Abstract:Pyropia katadae var. hemiphylla is an important Pyropia species in China. Increasing consumer demand for P. katadae var. hemiphylla has led to its commercial breeding and floating raft cultivation in Jiangsu Province and Shandong Province in China in the past two years. However, it remains to be determined what the optimum iron concentrations for the growth of conchocelis and conchosporangial formation of P. katadae var. hemiphylla are and to understand the physiological and biochemical adaptability to different iron concentrations. Therefore, relative growth rate, ratio of conchosporangial formation, and physiological and biochemical indexes (including chlorophyll fluorescence parameters, contents of reactive oxygen species, contents of antioxidant, and activities of antioxidant enzymes) under different iron concentrations were studied. From the results of these experiments, the main conclusions are as follows: Growth, maximum photochemical efficiency of photosystem Ⅱ (Fv/Fm), and quantum yield of regulated non-photochemical energy loss in photosystem Ⅱ [Y(NPQ)] of P. katadae var. hemiphylla increased significantly at an iron concentration of 0.040 mg/L, suggesting that this iron concentration improved the photosynthetic efficiency and photoprotective efficiency of vegetative conchocelis. Relative growth rate (RGR) decreased significantly in groups with high iron concentrations (0.160~0.800 mg/L), while the ratio of conchosporangial formation increased significantly at high iron concentrations. These results indicate that high iron concentrations inhibited the vegetative growth of conchocelis, while promoting the transition from vegetative growth state to developmental state. There was a significant positive correlation between the ratio of conchosporangial formation and Fv/Fm, indicating that the photosynthetic efficiency of conchocelis was significantly improved after the transformation of vegetative conchocelis to conchosporangia filaments. The addition of iron resulted in significant accumulation of reactive oxygen species (ROS) in conchocelis. The contents of carotenoids and proline, and the activities of SOD, POD, and GR in P. katadae var. hemiphylla may have increased so that the ROS level was reduced under high iron stress, thus balancing ROS production and ROS clearance. These results can provide a theoretical basis for the application of iron nutrition in the cultivation of P. katadae var. hemiphylla.
