Soil Microbial Legacy Effects And Its Interaction With Nitrogen Addition And Increased Precipitation In The Restoration Succession In The Songnen Grassland

Global climate change and irrational human utilization have led to the degradation of grassland ecosystems.The ecological restoration of degraded grasslands has become a worldwide challenge in grassland management.Soil microbial legacy effects critically impact plant growth,soil nutrient cycling,and plant community succession in grassland ecosystems.Therefore,soil microbial legacy effects are a potential factor in determining the success of grassland ecosystem restoration.Atmospheric nitrogen(N)deposition is an important global change factor.The soil acidification and excessive N input caused by N deposition significantly affect plant growth and microbial community structure,ultimately impacting soil nutrient cycling functions.Global climate change has increased precipitation in localized areas.Increased precipitation severely affects plant,soil microbial communities,and soil nutrient cycling functions in grassland ecosystems.Furthermore,climate change factors(i.e.,N deposition and increased precipitation)interact with soil microbial legacy effects during grassland restoration succession,and these interaction effects may determine grassland restoration succession processes.However,the main microbial taxa driving soil microbial legacy effects during grassland restoration succession remain unclear.Meanwhile,the interaction effect between soil microbial legacy effects and climate change factors on plant communities and soil nutrient cycling still needs to be better understood.This study conducted two field surveys and soil sampling in different restoration succession stages of Songnen degraded grasslands(in 2019 and 2022).These field surveys were used to determine the major microbial taxa of soil microbial legacies in the soil and their legacy effects on plant growth and soil nutrient cycling.Moreover,Leymus chinensis was planted in the soils of different restoration stages because L.chinensis is a dominant and establishment plant in Songnen grasslands.Soil sterilization was used to eliminate soil microbial legacy effects,then we combined with N addition and increased precipitation to investigate the interaction between soil microbial legacy effects and climate change factors.We tested L.chinensis traits,soil properties,soil microbial characteristics,soil extracellular enzyme activities,soil pathogen abundance,and N cycling functional gene abundance(i.e.,nif H,AOB amo A,nir K,and nir S).These factors were used to analyze the interaction effects of soil microbial legacy effects and climate change factors on plant growth and soil nutrient cycling functions.The main results and conclusions of this study are as follows:(1)The results of field experiments revealed the presence of “legacy microorganisms” in grassland restoration succession.These “legacy microorganisms” consisted of the bacterial always abundant taxa(AAT),which persisted in the soil and increased in richness with the restoration succession.These “legacy microorganisms” positively affected subsequent plant communities and soil nutrient cycling.Furthermore,the regulation effects of soil microbial legacy effects on plant communities and soil nutrient cycling were higher by 36% and 31%than bacterial diversity,respectively.The legacy effects caused by bacterial AAT may be a key driver of grassland restoration succession.(2)The interaction experiment between N addition and soil microbial legacy showed that bacterial AAT has positive legacy effects on N-degrading enzyme activities through bacterial networks,thus positively affecting L.chinensis growth.Likewise,the effect of N addition on the bacterial network was enhanced by 30% after the removal of soil microbial legacies.Bacterial networks under the influence of soil microbial legacies have a high degree of complexity.The complex bacterial networks have a buffering ability to N addition,which attenuated the effect of N addition on L.chinensis growth.(3)Soil microbial legacies promoted the soil N turnover process(i.e.,N fixation and nitrification functions)and increased the soil N mineralization rate through bacterial networks,thus having a positive legacy effect on the soil nutrient cycling functions.N addition increased denitrification by 5% and decreased net N mineralization rates by 6%,thus enhancing the potential for soil N loss and negatively affecting soil nutrient cycling functions.After the soil microbial legacies were eliminated,N addition reduced the soil N mineralization rate by 13%,which had a stronger negative effect on soil nutrient cycling functions.Therefore,soil microbial legacies attenuated the negative effect of N addition on soil nutrient cycling functions,especially N cycling functions.(4)The interaction experiment showed that the increased precipitation and soil microbial legacy have interaction effects on L.chinensis growth.Although the increased precipitation did not regulate the bacterial network under the soil microbial legacies,the increased soil water content reduces N-degrading enzyme activities and causes the leaching of soil nutrients.Ultimately,the increased precipitation attenuated the positive effect of soil microbial legacies on L.chinensis growth.(5)The increased precipitation and soil microbial legacies had an interaction effect on soil nutrient cycling functions.The increased precipitation reduced the association between bacterial α diversity and soil extracellular enzyme activities.The increased precipitation increased denitrification by 8% and decreased net N mineralization rates by 7% under the presence of soil microbial legacies.Moreover,after sterilization eliminates soil microbial legacies,the bacterial network loses its buffering capacity against the increased precipitation,and the increased precipitation can affect soil nutrient cycling functions by regulating the bacterial network.Overall,increased precipitation inhibited the positive effect of soil microbial legacies on soil nutrient cycling functions.In summary,this study used field surveys to investigate the major microbial taxa driving soil microbial legacy effects during the restoration succession of degraded grasslands.Subsequently,we used pot experiments to explore the interaction between soil microbial legacy effects and climate change factors(N deposition and increased precipitation).This study revealed the key role of soil microbial legacy effects on plants and soil(including soil nutrient cycling functions)and the buffering capability of soil microbial legacies to N deposition and increased precipitation.This study provides new insights into the mechanism of degraded grassland restoration under global climate change and provides a scientific reference for the management and ecological restoration of the grassland ecosystem.