Sulfate deficiency stimulates release of dissolved organic matter in synchronous cultures of Scenedesmus obliquus

In synchronous cultures of the green alga Scenedesmus 276–3a suboptmal sulfate supply increases the concentration of dissolved organics considerably. The highest level of extracellular organic substances occurs at sulfate dosages which reduce growth by 50‐70% as compared to control cultures growing under standard conditions. Sulfate deficiency causes increased synthesis of carbohydrate and reduces the production of crude protein and chlorophyll almost simultaneously at incipient sulfur deficiency. Since the concentration of extracellular organic substance rises at the same time, this symptom of partial sulfur deficiency is interpreted as resulting from an imbalance between the production and utilization of photosynthetic products. Part of the excess carbohydrate is retained in the cells.