Chan H K, Campbell N E
Appl Environ Microbiol. 1978 Jun;35(6):1052-60. doi: 10.1128/aem.35.6.1052-1060.1978.
Nitrate uptake in the epilemnetic waters of a small eutrophic Canadian Shield lake was studied by using a 15N method during summer stratification. Concurrent with inhibition of primary production, 3-(3,4-dichlorophenyl)-1,1-dimethylurea inhibited NO3- assimilation. Nitrate up to 1 mg of N/liter did not affect the rate of primary production during 3 h of incubation. The NO3- fertilizer added to the lake weekly was consumed through algal assimilation in about 3 days. Excretion of the photoassimilated NO3- as dissolved organic nitrogen represented a significant portion of the nutrient incorporated by the cells. Only 40% of the NO3- -15N which disappeared could be accounted for in the particulate fraction. Although the rest was presumably excreted, only 15% of the 15N label was accounted for as cationic dissolved organic nitrogen by isotope assays. These excreted organic forms were predominantly serine and glycine in the dissolved free amino acid fraction. Bacteria as well as algae might be expected to contribute to and modify the extracellular nitrogen pool.
在夏季分层期间，采用¹⁵N方法研究了加拿大盾形地带一个小型富营养化湖泊的癫痫水域中的硝酸盐吸收情况。在抑制初级生产的同时，3-(3,4-二氯苯基)-1,1-二甲基脲抑制了NO₃⁻同化作用。在3小时的培养过程中，高达1毫克氮/升的硝酸盐不会影响初级生产速率。每周添加到湖泊中的硝酸盐肥料在大约3天内通过藻类同化作用被消耗掉。光同化的硝酸盐以溶解有机氮的形式排泄，这占细胞吸收养分的很大一部分。消失的NO₃⁻-¹⁵N中只有40%可以在颗粒部分中得到解释。尽管其余部分可能是排泄掉了，但通过同位素分析，只有15%的¹⁵N标记以阳离子溶解有机氮的形式得到解释。在溶解的游离氨基酸部分中，这些排泄的有机形式主要是丝氨酸和甘氨酸。细菌以及藻类可能会对细胞外氮库做出贡献并对其进行修饰。
