| Aluminum (Al) toxicity is one of the principal factors limiting crop production in acid soils which is keeping growing worldwide. Jt has become a hot spot that seeking an economic, convenient and effective way to alleviate Al toxicity and to improve plant tolerance to aluminum in plant adverse circumstance research. In this paper, buckwheat of different Al genotypes were selected as materials, cultured in solution which treated by P and Al in turn. Photosynthetic changes were studied in physiological level. Effects of P on root cell wall polysaccharide, as well as PME, APA activity changes and the impact on aluminum tolerance of buckwheat were revealed in cell level. The changes of elements uptaking and transporting, aluminum forms and soil enzyme activity in buckwheat related to rhizosphere were studied. Experiments were conducted to study the interacted influences of P-Al on different aluminum duralumin genotype buckwheat as well as initially verify the phosphorus function and mechanism in the buckwheat duralumin. The results were summarized as foliowings:(1) Changes of photosynthetic system under P and Al treatment indicated that leaf area, Chl a, Chl T contents, maximum fluorescence (Fm) and electronic transfer rate (ETR) decreased in both two genotypes under 200μmol·L-1 Al stress. And minimal fluorescence (Fo) increased significantly while PSⅡmaximum fluorescence efficiency (Fv/Fm) decreased in Neimeng buckwheat. Therefore, there were no significant changes on values of Fo and Fv/Fm in Jiangxi buckwheat. Compared to 200μmol·L-1 Al stress, Chl a and Chl T contents increased significantly, value of Fv/Fm increased slightly and Fo decreased in two varieties of buckwheat affected by both P and Al alternatively, besides value of Fm and ETR increased at different level for Neimeng and Jiangxi buckwheat. All these results suggested that phosphorus could ameliorate the inhibition to arose and prevent damnification to photosynthesis organ arise caused by Al toxicity.(2) In comparison with that of Neimeng buckwheat, the effect of phosphorus on element uptaking and transporting under aluminum stress from tissue of Jiangxi buckwheat was characterized. The results indicated that the inhibition of root elongation induced by Al was ameliorated with the presence of 0.2 g·kg-1 P. After 30 d cultivation, the Al accumulation was significantly reduced at 0.4 g·kg-1 P level both in roots and shoots. Improving P nutrition affected the uptaking and transporting of Ca, Mg, Mn, Zn. The treatment of 0.4 g·kg-1 Al with 0.4 g·kg-1 P enhanced the absorption capability of Ca and Mg, and Mg content in the root of Neimeng buckwheat was increased 76.8% under supplement of P at 0.4 g·kg-1 compared with control (0 g·kg-1 P). However, P addition inhibited Ca transporting from roots to shoots. P addition increased the concentration of Zn in root. Furthermore, Zn was transported to shoots. All of these results suggested that phosphorus could ameliorate Al inhibition of buckwheat growth, reduce Al accumulation in roots and shoots and benefit uptaking of Ca, Mg, Mn, Zn and transporting of Mg, Zn in buckwheat.(3) The effects of P on buckwheat growth, Al forms and soil enzyme activities of root rhizosphere microecology under Al toxicity were studied. The results revealed that biomass of Neimeng and Jiangxi buckwheat supplied with 0.2 g·kg-1 P and 0.4 g·kg-1 Al were 67.9% and 21.2% higher than these supplied without P, respectively. P could ameliorate the inhibition of Al on root elongation, enhance the root biomass and root-to-shoot ratio. P significantly decreased the exchangeable Al (ExAl) content, the hydroxyl Al (HyAl) and organically complexed Al (OrAl) content were increased in rhizosphere soil. Catalase activities increased while urease activities decreased with the P application under Al stress. The P concentration of 0.2 g·kg-1 turn out to be the most convenient concentration for catalase activities. These results indicated that P fertilization may alleviate Al toxicity by decreasing ExAl content in rhizosphere soil and enhancing catalase activity.(4) Aluminum mainly concentrated in the apical cell wall on buckwheat. Monomeric Al content in root cell sap and Al content in root tips were decreased significantly when supplied with P and Al alternatively. Under 200μmol·L-1 Al treatment, Al content in root tip of Neimeng and Jiangxi buckwheat were dropped for 89.0% and 83.9% treated with 1.0 mmol·L-1 P compared with no P treatment respectively. Meanwhile, monomeric Al content in root cell sap reduced for 63.3% and 96.0%. Aluminum accumulation in the root tip decreased treated with P, thereby prevented the monomeric Al into the root cell sap. As a result, the relative root length of Neimeng and Jiangxi buckwheat were increased for 69.2% and 24.4% supplied with 1.0 mmol·L-1 P than no P suppliued under Al stress, respectively. The root elongation inhibition was reduced.(5) Polysaccharide contents in root cell wall and PME activity in root tips were significantly reduced when affected by P and Al alternatively. Under Al stress, pectin content in Neimeng and Jiangxi buckwheat roots decreased by 67.5% and 46.0% supplied with 1.0 mmol·L-1 P compared with no P supplied, while the PME activity were only 75.8% and 48.5% under 1.0 mmol·L-1 P compared to no P supplied, respectively. These results indicated that treatments with P effectively reduced pectin content and PME activity. The combination of Al to the carboxyl sites were prevented, so that the adsorption of aluminum in the cell wall was reduced, which resulted in induced root elongation.(6) Under aluminum stress, the toxicity of Al can be reduced through releasing aboudant Pi which could combine Al, especially in Jiangxi buckwheat. APA secretion hasn't shown signifigant change when P added. APA activity of Jiangxi buckwheat was more stable and significantly higher than the performance of Neimeng buckwheat. These results indicated that APA activity was an adaptation response to Al toxicity. |
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