| Forest-steppe ecotone,transition area between forest and steppe ecosystem at time and spatial scale,which has large species richness and high productivity.However,due to the interference of natural and human factors,it could be influenced by exceeding the critical threshold of ecosystem,which has a severe adverse impact on the community structure and function of ecosystem.Forest-steppe ecotone of the Greater Xing’an Range is the most representative ecotone in Northern China.In recent years,it was shown that the vegetation of Greater Xing’an Range had been degraded seriously due to agriculture cultivation and overgrazing under climate change scenarios.However,there are no study focusing on exploring the current situation of grassland degradation and analyzing driving factors of grassland degradation from a long-time scale in this forest-steppe ecotone.Therefore,field experiment was conducted at Erguna forest-steppe ecotone in Inner Mongolia to study the structure and function of aboveground plant communities and soil communities in different vegetation gradient in 2019,and soil microbial biomass were determined by PLFA.Moreover,we also used 63-year long-term land use change and meteorological data of Argun city and Chenbarhu Banner to analyze what kind of factors influence the grassland degradation in forest-steppe ecotone of the Greater Xing’an Range.Main results were as follows:(1)There were 48 families,151 genera and 226 species of vascular plants in Erguna forest-steppe ecotone in 2019.Compositae was the main species composition in the area,and the number of species accounts for 20%of floristic composition;species diversity of the regional community showed a single peak trend,with the highest in the understory forest community and the lowest in the overgrazing community with 42 species;the composition of plant functional groups was obviously different.Perennial grass was the main component of community,accounting for more than 50%of the whole region.Compared with the data of 10 years ago,the proportion of high-quality forages decreased by 20%in 2019;the aboveground productivity decreased by 50%,and the community on the meadow steppe have significantly decreased by 68%.(2)Soil physical and chemical properties and nutrients were significantly different of each section in the ecotone.The highest soil p H value was shown in meadow steppe with 6.70,and the lowest was only 5.54 in forest community.Soil water content,soil organic matter,total nitrogen and total phosphorus had the highest value in understory forest community,and lowest value in the grazing community.Compared with the data from 10 years ago,we found that the content of soil organic matter and total nitrogen significantly decreased in 2019,especially in the meadow grassland.Soil microbial community structures were significant different in each section.The total microbial biomass,bacterial biomass and fungal biomass were the lowest in heavy grazing community,and highest in the understory forest.Through soil nutrient properties and microbial biomass analysis,the understory forest community had the highest soil ecosystem stability due to its high soil nutrient contents and microbial biomass,while the heavy grazing community had the weakest anti-interference ability to the external environment due to its lowest soil nutrient contents and species diversity.(3)Using 63-year long-term land use change and meteorological data analysis,we found that from 1957 to 2019,mean annual temperature significantly increased2.9℃to 3.1℃in Argun city and Chenbarhu Banner,respectively.Mean annual precipitation fluctuated dramatically between 150 and 550 mm,the precipitation exhibited an overall decreasing trend from year 2000 to 2019.Livestock density has increased greatly among different business entities.The average livestock density increased from less than 1 standard sheep unit/hm~2to 2-5 standard sheep unit/hm~2in the state-owned farms,while the average livestock density of the individual herdsmen increased from 0.5 standard sheep unit/hm~2in 1980 to 7 standard sheep unit/hm~2in2019,resulting in a serious grass-livestock imbalance.The reclaimed areas of Shangkuli Farm and Taohai Pasture fluctuated upward,peaking at 37000 hm~2and7000 hm~2respectively in 2014.Since then,the reclaimed area has decreased due to the policy of returning farmland to forest.Results of a principal component analysis(PCA)using climate,grazing,reclamation and grassland degradation in this area showed that overgrazing was the dominant factor that led to grassland degradation in the ecotone under the scenarios of regional climate warming and drought.In conclusion,under the background of climate warming and drought,plants and soil degraded significantly in the ecotone,and it was the most significant degradation of the meadow grassland community by overgrazing.These findings suggest the need to strengthen the construction of grassland supervision and management systems to cope with the dual pressures of regional climate change and land degradation.The reward and subsidy funds from the central government should be used to return farmland to forest and grassland and herdsmen’s animal husbandry.Furthermore,we suggest that local governments establish multiple species artificial grasslands and adopt new technologies to restore and reconstruct degraded grassland to achieve sustainable utilization of grassland resources in the forest-steppe ecotone of northern China. |
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