Research On Leaf Stoichiometry And The Economic Spectrum Of Plant Species Under Flooding Stress In Riparian Zone

In recent years,the vegetation along the Lijiang River riparian zone has deteriorated significantly and seriously affects its ecological and landscape functions.Vegetation restoration has become the focus of recent research.Since the riparian vegetation is suffered from frequent flooding disturbance,understanding the adaptation mechanism of these plants dealing with flooding stress has become the key part of vegetation restoration work.Leaf C,N and P concentrations and their stoichiometric characteristics are indicators of many ecological processes.This study evaluated the leaf leaf stoichiometry of the plants along the Lijiang River riparian zone in different seasons and inundation zones and investigated the soil's physical and chemical properties and plant community structure.Through correlation analysis,the main environmental factors that affected the leaf stoichiometry were identified.Furthermore,seven leaf functional trait indexes of dominant plants in different inundation zones are measured in the spring,including leaf maximum net photosynthesis rate per mass(A_mass),leaf mass per area(LMA),leaf nitrogen content per mass(N_mass),leaf phosphorus content per mass(P_mass),and leaf potassium content per mass(K_mass),photosynthetic nitrogen use efficiency(PNUE),photosynthetic phosphorus use efficiency(PPUE).By comparative analysis,this study reveals the physiological response mechanism of plants for flooding habitats.Based on the above research results,the adaptability of different functional plants dealing with flooding stress was compared.Also,the pioneer plant species were screened,inter-species association analysis and functional grouping for these species were conducted.Typical plants were selected for vegetation restoration experiments in order to explore the possibility of applying the result of functional group division to practice.The main findings of this research are as follows:(1)The special habitat of repeated flooding in the riparian zone has a significant impact on the ecological stoichiometric characteristics of plant leaves C,N,and P.The plants in the submerged zone are under long-term repeated flooding environment and are frequently interfered by hydrologic disturbance.The leaves increase the absorption of N and P to improve the photosynthetic efficiency and quickly synthesize organic matter.This may be one of the key strategies for these plants to adapt to the special habitat of riparian zones.The eutrophication of the river caused by human activities may change the potential restrictive elements of plant growth in the Lijiang River riparian zone from the traditional P limitation of the water ecosystem to the N limition.(2)The ecological stoichiometry characteristics of leaves C,N,and P in riparian plants show a certain seasonal variation.The autumn leaves have higher N and P content and lower C content,indicating that the plant adopts a quiescent strategy to improve its flooding tolerance.The soil stoichiometry has a significant influence on leaf stoichiometry.(3)There are differences in the adaptability of different functional plants in the same environment.The leaf mass per area of the leaves of trees and shrubs are relatively close and are significantly higher than those of herbs,while the contents of A_mass,PPUE,N_mass,and P_mass are significantly lower than those of herbs.Compared with trees and shrubs,the herbaceous plants respond more actively to the flooded environment.In the process of vegetation restoration in the submerged zone,the herbaceous plants should be selected as the pioneer species.(4)The relationship of plant leaf traits in the land-lake ecotone is consistent with the global scale,and the leaf economic spectrum also exists in the land-lake ecotone of the Lijiang River.The leaves of plants in the submerged zone have low LMA,high A_mass,N_mass,and P_mass,which belong to the"rapid investment-return"type species in the economic spectrum.When artificial measures are taken to restore vegetation,priority should be given to investing resources in fast-growing plant species to ensure the survival rate and restoration effect of the plants.(5)Among the 300 species pairs of the 25 dominant herbaceous species in the riverbank zone of Lijiang River,the positive and negative correlation ratio is 0.96,which suggests that the interspecific association was relatively weak.The structure of herbaceous community is unstable and it is easy to be disturbed by the external environment.Based on the analysis result of?² test,combined with the association coefficient and the percentage of co-occurrence,the 25 dominant species of the herbaceous plant community in the Lijiang River riparian zone were divided into 6functional groups:broad-spread type,flood-resistant type,wet type,mesophyte type,climbing type and sensitive type.(6)Using grasses with flooding tolerance and appropriate artificial intervention,including soil consolidation techniques with solidifying agent,stolon spreading techniques,and planting techniques with sand bag,can obtain great vegetation restoration effect In bare gravel riparian zone.The functional group division of dominant herbage can provide theoretical support for vegetation restoration in degraded riparian zone of Lijiang River.