Combined effects of light and nitrate supplies on the growth, photosynthesis and ultraviolet-absorbing compounds in marine macroalga Gracilaria lemaneiformis (Rhodophyta), with special reference to the effects of solar ultraviolet radiation

Authors

  • Yangqiao Zheng

    Corresponding author
    • Key Laboratory of East China Sea and Oceanic Fishery Resources Exploitation and Utilization, Ministry of Agriculture, East China Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences, Shanghai, China
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  • Communicating Editor: H. Miyashita.

To whom correspondence should be addressed.

Email: zhengyangqiao@126.com

Summary

It is well known that light and nutrients are essential to plants; however, there are few investigations in which these have been studied in combination on macroalgae, especially when solar ultraviolet radiation (UVR) is concerned. We cultured the red alga Gracilaria lemaneiformis (Bory) at different nitrate concentrations and light levels with or without UVR for 24 days. The results showed that nitrate supply markedly enhanced the growth and photosynthesis, increased the absorptivity of UV-absorbing compounds (UVACs), and decreased photoinhibition in the presence of UVR. The thalli that received photosynthetically active radiation (PAR) treatment exhibited higher growth rates than those that received PAR + UVR at ambient or enhanced nitrate concentrations. However, under PAR + UVR treatment, the absorptivity of UVACs was higher than that of PAR and fluctuated with light levels. UVR was found to reduce the maximal net photosynthetic rate, apparent photosynthetic efficiency and light-saturating irradiance while increasing the dark respiration rate, and inducing higher inhibition of growth and photosynthesis under high light versus under low light. Ultraviolet B significantly induced the synthesis of UVACs but led to higher inhibition on growth and photosynthesis than ultraviolet A.

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