Study On Seed Germination Ecology Of Several Dominant Plant Species Growing In Arid Desert Region, China

The situation of vegetation degradation and plant species endangerment has been serious in arid desert region of northwest China these years. Vegetation recovery as well as natural resource conservation had become the key work the government encountered. There were many valuable native xerophytes in the arid desert region. Most of them possess unique eco-adaptations to the adverse environments, including the special germination characteristics as well as the strategies for seedling survival. Studies in deep on the ecology of seed germination of these plants will benefit the better understanding of the adaptation mechanisms of these plants. All of the five plant species, Nitraria tangutorum Bobr., N. sibirica Pall., Peganum harmala L. P. nigellastrum Bunge and Agriophyllum squarrosum (L.) Moq., are dormant plant species in arid desert of northwest China. Their habitat preference as well as geographical distribution of these species differed. The hypotheses proposed that, the key characteristics of seed germination for seeding survival in this area can be concluded by comparing seed germination responses of these species to key environmental elements. Moreover, seeds of Nitraria showed slow and dispersive germination patterns, with dormancy. The hard endocarp makes it hard to cut and expose embryos for tetrazolium testing. Consequently little is known about seed quality evaluation in Nitraria species; the use of the seed has been seriously impeded. So it should be valuable do studies on seed dormancy and dormancy breaking, as well as developing the methods of topographical tetrazolium testing for seed viability of Nitraria.Mature seeds of the five species used in this study were collected from their mother plant in Alashan plateau, which is one of the typical desert (cold desert) region of northwest China. Aims to verify the proposed hypotheses and determine the appropriate methods for dormancy breaking and tetrazolium testing for seed viability for the two species of Nitraria. Experiments were used to compare the followings:seed germination responses to. temperature, water limitation and salinity stress for the five tested species; seed germination responses to prichilling, preheating, soaking, KNO3, GA3, alternating temperature and acid scarification as well as the effects of two approaches to expose tissues for staining in tetrazolium solution for evaluation of seed viability for the two species of Nitraria. The main results and conclusions were listed as followings:(1) The key characteristics of seed germination of dominant species for adapting Alashan arid desert climates should be: seed should have dormancy; seed should show reduced or delayed germination under water limiting conditions; seed germinating selected alternating and high temperature.(2) The optimum temperature of seed germination for both N. tangutorum and P. nigellastrum were 25/35℃alternating temperature; for N. sibirica,25-30℃constant temperatures and 20/30℃; for P. harmala,15/25℃,20/30℃and 25/35℃; for A. squarrosum,20/30℃. The cubic curve model fitted the relationship between seed percentage germination and drought stress or salinity stress better than did of linear model or quadratic model.(3) Water limitation had negative effects on seed germination for all tested species. The most negative osmotic potential (PEG 6000 solution) under which seed could germinated was-0.9 MPa for N. tangutorum;-1.5 MPa for N. sibirica;-0.6--1.2 MPa for P. harmala and -0.9--1.5 MPa for P. nigellastrum.(4) For N. sibirica, seed germination was promoted under light salinity condition (-0.3 MPa NaCI solution); however, salinity stress had negative effects on seed germination for other tested species. The most negative osmotic potential of NaCI solution under which seed could germinate was-1.2 MPa for N. tangutorum;-1.8 MPa for N. sibirica;-0.9 MPa for P. harmala and-1.5 MPa for P. nigellastrum.(5) Soaking is one of the most effective methods to breaking dormancy for the two Nitraria species. Seeds of tested Nitraria species possess physiological dormancy, and the dormancy degree of N. tangutorum was deeper than that of N. sibirica.(6) The key of exposure tissue for tetrazolium testing for seed viability for two Nitraria species should be transversely cut one third of the drupe at the lower part of the drupe, soak in water for 4 hours, then squeeze embryos out carefully.