Effects Of The Temperature Change On Shrub Ecosystems In The Alpine Tundra Of Changbai Mountain

The alpine tundra is a unique and fragile ecosystem that is highly sensitive to environmental change.In recent years,the alpine tundra has experienced rapid climate warming,thereby exerting a significant impact on the growth,distribution,and composition of plant communities.Concurrently,climate warming also has significantly altered the composition,activity,and functionality of the soil microbial communities in the alpine tundra,subsequently affecting soil nutrient content.Given the close linkages between the above-ground and belowground biotic communities,modifications in below-ground soil ecological processes inevitably influence the growth of above-ground plant communities.Therefore,climate warming not only directly affects alpine tundra plant communities,but also indirectly influences plant growth by changing the characteristics and functions of soil microorganisms.However,the specific mechanisms of such direct and indirect effects is currently unknown.In this study,we focused on the shrub ecosystems in the tundra of Changbai Mountain.To simulate temperature change(warming and cooling),a unique translocation experiment was conducted using the natural lapse rate of temperature along an elevational gradient.Through this experiment,we investigated the effects of temperature change on the below-ground soil physicochemical properties and the soil microbial community structure and function,as well as above-ground functional traits of plants.Furthermore,we revealed the underlying impact mechanisms of temperature change on the growth of shrub growth in the alpine tundra.The following are the key findings of the study:(1)Temperature change could affect soil bacterial and fungal communities differently in the Changbai Mountain tundra,with fungal communities would be more sensitive to temperature changes.Our results showed that warming significantly increased the Richness index of soil bacterial communities in the early growing season,while significantly decreased the Richness index of soil fungal communities.Both warming and cooling significantly altered the composition of soil fungal communites,but had little effect on the composition of soil bacterial communites.Notably,warming would intensify the interactions between soil bacteria,causing the bacterial network to become tighter.In contrast,both warming and cooling would weaken fungal interactions,leading to a looser fungal network.Furthermore,we found that dispersal-based stochastic processes predominantly regulated the assembly of the soil bacterial and fungal communities.However,the role of stochasticity would significantly decline under temperature change,indicating a potential deterministic environmental filtering.(2)Temperature changes significantly affect soil microbial community functions in the tundra of Changbai Mountain.Specificly,the abundance of soil microbial labile carbon functional genes would increase under climate warming,which accelerated the decomposition of unstable organic carbon of tundra soils.Furthermore,warming would stimulate the abundance of functional genes involved in ammonification,denitrification,and nitrogen fixation,consequently enhancing nitrogen fixation and denitrification processes in the tundra soils.Moreover,warming could also increased the abundance of functional genes related to the phosphorus phosphorus cycle.Comparatively,cooling would lead to a decrease in the abundance of soil microbial refractory carbon functional genes,which inhibits the decomposition of refractory carbon in tundra soils;however,cooling leads to an increase in the abundance of soil microbial nitrogen-fixing functional genes,which contributes to nitrogen fixation in tundra soils.(3)Temperature change would significantly affect soil physicochemical properties in the Changbai Mountain tundra.We found that the soil moisture content,total nutrient,soluble nitrogen,and ammonium nitrogen content would significantly decrease,while soil pH and nitrate nitrogen content would significantly increase with warming.However,soil water content,soil total nutrients,soluble and ammonium nitrogen would increase significantly,but soil pH and nitrate nitrogen content would decrease significantly after cooling.In addition,the content of soil available phosphorus was relatively unaffected by both warming and cooling.(4)Functional traits of shrub leaves in the tundra of Changbai Mountain would respond rapidly to temperature change,with differences observed between both species.Our results showed that plants can enhance photosynthesis and carbon fixation capacity by augmenting specific leaf area,leaf dry matter content,and leaf carbon content in response to warmer conditions.They can also adaptat to water stress induced by warming through decreasing the leaf length-to-width ratio,leaf thickness,leaf weight,and leaf area.Conversely,in a cooler condition,plants could light energy absorption and heat radiation by decreasing leaf aspect ratio,leaf area,and specific leaf mass.In this context,the deciduous shrub Vaccinium uliginosum would display greater ecological adaptability compared to the evergreen shrub Rhododendron chrysanthum.(5)Finally,we found that temperature change would exert both direct and indirect effects on the growth of shrubs in the alpine tundra,primarily through changes in physiological characteristics of plants and soil nutrient availability.Specifically,warming not only directly stimulates the growth of alpine tundra shrubs,but also indirectly enhances soil nitrogen availability by modifying leaf functional traits and affecting the structure and function of soil microbial communities.These changes collectively further promote the growth of shrubs in the alpine tundra.Conversely,cooling would impose constraints on the growth and soil nutrient uptake abilities of tundra shrubs,which in turn inhibiting their growth.Overall,our study deepens our understanding of the effects of temperature change on the shrub ecosystems in the Changbai Mountain tundra.We comprehensively assessed the impacts of temperature change on belowground soil ecological processes and aboveground shrub physiological traits,and further revealed the mechanisms affecting shrub growth in the alpine tundra.These findings contribute to the understanding and conservation of biodiversity in alpine tundra ecosystems,and also provide a valuable basis for forecasting future vegetation changes in alpine tundra.