Effects Of Warming On Growth And Nutrient Partitioning Of Abies Faxoniana And Subalpine Meadow

Under the global climate warming background,timberline is predicted to be higher,and there were seedings was found above timberlines.In the alpine and subalpine meadow above timberline,survival and growth of seedings is influenced by herbaceous community.Understanding the response of seeding establishment and the response of alpine meadow to climate warming is of great important to timberline reformulation and forest restoration.The experiment was located in the subalpine meadow of Balang Mountain,Wolong nature reserve,Sichan province.Seedings of local timberline tree speciese Abies faxoniana and subalpine meadow was choosen as study subjects.To understand the combined effects of climate change and human disturbance on the alpine meadows,we conducted an field experiment to test effects of warming(by using open top chambers,OTC),N addition and weeding on an subalpine meadows.To understand the effects of simulated warming and functional group removal on A.faxoniana seedings,we conducted and simulated warming and functional groups removal experiment to analyzing the change of grwoth and pfysiological index of A.faxoniana seedings and herbaceous functional groups.The results are as follows:(1)The response of subalpine meadow to climate change.Warming increased sum of additive cover of the meadow community,but N fertilization decreased it.Community height was increased by warming and N fertilization.The number of individuals of subalpine meadow was generally decreased by fertilization.Warming increases both aboveground and belowground biomass,while weeding reduced aboveground biomass but increased belowground biomass.Weeding decreased aboveground biomass but increased belowground biomass.The effect of N fertilization on biomass was influenced by warming and weeding.Warming,N fertilization and weeding have negative effects on species diversity(P<0.05).Warming promoted the growth of grasses and forbs but inhibited the growth of sedges,however,warming increased the growth of sedges under N fertiliation or weeding.Warming enhanced the importance value of grasses but reduced the importance value of forbs.Weeding promoted the importance value of grasses but reduced the importance value of forbs without warming,and promoted the importance value of forbs but reduced the importance value of grassed with warming.(2)The interaction among different functional groups and its response to climate warming.Warming promoted the growth of grasses,increased the height of sedges and forbs(P<0.05),increased the biomass of sedges but decreased biomass of forbs.The existence of grasses increased biomass of sedges but decreased biomass of forbs without warming.However,the inhibition of forb biomass from grasses disappeared with warming.The existence of sedges increased the biomass of grasses and forbs.The aboveground total nitrogen and phosphor content of sedges increased after removing any herbaceous functional groups(P<0.05).(3)The response of Abies faxoniana seedings to herbaceous and climate warming.Warming increased survival and non-structural carbohydrate content but decreased the growth and root/shoot ratio of A.faxoniana.Seeding survival was significantly positively correlated with non-structural carbohydrate content(r=0.496,P<0.01),especially with soluble sugar(r=0.617,P<0.01).The existence of herbaceous speies decreased the survival of A.faxoniana without warming,but forbs increased it with warming.Sedges incrased growth and biomass of A.faxoniana(P<0.05).Grass and forbs increased height growth and aboveground biomass of A.faxoniana,but decreased root length and belowground biomass.After warming.Grasses and forbs decreased the height growth and aboveground biomass of A.faxoniana.Sedges dereased increased root length and belowground biomass but still increased height growth and aboveground biomass of A.faxoniana.To sum up,warming and N fertilization increased height and production but decreased diversity of subalpine meadow,and would impel the succession to grasses taking dominant position and inhibit forbs.Under climate warming and nitrogen deposition,human disturbance would promote the succession to grasses taking dominant position.Warming increased survival of A.faxoniana seedings but would made it to face with stronger competition from herbaceous,the growth and biomass of A.faxoniana seedings would be inhibited...