C_3和C_4禾本科作物的氮素利用效率——Ⅲ.不同苗龄和不同外源NO_3^-培养下幼苗叶片NO_3^-含量的比较

NITROGEN USE EFFICIENCY IN C_3 AND C_4 CEREALS Ⅲ. COMPARING THE LEVELS OF LEAF NO_3^- AMONG THEIR 5d TO 10d OLD SEEDLINGS AND IN DIFFERENT EXTERNAL NO_3^- LEVELS

在供试5.0mmol/l KNO_3培养下,发现5、6、7、8、9、10天龄大麦和玉米幼苗叶片内NO_3^-含量随苗龄的变化趋势是一致的,都在8天龄达最高,苗龄大于或小于7天都稍低;在5-10天任一苗龄下,大麦都比玉米有较高的叶片NO_3^-含量。当在0、0.5、1.0、5.0、10.0、20.0、40.0m mol/l KNO_3培养下时,发现一方面,随着外源NO_3^-水平的提高,7天龄大麦和8天龄玉米幼苗叶片内的NO_3^-积累也相应增加;连续培养处理(从种植开始便加入KNO_3)植株体内的NO_3^-积累比测定24小时前才加入KNO_3的处理要高;另一方面,不管是连续培养还是24小时前加入NO_3^-,大麦都较玉米有较高的NO_3^-积累。造成这种差异的原因可能在于大麦比玉米其根系有较高的NO_3^-吸收能力而其叶片有较低的NO_3^-还原能力。

The change dynamic trends of leaf NO_3^- contents in 5-10d old barley and maize seedlings which irrigated with 5.0 m mol/L KNO_3were consistent with each other. The results showed that the leaf NO_3^- contents of them went up to the highest point at their 8d old seedlings but were lower than that of their bigger or smaller 7d old seedlings respectively. However,as for 5d to 10d old plants, barley seedhngs had always higher levels of leaf NO_3^- than that of the same age old maize seedlings under the same growth solution mentioned above. And the leaf NO_3^- contents of 7d harley and 8d maize seedlings had a relevant increase respectively as the increase of external NO_3^- levels among 0.0.5, 1.0, 5.0, 10.0, 20.0, 40.0 m mol/L NO_3^- and the treatment ofadding KNO_3 from the beginning of growing the plants had a higher leaf NO_3^- content than that of the treatment of adding NO_3^- before 24 hours collected their leaf samples. However. barley seedlings had always higher leaf NO_3^- contents than that of maize seedlings under those two treatments mentioned above. As a results the authors would suggested that the reasons for the difference of leaf NO_3^- contents between barley (C_3) and maize (C_4) could be that barley roots had higher NO_3^- uptake ability than that of maize roots but barley leaves had lower NO_3^- reduction ability than that of maize leaves at the same time