Effects Of Nitrogen Addition And Warming On Plant Reproductive Strategy In An Alpine Meadow On The Tebetan Plateau

Alpine meadow has a very important ecological function,which is one of the most widely distributed ecosystems on Tibet Plateau,and one of the most important grazing areas.As an ecosystem formed in alpine extreme environments,alpine meadow is very sensitive to climate change.In the current context of global change,the response of plants in alpine meadow ecosystem to global change can function as an indicator of future environmental changes.Reproduction,as the most critical period in plant life history,is an important process driving the evolution process.Plant growth and reproduction are the process of obtaining resources and utilizing resources from the environment.How plants obtain limited resources and allocate them is an essential issue of plant life-history strategies.Using a classic allometric model R=βVα(The linear model is represented by the commonly used transformations:log R = log β + α log V),we investigated the effects of nitrogen application and warming on the resource allocation and reproductive strategy of plants in an alpine meadow on the Tibet Plateauat the species level,functional group level and the community level,respectively.Based on the slope and intercept of the regression relationship of allometric model,we can determine whether the plant reproductive allometry and the trade-off between seed mass and seed number change.The main results are as follows:1)At the species level,the plant reproductive allocation is not consistent in response to nitrogen addition;at the functional group level,high concentrations of nitrogen addition significantly reduced the slope of the regression relationship between the reproductive and vegetative biomass for graminoids.The allometric relationship of forbs did not change significantly under nitrogen addition.2)With nitrogen addition,vegetation biomass of graminoids increased significantly,but the seed mass and seed number of graminoids did not change significantly,so the slope of the regression relationship between the reproductive and vegetative biomass of the graminoids decreased;however,both the vegetative biomass and seed number of forbs increased significantly,which led to no change in the slope of the regression relationship between the reproductive and the vegetative biomass.3)Graminoids,as the main forage grass of grazing,dominate the alpine meadow ecosystem.Nitrogen addition changed the resource allocation pattern of graminoids,and they allocated more resources to the vegetation part,which is better to survival and competition of graminoids in the environment.Therefore,graminoids tend to be more dominant,while forbs were to be eliminated by resrouces competition.4)The trade-off between seed mass and seed number for graminoids changed under nitrogen addition.In nitrogen addition,graminoids prefer to produce smaller and more seeds.The trade-off between seed mass and seed number did not change significantly for forbs.5)Effects of nitrogen addition and warming on reproductive allometry were different over years.Nitrogen addition and warming did not change plant reproductive allometry at the community level in the first year,while the intercept of reproductive allometry was significantly decreased the second year.6)At the species level and functional level,there was no significant trade-off between seed mass and seed number;at the community level,there was a significant trade-off between seed mass and seed number,and the trade-off was not affected by short-term nitrogen addition and warming.