Temperature response of photosynthetic light- and carbon-use characteristics in the red seaweed Gracilariopsis lemaneiformis (Gracilariales, Rhodophyta)

The red seaweed Gracilariopsis is an important crop extensively cultivated in China for high-quality raw agar. In the cultivation site at Nanao Island, Shantou, China, G.lemaneiformis experiences high variability in environmental conditions like seawater temperature. In this study, G.lemaneiformis was cultured at 12, 19, or 26 degrees C for 3weeks, to examine its photosynthetic acclimation to changing temperature. Growth rates were highest in G.lemaneiformis thalli grown at 19 degrees C, and were reduced with either decreased or increased temperature. The irradiance-saturated rate of photosynthesis (P-max) decreased with decreasing temperature, but increased significantly with prolonged cultivation at lower temperatures, indicating the potential for photosynthesis acclimation to lower temperature. Moreover, P-max increased with increasing temperature (~30 mu mol O-2 center dot g(-1)FW center dot h(-1) at 12 degrees C to 70 mu mol O-2 center dot g(-1)FW center dot h(-1) at 26 degrees C). The irradiance compensation point for photosynthesis (I-c) decreased significantly with increasing temperature (28 mu mol photons center dot m(-2)center dot s(-1) at high temperature vs. 38 mu mol photons center dot m(-2)center dot s(-1) at low temperature). Both the photosynthetic light- and carbon-use efficiencies increased with increasing growth or temperatures (from 12 degrees C to 26 degrees C). The results suggested that the thermal acclimation of photosynthetic performance of G.lemaneiformis would have important ecophysiological implications in sea cultivation for improving photosynthesis at low temperature and maintaining high standing biomass during summer. Ongoing climate change (increasing atmospheric CO2 and global warming) may enhance biomass production in G.lemaneiformis mariculture through the improved photosynthetic performances in response to increasing temperature.