The Kinetics of Organic Acid Uptake by Three Chlorophyta in Axenic Culture1

The uptake of 814C‐labelled dissolved carboxylic acids byAnkistrodesmus falcatus(Corda) Ralfs,Chlamydomonas segnisEttl andChlorellasp. was measured. The acids were acetic, citric, fumaric, glycollic, lactic, malic, pyruvic and succinic acids. For some substrates uptake was active, but for others it was apparently passive. The respiratory loss of substrates ranged from 5.0 to 95.0% of the total amount of C assimilated. The potential ability of these organisms to compete with bacterial populations for such substrates in natural waters was examined. In terms of the kinetics of assimilation it appeared thatA. falcatusmight compete successfully for glycollate, lactate, pyruvate and succinate; C. segnisfor glycollate and lactate andChlorellasp. for lactate, malate and possibly glycollate. Calculated replacement times of the algae on the 8 substrates did, however, indicate that although they might compete successfully for some substrates they were generally unable to grow upon them at the concentrations provided.