Study On The Effect Of Plant-soil Feedback During Succession Process Of Glacier Retreating Area Of Gongga Mountain

Plant-soil feedback is a key link in the dynamics of terrestrial vegetation communities,which is important for understanding plant community succession and ecosystem diversity.The glacial retreat area of Gongga Mountain has formed a complete succession sequence after a long period of evolution,thus providing a natural laboratory for studying the succession process and influencing factors of vegetation communities.However,the driving mechanism of vegetation succession in glacier retreat areas is not clear.In this study,the dominant plants,soils,and stands in three stages of primary succession,early(5-10 years),middle(30-40 years),and late(80-100 years),in the glacial retreat area of Mt Gongga were studied.This study combines potted control experiments with field surveys to investigate the driving effect of plant-soil feedback on vegetation succession in this glacial retreat areas.Our study quantified the direction and intensity of plant interactions and plant-soil feedbacks by comparing the biomass of dominant plants under different soil conditions.The important role of microbial communities in plant-soil feedback was revealed by comparing plant-soil feedback under sterilized versus living soil conditions and the differences in soil microbial structure and function between plants in native and guest soils.In addition,the plant-soil feedback effects under competition and monoculture were compared,and the intrinsic association between stand competition and plant-soil feedback driving vegetation community succession was explored in the context of intra-species competition among stand plants at each stage.The main findings are as follows.(1)The direction and intensity of plant-soil feedbacks differed under different successional stages.We quantified the plant-soil feedback strength of dominant plants at different successional stages,and the total feedback coefficient varied from-0.78 to2.14 as succession progressed.It was found that the direction of plant-soil feedback at each stage of succession ranged from negative feedback in the early stage,neutral feedback in the middle stage,and transitioned to positive feedback in the late stage.Showed that the early stage Hippophae rhamniudes and adjacent plants promoted each other's growth,while the middle stage Populus purdomii and adjacent plants Populus purdomii and neighboring plants without mutual promotion and competition,the late stage Abies fabir and adjacent plants promote each other.Plant-soil feedback effectively reflects plant growth in the native,e.g.,H.rhamniudes grows worst in the native;A.fabir grows best in the native.And relative competition index indicates the relationship between neighboring plants.The relative competition index between early successional H.rhamniudes and middle and late plants was negative;the relative competition index between middle P.purdomii,Salix rehderiana and early and late plants was close to zero,and the relative competition index between late A.fabir,Picea brachytyla and early and middle plants was positive values.(2)Plant-soil feedback is closely related to the structural composition and function of the microbial community.By studying the structural composition and function of native and guest soil microorganisms of dominant plants at each stage,it was found that soil bacteria of dominant plants could all be divided into two different clusters and fungi could all be divided into three different clusters.While there was no significant difference in microbial function between native and guest soils for bacterial function,there was a difference in fungal function.The plant-soil feedback intensity of soil microbial functions and dominant plants at each stage was further explored.It was shown that the plant-soil feedback intensity at each successional stage was negatively correlated with metabolic functions in bacteria and positively correlated with cellular process functions,environmental information processing functions,and biological system functions.On the other hand,plant-soil feedback intensity was negatively correlated with soil pathotroph,and more soil pathotroph was accumulated in the early successional stage;symbiotic fungal symbiotroph was positively correlated with plant-soil feedback,and plants were easily bound to symbiotroph in the late successional stage.(3)Interspecific intraspecific competition and plant-soil feedback together drive vegetation succession.Competition was found to reduce the plant-soil feedback effect,which was investigated by examining the plant-soil feedback effect under monoculture versus competition,as well as the mode of competition in forest stands at each stage of succession.We explored the intraspecific and interspecific relationships at each successional stage.The early Hippophae rhamniudes intraspecific competition index was 250.79 greater than the interspecific competition index of 114.51.The interspecific competition index of Populus purdomii at the intermediate stage was93.95,which was greater than the intraspecific competition index of 31.19.The late Abies fabir intraspecific competition index was 59.38 greater than the interspecific competition index of 54.26.The stand competition index decreased with increasing diameter at breast height of the dominant species at each successional stage.In this study,we quantified the intensity and direction of plant-soil feedbacks and identified the main microbial functional groups affecting plant-soil feedbacks by using the primary succession sequence in the glacial retreat area of Gongga Mountain.Competition and plant-soil feedbacks were found to drive the rapid succession of vegetation communities to climax community in the glacier retreat area of Mt.Gongga.This study clarified the driving factors of vegetation community succession in the glacier retreat area of Mt.Gongga from the perspective of plant-soil feedback,and also providesed new ideas for understanding vegetation succession under future climate change.