Studies On Physiological And Ecological Characters Of S. Jishouensis Of Canyon Special Microhabitat

A typical and important physical feature of mountainous region is the naturalhabitats associated with the deeply cut river valleys. Having a certain amount of streamor river runoff is one of significant ecological characteristics of river valley. Canyons,rivers and mountain valleys are three typical river valleys. So far, the ecologicaladaptation mechanism of plant growing in special habitat is one of the hot issues inresearch of plant physiological ecology. This thesis selects the canyon microhabitatspecies--Sinosenecio jishouensis as the research material, and studies the S.jishouensisand associated plant mineral element content characteristics, the leaf morphology andchlorophyll fluorescence parameters in leaves of S. jishouensis within different habitat,influence of photosynthesis and chlorophyll fluorescence parameters of S.jishouensisdrought stress. The results are as follows:(1) The content of K, Mn in S. jishouensis root were higher than that of itsaccompanying species. The content of K, Cu, Fe in stem were higher than that of itsaccompanying species. The content of K, Mn, Zn, Cu in leaf were higher than itsaccompanying species, and the content of Fe, Mg in leaf were at a higher level. In S.jishouensis body, the content of Mg, Mn, P, Zn, B is high in the leaves, while thecontent of Fe, Ba is high in the root. And the highest content of K, Cu is in the stem.The maximum concentration factor of Zn and Cu is in the stem, besides, theconcentration coefficient of K, P, Mg, Fe, Ba, Mn, B in leaf is the largest one in all parts.The basic performance of concentration is for leaf> root> stem>. S.jishouensis hasstrong accumulation ability on mineral elements, especially the strongest ability ofenrichment mineral elements in the leaf which has exuberant ability of metabolism.(2) Generally, its natural habitats consist of valley falls habitat, valley sidehillhabitat and valley understory habitat. In order to reveal the adaptive ability to differentenvironments and the underlying mechanisms, S. jishouensis were transplanted fromvalley to sun habitat and shade habitat. Since the light intensity and the relativehumidity are different among5habitats, especially, there are higher light intensity andlower relative humidity in2artificial distribution habitats than in3natural distributionhabitats, the leaf morphology in leaves of S. jishouensis within above5habitats wereinvestigated The results showed that.as compared with3natural distribution habitats,the leaf area, specific leaf area of S. jishouensis were smaller and their stomata density,SPAD value were higher in2artificial distribution habitats, especially in sun habitat. Itthus indicated that S. jishouensis had tolerance to greater light intensity and moderate airhumidity realized by reduced leaf area, specific leaf area, and increased stmata density,SPAD value, while low light intensity and high relative humidity was not an importantecological factor in limiting development of S. jishouensis, providing a theoretical foundation for ex situ conservation of S. jishouensis.(3) The maximal PSⅡquantum yield (Fv/Fm), latent PSⅡ quantum yield (Fv/Fo),the quantum yield of regulated energy dissipation (Y(NPQ)) had no significantdifference between5habitats. However, the maximal electron transport rate (ETR max),minimum saturating irradiance(Ik), the coefficient of photochemical quenching (qP) andthe effective PSⅡ quantum yield (Y(Ⅱ)) of S. jishouensis in sun habitat were higherthan other4habitats, and above4parameters in valley understory habitat weresignificantly lower than other4habitats. At the same time, those values showed nosignificant difference among valley falls habitat, valley side-hill habitat and shadehabitat.(4) we investigated the effects of drought stress on photosynthetic physiology ofS. jishouensis, the leaf relative water content (RWC), photosynthesis parametersincluding net photosynthetic rate (Pn), stomatal conductance (gs), Transpiration rate(Tr), intercellular CO2concentration (Ci), and chlorophyll fluorescence parametersincluding the minimal fluorescence of dark-adapted state (Fo), the maximalfluorescence of dark-adapted state (Fm), the maximum efficiency of PS II (Fv/Fm), themaximum electron transport rate（ETR max）, initial slope（α）, effective quantum yieldof PS II photochemistry (Y(Ⅱ)), quantum yield of regulated energy dissipation in PS II(Y(NPQ)) and quantum yield of nonregulated energy dissipation in PS II (Y(NO)) of S.jishouensis living shade environment were investigated in July. The result showed：Inthe heat of the summer-autumn season, the S. jishouensis photosynthetic physiology issensitive to the drought stress of short time. Without watering for6days, PS Ⅱof S.jishouensis were significant harm. With photochemical reduction of energy use and agreater inhibition of electron transfer, net photosynthetic rate approached0. Especiallyafter no watering for12days, the S. jishouensis plants were dead.