The impact of irradiance on optimal and cellular nitrogen to phosphorus ratios in phytoplankton

摘要

Phytoplankton acclimates to irradiance by regulating the cellular content of light-harvesting complexes, which are nitrogen (N) rich and phosphorus (P) poor. Irradiance is thus hypothesised to influence the cellular N:P ratio and the N:P defining the threshold between N and P limitation (the optimal' N:P). We tested this hypothesis by first addressing the response of the optimal N:P to irradiance in a controlled experiment with Chlamydomonas reinhardtii. Then, we did a meta-analysis of experimental data on optimal and cellular N:P ratios across light gradients to test the generality of an N:P to light response within species. In both the experiment and the meta-analysis, N:P ratios decreased with irradiance, indicating that factors affecting underwater irradiance, like depth and the composition of the water, may influence the relative N:P requirement. The effect of irradiance did not differ between optimal and cellular N:P ratios, but observations of optimal N:P were on average 2.8 times higher than observations of cellular N:P.