Effects of nutrient addition on phytoplankton in Lake Nakanuma, Japan

Abstract

We measured the uptake of carbon and inorganic nitrogen in nutrient-enriched water samples during 15-days incubation in summer in Lake Nakanuma, Japan. We calculated daily variations in neutral sugars and amino acids of the phytoplankton and estimated the efficiency of the increases in sugars and amino acids relative to photosynthetic activities. Only a small portion of carbon incorporated via photosynthesis was used for synthesis of sugars and amino acids during the incubation periods. The percentage increase in neutral sugars plus amino acids compared to photosynthetic rates ranged from 3.7 to 26.9% with an average of 12.8%. These findings suggest that large amounts of photosynthates were not used for the synthesis of cell components of phytoplankton and were lost through processes such as excretion and respiration.