水稻不同时期吸收的氮素的行为

为研究水稻不同时期吸收的氮素在其体内的行为，作者利用^15NH^4＋和^15NO3^-双标记，对Indica水稻亚种（品种Hinohikari）进行水培，在分蘖期、幼穗分化期、开花期施用，将培养液卢州）20mg／L的NH4NO3换成相同质量浓度的^15TH4NO3或NH4^15NO3；部分水稻在一周后收获，其他分别在分蘖期、幼穗分化期、开花期、成熟期收获。植株分成根系、地上部的底部、地上部的顶部、旗叶和穗部，对各自的全氮、^15N进行测定，计算植物的总吸收量。从施用量、植株总吸收量以及三部分总和的植株氮残存量的比较来研究氮素在两种水稻亚种中的行为。研究结果表明，各个时期的^15NH4NO3或NH4^15NO3处理下水稻的N吸收总量上没有差别，但1周后收获的^15NH4-N处理的水稻中^15N的含量比^15NO3-N要高得多，直到成熟期收获的水稻都有同样的结果，这意味着各个时期吸收的NH4-N和NO3-N有着不同的损失量，吸收的NO3-N比NH4-N要损失得多。水稻叶片的氮素损失可能以N2O和NH3的形式。不同氮肥形态的处理下转移到穗部的氮素的量和来源也不相同，在NH4^15NO3的处理中穗部的^15N主要来自地上部的底部，而在^15NH4NO3的处理中穗部的^15N主要来自分蘖期吸收的^15N，少量来自成熟期并且^15N主要来自植株的各个部分。

Behavior of Nitrogen Absorbed at Different Growth Stages of Rice Plants

To investigate the distribution of 15NH4-N and 15NO3-N in rice plant at different growth stages, a pot experiment by solution culture was carried out in a green house using rice (Oryza sativa L.) variety, namely Hinohikari. At tillering (TI), panicle initiation (PI) and heading stages (HD), 15NO3-N or 15NH4-N was applied to the plants for one week. Some of rice plants fed with 15N were immediately harvested after one week of 15N feeding and the others were done at subsequent stages. After harvesting, rice plants were separated into roots, lower parts, upper parts, flag leaves and ears, and ground into powder for total N and 15N determination. There were no differences in 15N amount absorbed from the culture solution at each stage between 15NO3-N and 15NH4-N treatment. However, the 15N amount of rice plant that immediately harvested after absorption of 15N was less in the 15NO3 treatment than in the 15NH4-N treatment. Furthermore, the 15N amount of rice plant at the maturity stage was also less in the 15NO3-N treatment compared with that of the 15 NH4-N treatment. The results suggest that the loss of nitrogen from the rice plant was more in nitrogen absorbed from NO3-N than in that absorbed from NH4-N. The loss of N during 15N absorbing may be due to volatilization from rice plant as N2O and NH3, respectively, and loss of N from heading stage may be due to volatilization of NH4-N generated by decomposition of organic compound. 15N amount and 15N source translocated to ear were different in N supplying forms. In NO3-N form, the most nitrogen of ear depends upon the translocation from lower part. On the other hand, in NH4-N form, the most amounts of that at tillering stage and small amount of that at the maturity stage depend on root, lower part, upper part and flag leaves, respectively.