Activation Of Plant Root Exudates Of Insoluble Phosphorus And Potassium And Soil Selenium

Taking the rise., maize differently genetic kinds of rapes and differently genetic kinds of tobaccos as the test material , the different activating reactions of root exudates of these plants on the insoluble Phosphorus and Potassium as well as the Seleniuni were investigated in this paper. P-deficiency and K-deficiency induced the decrease of pH in culture solution .The acidification ability of maize was the greatest and its pH decrease by 2 units in 12 h. The rise was lower compared with the maize. The p1-1 of differently genetic kinds of tobaccos decreased than the controls. At the beginning stage of the culture, the acidification to the rhizosphere under P stress and K stress were strong and with time passing this acidification turned down. The speed of i secretion of plants was stronger than in weak light. During the Selenium stress the differently genetic kinds of rapes showed the increasing tendency. The pH of the cultural solution of Sc-enriched plant, Indian mustard (Brassica juncea) increased 2.5 units of pH value in 12 h, and the Luzhou mustard also increased I unit pH value, but the other genetic kinds of rapes seemed have not the obvious increasing trend. This can explain the differently genetic kinds of rapes have different absorbing ability to the Selenium, and this is thanks to the alkalion. The root exudates of differently genetic kinds of tobaccos had the different activating ability to the mica and feldfspar. Only the K326 can extract the Potassium 60% beyond the control. In the K stress, the activating effect of other kinds of tobaccos were not obvious. All kinds of tobaccos had the strong activating ability for the mica.Root exudates could mobilize sparingly soluble P , but its effect depend on the forms of sparingly soluble P. For moblization of Ca-P, organic acids in root exudates was no any markedly role, pH of root exudates was the key factor. The extract P(mg/kg) from Ca-P at p11 5.0 is almost twice as at pH 9.0. The extract under P stress could extract more P from Fe-P than control, especially in low pH. The different variation of enzyme activity between the maize and rice may be one of the reasons which cause the difference of acidification ability. The amount of extracted organic acids is realated with the mobilizing ability, and the temperature perhaps also is one of the influencing factors. With the reaction temperature raising, the extracted amount of P and K increase. There stay obviously different activating abilities for different plants to activate the Selenium in the soil according to the different concentration of Selenium in the soil. The higher ability of enriching selenium, the stronger ability of the root exudates to activate the Selenium in the soil. .The mustard has the strongest activating effect to the Selenium in the soil. With the reaction temperature raising,, the mobilizing ability of the differently genetic kinds of rapes. There has another mechanism. In the mimic cultural trial, the short ratios of nutritional elements in the rhizosphere accord to the results of the activating abilities of root exudates. This shows that the root exudates play a key role for plants to use the nutritional elements.