistance to osmotic stress),higher superoxide dismutase(SOD)activity(stronger ability to scavenge reactive oxygen species),higher NO₃^-content in the leaves,total nitrogen content in the leaves,and nitrate reductase activity(NRA)(more"nitrogen sources"absorbed and utilized),the density of salt vesicles increased,and the degree of rupture of salt vesicles increased(more favorable for salt discharge).It was shown that the growth of A.centralasiatica was inhibited when plants treated with 200 mmol/L Na Cl.In addition,the seedlings germinated from the brown seeds of A.centralasiatica grew better,and had better resistance to salt stress than those from the black ones,probably because the brown seeds were larger,had larger embryos and more nutrients in the endosperm,which provided more nutrients for the early germination of plants.The study of the photosynthetic gas exchange parameters,actual PS? photochemical efficiency(?PS?),the maximal photochemical efficiency(Fv/Fm),photochemical quenching(q P),photosynthetic nitrogen use efficiency revealed that the decrease of the photosynthetic capacity of A.centralasiatica under nitrogen and salt treatments was mainly due to non-stomatal limitation factors.Pn,utilization efficiency of light energy,and photosynthetic nitrogen use efficiency of A.centralasiatica were highest at the condition of 1 mmol/L Na Cl and 8 mmol/L nitrogen treatment,the Pn,utilization efficiency of light energy,and photosynthetic nitrogen use efficiency were highest when treated with 200 mmol/L Na Cl and4 mmol/L nitrogen,but there was a certain inhibition at the condition of 200 mmol/L Na Cl and8 mmol/L nitrogen treatment,which indicated that the light energy absorbed by plants is not effectively used.Under the treatment of 1 mmol/L Na Cl and 8 mmol/L nitrogen,200 mmol/L Na Cl and 4 mmol/L nitrogen,the photosynthetic rate of plants could maintain at a high level,because the inhibitory effect on OEC was reduced and the number of response centers and the size of the PQ pool were increased to enhance the absorption of light energy,the number of inactivated reaction centers was reduced and the openness of the reaction centers was increased,the energy used in electron transfer was also increased,and the energy used in heat dissipation was reduced,PI_ABS and D.F.were increased.The experiment found that A.centralasiatica germinated from brown seeds had better photosynthetic indicators than those from black seeds.This is also the reason why the plants germinated from brown seeds grew better than the plants germinated from black seeds.3.Effects of salt-nitrogen interaction on fruit-set pattern and reproductive allocation of plants germinated from dimorphic seeds of A.centralasiatica.The size and thickness of seed bracts were altered by different salt and nitrogen treatments.Compared with the brown seeds,plants germinated from black seeds with less resistance to stress,and their progeny had thicker bracts when treated with 200 mmol/L Na Cl.With the treatment of 1 mmol/L Na Cl,the number of seeds,reproductive allocation,the number of branches and the length of branches,etc.of A.centralasiatica showed increased trends with the increase of nitrogen concentration,indicating that the reproductive growth of plants germinated from brown and black seeds was promoted by applying nitrogen at 1mmol/L Na Cl.When treated with 200 mmol/L Na Cl,most of the above indicators reached the maximum at the condition of 4 mmol/L nitrogen,indicating that the reproductive growth of A.centralasiatica did not require too high concentration of nitrogen.When treated with 0.3mmol/L nitrogen,no secondary branches were formed in A.centralasiatica,indicating that too low nitrogen concentration will inhibit the vegetative growth,and further reduce the number of fruits(seeds)and inhibit the reproductive growth of A.centralasiatica.