Abstract:

The purpose of this study was to explore effects of two duckweed (Lemma minor and Spirodela polyrrhiza) on the changes of nitrogen content in floodwater under variable nitrogen fertilizer application. In our study, the concentrations of ${NH_{4}}^{+}$-N, $NO_{3}^{-}$-N, and total N in floodwater were analyzed to explore the influence of duckweed on nitrogen (N) content under five nitrogen gradients (0, 90, 180, 270, 360 kg N·hm^-2). Results showed that the concentrations of ${NH_{4}}^{+}$-N and total N in floodwater increased with the nitrogen fertilizer gradients, and similar trends were observed for Lemma minor and Spirodela polyrrhiza. Lower ${NH_{4}}^{+}$-N concentrations were found in Spirodela polyrrhiza than Lemma minor treatments, suggesting Spirodela polyrrhiza may be more efficient in reducing nitrogen loss. Under N270 and N360 treatments, the total N concentration decreased at first then slowly increased in 30 days and decreased at last. The results indicated that that duckweed could modify the balance of nitrogen by regulating its growth. When the nitrogen concentration was high, it could absorb nitrogen, and release nitrogen into the floodwater through its own decay under low nitrogen concentration. It played an important role in reducing the potential of nitrogen loss in the floodwater at the initial stage of fertilization and warrant the nitrogen nutrition supply of crops at the later stage of fertilization. This study provides theoretical basis for optimizing nitrogen and reducing nitrogen loss in rice field by using duckweed.

Key words: nitrogen gradient, duckweed, floodwater, nitrogen loss

摘要：

为探究不同施氮量下2种浮萍[青萍(Lemma minor)和紫萍(Spirodela polyrrhiza)]对稻田田面水氮含量动态的影响,设置5个氮梯度(0、90、180、270、360 kg N·hm^-2),研究浮萍对稻田田面水氨态氮(${NH_{4}}^{+}$-N)、硝态氮($NO_{3}^{-}$-N)及全氮含量动态的影响。结果表明,田面水${NH_{4}}^{+}$-N和全氮含量随着施氮量的增加而增加,添加2种浮萍的稻田田面水${NH_{4}}^{+}$-N含量随培养时间延长呈逐渐降低的趋势。通过对不同氮梯度下${NH_{4}}^{+}$-N含量进行比较分析,发现添加紫萍的田面水${NH_{4}}^{+}$-N含量较青萍低,表明添加紫萍更有利于减少稻田${NH_{4}}^{+}$-N的流失。在N270和N360处理下,全氮含量在整个培养期间呈先降低后升高再降低的趋势,表明高氮量输入(270 及360 kg N·hm^-2)下,添加的浮萍在前期氮素浓度较高时可吸收氮素,而在后期浓度较低时可通过自身腐解向田面水中释放氮素,从而提高后期(培养30 d)田面水氮含量,对于降低施肥初期田面水氮素径流流失风险和保证施肥后期作物的氮营养供应具有重要的作用。本研究为通过放养浮萍优化稻田氮素利用、减少稻田氮素流失提供了理论依据。

关键词: 氮梯度, 浮萍, 稻田田面水, 氮素流失