| As soil pH value can affect plants’ growth and development directly or indirectly, it perhaps will be an important factor in determining the suitable place of Paeonia rockii. With three Northwest cultivars of potted Paeonia rockii(Bingshan Cangyu、 Jincheng Nvlang and Zhoumei Gui) as materials, this study investigated the membrane permeability, including morphological characteristics, the growth of plant height and the very year branches’ length and width, leaf area, and physiological changes including leaf relative water content, membrane permeability, soluble sugar content, soluble protein content, SOD activity and photosynthetic characteristics of three cultivars under different soil pH treatment. It aims to explore the soil conditions for Paeonia rockii growing, provide theoretical guidance of nationwide adaptability cultivation for Paeonia rockii, in order to promote the development of Paeonia rockii industry. Comparing the acid and alkali capacity of three cultivars by membership function method to filter out fine varieties in order to provide scientific guidance for its excellent resistance breeding and cultivation. The main conclusions are as follows:1.Three cultivars have different morphological characteristics under different soil pH treatment. Compared with alkali stress, acid stress make three cultivars damage earlier and more severe. Three cultivars grow in good condition between pH 6.5 to 8.5.There is no victim symptom. It suggests that three cultivars adjust to weak base soil, not to acidic or alkali soil environment. The damage degree of Bingshan Cangyu are the largest, while of Zhoumei Gui are the least.2.pH stress inhibits the growth of Paeonia rockii, and this inhibition largely reflected in the growth of height, the very year branches’ length and leaf area. The growth index of the control department are the largest. The degree of inhibition to three cultivars under acid stress are more obvious than alkali stress. The deeper degree of the stress is, the more obvious of inhibition are. The growth index of Zhoumei Gui under different treatment are the largest, while of Jincheng Nvlang are the second.3.In this study, the plasma membrane of three cultivars were damaged irreversibly under pH stress. The deeper degree of the stress is,the more membrane permeability increases. The decline of leaf relative water content of three cultivars under pH stress has a consistent trends as: pH4.5> pH5.5> pH9.5> pH8.5, and the tolerance to the alkali stress is much stronger. The leaf relative water content of Jincheng Nvlang and Zhoumei Gui don’t change obviously from pH6.5 to 8.5 and their membrane permeability are at a low level. Compared with them, the leaf relative water content of Bingshan Cangyu decreases significantly under week alkali soil conditions, which showed that its water retention capacity is weaker. At the same time, the membrane permeability content increases significantly, which showed its ability of anti-weak alkali is low.4.The soluble sugar content, soluble protein content and SOD activity of three cultivars increase under pH stress in early time, and increase with the deepening of pH stress. But these indicators decrease after a period of stress time, which showed that the ability to resistance pH stress of three cultivars decrease. SOD activity of Bingshan Cangyu and Jincheng Nvlang declines continually, while Zhoumei Gui has complex trends as up-down-up-down changes to regulate its tolerance ability.5.The net photosynthetic rate(Pn) of three cultivars increase as the processing time increasing from pH6.5 to 8.5, while decreased under treatment of pH4.5, pH5.5, pH9.5, which has positive correlation with stomatal conductance(Gs), transpiration rate(Tr) and water use efficiency(WUE). The net photosynthetic rate(Pn) and stomatal conductance(Gs) of Bingshan Cangyu decrease under pH stress accompany with intercellular CO2 concentration(Ci) increasing, which showed that the non-stomatal control are the main reason for the net photosynthetic rate(Pn) declining. The net photosynthetic rate(Pn) of Jincheng Nvlang and Zhoumei Gui is decreased by non-stomatal control under acid stress, while that under alkali stress by transforming from stomatal control to non-stomatal control gradually.6.The curve of diurnal variation of net photosynthetic rate(Pn) of three cultivars is demonstrated two peaks with appeared midday depression of photosynthesis. Except for the stomatal control under Jincheng Nvlang’s pH9.5 treatment and Zhoumei Gui’s pH6.5, pH8.5 treatment, the curve of diurnal variation of the net photosynthetic rate(Pn), the apparent quantum yield(AQY) and the carboxylation efficiency(CE) of three cultivars are all demonstrated two peaks under other treatment.7. According to the Pn-light response curves of three cultivars under different soil treatment, the light saturation point(LSP), maximum net photosynthetic rate(Amax) and apparent quantum yield(AQY) decline as the degree of stress deepen. While the light compensation point(LCP) and dark respiration rate(Rd) increase, which showed that the ability of taking advantage of low light is lower and the dark respiration rate is faster. Among the three cultivars, the range of maximum net photosynthetic rate(Amax) of Zhoumei Gui is from 7.361 to 11.21μmol ? m-2 ? s-1, which adapts light widely. Jincheng Nvlang followed, from 6.716 to 10.509μmol ? m-2 ? s-1. Bingshan Cangyu is the weakest, from 5.189 to 9.076μmol ? m-2 ? s-1.8.In this study, the chlorophyll a, chlorophyll b and carotenoids content of three cultivars declined, and the decline increased as the degree of stress deepen. The chlorophyll content has positive correlation with the net photosynthetic rate, which showed that the chlorophyll content under stress decreasing becomes an important reason for the net photosynthetic rate descend. The ratio of chlorophyll a and b, carotenoids and chlorophyll increase with the deepen of stress degree in order to reduce the risk of suffering photo-oxidation damage.9.The comprehensive evaluation of the 24 indexes(the growth etc.) of three cultivars under different soil pH by membership function method indicated that, the ability of alkali and acid stress resistant of three cultivars decreased in the order of Zhoumei Gui>Jincheng Nvlang>Bingshan Cangyu.In summary, the growth and physiological characteristics of three cultivars are the best range from pH6.5 to 7.5, better in weak alkali soil conditions. Paeonia rockii grows unsuitably in acid or alkali soil conditions because of the damage to Paeonia rockii ’s growth. So it can grow best in neutral and weak alkaline soil. |
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