模拟酸雨对西洋杜鹃生理生态特性的影响

采用盆栽方法,研究了不同pH值条件下的模拟酸雨对西洋杜鹃生长及其叶片主要生理生化特征的影响。结果表明:在酸雨胁迫下,随着酸雨胁迫的增强,西洋杜鹃叶片受害程度逐渐加重;叶片丙二醛含量逐渐升高;可溶性蛋白含量先升后降;过氧化氢酶(CAT)、过氧化物酶(POD)和超氧化物歧化酶(SOD)活性均呈先升后降的单峰曲线变化,其中pH值为4.3的处理下西洋杜鹃叶片CAT和SOD活性最高,pH值为3.0的处理下其POD活性最高;其叶绿素含量逐渐下降;叶片净光合速率(Pn)、蒸腾速率(Tr)、气孔导度(Gs)及水分利用率(WUE)均呈先升后降的趋势,而胞间CO2浓度(Ci)则持续下降,pH值为4.3的处理下其Pn、Tr、Gs和WUE均达到最高。研究表明,大致可以认为pH值≤3.0是酸雨对西洋杜鹃造成隐形伤害的阀值,而酸雨灾害严重地区的降水pH值为2.0—4.0左右,说明西洋杜鹃可以在酸雨灾害较重的地区生长,可作为酸雨灾害严重地区园林绿化及植被构建的物种之一。

Effects of simulated acid rain on the physiological and ecological characteristics of Rhododendron hybridum

Acid rain has become a serious worldwide environmental problem, and it negatively affects both crops in agricultural areas and garden plants in city environments. The aim of this study was to evaluate the tolerance of Rhododendron hybridum to acid rainwater to determine whether it is suitable for use as a landscaping plant in areas affected by acid rain. We conducted a series of pot experiments to study the effects of simulated acid rain on the growth and the physiological and ecological characteristics of R. hybridum. We used 3-year-old trees of R. hybridum var. "Zijinguan" as the experimental materials. The leaves were sprayed with simulated acid rain (pH=2.0, 3.0, 4.3, or 5.6) or tap water (pH=6.5) as the control. The plants were sprayed once every 7 days, until the leaves were saturated with the liquid, for 2 months. We evaluated the plants before the start of the experiment, after 1 month, and at the end of the experiment. We measured the chlorophyll (Chl) content, malondialdehyde (MDA) content, and soluble protein content, and determined catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD) activities in the leaves. At the end of the experiment, we evaluated the degree of leaf injury and photosynthetic indicators including net photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductance (Gs), intercellular CO₂ concentration (Ci), and water use efficiency (WUE). The results showed that under simulated acid rain stress, the leaves of R. hybridum were damaged more severely as the pH of the rainwater decreased. In the pH=2.0 rainwater treatment, there was a high rate of leaf abscission, some of the leaves turned red, many leaves were curled and withered, and the leaf injury was up to 33%. In the pH=3.0 treatment, the negative effects were smaller than those of the pH=2.0 treatment; there was 16% leaf injury, some of the leaves were yellow and wilted, and there was a moderate rate of leaf abscission. When the pH of the rain water was higher than 4.3, the damage was minimal and plants were able to grow normally. There were stronger effects of simulated acid rain on Chl content in R. hybridum leaves as the pH value decreased, and the negative effects of low-pH rainwater became greater over time. The Chl contents of plants in the pH=3.0 and pH=2.0 rainwater treatments were significantly lower than those of leaves of control plants. In all of the acid rain treatments, the MDA content of R. hybridum leaves gradually increased during the experimental period; the soluble protein content first increased and then decreased. The activities of CAT, POD, and SOD showed a single-peak curve, first increasing and then decreasing during the experimental period. The highest CAT and SOD activities were detected in leaves of plants in the pH=4.3 rainwater treatment while the highest POD activity was detected in leaves of those in the pH=3.0 rainwater treatment. The Chl content gradually decreased in all of the acid rain treatments. The Pn, Tr, Gs, and WUE showed trends to first increase, and then decrease, during the acid rain treatments. The Ci steadily decreased in all of the acid rain treatments over the 2-month experimental period. The maximum values for Pn, Tr, Gs, and WUE were in plants in the pH=4.3 treatment. Based on the above results, we conclude that a rainwater pH of 3.0 is the threshold for damage to R. hybridum. The pH of rain in areas badly affected by acid has an approximate range of 2.0 to 4.0. Our results show that R. hybridum can grow and be used as a landscaping and vegetation construction plant in some acid rain-hit areas.