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Biogeosciences An interactive open-access journal of the European Geosciences Union
doi:10.5194/bg-2017-106
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
24 Mar 2017
Review status
This discussion paper is under review for the journal Biogeosciences (BG).
Effects of ultraviolet radiation on photosynthetic performance and N2 fixation in Trichodesmium erythraeum IMS 101
Xiaoni Cai1,2, David A. Hutchins2, Feixue Fu2, and Kunshan Gao1 1State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen, Fujian, 361102, China
2Department of Biological Sciences, University of Southern California, 3616 Trousdale Parkway, Los Angeles, California, 90089, USA
Abstract. Biological effects of ultraviolet radiation (UVR; 280–400 nm) on marine primary producers are of general concern, as oceanic carbon fixers that contribute to the marine biological CO2 pump are being exposed to increasing UV irradiance due to global change and ozone depletion. We investigated the effects of UV-B (280–320 nm) and UV-A (320–400 nm) on the biogeochemically-critical filamentous marine N2-fixing cyanobacterium Trichodesmium (strain IMS101) using a solar simulator as well as under natural solar radiation. Short exposure to UV-B, UV-A, or integrated total UVR significantly reduced the effective quantum yield of photosystem II (PSII) and photosynthetic carbon and N2 fixation rates. Cells acclimated to low light were more sensitive to UV exposure compared to high-light grown ones, which had more UV absorbing compounds, most likely mycosporine-like amino acids (MAAs). After acclimation under natural sunlight, the specific growth rate was lower (by up to 44 %), MAAs content was higher, and average trichome length was shorter (by up to 22 %) in the full spectrum of solar radiation with UVR, than under a photosynthetically active radiation (PAR) alone treatment (400–700 nm). These results suggest that prior shipboard experiments in UV-opaque containers may have substantially overestimated in-situ nitrogen fixation rates by Trichodesmium, and that natural and anthropogenic elevation of UV radiation intensity could significantly inhibit this vital source of new nitrogen to the current and future oligotrophic oceans.

Citation: Cai, X., Hutchins, D. A., Fu, F., and Gao, K.: Effects of ultraviolet radiation on photosynthetic performance and N2 fixation in Trichodesmium erythraeum IMS 101, Biogeosciences Discuss., doi:10.5194/bg-2017-106, in review, 2017.
Xiaoni Cai et al.
Xiaoni Cai et al.
Xiaoni Cai et al.

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Short summary
Trichodesmium is significant marine N2-fixer, we conducted short- and long-term UV exposure experiment to investigate the how UV affect this organism, our results showed N2 fixation and carbon fixation rates were significantly reduced under UV radiation. As a defense strategy, Trichodesmium is able to synthesize UV-absorbing compounds to protect from UV damage. Our results suggest that if shipboard experiments in UV-opaque containers may have substantially overestimated in-situ N2 fixation rate.
Trichodesmium is significant marine N2-fixer, we conducted short- and long-term UV exposure...
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