Effects Of Fire Cues On Seed Germination Of Typical Plants In The Songnen Grassland Under Salinity Stress And Its Mechanism

Fire,as a fundamental ecological factor,profoundly affecting many terrestrial ecosystems,including forest and grassland ecosystems.Seed germination is an important stage of plants’ life history,as the main strategy for the regeneration and restoration of vegetation after fire events.The combustion of vegetation,which plays critical roles in breaking seed dormancy and seedling establishment,produces smoke,heat and a series of fire cues related to smoke.In the past,the studies on the effects of fire cues on seed germination were mainly focused on the Mediterranean climate zone and savanna ecosystem.Songnen Plain,a high-risk area for fire,is characterized by natural fire and farmland fire.However,the effects of fire cues on seed germination of typical plants in Songnen grassland have not been studied.In addition,as a typical ecological fragile,salinity stress is the main limiting factor affecting seed germination and seedling establishment in Songnen grassland.The structure and function of Songnen grassland ecosystem were affected by fire and salinity.However,the studies on the interaction between fire cues and salinity stress are relatively limited,especially alkaline salt on seed germination and seedling growth.Therefore,in this paper,a series of studies were carried out on typical plants from Songnen grassland to investigate the different factors on seed germination,such as the concentrations of smoke water,the duration of smoking,the heat shock intensity,in order to have a further exploration of the interaction of the heat shock and smoke and the compound effects of heat shock and smoke water.What’s more,the responses of seed germination and seedling growth to different types of fire cues under salinity stress were clarified.And the mechanisms of fire cues on seed germination under salinity stress were illuminated from the aspects of external environment and endogenous germination regulatory substances.The main conclusions were as follows:Fire cues significantly promoted seed germination and seedling growth of some typical plants,such as Setaria viridis,Suaeda glauca and Melilotus officinalis.The heat shock promoted seed germination of Melilotus officinalis,Lespedeza bicolor,Kochia scoparia var.sieversiana,Abutilon theophrasti,S.suaeda,and Lespedeza juncea.The legumes were more resistant to high temperatures than other plant families.Smoke significantly increased seed germination percentage of S.viridis and S.glauca and K.scoparia.High intensity heat shock and high concentration of smoke water inhibited seed germination and seedling growth notably.For most species,the combination or interaction of fire cues did not significantly promote or inhibit seed germination,compared with single fire cue.In similar taxa,the response of seed germination to fire cues was not consistent.Among the four tested poaceae species,the seed germination of S.viridis is the only one that responded to smoke.The temperature response thresholds of the four legumes to heat shock were significantly different.There was a close correlation between seed germination response to fire cues and seed dormancy type,but the correlation was not strictly corresponding.Smoke can effectively alleviate salinity stress of S.viridis and S.suaeda,and promote seed germination and seedling growth.Heat shock significantly alleviated salinity stress of S.suaeda,but the effect was not as good as smoke.There was significant interaction between smoke and salinity stress on seed germination and seedling growth.It indicates that in practical application,the appropriate fire cues should be selected according to the degree of salinity.No matter what kinds of fire cues treatments,they could not alleviate the salinity stress of Leymus chinensis and M.officinalis significantly.Therefore,the method of fire cues alleviating salinity stress is only useful for germination-responsive species,which is species-specific.High temperature caused by vegetation burning destroyed the thick seed coat structure of M.officinalis seeds,broke physical dormancy and promoted seed germination.Although the p H of the solution decreased significantly,the composition and concentration of ions in the solution remained unchanged.The mechanism of smoke alleviating plant salinity stress is not consistent with the principle of soil conditioner.Under salinity stress,there was no significant difference in α-amylase activity between different fire cues treatments.In conclusion,this study systematically explored the response of seed germination and seedling growth of typical plants to different types and intensities of fire cues in Songnen grassland,and revealed the effects and mechanisms of fire cues on seed germination under salinity stress.This study would provide a scientific basis for further understanding the ecological function of fire,strengthening the scientific management and application of grassland fire,and vegetation restoration of degraded ecosystems.