| Objectives: Under the influence of Formica aquilonia Yarrow,the change characteristics of physicochemical properties of ant nests and surrounding soil,the allelopathic effects of ant nest material extracts on seed germination and seedling growth,and the composition characteristics of seed banks in ant nests and surrounding soil were determined,and finally the influence of ant nests on plant community structure was explored.Methods: In August 2019,Formica aquilonia Yarrow nests were searched in the warm desert steppe,warm steppe and mountain meadow respectively.(1)Taking the center of the ant nests as the origin point,the soil at a depth of 20 cm was measured at the distance of 0cm,50 cm,100cm,150 cm,200cm and 500cm(CK),and the soil moisture content,p H value,organic matter,total nitrogen,total phosphorus,alkali-hydrolyzed nitrogen and available phosphorus were measured.(2)The contents of 0.1g/m L,0.05 g/m L and 0.02 g/m L extracts were prepared from the nest materials of Formica aquilonia Yarrow in each grassland,and the germination tests were carried out on the seeds of Bromus inermis,Dactylis glomerata,Festuca ovina,Poa pratensis,Piptatherum munroi and Seriphidium transiliense with distilled water as the control,explore the seed germination and seedling growth.(3)0?10cm,10?20cm deep soil samples were collected at the distance of 0cm,50 cm,100cm,150 cm,200cm and 500 cm from the nest,respectively.After germination test,identification and counting were conducted to explore the change characteristics of soil seed bank.(4)Plant species composition,functional group importance value,aboveground biomass,and species diversity index were analyzed by selecting a 0.5×0.5m sample box from the ant nest and 5m away from the ant nest(CK).Results:(1)Grassland type,distance from the nest and their interaction had significant effects on soil parameters(P<0.01).Alkali-hydrolyzable nitrogen and available phosphorus were mainly affected by distance from the nest,while the other parameters were more affected by grassland type.With the increase of nest distance,the nest center soil p H was significantly lower than the nest edge(P<0.05),and was significantly positively correlated with nest distance(P<0.01).The other parameters were significantly higher than those of surrounding soil(P<0.05),and soil parameters were negatively correlated with the distance from nest(P<0.01).Through the fitting curve,the soil parameters and the distance from the nest in different grasslands all accord with the function model.According to the analysis of soil parameters,except the distance from nest and available phosphorus had no correlation with p H value,other parameters showed significant correlation(P<0.05).(2)Compared with the control,the concentration of 0.1g/m L extract significantly reduced the germination rate,germination potential,germination index,root length and stem length of six kinds of seeds,but the biomass did not significantly reduce.In the same habitat,the allelopathic inhibition of seeds decreased with the decrease of extract concentration,but there were differences among species.The comprehensive effect index showed that Dactylis glomerata was the most inhibited in temperate desert grassland,Bromus inermis was the most inhibited in temperate grassland when the concentration was 0.1g/m L,Piptatherum munroi was the most promoted when the concentration was 0.02g/m L and 0.05g/m L,and Festuca ovina was the most inhibited in mountain meadow.The results of variance analysis showed that the effects of three factors on seed germination and seedling growth were as follows: species > grassland type >nesting material extract.(3)In the three types of grassland,the number of species and species in the soil seed bank of 0-10 cm and 10-20 cm depth in the center of ant nest were significantly higher than those in the surrounding soil.Perennial herbs were dominant,followed by annual herbs.With the increase of the diameter of ant nest,the number of seeds in the center of ant nest increased significantly(P<0.05).In temperate desert steppe,species diversity index of ant nest center increased significantly(P<0.05),Shannon Wiener diversity index and Pielou evenness index in temperate steppe and mountain meadow increased significantly(P<0.05).RDA analysis showed that the species composition of soil seed bank was most affected by available phosphorus and water content in temperate desert steppe,total phosphorus and p H value in temperate steppe,and available phosphorus in mountain meadow.(4)In the three types of grassland,compared with the control,the number of species of ant nest plants decreased,the important values of Gramineae and Cyperaceae and aboveground biomass increased significantly(P<0.05),the important values of Leguminosae and miscellaneous grasses decreased significantly(P<0.05),and the aboveground biomass did not increase or decrease significantly(P<0.05).Margalef index,Shannon Wiener index and Simpson index were significantly lower(P<0.05),and alatalo evenness index was significantly higher(P<0.05).Conclusion: Nest building activities of Formica aquilonia Yarrow can significantly improve the soil nutrient content,the number of seeds and species in the center of the nest,but the high concentration of nesting material extracts on the surface of the nest can inhibit the seed germination and seedling growth,and ultimately affect the succession of the nest plant community to Gramineae and Cyperaceae. |
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