The Effects Of Solar UVR And Other Important Environmental Factors On The Physiological Characteristics Of Hizikia Fusiformis

Hizikia fusiformis (Harrey) Okamura (Sargassaceae, phaeophyta) is an important economic macroalga. Little is known about the relationship between the physiology of this species and solar UV radiation. The present study aimed to research the responses to UVR of the physiological characteristics, such as growth, photosynthesis and pigments in Hizikia fusiformis grown at different supplies of N or CO₂ levels. The main results are as follows:The effective photosynthetic quantum yield and rETR were dramatically reduced when the thalli were when exposed to high solar radiation, with this redution being much greater in the thalli treated with PAB than those treated with PAR. During the exposure to PAB, the rETR of the thalli grown at high N level was higher than those grown at normal N level, indicating that the algae cultured at high N level exhibited higher capacity of defending UV radiation. This could be ascribed to the higher contents of UVAC and carotenoids in thalli grown high N compared to normal N levels. During the recover period, the rETR of the thalli recovered much more slowly (at least 24h) than the effective photosynthetic quantum yields did.Elevated N levels had no significant effect on the growth of the seedlings of Hizikia fusiformis. However, compared to the growth condition with normal N level, elevated N levels sharply increased the contents of Chl a, Carotenoid and UVAC of the seedlings. The ability of recovery for UV damage in the thalli cultured under high N level was lower than that under normal N level.The growth of Hizikia fusiformis was enhanced by elevated CO₂ concentrations, but was inhibited with the presence of UVR. This inhibition of growth by UVR could be alleviated by high CO₂. The affinity for inorganic carbon and the carbon-saturated maximum photosynthesis were significantly reduced in Hizikia fusiformis cultured under high CO₂ with respect to normal CO₂. However, the photosynthetic ability was increased with the presence of UVR, indicating the positive effects of UVR on photosyntheses.