Effects of elevated CO₂ and phosphorus supply on growth, photosynthesis and nutrient uptake in the marine macroalga <i>Gracilaria lemaneiformis</i> (Rhodophyta)

Abstract

Abstract The red alga Gracilaria lemaneiformis was cultured under different CO 2 and phosphorus conditions for 16 days, and its growth, photosynthesis and uptake of nitrate and phosphate were examined in order to establish the longer-term impacts of elevated CO 2 and phosphorus supplies on this economically important seaweed. Enrichment with either CO 2 or phosphorus in culture markedly increased the growth of G. lemaneiformis compared to the control. Light-saturated photosynthetic rate was enhanced significantly by phosphorus enrichment, but hardly affected by the elevation of CO 2 when G. lemaneiformis was grown under low phosphorus conditions. High phosphorus stimulated photosynthetic inorganic carbon utilization and nitrogen uptake. Under low phosphorus conditions, the thalli grown at the high level of CO 2 had a lower carbon utilization capacity and a higher nitrogen uptake rate compared to those grown under ambient CO 2 . Reversed results were found when the algae were grown under high phosphorus conditions. Hence, available phosphorus may regulate inorganic carbon utilization of G. lemaneiformis grown at different CO 2 levels, and growth reflected a balance between carbon and nutrient metabolism.