Research On Seed Development, Dormancy Characters And The Relations To Salt-alkaline Tolerance Of Leymus Chinensis From Songnen Grassland

Leymus chinensis （Trin.） Tzvel. is a perennial rhizomatous high quality species of thefamily Poaceae. It not only has high forage value and good palatability, but also has greattolerant to drought conditions, cold extremes and salt-alkaline conditions. This plant is adominant grass species in Songnen Plain of Northern China, and also an ideal grass forrangeland use in arid and semiarid regions. In recent years, with the development of animalhusbandry and the intensified efforts on ecological environment, artificial grasslands of L.chinensis were constantly built. Therefore, the request on the quantity and quality of L.chinensis seeds was also more and more high. In this paper, we investigated seed development,dormancy characters and salt-alkaline tolerance of Leymus chinensis. On the one hand, weclearly determined the optimum seed harvest time of this species, and provided scientificbasis for agricultural production and high quality seed harvest. On the other hand, weexcavated seed germinating potential, deeply analysed the stresses tolerance mechanism, andprovided theoretical basis for the utilization rate and breeding the new varieties of Leymuschinensis. The main results and conclusions from our experiments were as follows:（1） The results of seed development of Leymus chinensis showed that, seed colorchanged from green to light green, yellow and heavy brown into the final along with seedmaturity.1000seeds weight increased constantly, and reached hightest at33days after peakanthesis. However, water content and electric conductivity of the seeds showed a decliningtrend, water content reached lowest at36days after peak anthesis, and the values of electricconductivity of two experimental years were different, which reached minimum at27and30days after peak anthesis, respectively. The results of standard germination test showed thatgermination percentage was highest at39days after peak anthesis. At this time, germinationstarting days,50%germination days and germination energy were all reached the optimalvalue. Although slightly difference was found between standard germination test andaccelerated aging test, seeds at39days after peak anthesis also had the strongest anti-agingcapability. Above results showed that seeds at39days after peak anthesis has the hightestvigor and best quality, and is the optimum seed harvest time of Leymus chinensis.（2） Response to burial depth and salt-alkaline stress of Leymus chinensis seeds atdifferent maturation time were also greatly differed. The ability of seedling emergence andgrowth were decreased with increasing burial depth, and1cm was the most suitable plantingdepth. At this time, the seedling emergence rate was highest, time to seedling emergence wasshortest, and the length and biomass of the shoot and root were also highest. In addition, theability of seedling growth of the seeds at different maturation time was also different. Seeds at 39days after peak anthesis had the highest vigor, the above index of seedling growth wereoptimum. Germination percentage and energy were significantly affected by seed maturationtime, salt-alkaline stress and their interactions. Highest germination percentage andgermination energy were occurred at at39days after peak anthesis, especially at highest salinrstress （400mM）. The recovery test showed that recovery percentage was also highest at39days after peak anthesis. Above results show that although seed of different maturation timehas germination ability, the ability of seedling emergence and resistance to salt-alkaline stressis highest at39days after peak anthesis, which further support the view that39days afterpeak anthesis is the optimum seed harvest time of Leymus chinensis. In addition, shallowsowing is suitable for Leymus chinensis, and1cm is the most optimum planting depth.（3） Artificial treatments can obviously break the seed dormancy of L. chinensis. Theresults showed that many methods such as H2SO4, cold stratification, PEG, GA₃, KNO₃andsoaking in the water all enhanced germination percentage, germination rate, startinggermination time, and50%germination time. However, in production practice, bothefficiency and ecomomic cost should be considered, and combined with our results, werecommend the way of soaking seeds in water under lower temperature for20d in order tobreak seed dormancy and increase germination percentage of Leymus chinensis.（4） Lemma is an important fator inhibiting seed germination of Leymus chinensis, but itcan also improve salt resistance of the seeds. We investigated the effects of lemmas on seedimbibition and dehydration, germination responses to various temperature regimes and theimpact of different duration salt stress on seed germination. The results showed that lemmascould significantly enhance water absorption, and slowed down the dehydration rate underdrought conditions. Lemmas, temperature regimes and their interactions significantlydecreased germination percentage and germination rate, indicating that lemmas could inhibitgermination process of Leymus chinensis. Under different duration of salt stress, recoverypercentages of non-germinated seeds with lemmas were higher than that without lemmas,especially under long duration of salt stress, indicating that lemmas could enhance the saltresistance of seed. Once the precipitation and melting snow decreased salinity concentrationin the soil, seeds with lemmas can geminate again.（5） Germination percentages and rates were inhibited by either an increase or decreasetemperature from the optimal temperature20-30°C, and this temperature can alleviate theinhibitory effects of salt-alkaline stress on seed germination. With the increasing salinity andalkalinity, seed germination and germination rate were both decreased, and the reductionswere much greater under alkaline stress. Under salt stress, when salinity＜200mM, lowertemperature was the main factor inhibiting seed germination. With the increasing salinity,higher temperature aggravated the adverse effects. While under alkali stress, germinationpercentage and germination rate were both decreased markedly at25-35°C even though the alkalinity was very low. Recovery percentage of non-germinated seeds increased with theincreasing salinity, but increased at first and then declined under alkaline stress, and recoverypercentages were lowest in both stresses at25-35°C, especially under alkaline stress. Seedlinggrowth had similar response to the interactions of temperature and salt-alkaline stress,20-30°C was also the optimum temperature. In addition, both of the two stresses inhibitedroot growth much stronger. Due to the above results, early July sowings in field would berecommended, when temperature is appropriate and salinity-alkalinity concentrations arealways reduced by the high rainfall.（6） Under mixed salt-alkaline stresses, germination percentage and germination ratedecreased with increasing salinity under all the stress treatments, and the reductions weregreater under treatment which the proportion of alkaline salts was greater. At250mM salinity,germination percentage of treatment A was6.5%, but the other five treatments were0.Seedling growth was also affacted by salinity, pH and their interactions. However, radiclelength decreased more markedly with increasing salinity and pH. Stepwise regression analysisresults showed that salinity was the dominant factor for seed germination under mixedsalt-alkaline stress conditions. However, once radicle break through the seed coat, and pHchanged into the dominant factor for seedling establishment. Above results indicate thatmixed salt-alkaline stresses has different impacts on germination and early seedling stages ofL.chinensis. The interactions of high salinity and high pH have the strongest inhibition onseed germination and seedling growth.（7） Both saline stress and alkaline stress significantly decreasd seedling length, freshweight and water content, and the reductions were much greater under alkaline stress. TheNa⁺concentration, Na⁺/K⁺ratio increased butK⁺concentration decreased under both stresses,and the changes were greater under alkali stress. Under salt stress, shoots mainly accumulatedCl^-and little change was found in organic acids. While under alkali stress, the concentrationsof Cl^-, NO₃^-and H₂PO₄^-were all decreased, and organic acids were accumulated, especiallymalic acid and citric acid. In addition, soluble sugar was the same osmoregulation under thetwo stresses. Above results indicate that alkali stress inhibited early seedlings of Leymuschinensis much greater because of the high pH, different accumulation characters of Cl^-andorganic acids indicated that different adaptive mechanism to saline and alkaline stresses wereexist of Leymus chinensis during early seedling stage.