| The forest-steppe ecotone in Northern China is the transition zone from forest to steppe in eastern China,which is both ecological and agro-pastoral ecotone.Under the influence of climate change and human disturbances,the poor stability of vegetation and soil,easy to damage and difficult to restore.At the same time,it bears the responsibility of sand erosion control in the source of sandstorm in Beijing and Tianjin,and faces many problems such as windbreak and sand fixation,grassland ecological restoration and protection.Based on the forest-steppe ecotone on the eastern edge of Xilingol Grassland in Inner Mongolia,we obtained the species composition,coverage,height,aboveground biomass,and soil nutrient data,including organic matter(SOM),total nitrogen(TN),alkali-hydrolyzable nitrogen(AN),total phosphorus(TP),available phosphorus(AP),total potassium(TK),and available potassium(AK),through field sampling.Based on geostatistical analysis,spatial interpolation was conducted to obtain the spatial variation patterns of soil nutrient indexes and the quantitative characteristics of plant communities,and to identify the soil nutrient indexes of different slope aspects and topographic conditions(sloping land and flat land),as well as the differences of spatial variation characteristics of plant communities.Then,variance partitioning analysis was used to explore the effects of soil nutrients on the spatial distribution pattern of plant communities at small scales.The main results were as follows:(1)The overall content of soil nutrients in the study area soil nutrient level was higher.The contents of SOM,N,and K were high,while that of P was relatively low.The variance of available nutrient content in the study area was larger,while that of SOM and total T,P,and K were less.(2)Soil nutrients in the study area showed a certain spatial autocorrelation.The spatial heterogeneity of available nutrients was stronger than that of nutrients like TN,TP,and TK.For the same elements,the spatial autocorrelation of total nutrients was usually stronger than that of available nutrients,and the spatial autocorrelation distance was also larger.In terms of topography,SOM and total nutrients like TN,TP,and TK,changed less in the study area,while the content of available nutrients in sloping land was much higher than that in flat land.The correlation between N and P was significantly positive,which was also reflected in the change of the north-south slope direction.The content of SOM,N,and P decreased gradually in the change of the south slope direction and was the lowest in the south slope.On the contrary,the contents of TK and SOM changed,and the content of TK gradually increased in the north-south slope direction.There was no significant correlation between AK and other soil nutrients.In the north-south slope direction,the content of AK increased and then decreased.The spatial variation of soil nutrients was different from that of other soil nutrients.(3)Plants in the study area are mainly composed of Compositae,Leguminosae,Gramineae,and Rosaceae,with complex community structure and rich species composition,with typical characteristics of the forest-steppe ecotone.Gramineae plants less relative to the typical grassland,plant diversity was rich,showed that the region relatively humid climate,relatively abundant moisture conditions(4)There was spatial autocorrelation between the community coverage and the number of species in the study area,and the autocorrelation distance of the community coverage was far greater than the number of species richness,exceeding 200 m.Except for the aboveground biomass,the content of all the community indexes was higher on the slope than on the flat land.In general,plants on the eastern slope were growing well,and with higher species richness than those on the southern and northern slopes.There was little difference in plant diversity on the north and south slopes,but the growth of plants on the north slopes was better.(5)The results of variance partitioning analysis showed that available nutrients had more influence on the species composition and spatial distribution of plant communities than SOM and total nutrients in the study area.The individual contribution of available nutrients to biomass and coverage was stronger than that of total nutrients,and the species diversity of the plant community was also affected by available nutrients.Due to the high spatial heterogeneity of available nutrients in the study area,the distribution of plant communities was not uniform.Available nutrients had a great influence on plant community characteristics,especially Shannon diversity and community coverage.At the same time,the single contribution rate of available nutrients to the number of plant species in the community was more than 60%,which was the main reason for the change in the number of plant species in the community.(6)Aboveground biomass was mainly affected by total nutrients in flat land and available nutrients in sloping land.Available nutrients were also the main soil nutrients that affected the change of community coverage in the study area,but the single contribution rate of total nutrients to community coverage was still higher than that of available nutrients in local areas.In the north-south slope direction,the content of AK increased and then decreased,which was consistent with the changes of aboveground biomass,species richness,and Shannon diversity.The contribution of soil nutrients to species evenness was greater on the northern and eastern slopes.The contribution to coverage and species number was greater on the south slope.Total nutrients played a greater role in the change of plant community on the southern slope. |
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