| The balance of ozone layer in stratosphere was broken due to human activities, which reduced the ozone layer and increased the irradiation of ultraviolet-B (UV-B) to earth surface. However, the buffer action of atmospheric particulates on acid rain (AR), especially alkaline large particles, was lowered by industry dust removal and afforested work. Additionally, increased UV irradiation benefits the formation and transformation of fine particles and thus enhancing the acidity of atmosphere. As a result, acid rain issues might occur outside the acid ram regions.To scientifically estimate the biological and ecological effects of environmental factors on plants considering the global climate changing, NADP-ME C4 photosynthetic pathway monocotyledon plant waxy corn(Zea mays L. certain Kulesh) and NAD-ME C4 photosynthetic pathway dicotyledon plant edible amaranth (Amaranthus mangostanus L.) were studied through ecological simulation. The samples were treated with simulated acid rain [pH6.5 (Ao),4.5 (A1) and 3.5 (A2)] and UV-B irradiation [0 (Bo),2.88 (B,) and 5.76 (B2, maize) or 4.32 (B2, amaranth) kJ·m-2·d-1] used self-control facility. The present research aimed at explored the influences of enhanced UV-B irradiation and simulated acid rain alone or combined each other on individual growth and population physiological ecology of different C4 plants in the similar field conditions. Moreover, the mechanism on different C4 plants, especially important crops, to resist the environmental stress when UV-B irradiation increasing and acid rain area augmenting were also discussed in this dissertation. This research would provide references and theoretical supports to countermeasures of global climate changing and explore the effective means in maintaining and enhancing grains and vegetables yield. Results in this study are as follows:1. The biomass distributions of maize and edible amaranth were affected by enhanced UV-B irradiation, simulated acid rain or their combination, and the growth and development of both plants were inhibited. Under UV-B irradiation, maize growth period lagged in the late growth stage while that of edible amaranth was in the beginning of bolting stage. The maize height and leaf area reduced and reached the least in the late growth stage, while edible amaranth height in bolting stage and leaf area in harvesting stage showed most significant response to UV-B irradiation. UV-B irradiation significantly affected biomass of root, stem and leaf of both maize and amaranth. The UV-B irradiation had no significant effect on the root/shoot ratio of these two plants except for root/shoot ratio of maize reduced by high level UV-B irradiation. Average stress response index under UV-B stress of maize was lower than that of edible amaranth. On the other hand, acid rain had the most effects on maize in jointing stage and harvesting stage, while flowering stage and harvesting stage were the most vulnerable stages for edible amaranth. The sensitivity of two plants height and leaf area to acid rain varied in different developmental stages:maize was most sensitive in harvesting stage, while leaf area of amaranth was most significant influenced in bolting stage. Root and fruit biomass of maize decreased, and stem, leaf and fruit biomass of amaranth significantly decreased under acid rain conditions. Root/shoot ratio of maize decreased significantly with the decline of acid rain pH, while that of amaranth decreased more under mild acid rain than severe acid rain. Average stress response index in maize under acid rain stress was also less than edible amaranth. What’s more, under combination of UV-B and acid rain treatments, maize displayed antagonistic effects on growth delay and biomass decline while edible amaranth showed synergistic effects. The average stress response index of maize was 0.85, lower than that of edible amaranth,1.73. In terms of the whole growth season, maize showed a better tolerance to adversity and edible amaranth was more easily to be influenced.2. Enhanced UV-B irradiation and simulated acid rain singly and in combination played a great role on plant photosynthesis physiological traits of maize and edible amaranth. Under single UV-B irradiation treatment, net photosynthetic rate of maize decreased with UV-B irradiation increased. In the early development stage of maize, the content of photosynthetic pigments increased, including chlorophyll a, chlorophyll b and carotenoid, but decreased at late development stage. The chlorophyll a/b ratio decreased significantly in jointing stage and harvesting stage, while there showed a stable tendency in seedling and flowering stage in contrast with the control treatment, and no significant difference was found on the ratio of carotenoid and total chlorophyll between treatment and the control treatment. In addition, PEPCase and RuBPCase activity, and the ratio of PEPCase activity/RuBPCase activity of maize decreased under UV-B irradiation. In terms of edible amaranth, net photosynthetic rate, photosynthetic pigment content, PEPCase activity, RuBPCase activity, and PEPCase activity/RuBPCase activity ratio decreased significantly with UV-B irradiation increased. However, its chlorophyll a/b ratio and carotenoid/total chlorophyll ratio had no significant difference to the control treatment. The net photosynthetic rate of maize decreased under simulative acid rain treatment. The net photosynthetic rate was hardly affected in the early development stage of edible amaranth, but decreased in flowering and bolting stage. The content of photosynthetic pigment of maize and edible amaranth influenced by acid rain, at the early development of maize and the whole growth stage of edible amaranth, the content of photosynthetic pigment was higher under severe acid rain than mild acid rain stress. The chlorophyll a/b ratio and the ratio of carotenoid and total chlorophyll were mostly uninfluenced. Under acid rain treatment, PEPCase activity of maize and edible amaranth decreased and RuBPCase activity of maize decreased except in harvesting stage. RuBPCase activity of edible amaranth was not sensitivity to mild acid rain, but it decreased under severe acid rain except in flowering stage. The ratio of PEPCase activity/RuBPCase activity of edible amaranth decreased with decreased pH of acid rain. But the ratio of PEPCase activity/ RuBPCase activity increased in early development stage of maize, except for A1 treatment in harvesting stage, the ratio of the others treatments in various stages had no significant difference. Under the combined stresses of UV-B radiation and simulated acid rain, antagonistic effects between two factors were shown. But the plant self-restoration capability was limited, net photosynthetic rate of maize and edible amaranth decreased, the content of photosynthetic pigment had changed, PEPCase activity and RuBPCase activity decreased, and the ratio of PEPCase activity/RuBPCase activity mostly decreased. The chlorophyll a/b ratio of maize decreased significantly in jointing stage and harvesting stage, the ratio of carotenoid and total chlorophyll had no significant difference compared with the control treatment. In terms of edible amaranth, the chlorophyll a/b ratio was similar to the control treatment except for bolting stage; ratio of carotenoid and total chlorophyll almost increased significantly except for A2B2 treatment in harvesting stage. The edible amaranth had larger mean plasticity index of photosynthetic traits than maize no matter under UV-B irradiation, acid rain or their combination, and the plasticity index of photosynthetic traits of maize and amaranth under UV-B irradiation was better than acid rain.3. Enhanced UV-B irradiation and simulated acid rain singly and in combination had significant influence on material metabolism of maize and edible amaranth. Under single UV-B irradiation treatment, soluble protein content of maize and edible amaranth decreased, and the harvesting and flowering stage were the most influenced stage. Content of total free amino acid of two crops was higher than the control treatment except for it in harvesting of maize at lower level enhanced UV-B irradiation, while those were little influenced at high level enhanced UV-B irradiation except for in harvesting both of the two plants. Content of soluble sugar and ATP decreased significantly with UV-B irradiation intensity increasing, but flavonoids and polyphenol content increased. The acid rain stress could also cause the decline of soluble protein content of maize and edible amaranth. However, maize was insensitive to A1 treatment of acid rain in jointing stage and flowering stage, while insensitivity was found in edible amaranth in two degrees of acid rain in bolting stage. Content of free amino acid increased along acid rain stress, which was larger than the control treatment in the whole growth stage, with the tendency of increased first but decreased afterwards, and it was higher under A1 condition than A2 in both two plants. It showed a less content of soluble sugar and ATP of maize and edible amaranth under acid rain than the control treatment. There was almost no influence of acid rain to flavonoids of maize leaf under single acid rain treatment, and the same with amaranth from seeding to flowering stage. However, that of edible amaranth increased significantly in harvesting stage. In addition, content of polyphenol in both of the crops increased with decreased pH of simulated acid rain. On the other hand, with the combination of enhanced UV-B irradiation and simulated acid rain, antagonistic effect between two factors was showed. Soluble protein, soluble sugar, and ATP content still had small decline compared with the control treatment, but flavonoids and polyphenol content increased. Every index failed to restore to the former level. Equal to mean plasticity index of various metabolite indices of maize and edible amaranth was found. However, in terms of specific metabolite index, acid rain had greater effect on plasticity of their free amino acid content, while UV-B had larger plasticity to other metabolite index. Variance analysis showed that UV-B irradiation has more significant influence on metabolism of the two crops.4. Enhanced UV-B irradiation, simulated acid rain or their combination had significant influence on active oxygen metabolism of maize and edible amaranth, damaged plant membrane system. Under single UV-B irradiation treatment, cell membrane permeability of maize and edible amaranth leaf increased significantly with the intensity of enhanced UV-B irradiation, and showed a more significant damage at later developmental stage. MDA content of maize increased significantly under the both levels of enhanced UV-B irradiation, while in terms of edible amaranth, it increased more under high level UV-B irradiation than low level irradiation. SOD activity of maize showed a significant increase under UV-B irradiation, and along with extension of the experimental treatment, SOD activity at harvesting stage, which was close to the control treatment, decreased sharply in contrast with early development stage. SOD activity of edible amaranth in early development stage increased significantly but decreased later. POD and CAT activity of two crops decreased as well. Meanwhile, under simulated acid rain stress, plasmalemma permeability of these two plants improved and leaf MAD content increased to different extents. The change of SOD activity in maize and edible amaranth experienced similar changes under single AR and UV-B treatment. POD activity decreased significantly except for that of edible amaranth in bolting stage and A1 treatment of maize in flowering stage. Light acid rain had little influence on CAT activity of maize and edible amaranth leaves. However, CAT activity decreased sharply in further decreased pH of acid rain. More antagonistic effect of two factors was indicated than additive, synergistic effects under the dual stresses (AR+UV-B). Plasmalemma permeability of maize and edible amaranth in each development stage under combined stress was lower than single UV-B treatment, whiles those still higher than the control treatment, with a same trend as MDA content, and showed a limited ability of plants to utilize interaction of multiple adversity factors to resist impairment. The activity of protective enzymes, such as SOD, POD, and CAT, could interact and alleviate the damage from outside under adversity factors. In terms of the average plasticity index of active oxygen metabolism indices between two crops, edible amaranth hurt even more, and membrane system of maize has better resistance to UV-B irradiation and/or acid rain. Moreover, each plasticity index of active oxygen metabolism indices showed more serious damages under enhanced UV-B irradiation than under on two crops’membrane system.In sum, the present study suggested that damages caused by enhanced UV-B irradiation on maize and edible amaranth was more serious than acid rain. Impairment from UV-B irradiation could be reduced through combined treatment to some extent, but this capability was limited. The dynamic changes of physiological and biochemical indices under the dual stresses (AR+UV-B) were not identical, and none of them showed a simple linear variation, but displayed additive, synergistic or antagonistic effects depending on the different treatment periods and/or degree of stresses, indicating that plants had different mechanisms of resistance and adaptability under different stresses. The two different C4 plants had different sensitivity to AR and UV-B treatment at different development stages. Maize was in general more tolerant to stresses than edible amaranth under the experimental conditions. |
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