| Acid rain, one of the global environmental problems, is also major environmental issue of China. It has reported that acid rain gives rise to a large amount of economic losses and it does harm to the plants as well as ecological balance, Threaten from acid rain has become increasingly a cause for concern.In this study, Michelia alba.DC growing in a good condition and in the same age were planted in pots and treated by simulated acid rain under different pH values (pH= 2.0,3.0,4.0, 5.6). The morphological indices, the growth index and some physiological and biochemical indicators were determined to exploring the acid rain resistance mechanism of Michelia alba.DC. The work provides an experimental basis for acid rain theory on a certain plant species, and also it gives an important reference to the selection of urban green plants in acid rain control area. The experimental results are as follows:(1) Damage to Michelia alba. DC from acid rain is closely related to the acidity. The higher acidity and the higher occurrence frequency of acid rain, correspondingly, the heavier damage and the greater inhibition on Michelia alba. DC. The visible damage threshold of acid rain on Michelia alba. DC were pH= 3.0; the sensitivity of Michelia alba.DC to acid rain pollution are in gradeâ…¡under pH= 2.0.(2) The new branch increment rate and the growth rate of Michelia alba. DC were decreased in accordance with the decreasing of pH values, The branch increment rates and growth rates in all treatment groups were unexceptionally different from the CK (p<0.05). The growth rate was a sensitive indicator to acid rain for Michelia alba. DC.(3) The stress of acid rain has an evident effect on the photosynthesis of Michelia alba. DC. The contents of chlorophyll, the contents of chlorophyll a/b, the net photosynthetic rates (Pn), the stomatal conductances (Gs), the intercellular CO2 concentrations (Ci), and the transpiration rates (WUE) were all decreased in accordance with the decreasing of rainfall acidity, indicating that the photosynthetic capacity of Michelia alba. DC is suppressed and the growth of Michelia alba. DC is inhibited.(4) The malondialdehyde (MDA) levels in the leaves of Michelia alba.DC under acid rain treatment showed up-down-up trends, implying that the orchids have some adaptability to acid rain. The antioxidant system make an active response to resisting outside hurts: eliminating free radicals, preventing peroxide of membrane lipid. With the increasement of the frequency of acid rain, the peroxidation of lipid in the leaves of Michelia alba.DC are aggravated, which injures the leave cells, the stronger the acidity of acid rain, the more serious injuries.(5) Acid rain stress also destroys the vitality and balance of endogenous protective enzyme system in Michelia alba. DC, the reactive oxygen species were accumulated, and the lipid peroxidation were enhanced as well as the bulk membrane was damaged. Under repeat acid rain stresses, the protective function of enzyme systems is heavily impaired, which can not remove excess free radicals, and it also can not prevent the Michelia alba. DC from outside hurts effectively.(6) The Michelia alba. DC is a Magnoliaceae species relatively sensitive to acid rain stress. The injury on Michelia alba. DC became heavier with the decreasing of pH values of acid rain and with the increasing of the stress frequency of acid rain.
|
PDF Full Text Request