Synergistic effects of warming and low salinity enhanced the production of Gracilariopsis lemaneiformis in the warming drainage zone of Tianwan Nuclear Power Plant, China

Abstract

Tianwan Nuclear Power Plant in China is the world's largest coastal nuclear power plant in terms of its total installed capacity both in operation and under construction. Its operations create a warming drainage zone that is potentially beneficial to the large-scale cultivation of macroalgae. Moreover, natural freshwater river flow and ocean acidification caused by increasing levels of atmospheric CO2 bring new uncertainties to the growth and photophysiology of commercial macroalgae. In this study, two CO2 concentrations (LC, 400 μatm; HC, 1000 μatm), two salinity levels (LS, 20 ppt; HS, 30 ppt), and two temperatures (LT, 20 °C; HT, 26 °C) were tested to examine the synergistic effects of warming and salinity on the economically important macroalga Gracilariopsis lemaneiformis under ocean acidification. The results showed that the synergistic effect of LS and HT treatments significantly promoted the growth of G. lemaneiformis under LC treatment, but this promotion effect was more obvious under HC treatment. In contrast, HSLT conditions inhibited G. lemaneiformis growth under both LC and HC conditions. Under HC treatment, warming and low salinity together increased the maximum photosynthetic rate and the maximum electron transport rate of G. lemaneiformis. Photosynthetic pigment analysis revealed that LS had a significantly negative effect on the contents of chlorophyll a (Chl a) and carotenoids (Car.), and HT had an obviously adverse influence on the contents of Chl a, Car., phycoerythrin, and phycocyanin. Moreover, the dual limitation of LSHT conditions significantly reduced the contents of Chl a and Car. under HC and LC conditions. These findings suggested that warming and low salinity synergically improved the growth and photosynthetic performance of G. lemaneiformis, especially under ocean acidification. The results provide a scientific basis for macroalgal cultivation as part of environmental restoration around nuclear power plants generally and year-round cultivation of G. lemaneiformis in northern China specifically.