Herbage Seed Germination Responses To Temperature And Drought Stresses

This thesis reports the study on germination behaviors and germination tolerance to high temperature of several forage seeds. Changes of ambient temperature and temperatures at different soil layers during sowing season were monitored and effects of temperature regimes on seed germinations of several grasses of Elymus dahuricus, E. sibiricus, Agropyron mongolicum and Bromus ciliatus were investigated. Seed imbibition and germination characters were observed and measurements on seed germination after hydro-conditioning treatments were conducted. Biological and physiological responses of seed germination to the hydro-treatments were probed. The aim of the study is to search for the optimum sowing times based on seed germination requirement and temperature conditions in the sowing season, and to seek the possibility of pre-sowing treatment in improving seed germination performance in order to overcome the difficulties for herbage crop seedling establishment in the Northern China grassland region. Main research results are summarized as follow:1, Ten measurement indexes, i.e., germination percentage, dead seed percentage, dormant seed percentage, abnormal seedling percentage, peak germination percentage, daily germination percentage, final germination rate, germination co-efficiency, germination index, seedling weight and vigour index, are evaluated for their contributions to germination performance. The results showed that germination percentage, germination index, vigour index, dead seed percentage and dormant seed percentage are the most important indicators reflecting seed vigour level. Under unfavourable conditions, dead seed percentage and seed dormancy were the best alternative indicators, which can be used as reliable indexes for evaluating seed vigour when other measurements were not so effective.2, Suitable germination temperature for the tested seeds is in the range of 15-35℃. Optimum germination temperatures for the grasses seeds of E. dahulicum, E. Sibricus, A. mongolicum and B. ciliatus are 25℃, 25℃or 20/30℃, 20/40℃and 20/30℃, respectively. Optimum germination temperatures for the legume seeds of Pisum sativum, Vicia sativa, Astragalus adsurgens and Medicago sativa cv"Aohan"are E. dahulicum, E. Sibricus, A. mongolicum and B. ciliatus are 15℃or 20/30℃, 10/20℃, 20℃and 20℃, respectively. High germination percentage, high germination index and high vigour index were observed under alternative temperatures. In contract, low dormancy percentage and low dead seed percentage were observed under the alternative temperatures.3, Research on ambient and soil temperature changes during the period from April to August indicated that end of May to early July is the most suitable sowing time for the tested species in Hohhot area. Optimum sowing times for Hulunbeer area, Bayanhusu in Xingan League and Kerqin area, Wulanchabu and Erdos areas are in June, end of May, Autumn, respectively. No sowing should be made later than early August.4, In regards to the seed imbibition behavours, tested seeds showed a fast-slow imbibition pattern. Agropyron mongolicum has the strongest imbibition capacity. Elymus species have similar imbibition capacities. Bromus ciliatus has the lowest imbibiton capacity.5, The results of hydro-treatments showed that germination performances, in terms of germination speed and percentage, were enhanced by hydration treatments. However, the treatment reduced the seedling establishment and drought resistances of the seeds. Hydration - dehydration treatments had little effect on germination speeds and percentages of E. dahuricum and E. sibiricus. Low imbibition enhanced germination percentages of A. mongolicum and B. ciliatus High imbibation rates reduce seed germination percentages and seed vigour. Hydration-dehydration treatments enhanced seed vigour levels. Maximum enhancement was found when the seed had a moisture content of 30% of maximum imbibition. Hydration-dehydration treatments enhance seedling emergency rates, but reduce drought resistances of seedlings (except for the seeds of E. sibiricus in 30% of maximum imbibation. Two or three cycles of hydration-dehydration reduce germanition percentages of A. mongolicum and B. ciliatus seeds, but have little effects on other seeds. In summary, hydro-treatments had complicated effects on the seeds under different treatment conditions and seeds of different species had various responses to the treatments. Suitable hydration-dehydration treatments fordiferent seeds are recommended.6, Hydration-dehydration treatment has positive effects on membrane re-organization, enhancing dehydration and peroxide enzyme activities. Under low imbibition conditions, dehydration enzyme activities have been greatly enhanced. Peroxide enzyme activities are enhanced after 48 hours of seed germination for E. dahuricum and E. sibiricus seeds under hydration-dehydration treatments. For A. mongolicum seeds, high peroxide enzyme activity is enhanced at 12 hours after germination. High enzyme activities were found at 48 hours and 72 hours after germination for B. ciliatus with T30 treatments.