不同硝/铵比值对小麦幼苗根系释放氢氧根的影响

Effect of NO_3^-/NH_4^+ Molar Ratio on Hydroxyl Release From Wheat Roots

为研发酸化土壤的生物修复技术,采用水培试验和自动电位滴定装置研究酸性条件下氮素形态对小麦幼苗根系释放氢氧根及培养液pH变化的影响。结果表明,小麦幼苗在初始pH值为4.0,n(NO3-)∶n(NH4+)比值(以下简称硝/铵比)分别为15∶1、3∶1和1∶1的营养液中培养6 d后营养液pH升高,且增幅随硝/铵比的增加而增大,小麦对硝态氮的吸收量和氢氧根释放量呈相同的变化趋势,说明小麦对硝态氮的吸收偏好导致根系释放氢氧根,进而使得培养液pH升高。小麦幼苗在硝/铵比为3∶1,初始pH值分别为4.0、4.5和5.0的营养液中培养6d后,培养液pH和氢氧根释放量的增幅随初始pH的升高而降低,说明低pH条件有利于小麦幼苗对硝态氮的吸收,可促进小麦根系释放更多的氢氧根。10 h的恒定pH试验结果表明,恒定pH条件下小麦根系释放的氢氧根数量大于非恒定pH条件,且硝态氮比例越大,差值越大。因此,可以根据小麦在酸性条件下对硝态氮的吸收偏好建立酸化土壤的生物修复方法,即调节硝态氮含量以加大小麦根系的氢氧根释放量,进而提高土壤pH。

In order to develop methods for bioremediation of acid soils,hydroxyl release from roots of wheat seedlings in a hydroponic experiment as affected by form of nitrogen fertilizer under acidic conditions was investigated with an automatic titration system.Results show that pH of the nutrient solutions,4.0 in initial pH and 15：1,3：1 and 1：1 in NO-3/NH＋4 molar ratio separately,increased after 6 days of wheat culturing.The higher the molar ratio,the greater the increase in solution pH.Correspondingly,the absorption of nitrate by wheat and the release of hydroxyl from wheat roots also increased with the rising molar ratio.These findings suggest that the preferential absorption of nitrate by wheat and subsequent release of hydroxyl from wheat roots cause increase in solution pH.In solutions the same in NO-3/NH＋4 molar ratio,being 3：1,and varied in initial pH,the increases in solution pH and hydroxyl release followed the order of：initial pH 4.0〉initial pH 4.5〉initial pH 5.0,suggesting that lower pH condition favors nitrate uptake by wheat and hydroxyl release from wheat roots.A 10-hour pH-stat experiment shows that wheat roots released more hydroxyl under pH-stat conditions than under non-pH-stat conditions.The higher the molar ratio,the greater the difference.It is,therefore,feasible to develop a new method for bioremediation of acid soil based on the preference of wheat to absorb nitrate and release hydroxyl from roots under acidic conditions,that is to say,to increase the release of hydroxyl by regulating nitrate content in the soil and hence to increase soil pH.