Effects Of Qinghai-tibet Highway On Grassland Ecosystem In Disturbed Areas Along The Highway

In the area of Qinghai-Tibet Plateau,social development and people’s well-being are dependent on the construction and transportation of highways,which is crucial for regional stability and national security.In recent years,great achievements and progress have been established for the highways in Qinghai-Tibet Plateau,and such development will persevere.However,due to the climate and geographical condition in Qinghai-Tibet Plateau being unique and the ecological environment being fragile,the impact of the construction and transportation of highways on the ecological environment along the road is not clear.In particular,the outcome and mechanism of highways toward the ecosystem of grassland and soil microorganisms have not been investigated in the Qinghai-Tibet Plateau region.In this research,we evaluated the current status of the vegetation and soil that were potentially affected by the highway by analyzing the imaging data from Landsat-8 and conducting fieldwork.Specifically,the section between Golmud and Lhasa was chosen as the research object based on the state of construction and development of the Qinghai-Tibet Highway.It is assumed that 5km on both sides of the highway is the road area,and 400 m on both sides is the highway disturbance area.Three typical types of grassland that traversed through the research section were selected,and five distance gradients were constructed.The mechanism of the highway impact on the plant-soil-bacteria system along the route was discovered using conventional and high-throughput sequencing approaches.Besides,the interaction and regulation between different groups were analyzed.Our results suggested:(1)The changes in vegetation cover in the disturbance zone have resulted from both highway constructions and climate change.The disturbance area of the Qinghai-Tibet Highway was significantly degraded,including the decrease in cover,biomass,and diversity.The grass community structure has changed from Cyperaceae and Poaceae to other weeds such as Compositae.Notably,the extent of degradation diminishes with the distance,and the changes are mainly concentrated within 100 m of the highway,while it may reach as far as 300-400 m.(2)The construction and transportation of the Qinghai-Tibet Highway have significantly altered the physical and chemical properties of the soil in the disturbed area.For example,the soil water content and p H value were reduced,and the nutrient contents of soil,such as organic carbon,total nitrogen,alkalihydrolyzed nitrogen,etc.,have also decreased dramatically.These alternations led to the decline in soil microbial biomass carbon and nitrogen.Interestingly,the enrichment of soil lead and cadmium within 20-50 m of the disturbance zone of the highway.The impact of the highway on soil quality gradually increased with the shortened distance,and the impact was most obvious in the meadow steppe at high altitudes.(3)Highway-related activities significantly affected soil bacteria diversity and community structure,resulting in a decrease in the relative abundance of the original dominant species of soil bacteria and an increase in non-dominant species.Characteristically,Gemmatimonas,Terrimonas,Nitrospira,and Bacillus are more resistant to environmental changes along the highway,while Barnesiella and Blastococcus are more sensitive.In the highway disturbance zone,the abundance of Faprotax functional structure,including nitrification,hydrocarbon and sulfide degradation,and cellulolysis increased.In contrast,the abundance of bacterial species related to wild animals decreased.(4)The main factors that caused the differences in soil bacterial community structure in the road disturbance area include aboveground biomass,p H value,organic carbon,total nitrogen,alkaline hydrolyzed nitrogen,and ammonium nitrogen,while organic carbon and total nitrogen were most crucial.The main driving force regulating the soil bacterial structure is soil water content,available potassiumhydrolyzable nitrogen,and nitrate nitrogen content.In the disturbance zone,the vegetation and soil environmental factors on the change of soil bacterial community structure and Faprotax functional structure are 32.71 % and 34.89 %,respectively.At the same time,the explanatory degree of interaction of soil vegetation factors are 12.42 % and 14.76 %,respectively.Generally,under the influence of the road,the grassland vegetation and soil degradation,the differences of tolerance and adaptability of different bacterial species to environmental factors and metabolic substrates,resulting in changes in community and functional structure.At the same time,the change of bacteria in turn affected the direction and process of soil nitrogen cycle,nitrogen cycle and sulfur cycle,and there was a coupling effect between the cycles of different elements,and the soil material composition and element content changed under the action of bacteria.Overall,the results revealed the main factor for the grassland ecosystem disturbance of the QinghaiTibet Highway is the reduction of soil nutrient content.In addition,our results defined the disturbance range of the highway within the research area and demonstrated the principle of changing environmental factors(e.g.,vegetation and soil)with the distance from the highway.Furthermore,we identified the critical environmental factors that affected the change of soil bacterial community,and analyzed the interaction between the plant change,soil,and bacteria within the road disturbance area.