Biomass Allocation And Stoichiometric Characteristics Of Degraded Alpine Meadow In Northwesten Sichuan

Affected by climate change and human factors,alpine meadow has been degraded,which not only endangers the ecological security of meadows,but also affects the sustainable development of pasturing area economy.Studying the biomass allocation of plant communities and dominant species,and the ecological stoichiometry of plant and soil is helpful to understand the ecological adaptation strategies and maintenance mechanism of plants under degradation.Therefore,we selected alpine meadows with different degradation degree(non,light,moderate and heavy degradation)as objects to study the biomass and C,N and P stoichiometric characteristics of plant communities(aboveground plants and belowground roots)and dominant species(leaves,stems and reproductive organs)and soil physicochemical properties.The results are as follows:1.Biomass and biomass allocation of plant communities changed under degradation.Aboveground biomass increased first and then decreased under degradation,and was significantly lower than other gradients under heavy degradation(P < 0.05).Belowground biomass decreased first and then increased under degradation,and was significantly higher than other gradients under non degradation(P < 0.05).Under heavy degradation,the allocation of root biomass in 0-10 cm soil depth was significantly lower than other gradients,and in 10-20 cm and 20-30 cm soil depth was significantly higher than other gradients(P < 0.05).Root to shoot ratio decreased first and then increased,and it was significantly higher in non and heavy degradation than under moderate degradation(P < 0.05).2.Biomass allocation of dominant species changed under degradation.In grass,reproductive allocation increased under degradation.In sedge,reproductive allocation increased under light and moderate degradation.In legume,there was no significant change in organ allocation.In forb,the reproductive allocation of Ranunculus tanguticus increased under degradation,which of Taraxacum mongolicum increased under light and moderate degradation,and in Polygonum viviparum,leaf allocation increased,while stem and reproduction allocation decreased under degradation.3.Compared with non degradation,in plant community,light degradation significantly increased C content and every gradient all significantly increased the N content and N: P,and significantly decreased the C:N.In root,ight degradation significantly increased P content and significantly decreased C:P and N:P,moderate degradation significantly increased P content and significantly decreased C:P,and heavy degradation significantly increased C content(P < 0.05).4.The stoichiometric characteristics changed little in the dominant species of grass and legume.In segde,P content in leaves of Kobresia humilis decreased significantly and C:P increased significantly under light and moderate degradation,while Carex enervis on the contrary.In forb,the N and P content in leaves and stems increased.In Taraxacum mongolicum reproductive organs,P content increased significantly,while C:P and N:P decreased significantly under moderate degeneration.In Polygonum viviparum reproductive organs,N and N: P increased significantly,and C: N decreased significantly under heavy degradation(P < 0.05).5.Stoichiometric homeostasis of C,N,P and their ratios in dominant species generally belong to steady state or weak steady state.The stoichiometric homeostasis of C,N and P is C > N > P as a whole.Stoichiometric homeostasis of C,N,P and their ratios was higher in reproductive organs than in leaves and stems in grass.In sedge,the stoichiometric homeostasis of leaves was higher than that of reproductive organs.The stoichiometric homeostasis of legume was not consistent.The stoichiometric homeostasis of leaves is higher than that of stems,and the stoichiometric homeostasis of P in leaves is lower than that of other elements,and the stoichiometric homeostasis of Polygonum viviparum is lower than that of other species.6.Soil moisture,C,N and P content decreased,while the soil bulk density,p H and C:N increased under degradation in 0-10 cm,10-20 cm and 20-30 cm soil depth.7.Structural equation model(SEM)showed that the degradation gradient directly affected soil p H,aboveground plant community element content and stoichiometric ratio,aboveground and underground biomass,root shoot ratio,and indirectly affected soil element content and stoichiometric ratio,root element content and stoichiometric ratio.In conclusion,plants will adjust their biomass allocation and use of C,N and P to adapt to the adverse effects of ecosystem degradation.In plant community,the root to shoot ratio changed to compete for resources,the aboveground plant N content and N:P increased and C:N decreased to accelerated the growth rate,and the root P content increased and C:P decreased to maintain the metabolic rate.In species,grass maintained stable nutrient absorption and increased reproductive allocation.Sedge has high leaf stoichiometric homeostasis and increases reproductive distribution under light and moderate degradation.Legume has little change and high internal stability.In forb,N and P content increased,the growth rate accelerated.In Ranunculus tanguticus,reproductive allocation increased,P content of reproductive organs increased.In Polygonum viviparum,the stoichiometric homeostasis was low,the leaf allocation increased,the reproductive allocation decreased,and reproductive N content increased.