Effect Of Water Stress On Seed Germinations And Photosynthetic Characteristics Of Dominant Species At Different Successional Stages In Abandoned Arable Land Of Loess Plateau

The study selected several common species, Heteropappus altaicus, Setaria viridis, Artemsia annua, Artemisia frigida, Elymus Dasysachys, Plantago asiatica and Stipa Breviflora, in semi-arid environment of Loess Plateau to evaluate the responses of germination to PEG water stress and the effect of mediate water stress on photosynthetic features. PEG water solution were OMPA,-0.2MPa,-0.4MPa,-0.8MPa and-1.2MPa, Our main results are as follows:1. seed water absorbability of control seeds (OMPa) of five species (H. altaicus, S. viridis, A. annua, A. frigida, E. Dasysachys, P. asiatica and S. Breviflora) were significantly higher than those under-1.2 MPa solution. The order of seed water absorbability was as followings:A. frigida> A. annua> P. asiatica> S. Breviflora> E. Dasysachys. A. frigida had the highest seed water absorbability which was 279% of its own weight and E. Dasysachys showed the lowest one which was 113% of its own weight. The seed water absorbing capacity had a negative correlation with seed size in five species.2. The germination of five species were restrained by severe water stress in different extent increasing with PEG concentration and the germination rate, germination index and germination potential decreased by increasing concentration of PEG-6000 solution. Under the moderate water shortage (-1.2MPa), the germination ratio of A. annua, A. frigida, E. Dasysachys, P. asiatica and S. Breviflora, compared with control experiment, decreased 46.5%,47.3%,62.7%,56.7% and 100%, respectively. According to the correlation between seed maximal germination ratio and PEG osmotic potential, so we predicted that the critical germinating potential of A. annua, A. frigida, E. Dasysachys, P. asiatica,S. Breviflora was-1.03MPa,-1.3MPa,-0.68MPa,-0.84MPa,-0.05MPa, respectively, and their ultimate potential was 2.49MPa,-2.58MPa,-1.9MPa,-2.15MPa,-0.99MPa, respectively. Thus, we concluded that the ability of seed drought tolerance for five species was A. frigida> A. annua> E. Dasysachys> P. asiatica> S. Breviflora. 3. With decreasing of water potential, not only the half germinating time was prolonged, but also the rate of germination germination index and germination potential was slowed down. Compared all PEG osmotic potential with each other, we found that the germinating rate of five species was A. frigida> P. asiatica> A. annua > E. Dasysachys> S. Breviflora, and the order of germination index and germination potential reflected the germination was A. frigida> A. annua> P. asiatica> E. Dasysachys> S. Breviflora.4. For H. altaicus, S. viridis, A. annua, A. frigida, E. Dasysachys, P. asiatica and 5. Breviflora, the net photosynthetic rate (Pn), stomatal conductance (Gs) and transpiration rate (E) was decreased significantly under mediate water stress while water use efficiency (WUE) was increased, especially, in S. viridis, A. annua, A. frigida, and S. Breviflora. S. Breviflora, the later succession species, had the highest photosynthetic rate, stomatal conductance and water use efficiency under sufficient water supplying or water shortage, therefore, we considered that S. Breviflora had the biggest adaptability to mediate water stress. A. frigida, E. Dasysachys and S. Breviflora, the medium-term succession species, had the mediate photosynthetic rate, stomatal conductance and water use efficiency and H. altaicus, S. viridis and A. annua, the earlier succession species, had the lowest photosynthetic rate, stomatal conductance and water use efficiency. The basis fluorescence (Fo) and non-photochemical quenching coefficient (NPQ) of seven species increased and the maximal photocheimcal efficiency (Fv/Fm), actual photocheimcal efficiency ((?)PSâ…¡) and photochemical quenching coefficient (qP) decreased under mediate water stress, while Fv/Fm had not obvious variation, and actual photocheimcal efficiency ((?)PSII) decreased obviously. Compared with control experiment,(?)PSII of H. altaicus, S. viridis, A. annua, A. frigida, E. Dasysachys, P. asiatica and S. Breviflora decreased 34 %,44%,27%,38%,36%,30%,25%respectively. In summary, the later succession species (S. Breviflora) had the lowest variation in all photosynthetic feature among seven species, the average decreasing of photosynthetic feature values for the medium-term succession species (A. frigida, E. Dasysachys, P. asiatica) was lower than the three earlier succession species (H. altaicus, S. viridis and A. annua), our results, herein, indicated that the species evolved their photosynthetic feature to raise their drought tolerance by the succession of plant community.