Lu Y X, Li C J, Zhang F S
The Key Laboratory of Plant Nutrition, Ministry of Agriculture, Key Laboratory of Plant-Soil Interactions, Ministry of Education, China Agricultural University, Beijing 100094, China.
Ann Bot. 2005 May;95(6):991-8. doi: 10.1093/aob/mci104. Epub 2005 Mar 4.
Ammonium can result in toxicity symptoms in many plants when it is supplied as the sole source of N. In this work, influences of different nitrogen forms at two levels (2 and 15 mm N) on growth, water relations and uptake and flow of potassium were studied in plants of Nicotiana tabacum 'K 326'.
Xylem sap from different leaves was collected from 106-d-old tobacco plants cultured in quartz sand by application of pressure to the root system. Whole-shoot transpiration for each of the treatments was measured on a daily basis by weight determination.
Total replacement of NO(3)(-)N by NH(4)(+)-N caused a substantial decrease in dry weight gain, even when plants grew under nutrient deficiency. Increasing nutrient concentration resulted in a greater net dry weight gain when nitrogen was supplied as NO(3)(-) or NH(4)NO(3), but resulted in little change when nitrogen was supplied as NH(4)(+). NH(4)(+)-N as the sole N-source also caused reduction in transpiration rate, changes in plant WUE (which depended on the nutrient levels) and a decrease in potassium uptake. However, the amount of xylem-transported potassium in the plants fed with NH(4)(+) was not reduced: it was 457 % or 596 % of the potassium currently taken up at low or high nutrient level, respectively, indicating a massive export from leaves and cycling of potassium in the phloem.
Ammonium reduces leaf stomatal conductance of tobacco plants. The flow and partitioning of potassium in tobacco plants can be changed, depending on the nitrogen forms and nutrient levels.
当铵作为唯一氮源供应时，许多植物会出现毒性症状。本研究以烟草品种‘K 326’为材料，研究了两种氮水平（2和15 mM N）下不同氮形态对其生长、水分关系以及钾吸收和运输的影响。
对培养在石英砂中的106日龄烟草植株的根系施加压力，收集不同叶片的木质部汁液。通过称重法每日测定各处理的整株蒸腾量。
即使在养分缺乏条件下生长，用铵态氮完全替代硝态氮也会导致干物质积累显著减少。当以硝态氮或硝酸铵供应氮时，增加养分浓度会导致更大的净干物质积累，但以铵态氮供应氮时，几乎没有变化。以铵态氮作为唯一氮源还会导致蒸腾速率降低、植物水分利用效率发生变化（这取决于养分水平）以及钾吸收减少。然而，以铵态氮施肥的植株中木质部运输的钾量并未减少：在低养分水平或高养分水平下，分别是当前吸收钾量的457%或596%，这表明钾从叶片大量输出并在韧皮部中循环。
铵会降低烟草植株的叶片气孔导度。烟草植株中钾的运输和分配会因氮形态和养分水平而改变。
