Effects Of Potentilla Froticosa On Vegetation Characteristics And Soil Properties In Alpine Meadow Of Tibetan Plateau

Potentilla fruticosa shrub meadow,as an important vegetation type in the whole Tibetan Plateau,is widely distributed in 3200-4500 a.s.l.on the alpine region,which area only rank second to alpine Kobresia meadow and has a significant ecological and economic benefits.Potentilla fruticosa shrub meadow was regarded as a product formed of the cold and wet climate changes after the uplift of the Tibetan Plateau.In recent years,with the global climate change and human activity-induced grazing disturbance,the ecosystem in this area is particularly vulnerable and unstable,and there is a trend of further expansion of alpine shrub(Klein et al.,2007;Elmendorf et al.,2012).In arid and semi-arid regions,the encroachment of woody plants and expansion in large areas has caused extensive concern and research by ecologist in the world,shrub encroachment usually leads to changes of the structure and function in grassland ecosystem,even caused land degradation and desertification in arid areas.At present,the researches on shrub encroachment grassland in the world were mainly distributed in the arid and semi-arid regions in North America and southern Africa,it was little found in alpine regions,particularly,there were no studies about the effects of Potentilla fruticosa on changes of the vegetation characteristics and soil properties in an alpine meadow ecosystem of Tibetan Plateau,therefore,to study the characteristics of aboveground vegetation and the belowground nutrients in Potentilla fruticosa shrub meadow has important practical significance for evaluating the effect of Potentilla froticosa expansion on alpine meadow and scientific management of shrub grassland on Tibetan Plateau.In this study,we selected three altitude levels(3000 m,3280 m and 3650 m)of Potentilla fruticosa shrub grassland in Tibetan Autonomous Prefecture of Gannan which located in the eastern of Tibetan Plateau,at the patch scale,we surveyed aboveground plant communities characteristics,Analyzed the differences about physical and chemical properties of topsoil(0-0.3m)and spatial distribution characteristics of soil carbon,nitrogen,phosphorus and other nutrients in 0-1 m soil layer both in Potentilla fruticosa shrub patches and herbaceous plant patchesbetween shrubs.the following main results were obtained:1.42 species,belonging to 18 families,were recorded in three Potentilla fruticosa shrub meadows,which indicated that alpine shrub grassland had high species richness.The species richness showed no significant difference between Potentilla fruticosa shrub patches and herbaceous plant patches between shrubs across the three altitudinal levels(P > 0.05),but the species diversity index(Shannon-Winner index and Simpson index)and species evenness index(Pielou index)all had significant differences(P < 0.01).At the patch scale,the results found that Potentilla fruticosa significantly decreased the dominance of sedge species and weeds on the Potentilla fruticosa shrub alpine meadow in Tibetan Plateau,but the effects on grasses dominance is not significant.2.The biomass of both the aboveground and belowground of Potentilla froticosa shrub patches was significantly higher than herbaceous plant patches(P < 0.01),the height and aboveground biomass of Potentilla froticosa shrub decreased with altitude increase and the belowground root biomass increased with altitude increase.Our study found that Potentilla fruticosa shrub grassland in alpine regions had very developed in roots,the Potentilla froticosa shrub roots could extend to 0.5 m of soil profile,while herb roots mainly distributed within 0.2m.3.The content of soil organic carbon,total nitrogen,total phosphorus and soil available nutrients under Potentilla froticosa shrub patches were all significantly higher than herbaceous plant patches(P < 0.05),it indicated that "fertile island effect" can also be formed at high altitude areas in alpine meadow of Tibetan Plateau.The higher nutrients content of the " fertile island" under Potentilla froticosa shrub patches had significantly positive correlation with the input of the aboverground litter and the underground root biomass.4.The variation of soil nutrients content in the depth 0-1 m of soil profile were different between Potentilla froticosa shrub patches and herbaceous plant patches.In the top 0-0.3 m of soil layer,the content of soil organic carbon,total nitrogen,total phosphorus,available nitrogen and available phosphorus under Potentilla froticosa shrub patches were all significantly higher than the area of between Potentilla fruticosa shrub patches(P < 0.05),however,in the depth of 0.3-1 m of soil layer,the content of soil total carbon and nitrogen showed the same trends with the 0-0.3 m of soil layer,but the content of soil total phosphorus and available phosphorus under Potentilla froticosa shrub patches were all significantly lower than herbaceous plant patches between shrubs(P < 0.05),It indicated that Potentilla fruticosa had a greater capacity to translocate phosphorus from the lower to the upper soils than herbaceous plants.5.The total content of soil organic carbon and total nitrogen in 0-1 m soil profile underPotentilla fruticosa shrub patches is significantly higher than herbaceous plant patches between shrubs,but the total content of soil total phosphorus and available phosphorus in the 0-1 m soil profile the were significantly lower than herbaceous plant patches(P < 0.05),it suggested that greater C and N accumulation versus a depletion in P in the top 1 m soil layer occurred under P.fruticosa,compared to under the herbaceous plants.6.The soil P mineralization and mineralization rate under Potentilla fruticosa shrub patches is significantly higher than herbaceous plant patches in 0-0.3 m soil layer after 180 days incubation,it indicated that the shrub island formed by Potentilla fruticosa had higher soil P mineralization potential.7.The RDA correlation analysis as regards vegetation characteristics and soil environmental factors showed that: soil available phosphorus(AP),available nitrogen(AN),microbial biomass carbon(MBC)and microbial biomas nitrogen(MBN)had significant positive correlation with Species richness(P < 0.01),and had significantly negative correlation with the ground total biomass and the biomass of each function group,it indicated that the soil available and active nutrients were main soil environmental factors that affected the structure and characteristics of community in alpine shrub meadow of Tibetan Plateau,Potentilla fruticosa had caused the heterogeneity of soil nutrients spatial distribution in alpine meadow and resulted in a significant decline in the productivity of herbaceous plant community in alpine meadow.