PHOTOSYNTHETIC RESPONSE OF LAKE PLANKTON TO COMBINED NITROGEN ENRICHMENT 1
PHOTOSYNTHETIC RESPONSE OF LAKE PLANKTON TO COMBINED NITROGEN ENRICHMENT 1
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湖泊浮游生物对复合氮富集的光合响应 1
DOI：
10.1111/j.1529-8817.1982.tb03217.x
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发表时间：
1982
影响因子：
2.9
通讯作者：
F. R. Pick
中科院分区：
文献类型：
--
作者：
D. Lean;T. Murphy;F. R. Pick
对5个不同大小和营养状态的湖泊样品进行了光合作用和氮吸收之间的复杂相互作用的研究。当富含15NH4+时，被认为是缺氮的样品的光合作用速率通常会降低4-5小时。这表明，能量从光合作用重新分配到N的吸收和同化上，在低水平NH4+富集时刺激C吸收，然后随着NH4+进一步增加而逐渐下降。在其他无法检测到环境NH4+的情况下，浮游动物的营养再生提供了所需氮素的很大一部分。在这些时候，当浮游生物有足够的有效氮时，无论是NH_4+还是NO_3，−的增加通常都不会改变光合作用速率。通常情况下，只有少量的N3−被摄取，并且没有观察到光合作用反应。然而，在两种情况下，由于季节早期高N3−和低NH4+水平，对N3−的吸收是显著的。在这些时间中的一个时间，光合作用随着N3−的增加而减少。当光合作用随着NH_4+浓度的增加而降低，但随着NO_3-−浓度的增加而增加时，出现了进一步的并发症，尽管NO_3-−的吸收可以忽略不计。这些观察结果表明，对这两种氮源的复杂代谢还没有完全了解。在最佳光强下，C：N吸收比，即使在NH4+浓度增加的情况下，也只能维持细胞的C：N比，除非大量固定的C被呼吸或排泄。三个观察结果表明，光合作用和N吸收是不耦合的，(I)当低光适应种群暴露在强光条件下时，光抑制C吸收，而不是N吸收，(Ii)最大N吸收的光强略小于碳。(3)暗N吸收始终接近光照下最大吸收速率的50%，而C吸收始终接近POPT的2%。当然，这是有相互联系的，因为NH4+的富集会增强暗C的吸收。
The complex interplay between photosynthesis and the uptake of nitrogen was investigated in samples from five lakes of different size and trophic state. When enriched with 15NH4+, the photosynthetic rate was often reduced for 4–5 h in samples believed to be nitrogen deficient. This implies that energy was reallocated from photosynthesis to the uptake and assimilation of N. Stimulation in C uptake at low levels of NH4+ enrichment was followed by a progressive decline with further NH4+ enrichment. On other occasions when ambient NH4+ was undetectable, nutrient regeneration by zooplankton supplied a significant fraction of the required nitrogen. At these times and when the plankton had sufficient available N, there usually was no change in photosynthetic rate with either NH4+ or NO3−enrichment. Typically, little NO3− was taken up and no photosynthetic response was observed. On two occasions, however, the uptake of NO3− was significant due to high NO3− and low NH4+ levels early in the season. At one of these times there was a reduction in photosynthesis with NO3− enrichment. A further complication was observed when photosynthesis decreased with NH4+ enrichment but increased with NO3− enrichment despite negligible NO3− uptake. These observations illustrate that the complex metabolism of these two nitrogen sources is not fully understood. At optimum light intensity, C:N uptake ratios, even under NH4+ enrichment, are only sufficient to maintain the cellular C:N ratio unless much of the fixed C is respired or excreted. Three observations suggest that photosynthesis and N uptake are not coupled, (i) Photoinhibition of C uptake, but not N uptake was observed when low light adapted populations are exposed to high light conditions, (ii) The light intensity for maximum N uptake was slightly less than that for carbon. (iii) Dark N uptake was always near 50% of the maximum rate in the light whereas the C uptake was near 2% of Popt. Certainly, there is an interconnection because dark C uptake was enhanced by NH4+ enrichment.