Bofon Enhances Rhizopshere PH And Alleviates Aluminum Toxicity To Pea (Pisum Sativum)

The large areas of red soils in south China are critical food-producing and industrial crops producing regions,where iron and aluminum ions abound.Recent years,however,the development of agriculture has been seriously affected by the growing soil acidification.Boron deficiency and aluminum toxicity caused by soil acidification have become the main factors limiting crop production.Some studies have shown that boron can alleviate aluminum toxicity.Unfortunately,the mechanism is still unclearly.In particular,the detoxification of boron to aluminum under different rhizosphere pH,and the optimal level of boron are also unknown.In this study,the pea(Pisum sativum L.‘Zhongwan no.6')employed to reveal the possible mechanism of boron alleviate aluminum toxicity in different pH,and to investigate the alleviation effects with different boron concentrations to different aluminum contents.The results are as follows:1.Effects of boron on aluminum toxicity at different rhizosphere pH.The root relative elongation(RRE)of pea was significantly inhibited by low pH and aluminum toxicity.Low pH mainly affects the aluminum content of the meristematic zone,the transition zone,and the elongation zone.Under aluminum toxicity,the accumulations of active aluminum and callose in root apical increased with the increase of pH.Boron significantly promotes root growth by reducing the Al content and accumulations of active aluminum and callose in the transition zone at pH4.0.These results indicate that the alleviation of boron on aluminum toxicity has a close relation to rhizosphere pH,and the alleviation effect is more effective at low acid environment.2.Effects of boron on aluminum toxicity at different pH buffer solution.With MES buffer,the inhibition of RRE by low pH and aluminum toxicity is enhanced.Under aluminum toxicity,low pH mainly affects the aluminum content of the meristematic zone,the transition zone and the elongation zone.And the Al content of the meristematic zone,the transition zone and the elongation zone at pH4.5 is significantly higher than that at other pH,also the accumulations of active aluminum and callose were.Boron significantly promotes root growth by reduced the Al content and accumulations of active aluminum and callose in the transition zone at different pH.At pH4.8,the effect of boron on alleviatingaluminum toxicity was best,and it is contrast to MES buffer deficiency.It also revealed that the effects of boron on aluminum toxicity are relevant to the root rhizosphere pH.3.Mechanism of boron alleviating aluminum toxicity.Without aluminum stress,IAA significantly promoted rhizopshere acidification and inhibited root elongation.After treatment with boron,the effect enhanced,while the results are the same under Al stress whether boron exists.Without aluminum stress,RALF significantly promoted rhizopshere alkalization and root elongation with boron treatment.However it only promoted root elongation without boron treatment under Al stress.Therefore,the mechanism of boron to alleviate aluminum toxicity is that boron enhances the rhizopshere pH of the transition zone,reducing the accumulation of active aluminum and callose in the transition zone,and promoting the root elongation.4.Study on the optimal boron concentration to alleviate Al toxicity on acid soil.Boron supply can significantly increase the RRE of pea when the pea suffered from boron deficiency.In view of this situation,the best concentration of boron was 25 ?mol/L.Under aluminum stress,the application of 50 ?mol/L of boric acid can effectively alleviate the inhibition of aluminum toxicity on the RRE,active aluminum and callose on the transition zone.Therefore,the optimal concentration of boron under aluminum toxicity to the pea was 50 ?mol/L.Our results shown that low acid environment and aluminum toxicity both inhibit plant growth.Since boron can promote the increase of rhizosphere pH,and the alleviation of boron on aluminum toxitcity is more obvious in lower pH soil.It indicates that the application of boron is an effective measure to alleviate the aluminum toxicity in acid soil.Further studies have shown that,the amount of boron fertilizer applied,at least twice as high as the conventional amount,can alleviate the aluminum toxicity effectively in the southern acidic soil.Therefore,these studies provide a practical way to reduce the aluminum toxicity in acidic soils.It is of great significance to promote the agriculture sustainable development of acid soil in southern China and solve the problem of food safety from the source.