Studies On The Physiological Response And Resistant Mechanisms Of Ginkgo Under Cd And Pb Single And Combined Pollution

Ginkgo (Ginkgo biloba L.) is a relic woody plant for multi-value of economy, ecology, ornamental and scientific research, which has manifested the high resistance characters in the different living adversities. To elucidate deeply and systematically the toxicity and tolerance mechanisms of Ginkgo to heavy metals stress at the cellular, organ, and tissue level, respectively, this investigation was carried out to study effects of Cd and Pb single and combined pollution on the growth, leaf ultra-structure, photosynthetic characteristics, root ion micro-distribution, absorption and allocation of mineral elements, membrane lipid peroxidation and antioxidant enzymes systems, osmo-regulation physiological characteristics with observation of electron microscopy technique, X-ray electron probe microanalysis, photosynthesis and chlorophyll . fluorescence analysis system, atomic absorption spectral analysis technique and other physiological measurement methods. The major results were summarized as follows:1. Ultra-structure of Ginkgo leaves were damaged by cadmium and lead stress to some extent. The chloroplast was the most sensitive organelles among which were affected by heavy metals stress, such as thylakiods of chloroplast swelled, chloroplast membrane disrupted or disappeared, osmilphilic granule increased obviously, and chloroplast which was wounded serious disintegrated. The symptoms of damaged mitochondria were the reduction of cristae, disruption of mitochondria membrane and vacuolation of mitochondria. The wounded nucleus expressed the symptoms of disruption of nuclear membrane, agglomeration of chromatin and nucleoplasm of nucleus. The interactions of cadmium and lead combined stress on the chloroplast and mitochondria ultra-structure of Ginkgo leaves were synergistic effects.2. It was significantly negative correlation between chlorophyll(a), chlorophyll content and the concentration of Cd stress during the time of treatments, and all the indexes of chlorophyll were inhibited seriously by different concentration of Pb. The net photosynthetic rate, stomatal conductance and transpiration rate decreased with the increasing stress concentration, but the intercellular CO₂ concentration increased. The decreasing of net photosynthetic rate of Ginkgo under heavy metal stress was caused by nonstomatal limitation. The primary light energy conversion of PSII (Fv/Fm), quantum efficiency of PS II (φ PSII), photochemical quenching of chlorophyll fluorescence (qP) and non- photochemical quenching of chlorophyll fluorescence (qN) of Ginkgo obviously decreased with the increasing concentration of treatments. It showed PSII was suffered from being close and injured. Compared with single stress, the interactions of cadmium and lead combined stress on the photosynthetic characteristics of Ginkgo were the trend of synergistic effect. Correlation coefficients of indexes revealed the photosynthetic characteristics of Ginkgo were determined by multi-factors interactions.3. The micro-distribution analysis of the across sections of Ginkgo root with X-ray microanalysis indicated that ion micro-distribution of root was significantly affected by cadmium and lead single and combined pollution. The disrupted balances of most elements of...