| The riparian zone serves as a crucial ecological transition zone within the biosphere,yet remains vulnerable to human activities.The Three Gorges Dam project has altered the original riparian ecosystem,creating periodic riparian zones of alternating inundation and exposure.Understanding how riparian plant communities respond to and cope with the new hydrological environment induced by water level fluctuations is essential for understanding the ecological impacts of the Three Gorges Project.It also has important implications for the ecological restoration of riparian zones and the sustainable development of reservoir areas.Therefore,this study aims to address the following key scientific questions How do plants adapt to the severe environmental stress caused by fluctuating water levels in riparian zones;What adaptive strategies do they use and what are the underlying regulatory mechanisms.To answer these questions,this study first conducted field surveys and collected data on key traits of dominant plants,as well as leaf and root characteristics,during the exposure period in the riparian zones of the Three Gorges Reservoir area.Ecological niche width and overlap analyses were then used to reveal the adaptive responses of species to changes in reservoir hydrology.Statistical analyses such as redundancy analysis and correlation analysis were used to further investigate the response characteristics of leaf and root traits of plants,as well as the trade-offs between them,under water level changes.Finally,the integration of field data with laboratory simulation experiments elucidated the adaptive strategies of plants to reservoir water level changes and the key soil-driven mechanisms.The main conclusions of this study are as follows:(1)Revised negative perceptions of the ecological impacts of hydroelectric projects:The study found that plants have self-regulatory capabilities and ecological resilience in response to environmental changes.Data from 2019 to 2021 showed that riparian plant community succession was faster in the upstream section of the reservoir(with an increase of four dominant species),while the downstream section showed relatively stable structure and adaptability.Niche analysis showed that differences in herbaceous successional stages in different sections of the riparian zone were influenced by the distribution of plant niches.In addition,plants in the riparian zone exhibited niche shifts to adapt to new site conditions under different water level changes.The study also found that niche shifts occurred not only at the community level,but also at the intraspecific level.Data from 2022 showed significant differences in niche overlap between species under different water levels(with Cynodon dactylon having niche widths of 0.30,0.04,and 0.11 under strong,medium,and weak flooding,respectively),indicating that plants adjusted their niche occupancy and resource use strategies through interspecific relationships.The overlap in resource use strategies or ranges between the niches of different species highlighted the competitive nature of resources and revealed that plants maximise their environmental adaptability within specific niches,providing a new perspective for understanding ecological impacts of the Three Gorges Project.(2)Extending the scope of ecological impact studies for hydraulic projects:The study investigated the coordinated response of above-and below-ground plant traits to water level changes.Data analysis showed that plants dynamically adjusted the relationship between leaf and root traits to adapt to environmental changes,particularly at medium and high water levels(with a 25%increase in specific leaf area and a 15%decrease in specific root length).The study also found that in the low-water riparian zone,plants exhibited extreme trait trade-offs without balancing leaf and root traits after experiencing severe flood stress.This finding was further validated by controlled indoor experiments.By constructing a CSR plant adaptive strategy model,the study found that with rising water levels,perennial plants such as Cynodon dactylon shifted from stress-tolerant resource conservation strategies to ruderal resource acquisition strategies,while annual plants such as Abutilon theophrasti and Xanthium sibiricum shifted from competitive to ruderal adaptive strategies.This finding reveals the self-regulatory capacity of riparian plants to adapt to new hydrological environments.(3)Central role of soil nutrients in coordinated resource use:The study demonstrated the importance of key soil nutrients in the formation of self-maintaining adaptive strategies in plants,providing new ideas for near-natural ecological restoration of the riparian zone.Analysis of in-situ data showed significant correlations between soil nitrogen and water content and plant traits(p<0.05),while controlled indoor experiments indicated that soil pH and phosphorus content were closely related to plant traits(p<0.05).Despite slight differences between the in-situ and indoor data,the results indicate that soil nutrient levels,such as nitrogen and phosphorus,play an important role in regulating plant trait adaptability,and that soil physical conditions(e.g.water content,pH)significantly influence this relationship.(4)Comprehensive analysis of the ecological impact of the hydropower project:Using multidimensional experiments and comprehensive analysis methods,the study systematically investigated the ecological effects of the hydraulic project.By integrating the above findings using a random forest model,the study further summarized the regulatory patterns of plant adaptive strategies in the riparian zone of the Three Gorges Reservoir.The random forest model and feature importance analysis showed that the adaptive succession of riparian zone plants was mainly maintained by th e adoption of differentiated key nutrient allocation strategies(with SRL R~2 being 0.89 under strong flooding,Leaf N R~2 being 0.90 under medium flooding,and RTD R~2 being 0.96 under weak flooding),which maintained individual growth and population continuity under water level regulation.In low water environments,species with developed roots and low leaf investment were more likely to survive,whereas in medium and high water environments,plants exhibited characteristics of low root investment and high leaf investment.The random forest model also suggested that riparian plant communities would continue to demonstrate ecological resilience under more extreme and uncertain future hydrological conditions.Despite changes in community species dominance and richness with succession,plants would adjust their adaptive strategies accordingly.This suggests that they are highly ecologically resilient and will succeed in the future with ecologically resilient moderating patterns of fitness strategies.In conclusion,this study systematically deconstructs the adaptive characteristics of plant communities and plant traits in the riparian zones of the Three Gorges Reservoir area,and shows that under reservoir regulation,riparian zone plant species adapt to hydrological environmental changes through coordinated responses between aboveground and belowground parts,with clarified soil regulation mechanisms.The study results indicate that riparian plant communities in the Three Gorges Reservoir area have transitioned from the initial bare ground succession to the current herbaceous succession stage,and have developed appropriate adaptation strategies.The main driver of this transition is the fluctuation of reservoir water levels.Under these new hydrological conditions,riparian plant populations and communities have demonstrated environmental adaptability and self-regulation,providing new insights into plant self-adaptation in environments with extreme water level changes and a new research perspective for understanding the ecological impacts of hydraulic engineering projects. |
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