| Aluminum has a widespread and high content in the earthcrust. In recent years, the phenomenon of soil acidification caused by acid rain frequency drop and the abuse of ammonia fertilizer had become more and more serious, and produced a large amount of active aluminum which was harmful to the plant, and aluminum-toxicity was found to be one of the main stress elements of limit plant growth on the acidic soil. In China especially suitable for planting eucalypt southern provinces, acid aluminum stress is quite common, accounting for about 1/3 of the area of cultivated land. Therefore, the inhibition of aluminum stress on the growth of crops and plants has become a major threat toyield and quality of crop and forest products. Phosphorus (P) is one of the 3 essential elements in plants, and it is more studied in plant fertilization. Nitric oxide (NO) is a small information molecule involved in the regulation of plant growth and development process. The study of exogenously applied P or NO on plant environmental stress was a popular and cutting-edge research in recent years, but so far, it was still no research on the mitigation effect of aluminum stress on Eucalyptus. Eucalyptus, as a rapid rising of the species of paper pulp timber standsin recent years, its economic value makes it more widely concerned. The purpose of our study was to explore the effects of different concentrations of exogenous P and NO inhibited the growth of Eucalyptus under acid aluminum stress, and to explore its mechanism and regulation process; study on different Aluminum-tolerance in different Eucalyptus varieties with aluminum tolerance. To provide a base on selection and breeding of plant varieties under different levels of aluminum stress.In this experiment, the test seedlings were 3 months old tissue culture E.urophyll × E.grandis DH32-29 and E.grandis × E.urophylla NO.9 seedlings. Set two experimental groups, respectively, P-Al and SNP-A1, experimental treatment using sand culture. (1)6 treatments of each Eucalyptus species in P-Al test group, including three P levels (0,50 and 200μM KH2PO4) and two Al levels [0 (-Al) and 5mM AICl3.6H2O (+Al)]; (2) 6 treatments of each Eucalyptus species in SNP-Al test group, including three SNP levels (0,10 and 500μM SNP) and two Al levels [0 (-Al) and 5mM AICl3.6H2O (+Al)]. For a total of 24 treatments,15 replicates each treatment. The conclusions of the study are as follows:1 The effects of aluminum stress on the growth and biomass accumulation of two varieties of Eucalyptus were obviously inhibited, and reduced the plant P content, increased the content of Al, it can cause oxidative stress on the physiology of Eucalyptus leaves,Aluminum can also damage the plasma membrane permeability, increase the oxidation product of MDA, and reduce the content of soluble sugar and protein, the photosynthetic product and nutrition. The common effect of Eucalyptus photosynthesis through stomatal and non stomatal factors, inhibiting their photosynthetic rate, reducing the organic acid content in leaves and roots. But the Eucalyptus also through increased root shoot ratio, specific leaf weight and leaf osmotic pressure regulator free proline content and other ways to against Al-toxicity.2 Exogenous applied P effectively alleviate the toxicity of aluminum stress on Eucalyptus growth and biomass accumulation, antioxidant physiological, photosynthetic characteristics and organic acid content. The pathway may improve Eucalyptus P absorption and utilization, as well as aluminum complexation reaction generated nontoxic compounds, etc., and a certain range to alleviate high concentrations of P applied effect is better.3 High concentration of SNP applied to on Eucalyptus produce a stresseffect just like Al-toxicity, it lead to the Eucalyptus growth and biomass accumulation was inhibited, and leaf physiological produced oxidative stress, reduced photosynthetic rate decreased photosynthetic ability and potential mainly by stomatal factors, reduced the organic acid content in leaves and roots, however the Eucalyptus also through increased root shoot ratio, specific leaf weight and leaf osmotic pressure regulator free proline content and increase the activity of protective enzymes like POD, CAT and SOD to against adverse circumstance just like suffer from Al-toxicity.4 Applying a low concentration of SNP can effectively alleviate aluminum toxicity, through the ways like transfer the stress signal, improve the activity of antioxidant enzymes, increase the absorption of nutrients in plants, and increase the content of organic acid in plants, and the mitigation effect was similar to applying P.5 Without aluminum stress, E.urophylla × E.grandis DH32-29 was better than E.grandis × E.urophylla NO.9 in growth, and has a higher biomass accumulation, but under the stress of aluminum, two varieties of Eucalyptus were the opposite, Physiological and photosynthetic indicators also showed that the effect of aluminum stress on E.urophylla × E.grandis DH32-29 was more serious, show that E.grandis × E.urophylla NO.9 aluminum resistance was stronger than E.urophylla × E.grandis DH32-29. Relatively speaking, E.urophylla × E.grandis DH32-29 for aluminum sensitive variety, E.grandis × E.urophylla NO.9 for aluminum resistant variety. In the determination of non acid aluminum stress and suitable for the growth of Eucalyptus area, it can be integrated with other factors to selection of the tree species, and did not have to be restricted by Aluminum tolerance. But in the presence of acid aluminum stress area, should give priority to the tree species resistance to aluminum, as far as possible to choice aluminum tolerant varieties as E.grandis × E.urophylla NO.9 and other. However if the exogenous P or low concentration of SNP can alleviated the aluminum stress, the two varieties of Eucalyptus planting effects have little difference, which can be freely selected according to other conditions. |
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