Leaf Functional Traits And Ecological Stoichiometry Of The Dominant Tree Species Along Forest Succession Of Korean Pine And Broad-leaved Mixed Forest In Changbai Mountain,northeastern China

Forest succession can significantly alter the community structure and ecosystem function,and leaf functional traits and ecological stiochiometry connect leaf traits and the elemental balance with ecological processes,respectively.A secondary successional sere from pioneer community,dominated by white birch(Betula platyphylla Suk.)and Chinese aspen(Populus davidiana Dode),to climax community,dominated by Korean pine(Pinus koraiensis Sieb.et Zucc.)and other broad-leaved tree species,can be identified in the Changbai Mountain Nature Reserve in northeastern China.This dissertation studied leaf functional traits and ecological stoichiometry of the dominant tree species along forest succession of Korean pine and broad-leaved mixed forest in Changbai Mountain,to provide new insights into understanding the dynamics and its mechanisms of community structure and ecosystem function during the course of forest succession.The main results are shown below:1.Data obtained from 11 plots(20 m × 20 m)of different stand ages revealed that,tree species composition and diversity changed markedly during forest development,meanwhile the estimated forest tree biomass increased continually from 16.0-32.5,171.1-206.7 and 226.2-285.2 t ha-1 at ~10-,30-and 70-year aged white birch and aspen mixed forests,respectively,to 328.3-514.2 t ha-1 at ~200-year aged Korean pine and broad-leaved mixed forests.Interestingly,the shade-intolerant Manchurian ash(Fraxinus mandshurica Rupr.,with a maximum longevity of 280 years)and slightly shade-tolerant mongolica oak(Quercus mongolica Fisch.ex Ledeb,with a maximum longevity of 270 years)kept their dominance from pioneer to late-successional community,while the shade-intolerant white birch and aspen(both with a maximum longevity of 150 years)died out from the late successional community,indicating that the replacement between tree species should be the coefficient outcome of shade-tolerance and life-span.2.For juvenile and mature trees of the six dominant species from contrasting successional stages under natural field conditions,the one-way analysis of variation(ANOVA)and principal component analysis(PCA)together showed that,among the analysed 13 leaf traits,it is the leaf mass per unit area(LMA)rather than photosynthetic capacity(ie.the net photosynthetic rate under saturated light intensity)or photosynthetic potential(ie.the max carboxylation rate and electron transport rate)that characterized the essential difference between the shade-intolerant early-and the shade-tolerant late-successional tree species.However,the difference was merely showed at their juvenile stages under different light conditions,it disappeared or even reversed as both the early and late-successional trees became mature and reached the canopy.3.The mass-based leaf photosynthetic capacity(Amass)decreased with tree ontogeny for all species,even the shade-grown late-successional juveniles had higher Amass than the canopy mature trees.The area-based leaf photosynthetic capacity(Aarea)declined with tree ontogeny of early successional species while increased significantly with ontogeny of late-successional species.Further quantitative analysis suggested that,during the course of tree ontogeny,early successional tree species regulated the leaf photosynthetic capacity mainly by changing within-leaf nitrogen allocation and photosynthetic nitrogen use efficiency,by contrast,late-successional tree species optimized leaf photosynthetic performance primary through altering leaf structure(ie.LMA).4.The climax species Korean pine is an evergreen coniferous species and thus holds various aged needles.Consistent with the hydraulic limitation hypothesis,the results showed that both Amass and stomatal conductance(gs)were higher in juvenile than mature Korean pine trees.Besides,when comparing functional traits between current-year-old and 1-year-old needles,it was found that the needle structural(ie.LMA)and photosynthetic physiological traits were more easier to be affected by needle age for the shade-grown understory saplings than the sun-exposed canopy trees,maybe due to the limitation of understory light availability on needle growth.5.Intraspecific leaf C,N and C:N ratios of seven tree species from contrasting successional stages remained stable along forest development;while C,N concentrations and C:N ratios changed significantly either in branches or in fine roots,and they varied with tree species except Chinese aspen.This indicated that leaf has a higher intraspecific C:N stoichiometric stability compared to branch and fine root.At the community scale,leaf C:N ratios kept stable for the white birch and Chinese aspen mixed forests where stand ages were below 70 years,while increased significantly at the Korean pine and broad-leaved mixed forests with stand ages of ~200 years,suggesting that the nitrogen use efficiency is higher at the climax.C concentrations scaled isometrically with N concentrations in surface soils(0-10cm),thus C and N remain coupled in mineral soils;however,the C-N coupling relationship was not found in plant organs or fresh leaf litters.