Relationship Between Seed Traits And Postgermination Traits,Species Diversity Of Alpine Meadow Plants On The Tibet Plateau

Plant functional traits are a series of plant properties that affect the growth,reproduction and survival of plants,and seed traits（including seed mass,dormancy,germination and dispersal）are the first functional traits expressed in plant life history,which directly/indirectly affect the expression of plant functional traits at post-germination stages.Thus,our study of seed functional traits will help us to understand the ecological mechanisms of plant population renewal and persistence,as well as the maintenance mechanisms of species diversity in communities.In the early stages of plant life history,plants face a higher risk of death,and the seed mass,which is the core of plant life history,significantly affects the germination strategy of plants.In addition,many adaptive traits or strategies have been formed to adapt to the environmental changes over the long course of plant evolution.Changes in plant functional traits determine the feedback of plants to various environmental factors.Seed traits and a range of post-germination traits provide a way to study the response of plants to environmental changes.Therefore,the study of seed functional traits,post-germination traits,and their relation to environmental changes can help further explore ecological issues such as niche differentiation,community species coexistence,and species diversity maintenance.This study was conducted on the alpine meadows of the Tibet Plateau by combining the field community sample surveys with indoor experiments.We examined the effects of different environmental changes（altitude,succession and human disturbance）on seed mass and the effects of altitude on seed germination traits and post-germination traits,determined the effects of soil physicochemical on seed traits by combined with the soil physicochemical properties at different altitudes.We then,analyzed the relationship between seed mass and germination,post-germination traits at the community level in response to altitude,and discussed the effect of germination traits on post-germination traits.In addition,compared and analyzed the relationships between germination traits and species diversity,between species diversity and functional diversity under different succession stages.The results were as follows:（1）Altitude,succession,and human disturbance had significant effects on seed size variation at the community level.SM_CWM decreased significantly with increasing altitude,with the SM_FDrao at 3900m was significantly higher than that at other altitudes;SM_CWM increased with succession years of increase and was stable in the climax community,but SM_FDrao did not significantly under different succession stages;Moderate grazing reduced the SM_CWM and increased the coefficient of variation（CV）of SM in alpine meadow.However,there was no significant difference between the functional diversity(SM_FDrao)in grazed and nongrazed meadows.Nitrogen addition significantly increased the SM_CWM,and it had a marginally significant effect on SM_FDrao,but no significant effect on CV of SM.（2）At the community level,the seed germination strategy changed significantly with altitude.The CWM of seed germination percentage and seed germination rate at different altitudes were significantly different under the five constant temperature.The CWM of seed germination percentage and seed germination rate at the same temperature decreased significantly with the increase of the altitude;The CWM of the response of seed germination to temperature alternation was mainly concentrated at lower altitudes（3000m and 3300m）.The CWM of the response to wet-cold storage did not show a fixed rule along the altitude gradient:seed at 3000m and 3900m had a significant positive response to wet-cold storage,but had a significant negative response at 3300m and 3600m;The CWMBTN narrowed with the increase of altitude.（3）The changes of seed mass and germination traits with altitude were significantly affected by soil physicochemical properties.SWC,SOC,p H and SAP significantly affected the seed mass,and all of them were positively correlated with the seed mass;STN,SWC,SOC and p H had the most significant influence on germination traits,and STN had a significant negative correlation with germination traits,while SWC,SOC and p H had a significant positive correlation.（4）The relationship between seed traits and post-germination traits was positively responsive to altitude.Firstly,There was a significant positive correlation between SM_CWM and germination traits,and the relationship was more significant at low altitude（3000m and 3300m）.Secondly,SM_CWM was positively correlated with H_CWM,SLA_CWM,LA_CWM and LCC_CWM,but negatively correlated with LDMC_CWM and LNC_CWM.The relationship between SM_CWM and post-germination traits were more significant at3000m;Finally,seed germination traits had a significant positive correlation with H_CWMand SLA_CWM,and a significant negative correlation with LDMC_CWM and LNC_CWM.The relationship between seed germination traits and H_CWM was more significant and had the highest explanatory degree.（5）Species diversity and functional diversity of germination traits changed significantly with succession progression,and seed germination traits and functional diversity were significantly correlated with species diversity.Firstly,SR,Shannon and Simpson indices increased with succession years of increase,and were stable in the climax community.Pielou index for the 5-year successional stage was significantly lower than that for the 15-year successional stage and the climax community.FRic was significantly higher in the 1-year successional stage than in the other stages,FEve was significantly lower in the 5-year successional stage,and FDiv decreased significantly.Secondly,SR,Shannon and Simpson indexes were negatively correlated with germination traits,Pielou index was positively correlated with the CWM of seed germination rate at 5℃,and negatively correlated with the CWM of the response of seed germination to temperature alternation;Finally,SR,Shannon and Simpson indexes were negatively correlated with FRic and FDiv,while Pielou index was positively correlated with FEve.In conclusion,the community environmental conditions（vegetation coverage,canopy density,vegetation patches,etc.）significantly changed along the different environmental gradients at the community level,which affected the selection of the environment on seed mass,seed germination and post-germination traits,resulted in the redistribution of traits,transformed the relationships between seed traits and other functional traits,and also changed the species diversity in the plant community.To some extent,this research can help us understand the influence mechanism of different environmental changes on species survival,species diversity maintenance and community structure of alpine meadow from the perspective of seed traits,and provide theoretical basis and data support for the restoration and reconstruction of degraded meadow ecosystem on the Qinghai-Tibet Plateau.