Analysis On The Seed Germination And Seedling Salt Resistance Of Polymorphic Seeds Of Atriplex Centralasiatica Iljin

At present,soil salinization in the world is still increasing.China also has a large area of saline-alkali soil of about 9913×10~4 hm2.It is a good biological method to gradually ameliorate saline-alkali land by planting halophytes.Atriplex centralasiatica Iljin is a salt-secretion plant of the Atriplex in the family Amaranthaceae(formerly Chenopodiaceae,now classified into the family Amaranthaceae).It belongs to the class I halophyte and is also one of the most important annual herbal economic halophytes.Seed polymorphism is a special reproduction strategy developed by many annual plants in the face of unfavorable environment conditions.Seeds of A.centralasiatica are divided into 4 morphic types according to the type of dispersing units and the color of their seed coats.We call them flat-brown,flat-black,humped-brown,humped-black.In this paper,A.centralasiatica was used as a material to study the germination characteristics and its changes on germination factors,salt resistance at seedling stage,differences in photosynthetic capacity,physiological mechanisms,fruit and seed-set patten and reproductive allocation of A.centralasiatica polymorphic seeds under NaCl treatment,to deeply understand the differences in salt tolerance of A.centralasiatica polymorphic seeds,and to provide effective theoretical and practical basis for further exploration of the adaptation strategies of A.centralasiatica.The results are as follows:1.Analysis on the difference of seed size,proportion and morphological characteristics of Atriplex centralasiaticaThe bracteoles of A.centralasiatica have two types,flat and humped,while the seeds have two colors,brown and black.That is,the polymorphic seeds of A.centralasiatica can be divided into four types:flat-brown,flat-black,humped-brown and humped-black.There is no significant difference in the size and weight of seeds of the same color.The morphology and structure of the seeds with brown seed coats and those with black seed coats are different:The seed coats of brown seeds are relatively thin,soft,non-glossy,and larger than black seeds;the black seed coats are thick,hard,and shiny.In terms of the number of seeds,most of the flat bracteoles contain brown seeds,while most of the humped bracteoles contain black seeds.The100-seed weight of brown seeds is heavier than that of black seeds,probably because the brown seeds are relatively large.2.Effect of different treatment on germination period of polymorphic seeds of Atriplex centralasiaticaThe effect of different NaCl concentrations on the germination of A.centralasiatica polymorphic seeds was investigated.The results showed that with the increase of NaCl concentration,the germination status of four types of A.centralasiatica would become worse and worse.With 0 NaCl treatment,the seed germination was the best,and almost all of them germinated,which indicated that NaCl stress would affect the germination of seeds.The germination of the seeds when the bracteoles were removed was significantly better than those without being removed,indicating that in addition to NaCl stress,the dispersing units of A.centralasiatica,the two types of bracteoles,can also inhibit the germination of seeds.In particular,the black seed bracteoles have a stronger inhibitory effect,but what exactly is in the bracteoles that inhibits germination still needs our in-depth investigation.Compared with the four types of A.centralasiatica,there is no significant difference in germination status of seeds with the same seed coat color.Compared with black seeds,brown seeds have a higher germination rate,germination potential,germination index.Brown seeds germinate more quickly than black seeds.3.Effect of different concentrations of NaCl treatment at seedling stage on the growth of polymorphic seeds of Atriplex centralasiaticaThis part of experiment mainly studied the growth response of four types of seedings of A.centralasiatica under NaCl treatment.There was no significant difference in the growth of plants with the same color seeds.The growth of four types of seedlings was the best when treated with 200 mM NaCl and the worst when treated with 400 mM NaCl,which indicated that low salt treatment could promote the growth of seedlings while high salt treatment inhibit it.The plant height and dry/fresh weight of A.centralasiatica seedlings increased at first and then decreased with the increase of NaCl concentration.Under the same NaCl concentration treatment,the biomass of brown seed seedlings was much larger than that of black seedlings,which was also related to the large size and fast germination of brown seeds.The number and volume of salt vesicles were positively correlated with the concentration of NaCl.With the increase of salt concentration,all the indexes of photosynthetic showed a trend of rising at first and then decreasing.The photosynthesis of seedlings with brown coat was slightly higher than that from black coat seeds.There was a negative correlation between the concentration of NaCl and the ratio of K~+/Na~+in the leaves of four kinds of seedlings.The K~+content in the leaves of brown seedlings was higher than that of black seedlings,while the Na~+content of brown seedlings was lower than that of black seedlings.The chlorophyll content,SOD enzyme activity,and soluble protein content of the plants were highest when treated with 200 mM NaCl,and decreased when treated with 400 mM NaCl.Both cell membrane permeability and leaf MDA content increased with the increasing salt concentration,and membrane damage increased.The results showed that brown seed seedlings had slightly higher salt tolerance than black seed seedlings.The optimal concentration of NaCl solution for the growth of four kinds of seedlings is 200 mM,and 400 mM NaCl concentration will inhibit to various degrees.4.Effect of different NaCl concentrations on reproductive growth of polymorphic seeds of Atriplex centralasiaticaThe effect of different concentrations of NaCl on reproductive allocation,seed number,branch number and node number of the whole plant,flat and humped seed number,fruit and seed distribution on primary and secondary branches of four plants of A.centralasiatica was studied.The results show that NaCl can significantly increase the reproductive allocation of A.centralasiatica,and increase the number of seeds in the whole plant and the number of seeds on each node of the branches at all levels.With the increase of NaCl concentration,the number of secondary branches of A.centralasiatica will decrease significantly,and the number of primary branches will not change significantly.Therefore,more resources will be allocated to the primary branches to make more fruits and seeds for propagating offspring.The branches of each level,the number of flat/humped bracteoles seeds and the number of brown and black seeds on each node also increased significantly.In the experiment,the number of flat bracteoles seeds was significantly higher than that of humped bracteoles,and the number of brown seeds was significantly higher than that of black seeds.This fruit-set pattern and reproductive allocation strategy will help A.centralasiatica to successfully settle in various unhealthy habitats,and it will improve the adaptability and viability of A.centralasiatica in saline environments.