Herrmann Beat, Mattsson Marie, Fuhrer Jürg, Schjoerring Jan K
Swiss Federal Research Station for Agroecology and Agriculture, Zuerich-Reckenholz and Liebefeld-Bern, Schwarzenburgstrasse 155, Liebefeld, CH-3003 Bern, Switzerland.
J Exp Bot. 2002 Jan;53(366):139-46.
Plant-atmosphere NH(3) exchange was studied in white clover (Trifolium repens L. cv. Seminole) growing in nutrient solution containing 0 (N(2) based), 0.5 (low N) or 4.5 (high N) mM NO(3)(-). The aim was to show whether the NH(3) exchange potential is influenced by the proportion of N(2) fixation relative to NO(3)(-) supply. During the treatment, inhibition of N(2) fixation by NO(3)(-) was followed by in situ determination of total nitrogenase activity (TNA), and stomatal NH(3) compensation points (chi(NH(3))) were calculated on the basis of apoplastic NH4(+) concentration ([NH4(+)]) and pH. Whole-plant NH(3) exchange, transpiration and net CO(2) exchange were continuously recorded with a controlled cuvette system. Although shoot total N concentration increased with the level of mineral N application, tissue and apoplastic [NH4(+)] as well as chi(NH(3)) were equal in the three treatments. In NH(3)-free air, net NH(3) emission rates of <1 nmol m(-2) s(-1) were observed in both high-N and N(2)-based plants. When plants were supplied with air containing 40 nmol mol(-1) NH(3), the resulting net NH(3) uptake was higher in plants which acquired N exclusively from symbiotic N(2) fixation, compared to NO(3)(-) grown plants. The results indicate that symbiotic N(2) fixation and mineral N acquisition in white clover are balanced with respect to the NH4(+) pool leading to equal chi(NH(3)) in plants growing with or without NO(3)(-). At atmospheric NH(3) concentrations exceeding chi(NH(3)), the NH(3) uptake rate is controlled by the N demand of the plants.
在含有0（以N₂为基础）、0.5（低氮）或4.5（高氮）mM NO₃⁻的营养液中生长的白三叶草（Trifolium repens L. cv. Seminole）中研究了植物 - 大气NH₃交换。目的是表明NH₃交换潜力是否受相对于NO₃⁻供应的固氮比例影响。在处理期间，通过原位测定总固氮酶活性（TNA）跟踪NO₃⁻对固氮的抑制作用，并根据质外体NH₄⁺浓度（[NH₄⁺]）和pH计算气孔NH₃补偿点（χ(NH₃)）。使用可控比色皿系统连续记录整株植物的NH₃交换、蒸腾作用和净CO₂交换。尽管地上部总氮浓度随矿质氮施用量水平增加，但三种处理中的组织和质外体[NH₄⁺]以及χ(NH₃)相等。在无NH₃的空气中，高氮和以N₂为基础的植物中观察到净NH₃排放率<1 nmol m⁻² s⁻¹。当给植物供应含有40 nmol mol⁻¹ NH₃的空气时，与从NO₃⁻生长的植物相比，仅从共生固氮获取氮的植物中产生的净NH₃吸收更高。结果表明，白三叶草中的共生固氮和矿质氮获取在NH₄⁺库方面是平衡的，导致在有或没有NO₃⁻生长的植物中χ(NH₃)相等。在大气NH₃浓度超过χ(NH₃)时，NH₃吸收速率受植物的氮需求控制。
