Absorption Kinetics And Mechanism Of Cr (â…¥) And Cr (â…¢) In Maize Seedling And The Responses Of Seedling Growth And Nutrient Uptake

In order to investigate the effects of hexavalent chromium and trivalent chromium Cr（VI） and Cr（Ⅲ） concentration on Cr absorption kinetics curves and absorption mechanism of maize seedling root, growth and development of maize seedling, nutrient absorption, solution experiments were carried out in Yangzhou University, China in 2014 and 2015 with suyu20 maize cultivar as plant material. The suyu20 maize was cultivated under different concentration of Cr（VI） and Cr（Ⅲ）. And with purpose of clarifing the effects of different nitrogen fertilizer types on growth and development, Cr absorption and nitrogen absorption of maize seedling under Cr（Ⅲ） stress, pot experiment was conducted in Yangzhou University, China in 2015 with suyu20 as plant material. The suyu20 maize was planted under differnet Cr（Ⅲ） concentration and nitrogen fertilizer types. The chief purpose of present study is to provide the valuable references for growth and development, nutrient absorption and application of nitrogen fertilizer in maize under soil Cr stress. Results shows as follows:（1） With increasing of Cr（VI） and Cr（Ⅲ） concentration, the Cr concentration of aboveground part, root and whole plant in maize seedling were correspondingly increasing. Cr content of root was much higher than that of aboveground part and whole plant in maize. The enrichment ability of Cr（Ⅲ） was higher than that of Cr（VI） in maize seedling root.（2） Absorption kinetics of Cr（VI） and Cr（Ⅲ） in maize root were both fit for the dynamic equation of Michaelich-Menten. The affinity of absorption site between Cr（Ⅲ） and the root cellula （Km） was less than that between Cr（VI） and root cellula in maize, but maximum absorption rate （Vmax） and absorption ability （Vmax/Km） of Cr（Ⅲ） in maize root were significantly higher than those of Cr（VI）, which may be one of reasons that the enrichment ability of Cr（Ⅲ） in maize seedling root was higher than that of Cr（VI）.（3） The toxicity of Cr（VI） to maize seedling was higher than that of Cr（Ⅲ）. The fresh weight of seedling, chlorophyll content, root characteristics and root parameters （root length, root surface area, root volume） under Cr（VI） treatments were less than those under Cr（Ⅲ） treatments in maize seedling. Especially under higher Cr（VI） concentration treatment, maize seedling showed obvious poisoned symptom, leaves withered and root rotting. And, the growth and development of maize seedling was also inhibited under higher Cr（Ⅲ） concentration.（4） The absorption of N, P and K were inhibited under relatively high Cr（VI） and Cr（Ⅲ） concentration. Compared with control test （Cr:Omg/L）, content of Ca, Mg, Fe, Mn, Cu and Zn decreased under both Cr（VI） and Cr（Ⅲ） treatments. The accumulation amount of N, P, K, Ca, Mg, Fe, Mn, Cu and Zn were higher under Cr（Ⅲ） treatment than that under Cr（VI） treatment.（5） The absorption of Cr（VI） in maize seedling root need not to expend energy, which possibly existed an passivity absorption way. While, the absorption of Cr（Ⅲ） in maize seeding root need to expend energy, which possibly existed an active absorption way. The transportation of Cr（Ⅲ） from outside of root cellula to inside of root cellula was not by Ca²⁺ and K+ channels, possible by the Fe³⁺absorption way.（6） Compared with no nitrogen fertilizer treatment, dry weight, amount of nitrogen absorption and amount of Cr absorption in maize seedling increased in nitrogen fertilizer treatments under Cr（Ⅲ） stress. Compared with urea fertilizer, maize seedling showed higher dry weight, amount of nitrogen absorption and amount of Cr absorption in slow release N fertilizer treatment under Cr（Ⅲ） stress.