Estimates of in Situ Rates of Nitrogen Uptake by Trichodesmium Sp. In the Tropical Atlantic Ocean1

Using the 15 N technique, the uptake rates of three inorganic nitrogen sources by Trichodesmium sp. occurring in the tropical Atlantic Ocean were measured. The uptake of ammonia was greatest followed by nitrate and molecular nitrogen. At some locations, assimilation of molecular nitrogen was considerable. The highest rate measured was 0.32 N liter −1 hr −1 , which is comparable to rates measured during nitrogen‐fixing blue‐green algae blooms in lakes.