| The forest-steppe ecotone in Greater Xing’an Range is key area,where the Greater Xing’an forest interacts with the Hulunbuir grassland.The ecotone is characterized by high biodiversity,frequent material flow,and strong spatiotemporal dynamics.For the last decades,climate change and human interference have caused dramatic changes of plant community.However,how the space-time variation of plant community responds to the dual stresses in the region remains unclear.Field investigation was conducted from meadow grassland to forest across the ecotone consecutively in 2008,2009,2010 and 2019 in the forest-steppe ecotone of Chenbalhu Banner in the Inner Mongolia.Combined with different land use patterns of grazing grassland,non-grazing grassland,mowing grassland and natural grassland.We evaluated the dynamics of species richness,Raunkiear life-form functional group,forage value,community biomass and soil factors.Then the species diversity-relationship was discussed in detail on variant spatial scales.We analyzed the variation in the species richness-biomass relationships under different environmental conditions.The main results were as follows:1.In general,forest-steppe ecotone presented the typical unimodal model of plants distribution.Species richness was significantly different in grassland outside of the forest section.Compositae dominated in all plots,perennial forbs were the most important components,and the aboveground biomass,species richness index and Shannon-Weiner index showed a trend from low to high and then to low,species productivity and species diversity index were the highest in inter-forest grassland.2.Compared with the average of 2008-2010,species richness significantly decreased in2019,and more than 10 species of gramineous were lost;functional groups significantly changed: the annual and biennial species was increased by 4%,and the perennial forbs were decreased by 8%;the proportion of high quality forages was decreased by 5%,and the proportion of inferior forages was increased by 7%;community aboveground biomass was significantly decreased by 35%.Importantly,the community structure and function of the meadow grassland were more strongly affected by climate change and grazing disturbance than other sections.In 2019,species richness of meadow grassland communities was reduced by 12%,and grassland community aboveground biomass was significantly reduced by 62%compared to the average value of 2008-2010.Meanwhile,soil p H,water content,total nitrogen and total phosphorus contents in the forest-steppe ecotone in 2019 were significantly decreased by 14%,50%,25% and 40%,respectively.3.In different land use patterns,Compared with natural grassland,the relative productivity of grazing grassland,enclosed grassland and mulching grassland decreased by84.07%,35.89% and 43.78%.Importantly,species richness of heavily grazing grassland lost more than 30 species,and the number of annual and biennial of the life-form functional group increased by 10%,and the proportion of inferior forage grass increased by 14%..4.There was no relationship between species richness and aboveground productivity in the forest-steppe ecotone.Species composition were significantly related with functional groups.Perennial forbs had no clear relationship with biomass.The functional groups of shrub and semi shrubs,perennial grass and annual and biennial exhibited positive liner or unimodal relationship with aboveground productivity in forest-steppe ecotone.Relationship between aboveground biomass and plant functional group was also influenced by soil conditions.Soil water content was an important factor influencing species richness and productivity.The structural equation model showed that aboveground biomass was directly affected by annual precipitation and soil properties,and indirectly affected by temperature.In conclusion,species composition,soil factors and community dynamics of forest-steppe ecotone in northern China have been significant altered due to climate change and human activity.Soil water content is the important factor,which is controlling plant composition and productivity.Plant functional groups are determinant factor for the species diversity-productivity relationship in the forest-steppe ecotone.In land use patterns,heavy grazing significantly reduced plant species richness and productivity compared with natural grasslands.Our results suggest that the pressure of grazing should be reduced in the region,and local government should pay more attention to protect species diversity and soil and ultimately fulfill the sustainable utilization of agricultural development Greater Xing’an Range. |
