| Desert steppe not only has stable ecological functions in wind prevention and sand fixation,soil and water conservation,and biodiversity protection,but also provides a material basis for the development of animal husbandry.However,its ecosystem stability is low,the ecological environment is fragile,and it is susceptible to human activities and climate change.Gramineae plants are the main components of desert steppe vegetation.They have the characteristics of strong tillering ability,high yield,high feeding value and nutritional value,and become the preferred plants for desert steppe restoration and improvement.Agropyron mongolicum,Elymus dahuricus and Bromus inermis Leyss are perennial herbaceous plants,which play important roles in ecological protection and restoration,genetic breeding and animal husbandry development of desert steppe in Ningxia.With global warming,extreme drought events occur frequently,which seriously threaten the growth and reproduction of desert plants and the sustainable development of ecological protection,restoration and utilization of desert grassland.As the beginning of plant life cycle,the adaptability of seeds to drought stress are crucial.The low germination rate of three gramineae plants seeds in Ningxia desert steppe,and the unclear adaptability and mechanism of seed adaptation to drought stress seriously restrict the high-quality development of desert steppe.Therefore,revealing the seed germination characteristics and adaptation mechanisms of several gramineous plants in Ningxia desert steppe,and exploring ways to improve seed germination rate under drought stress environment are the theoretical basis for the sustainable development of Ningxia grassland ecosystem.In this study,A.mongolicum,E.dahuricus and B.inermis were used as the research objects.By setting 10 temperature gradients(constant temperature,variable temperature)and 2 light conditions(alternating light and dark,completely dark),the effects of temperature and light on the germination of three gramineae plants seeds were studied,and the optimum temperature and light conditions for seed germination of three gramineous plants were explored.The response and adaptation of seed germination of three gramineous plants to drought stress were studied by simulating different gradients of drought stress with polyethylene glycol(PEG-6000).The effects of exogenous plant hormones on seed germination of three gramineous plants under drought stress(different osmotic potential stress)were studied by soaking seeds with different concentration gradients of exogenous plant hormones(gibberellin,naphthalene acetic acid),and the optimal methods and techniques for improving seed germination rate of three gramineous plants were explored.The main results are as follows:(1)Different temperature and light conditions can affect the germination of three gramineous seeds.Under the constant temperature of 10℃,light could effectively improve the germination rate of A.mongolicum and B.inermis,which increased by 10%and 28%respectively.Under the condition of lower variable temperature of 5/15℃ and 10/20℃,light showed an inhibitory effect on the germination rate of A.mongolica seeds,which reduced the germination rate by 55%and 43%,respectively.Under the constant temperature of 20℃ and 25℃,the germination potential of A.mongolicum seeds was increased by 7%and 18%,respectively.Under the conditions of constant temperature of 20℃,25℃ and 30℃,light showed an inhibitory effect on the germination potential of E.dahuricus seeds,which decreased by 33%～65%.Under the condition of 15/25℃～20/30 ℃,light had an inhibitory effect on the radicle length and germ length of A.mongolicum seeds and the radicle length of E.dahuricus seeds,which decreased by 0.25 cm～1.09 cm,0.62 cm～2.31 cm and 0.80 cm～1.39 cm,respectively.(2)The germination rate,germination potential,germination index,vitality index and radicle length of A.mongolicum seeds increased first and then decreased with the aggravation of drought stress,and the germ length decreased with the aggravation of drought stress.When the osmotic potential of drought stress was-0.3 MPa,the germination rate and germination potential of A.mongolicum seeds were significantly higher than those of other drought stresses,which were 75%and 10%,respectively,which were 7%higher than those without drought stress.When the osmotic potential of drought stress was-0.6 MPa,the radicle length(3.68 cm)of A.mongolicum seeds was significantly higher than that of other drought stresses,which was 1.74 cm higher than that without drought stress.The germination rate,germination potential,germination index,vitality index and seeding length of E.nutans seeds decreased with the increase of drought stress,and the radicle length increased first and then decreased with the increase of drought stress.The radicle length(3.88 cm)of E.dahuricus seeds under drought stress-0.3 MPa was significantly higher than that under other drought stresses,which was 1.06 cm higher than that without drought stress.The germination rate,germination potential,germination index and radicle length of B.inermis decreased with the aggravation of drought stress,and the vitality index and seeding length increased first and then decreased with the aggravation of drought stress.Under drought stress of-0.3 MPa,the seed vitality index of B.inermis was significantly higher than that of other drought stresses,which was 30.13,which was 5.27 higher than that without drought stress.When the drought stress was-0.3 MPa,the germ length(10.24 cm)of B.inermis was significantly higher than that of other drought stresses,which was 3.16 cm higher than that without drought stress.(3)Gibberellin soaking treatment had inhibitory effect on seed germination of A.mongolicum.Low concentration of naphthylacetic acid(0.3 mg/L<naphthylacetic acid concentration<0.6 mg/L)promoted seed germination of A.mongolicum under drought stress.Under low and moderate drought stress(0～0.9 MPa),gibberellin soaking had an inhibitory effect on seed germination of E.dahuricus,while under severe drought stress(-1.2 MPa),gibberellin soaking(50 mg/L<gibberellin concentration<250 mg/L)promoted seed germination.Low and medium concentrations of naphthylacetic acid(0.3 mg/L<naphthylacetic acid concentration<0.9 mg/L)promoted the germination of E.dahuricus seeds under severe drought stress(-1.2～-1.5 MPa).Low and medium concentrations of gibberellin(50 mg/L<gibberellin concentration<250 mg/L)could improve the germination rate of B.inermis seeds under drought stress.Soaking seeds with naphthalene acetic acid(0.3 mg/L<naphthalene acetic acid concentration<1.5 mg/L)promoted the germination of B.inermis seeds under drought stress.The response of seed germination rate of three gramineous herbaceous plants to temperature and light is different,and the optimum temperature and optimum light conditions are different.In the practice of grassland reseeding,the appropriate sowing time should be selected according to the local meteorological conditions.The seeds of three gramineae plants had different responses to drought stress,which were manifested in germination rate,germination potential,germination index,vitality index and radicle length.In practice,the appropriate soil moisture conditions can be selected according to the results of this study.The effects of soaking seeds with different concentrations of gibberellin and naphthalene acetic acid on the germination of three plant seeds are different,and are affected by the degree of drought stress.This study explored a series of methods and techniques to improve the germination rate of three gramineae plants under drought stress.It can effectively improve the seed germination rate under drought stress environment,and is helpful to improve the stability of desert grassland ecosystem and the ability to cope with extreme drought events in the context of climate change. |
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