Changes In Seed Germination Strategy Over Secondary Succession Of An Alpine Meadow On The Tibet Plateau

The alpine meadow on the Qinghai-Tibet Plateau is a unique ecosystem type developed under cold and wet conditions,which have rich and unique biodiversity.Due to the impact of human activities and climate changes,the degradation of alpine meadow ecosystems is becoming more and more serious,and the restoration and reconstruction of alpine meadow ecosystems has become the urgent matter.Seed germination is the earliest expressed trait in plant life history.To some extent,it can determine the post-germination environment of plant species.It also have a profound impact on the expression of other functional traits after germination.Therefore,the study of germination characteristics along community succession is important to restoration and reconstruction of grassland ecosystems.In this research,seed germination strategy and germination traits of the community along the succession were studied by combining the field sample survey with the indoor germination experiment.And to reveal the variation of functional diversity with community succession,its relationship with phylogenetic diversity was also studied.The field work was conducted in a series of alpine meadows in various stages of succession on the eastern Tibetan Plateau,using a space for time substitution chronosequence.This study can help us understand the mechanism of alpine meadow community construction and succession from the perspective of seed germination,and provide data foundation and theoretical support for the restoration and reconstruction of alpine meadow.The results shows:1)Succession gradient has a significant effect on seed germination.At the community level,the germination percentage and germination rate of communities in the early successional stage(1 year)are much higher than that of communities in the later successional stages.2)Communities in the initial stage of succession(1 year)and the climax community can get a high weighted germination percentage and germination rate at low temperature(10 °C,15 °C).But communities in the middle and late successional stages(5 years,15 years),the weighted germination percentage and germination rate at low temperature are very low.3)At the community level,wet-cold storage can inhibit the seed germination in communities of the initial succession stage and climax communities,while it can promote seed germination of the communities in the middle and late successional(1 year,15 years)stages.Temperature fluctuation can significantly promoted seed germination in middle and late successional stages,but it cannot significantly promote seed germination in the initial stage of succession(1 year),and it even has negative effects on seed germination of climax community.4)In the initial communities of succession,the functional richness(FRic)was relatively higher than that of communities of the later successional stages,and the functional evenness(FEve)of communities in the initial of succession and that of the climax community were relatively higher than that of communities in the middle and late successional stages.Functional divergence(FDiv)is highest in communities in the initial of succession and lowest in the climax community.5)The phylogenetic diversity(PD)of the climax communities was significantly higher than that of communities in the earlier successional stages,and phylogenetic diversity and functional richness(FRic)were positively correlated in the climax community.However,there was no significant correlations at other succession stages.6)Species richness and functional richness(FRic)were positively correlated in the late succession stage(15 years)and in the climax community,but not in the initial and middle stages of succession.At the community level,the seed germination strategies(germination percentage,germination rate,response to temperature fluctuations and wet-cold storage)have significantly changed along succession.The transformation of these germination traits may be caused by changes of vegetation coverage and canopy density along community succession,and may be related to changes of competition intensity and niche differentiation during community succession.