Ant-mound Promoted The Transform Of Alpine Meadow To Grass Community

Ants are bio-interference factors that can not be ignored in grassland ecosystems.They can lead to grassland vegetation heterogeneity by building ant-mound.Previous studies on ant-mound focused on its size and distribution,species composition of plant communities around the ant-mound,soil seed banks and microbial characteristics in grassland.Studies on soil seed bank composition under the effect of ant-mound on community structure are relatively lacking in different habitats.In the study,we analyze the plant community species composition,grassland stability and soil physical and chemical properties surrounding the ant-mound in two habitats(terrace and flat)in the eastern Qilian mountains alpine grassland,which will clarify the effect of ant-mound on the vegetation evolution in the alpine meadow.The main results are as following:1)Ant-mound significantly changed the species composition of grassland community.As far as the community at the edge of the ant-mound,the formation of ant-mound reduced the species richness and value of Simpson and increased values of Shannon-Wiener and Pielou.The important values of Stipa krylovii,Poa pratensis and Elymus nutans at the edge of the ant-mound were 1.82 times,2.55 times and 1.47 times that of the control in terrace,respectively;while they were 1.7times,3.3 times and 2.2 times that of the control in flat,respectively.The biomass of Kobresia and grass at the edge of the ant-mound in two habitats accounts for about 95% of the total above-ground biomass;while their biomass at the control in two habitats accounts for about 70%of the total above-ground biomass.2)Ant mound facilitated the accumulation of seeds in the 0-4 cm soil under the ant-mound.The soil seed bank density of A,B and C in 0-4cm depth were 50303.32 seed · m-3,29986.63seed·m-3,and 33796.02 seed·m-3,respectively.Ants changed the soil seed bank under the ant-mound in 0-8cm depth.Gramineae(28.2%)>Sedge(22%)> Plantaignaceae(7.5%)>Asteraceae(6.9%)>Liliaceae(6.8%),Polygonaceae(0.16%)were the least.Ant mound significantly increased the seed density of Poa pratensi(14260.74seed·m-3),Dandelion(2832.61seed·m-3)and Oxytropi(1074.43 seed·m-3)in the 0-8 cm depth under the ant-mound,which were 4.3 times,9.7 times and 10.9 times of the control,respectively.3)The soil moisture content and soil density in 0-10 cm depth under the ant-mound was lower than that the control.The formation of ant-mound had no effect on the total N,total P and organicmatter of soil in 0-20 cm depth.4)Four methods(Godron stability analysis,Raunkiaer frequency coefficient,degree of succession and variance ratio method)indicated that the community at the edge of the ant-mound was unstable.It had a non-significant positive inter-specific association,which were loose and independent.The community was at the positive succession stage.Ant-mound formation improved the proportion of grass and kobresia in grassland,and weakened the community stability at the edge of the ant-mound.It was benefit for the evolution of grass+kobresia community.