Methodological problems in the simultaneous assessment of photosynthesis and nutrient uptake in phytoplankton as functions of light intensity and cell size
The processes of nitrate, ammonia, and phosphate uptake in marine phytoplankton differed in the extent of dependence on light. Phosphate uptake in the 3–8‐µm size class, but not in the whole population, showed a saturation‐type relationship to light. Biomass‐specific photosynthesis and nutrient uptake rates were highest in the smallest, 0.2–3‐µm, size class, and decreased in the 3–8‐µm, and in the >8‐µm classes.C:N:P uptake ratios at ambient light were different in the 0.2–3‐µm, 3–8‐µm, and >8‐µm size classes. In the whole population, uptake ratios at ambient light differed from ratios based on light‐optimized data. However, the measurements are subject to many problems which preclude an assessment of the accuracy of the ratios.