The Study of Color-emerging Mechanism of Leaves at Different Leaf Position of Ulmus pumila 'Jinye'
This study probed the pigment content and photosynthetic physiological parameters of leaf blades at different leaf positions on Ulmus pumila 'Jinye',aiming at elucidating color-emerging mechanism of leaves.The results indicated that the content of chlorophyll a and b increased from the top to the base on the same branch,while carotenoids,anthocyanin and color parameters named L,a,b gradually decreased.Under the same light intensity,In terms of photosynthetic rate,leaves at the top of branches higher significantly than leaves in middle parts and basal parts of branches.It was noticed that there was no accumulation of photosynthetic products in the first blade from tops,and photosynthesis rate of seventh blade in the middle part of a branch was as high as 12 μmolCO2/(m2· s).ETO/CS increased significantly from the first leaf to the seventh leaf,and then became stable up to the 12th leaf at the base of a branch.DIO/CS,decreased along with the lowering of leaf position at a branch,which implied that the young and gold yellow leaves adopt a lightprotection mechanism by heat dissipation and fluorescence emission.Fv/Fm was higher than 0.8 in the leaves located lower than the 9th leaf,which meant that the leaves growing in base part of a branch were in good health.The performance index,photosynthetic driving force of 11th and 12th leaf was significantly higher than that of the leaves sited in upper part of a branch,and there was not significant difference compared to ordinary white elm.The results suggested that the green leaves growing in inner space of canopy or in lower part of a branch could absorb weak photon fluxes and produce photochemical reactions; meanwhile,they had high ability to resisting adversity.Experiment showed that the leaf blade color had a very significant positive correlation with carotenoid content,and the color of leaf was modulated by light conditions and photosynthesis state,which suggested that the gold yellow color of leaf in Ulmus pumila 'Jinye' was a kind of ecological phenotype.
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