Phenotypic Variation Of Alpine Cushion Plants And Its Effects On Species Interaction And Community Composition

Experiments of relationship between species mainly focused on negative interactions,such as competition,predation and parasitism while positive interaction or facilitation of species has been overlooked for a long time.Over the last two decades,since the importance has been gradually recognized by ecologists and botanists,positive interactions become one of the hotspots of ecological research.As a most widely existed and typical plant group,which facilitative interaction is common and enormous in Alpine ecosystem all over the world,cushion plant is a classic model for the investigation of positive interactions.However,few studies have been involved in the effects of cushion plant’s phenotypic variation on facilitation.We selected a typical cushion plant Thylacospermum caespitosum(Caryophyllaceae)with two contrasting phenotypes(loose and tight)as target species and conducted field survey at four Alpine sites in West China to assess phenotypic variation and its effects on species interactions,community composition and environmental variables.Results showed: 1)According to plant traits,Thylacospermum caespitosum can be divided into two types: loose and tight cushions.Comparing with loose cushions,tight cushions had higher value in height,convexity index and stem density.Along with the increase of environmental stress,cushion areas became smaller,height became shorter whereas stem density tend to increase.2)Loose cushions showed stronger facilitative interactions than tight ones.Meanwhile,for the interactions in richness,two phenotypes presented consistent response to different stress factors: unimodal model to thermal stress and linear model to water.However,for the interactions in abundance,loose cushions exhibited unimodal relationship whereas tight cushions exhibited monotonic relationship with temperature.The scenario was totally opposite for the aridity,where loose cushions exhibited monotonic relationship and tight cushion exhibited unimodal relationship.3)Significant phenotypic effects and habitat effects on understory community composition were only detected in Maya and Qilian low sites.Nevertheless,an overall cushion effects existed at four sampling sites.4)Besides,environmental variables showed no significant phenotypic effects on microhabitats.Namely,phenotypic effects on species interactions cannot be explained by the amelioration of environmental variables and there may be some potential processes,such as underground microbes,which been involved and triggered species interactions.In conclusion,the thesis,taking Thylacospermum caespitosum as our target plant,investigated the phenotypic effects of Alpine cushion plants on interspecific interactions and their response to environmental stresses.The results further revealed the important effect of the cushion plants on function and species diversity of Alpine ecosystems,thus providing theoretical support and scientific guidance for the protection and restoration of Alpine ecosystems under global climate change.