Research On The Community Productivity Stability Of Artificial Grassland In Tibetan Plateau

Human activities lead to serious biodiversity loss,resulting in an increasing interesting of ecologists on the issue about how ecosystem stability would been affected by this loss.Many theoretical and experimental researches focusing on the stability of species compositions and ecosystem functions have improved our understanding of this issue.However,few studies focus on the coexistence of species and the influences of biodiversity on ecosystem stability within a single functional group.Grass species have similar traits and specific ecological function,hence have been treated as one kind of function type in ecological researches.In order to understanding the stability of species composition and productivity within this function type,we conducted an experiment by using three common species(Elymus nutrans,Festuca sinensis,and Festuca ovina),associating with the disturbances of nutrient addition and cutting.The main objectives we got after a long-term observation are as follows: 1.Coexistence of three species under the influences of nutrient addition and cuttingDue to the relatively smaller intraspecific species interactions when comparing with averagely intraspecific species interactions,these grass species could stably coexist with each other for many years.Comparing with others,species show a worse co-existent ability in the F.sinensis\E.nutrans mixture and F.ovina\E.nutrans mixture,due to the smaller difference between intraspecific-and interspecific interactions.However,the ability increased over time.The lowest productive species F.sinensis performed better in mixtures than in monoculture,indicating that it could stably co-existed with the other two species.Nutrient addition promoted species coexistence via increasing the difference of intraspecific-and interspecific interactions in each mixture,whereas cutting weakened the ability of coexistence by reducing that difference.Morevoer,cutting suppressed the positive influence of nutrient addition on species coexistence2.The influence of species richness on productivity in our grass communities under the influences of nutrient addition and cutting.Mixtures performed better than monocultures,because of their high trait-independent complementary effects.However,the contributions of trait-dependent complementarity effects and dominance effects were relatively small in this process.The trait-independent complementary effects of three-species mixtures were only higher than that of two-species mixtures in 2006 and 2008,thus only in these two years the three-species mixtures performed better than two-species mixtures.Nutrient addition increased overyielding via increasing trait-independent complementary effects,while cutting reduced overyielding by reducing trait-independent complementary effects.Interestingly,cutting could effectively suppressed the positive influence of nutrient addition.We did not find any interaction effects between nutrient addition and species richness and between cutting and species richness,indicating that the influences of nutrient addition and cutting on complementarity effects are independent with species richness.3.The influence of sowing species composition and richness on the richness and biomass of weed species under the influence of nutrient addition and cutting.The weed species richness was only negatively influenced by dominant species.The dominant species varied with time and treatments,thus the species that influenced weed species richness varied.During the early phase(2004-2008),the dominant species was E.nutans,hence the sowing treatments containing this species shown lower weed species richness when compared with other species composition types,and the influence did not varied with nutrient addition and cutting treatments.During the later stage,nutrient addition increased the dominance of E.nutans,but reduced the dominance of F.ovina,while cutting reduced the dominance of F.ovina,but did not affect the dominance of F.ovina.Consequently,the F.ovina dominanted in control and cutting treatments,while E.nutans dominanted in the nutrient addition treatments,F.ovina and E.nutans dominanted in the nutrient addition and cutting treatment.As a result,weed species richness was highest in the treatments that did not contain these two species(i.e.the monoculture of F.sinensis).In addition,the weed species biomass was strongly influenced by the dominant species,and was weakly influenced by the other two species,hence weed biomass was significantly influenced by sowing species richness.The higher the sowing species richness was,the lower the weed species biomass was.Moreover,the dominant species could suppress the performance of the other two species,thus had an indirectly positive effect on weed biomass.These results indicated that the community could be affected by sowing species for a long period of time.4.The influence of realised species richness,species evenness and sowing species stability on the community-and population-level stability of productivity under the influence of nutrient addition in the later stage of our experimentF.ovina monoculture had lower realised species richness,and the species composition types containing F.ovina had lower evenness,when comparied withother composition types.However,these difference did not lead to the significantly lower stability of these communities.This is due to the fact that the stable influence of F.ovina on community productivity stability.Even so,the effects of species richness and evenness on community stability was still positive.The positive realised species richness – community stability relationship was contributed by statistical averaging and species asynchrony,while the positive species evenness-community stability relationship was contributed by species asynchrony.In addition,the negative relationship between realised species richness and population-level stability was only found in non-nutrient addition treatment,and E.nutrans played an important role in this process.