Response Of Seedling Emergence,Plant Growth And Reproduction To Warming In Alpine Meadow On Tibet Plateau

As the most vulnerable life history stage of plant species,seedling emergence is very sensitive to global warming.Seedling emergence also is the earliest stage of life history,it can directly and/or indirectly affect the expression of post-germination traits.Thus,making research on ecology of seedling emergence and its influence on the response of growth and reproduction of plants to warming is very helpful for us to understand the effect of warming on plants population dynamics,the structure and ecosystem function of plants community.Here,we have studied the ecology of seedling emergence of an alpine meadow on the Eastern Tibet Plateau.Meanwhile,the responses of seedling emergence,plant growth and reproduction to warming,and the relationships between these responses would be studied.Three experiment would be conducted: 1)the seedling emergence behavior(seedling emergence season,seedling emergence rate,and seedling emergence percentage)of 265 plants were monitored in the field through showing seeds in the pots;2)the effect of warming on seedling emergence were tested by simulating warming with Open Top Chamber(OTC);3)the influence of warming on growth and reproduction of 12 plant species were tested,and how seedling emergence behavior affecting the response of plant growth and reproduction to warming would be analyzed.The main results and conclusions as follows.(1)Seedling emergence behavior of plants from alpine meadow on Eastern Tibet Plateau.In general,field emergence percentage(FE)of plants from alpine meadows on the Eastern Tibet Plateau is fairly low.As compared to autumn and summer,spring is the most common emergence season for plants from the studied alpine meadow.Mean emergence timing is mainly affected by phylogeny and seed mass,while field seedling emergence percentage is mainly affected by peak emergence season and phylogeny.On average,large-seeded species emerged more later than small-seeded species.Furthermore,early-emerging species always had a higher FE than the late-emerging ones,which suggests that FE decreases with time after seed dispersal.Increasing number of seedlings of early-emerging species could help compensate for high mortality due to increased exposure to seasonal hazards(low temperature).Thus,there may be a trade-off between early emergence and late emergence.That is,if species delay germination until conditions for seedling establishment become more favorable they can gain some advantages in seedling establishment;however,the cost incurred is a decrease in FE(e.g.seed predation,loss of seed viability).On the other hand,if a species germinates immediately it will have a high FE and a long growing season and thus an advantage in resources utilization(priority in occupancy of space and in use of other resources).(2)Effect of warming on seedling emergence behavior in alpine meadowOverall,warming can reduce the mean seedling emergence percentage of plants from the studied alpine meadow,and seedling emergence of some species can be totally prevented by warming.The variation of seedling emergence time among species was reduced by warming.It means that seedling emergence of plants in the studied community occur under warming condition during a shorter period than under control condition.Warming have no significant influence on seedling emergence of annuals/biennials,however,warming can increase the variation of seedling emergence percentage of perennial and reduce the variation of their germination timing.Thus,warming results in the overlap of time niche of perennial and improve the competition between perennial.Under warming condition,the difference between the emergence timing of large-seeded species and that of small seeded species would disappear.And warming can significantly increase the emergence percentage of large-seeded species.It indicates that warming may be helpful to improve of the dominance of large-seeded species in alpine meadow.The interaction between phylogeny and warming can significantly affect seedling emergence timing and seedling emergence percentage.The response of seedling emergence behavior to warming is different from family to family.After warming,seedling emergence of some family get better,however that of the other families stay the same or get worse.Thus,warming maybe change the phylogenetic structure of the alpine meadow in the future.The variation of emergence timing of dominant species was reduced and seedling emergence of dominant species was delayed by warming.Warming can also increase the variation of seedling emergence percentage of rare species.As a result,the community structure of alpine meadow may be changed by warming.(3)Seedling emergence,plant growth and reproduction in relation to warming Seedling emergence of autumn-emerging species would be delayed by warming,however,seedling emergence of spring/summer-emerging species was brought ahead by warming.Plant height and biomass of autumn-emerging species was not significantly influenced by warming.However,plant height and biomass of spring/summer-emerging species was significantly increased by warming.And if all the studied species were taken into account,warming also can significantly increase plant height and biomass.The difference of response of plant height and biomass to warming between autumn-emerging species and spring/summer-emerging species might be caused by their different response of emergence timing to warming.Overall,warming have no effect on the R/S of species in the studied alpine meadow.It indicated that warming have no significant effect on absorption of water and nutrients,so plant in the studied alpine meadow does not need to regulate their water and nutrient absorption capacity through changing their R/S.Under warming condition,plant is allocated more resource on vegetative growth,which caused the reduction of reproductive allocation.Under control condition,emergence timing only have direct effect on reproductive biomass,but without indirect effect.However,under warming condition,emergence timing also can indirectly affect reproductive biomass through its influence on other plant traits.It means that emergence timing has a stronger effect on other plant traits under warming condition than under control condition.The interaction between warming and species can significantly affect plant growth and reproduction.It indicates that the response of plant growth and reproduction to warming always different form species to species.Thus,warming may change the relative dominance of species in the studied alpine meadow.