Study On Dose-Loss Model For Effects Of Acid Rain On Leafy Vegetables

Along with the increasing of industrial production and human activites, East Asia, including China, Japan and South Korea and so on, have become the third largest acid rain area of the world after Europe and North America. Main regions locate southern part of Yangtze River, with a growing acid rain area, with characteristics of low pH level, high concentration and high frequency of acid rain. At present, the chemical composition of rain in China is still sulfuric acid. However, with control of SO2 emissions, rapid increase of motor vehicle ownership and increased pollution of vehicle emissions, NOx emissions continue to increase. It will lead to the ratio change of SO42- and NO3-. As a result, the chemical composition of rain has being transformed to sulfuric-nitric acid.The domestic distribution of acid rain has obvious regional characteristics. Acid rain areas mainly distribute in the southeast part of northeast China, such as Tumen, Dandong and the East China Sea, most of north China, southwest and south coastal areas. In recent years, strong acid precipitation has happened in Tumen, Dandong and the East China Sea with rising acidity. In Jilin Provence, it mainly appears in the eastern part of Tumen, Hunchun and Yanji City, and most occurs in summer and autumn which are the crop growing seasons in Northeast China. As leafy vegetables could be affected by acid rain more easily than other vegetables or crops, they were chosen for the research objects.By now, although reports about impacts of acid rain on crops have been widely coverage, in northeast China, that on leafy vegetables have not been mentioned yet. Research on economic loss caused by acid rain only considered yield, without the physical and nutritional quality or other factors. The establishment of the dose-response model also just considers the relationship between loss and production, without factors such as physical and nutritional quality. Coupled with the large proportion of leafy vegetables in the diet, research on impacts of vegetables by acid rain in the Northeast region is of vital importance.In this study, three kinds of leafy vegetables, pakchoi, rape, and lettuce, which are sensitive to acid rain, have been chosen as the test material. Quantify the impacts on growth, physiological, nutritional quality of these vegetables by acid rain with different pH. According to the master data about these three kinds of leafy vegetables (pakchoi, rape, and lettuce) obtained by the simulation experiment, dose-loss model about acid rain effects on leafy vegetables can be established. The conclusions will be the scientific basis for making decision on acid rain control.Dose-loss model considered three factors:growth, physiological and nutritional quality. Linear method of partial least squares regression (PLSR) and non-linear method of back propagation (BP) neural network were selected as modeling methods. Test model fitting and accuracy of modeling results for the comparative study of the two models.The results by simulating procedures of acid rain dropping on the chosen vegetables indicated that extent of effects of SAR on the leafy vegetables is closely related with the pH value of SAR, the higher the acidity of the SAR, the more significant the inhibitions were. Strong acid rain significantly inhibited the growth of leafy vegetables. However, weak acid rain could slightly stimulate plant growth or cause no significant impact. Fresh weight of three kinds of leafy vegetables decreased significantly. And synthesis of dry matter of vegetables was inhibited. Compared with fresh weight, dry weight of vegetables had a smaller decrease. Acid rain can cause decrease in stem and root length, and inhibit growth of vegetables. In comparison, damage of lettuce fresh and dry weight caused by acid rain is larger than that of rape and pakchoi. Roots were damaged the most seriously than other parts of all the three kinds of vegetables. Acid rain can inhibit the synthesis of photosynthetic pigments of vegetables, resulting in decreased photosynthetic ability of plants and lead to increased lipid peroxidation and MDA content of plants. By the pH of acid rain became lower, photosynthetic pigments of three kinds of plants decreased gradually. The stronger the acidity was, the greater the decline in photosynthetic pigments would be. Content of total chlorophyll was consistent with chlorophyll a Content decline of total chlorophyll was caused by decrease both in chlorophyll a and chlorophyll b. Compared with pakchoi and rape, lettuce had the smallest photosynthetic pigment change. With lower pH, MDA content of three kinds of leafy vegetables increased negatively correlated with pH values of acid rain. MDA content of The most acidic group had the largest increase (22%) compared with the CONTROL It indicated that peroxidation of the plant membrane lipid increased, reactive oxygen and oxygen free radicals in plant cells accumulated, cell membrane severely damaged. As a result, vegetable plants were injured, thereby affecting plant growth and development.From the results obtained, the following general conclusions can be derived. Soluble protein, vitamin C, soluble sugar and total free amino acid were significantly inhibited by low pH values of acid rain. The stronger acid was, the more significant the inhibition would be. Under the treatment of the weak or neutral acid rain, nutritional substance contents lead to an increase in levels, compared with the controls. Nutrient quality indicators of the three kinds of vegetables had consistent trend with physiological indicators, indicating that the synthesis of nutrients was related to physiological activities. Acid rain cause photosynthetic capacity of plants decrease, synthetic substances reduced, and ultimately leaded to qualitative change in poor nutrition of vegetables. In summary, nutritional quality of lettuce was affected most under the exposure of acid rain, followed by pakchoi and rape. The change range of soluble protein content of pakchoi, rape and lettuce was higher than contents of vitamin C, soluble sugar and total free amino acid other three indicators.Results of dose-loss PLSR model showed that using the PLSR method to establish the model for effects of acid rain on leaf vegetables is feasible. Dose-loss PLSR model not only took the vegetable production index, fresh weight, into account. also considered other 15 factors, such as plant dry weight, plant height, photosynthetic pigments, vitamin C, soluble sugar, total free amino acids and soluble proteins. It reflected more comprehensive information, stimulated more realistic situation, and was conductive to modeling. It also had a small error range to meet the requirements, with a high model fitting.The results of the study show that many factors are considered during the establishment of dose-loss model, which can be better applied to practice. The BP model fully utilized the nonlinear mapping capabilities of the network and considered the nonlinear characteristics between vegetables value and vegetable growth, physiological and nutritional quality. BP network model get higher accuracy and easily learned. Thus modeling by using BP network model is feasible.This paper established a comprehensive and comparative study between linear methods PLSR model and nonlinear methods BP network model. Considering fitting error and accuracy error of the two models, the accuracy of BP network model is better than PLSR model. BP network model had a full consideration of the nonlinear characteristics between samples. The PLSR model only considered the linear relationship. From that point, nonlinear BP network model worker better. However, taking the model structure into account, the PLSR model could optimize the variables, so as to establish a more complete model. From this view, the PLSR model is superior to BP network model.