Study On Characteristics Of Forage Seed Defense And Its Influencing Factors

Natural grassland in the north of China is an important ecological barrier and production base of grass and livestock products.The local forage yield has been greatly influenced by environmental changes and pests and diseases.Seed,as the propagating organ of seed plants,is the basic and essential part of agricultural production,and the key to improving yield of the natural forage.Seed defense is an important component of plant defense.Most researches focus on the seed defense of woody plants or forest ecosystems,while few studies on the grass and grassland ecosystems.In this study,229 species of forage seeds were collected from northern meadow steppe,typical steppe and desert steppe.And the relationship between seed physical defense(seed coat thickness)and chemical defense(total phenol content)was quantified,the effects of seed functional traits(seed mass,volume,total carbon content,total phosphorus content,total phenol content,seed dispersal type,seed dormancy type)and plant characteristics(aboveground biomass,plant life form,fruit type,seed production)on the defense characteristics of forage seeds were well studied as well as the relationship between the defense characteristics of forage seeds and the pre-dispersal seed predation,and the key factors affecting the defense characteristics of forage seeds.And the phylogenetic signals of forage seed traits,in order to explore the defense mechanism of forage seed.The results showed that:Seed coat thickness of forage was great positively correlated with aboveground biomass,and negatively correlated with seed total carbon and seed production.There was no significant correlation between seed coat thickness and seed total nitrogen content,total phosphorus content,seed mass and volume.The total phenol content of forage grass was positively correlated with the aboveground biomass,total phosphorus content and seed mass,but not with total carbon content,total nitrogen content,seed volume and seed production.There were significant differences in seed coat thickness and total phenol content among different plant life forms and dormancy types.The seed coat thickness and total phenol content of shrub forage seeds were the highest,significantly higher than those of annual and perennial forage seeds.The seed coat thickness of physically dormant seeds was the highest,which was significantly higher than that of non-dormant and physiological dormant seeds.The total phenol content of non-dormant seeds was significantly higher than that of physiological dormancy seeds.However,there was no significant difference in seed defense characteristics of forage seeds with different fruit types and different seed dispersal types.There was a significant positive correlation between seed coat thickness and total phenol content of forage seeds,which may be mediated by seed mass,and was only significant in forage seeds with 1000-grain weight more than 1 g.There was no significant correlation between pre-dispersal seed predation and seed coat thickness and total phenol content.There was no significant difference in seed coat thickness and total phenol content between preyed seeds and unpreyed seeds before dispersal.The seed coat thickness and total phenol content of forage seeds did not play a good protective role against the natural enemies before seed dispersal.The seed coat thickness,total phenol content,seed volume,total carbon content and total nitrogen content of forage seeds are phylogenetic and conservative at the species level.However,the phylogenetic signals of seed mass and total phosphorus content of seeds were not significantly present.Therefore,seed size,fruit type,total carbon content,total nitrogen content and total phosphorus content of forage seeds were all important predictors that affected forage seed defense.These results will be of great significance to the theoretical and practical research on the study of plant seed defense,forages and crops’ cultivation and breeding,and weed control of farmland from the perspective of provenance.