Effect Of Different Al-Resistant Species And Exogenous Factors On The Activity Of Aluminum In Acid Soil

Aluminum (Al) toxicity has been recognized as one of the most important limiting factors of plant productivity in acidic soils. It is a reasonable method to screen and breed the Al-resistant species or cultivars for augmenting crop productivity in acidic soils. The degree of Al resistance in plants diversify between species and among cultivars within specie, including external exclusion mechanisms and internal tolerance mechanisms. Although considerable research have been explored in these fields, it is still not well understood or lack of evidence to clarify Al resistance mechanisms in some plants. In this article, buckwheat, Al accumulator, rice, Al excluder and wheat, Al sensitive plant were selected to investigate soil solution in plant root zone by a series of pot experiment, meanwhile a series of exogenous low-molecular-weight organic acids and phenol compounds were added to testify various Al resistance mechanisms. The results were listed as follows:1> The results of studies on effect of exogenous low-molecular-weight organic acids on the activity of aluminum,calcium and magnesium in acid soil pretreated by CaCO3 showed that in the solution of pH4.5, the soluble aluminum and the exchangeable Ca was increased significantly while the exchangeable Al was decreased significantly after the addition of oxalate, citrate and malate whether CaCO3 was amended or not; When CaCO3 was added, the exchangeable Mg was all increased under oxalate, citrate and malate treatment. The ability of organic acids to promote the aluminum dissolution by complexation follows the order as citrate> oxalate> malate, which is consistent with their stability constants of aluminum organic complexes. On the other hand, the pretreatment of CaCO3 caused the augment of soluble Al and the descent of exchangeable Al. The results of two-factor analysis of variance indicated that the effects of organic acids were overwhelming predominace on the soluble and exchangeable Al, Ca and Mg by complexing or precipitating, while CaCO3 only had significant effects on soluble Al, exchangeable Al and Ca dominantly by competing and exchanging between Al and Ca, Mg because of the control of pH buffer solution. On the whole, the addition of low-molecular-weight organic acids made the significant increase of active Al and the slightly higher of active Ca and Mg. The roles of organic acids in the actual acid soils need further evaluation from the effects of dissolution of cations.2,Study on low-molecular-weight organic acids on the mobilization aluminum in acid soil at different pH. The results indicated that at the different pH value (pH3.5,4.5,5.5), in oxalate system, the soluble aluminum decreased with increased pH. But in citrate and oxalate systems, the soluble aluminum increased with increased pH at firstly, and then inclined by degrees. Meanwhile, the mobilization of exchangeable aluminum increased with increased pH, one of the citrate system is the most obvious.3,Effect of exogenous phenol compounds on the activity of aluminum,calcium and magnesium in acid soil. The results showed that:in the pH4.5, exchangeable aluminum on soil solution decreased when pyrocatechol and morin were added to the soil, moreover, there is an decreased on soluble calcium and magnesium, and increased on exchangeable calcium and magnesium. Meanwhile, there is no significant effect on soluble aluminum but significantly decreased on exchangeable aluminum by adding calcium carbonate or not. The reason probably is calcium carbonate affecting the exchangeable aluminum on some extent.4,Effect of soil solution in root zones of different Al-resistant species. The results indicated that:the pH value of soil solution was an important but not exclusive factor controlling the Al concentration. Buckwheat is Al accumulator, it can not only accumulate high concentration of Al in leaves but also take up efficiently Ca, Mg and Zn in acid soils during the growing. While those in soil solution of rice and wheat had the tendency of converse parabola, whice is obvious different from buckwheat. pH is increased with growing by calcium carbonate, the fluctuation trend of cations including Al, Ca, Mg and Zn was the results of competition and exchangeable between Ca-Mg-H-Al on soil particle surfaces.