Interactions between ultraviolet radiation exposure and phosphorus limitation in the marine nitrogen‐fixing cyanobacteria Trichodesmium and Crocosphaera

Abstract

Increased stratification and mixed layer shoaling of the surface ocean resulting from warming can lead to exposure of marine dinitrogen (N2)‐fixing cyanobacteria to higher levels of inhibitory ultraviolet (UV) radiation. These same processes also reduce vertically advected supplies of the potentially limiting nutrient phosphorus (P) to N2 fixers. It is currently unknown how UV inhibition and P limitation interact to affect the biogeochemical cycles of nitrogen and carbon in these biogeochemically critical microbes. We investigated the responses of the important and widespread marine N2‐fixing cyanobacteria Crocosphaera (strain WH0005) and Trichodesmium (strains IMS 101 and GBR) to UV‐A and UV‐B under P‐replete and P‐limited conditions. Growth, N2 fixation, and carbon dioxide (CO2) fixation rates of Trichodesmium IMS 101 and Crocosphaera were negatively affected by UV exposure. This inhibition was greater for Trichodesmium IMS 101 than for Crocosphaera, which fixes N2 only during the night and so avoids direct UV damage. Negative effects of UV on both IMS 101 and Crocosphaera were less in P‐limited cultures than in P‐replete cultures. In contrast, no UV inhibition was observed in GBR, regardless of P availability. UV inhibition was related to different amounts of UV‐absorbing compounds produced by these isolates. Responses to UV radiation and P availability interactions were taxon‐specific, but our results indicated that in general, UV radiation effects on Trichodesmium and Crocosphaera range from negative to neutral. UV inhibition and its interactions with P limitation may thus have a substantial influence on the present day and future nitrogen and carbon cycles of the ocean.

Isolation, growth, and nitrogen fixation rates of the Hemiaulus-Richelia (diatom-cyanobacterium) symbiosis in culture

“…Thus, it seems possible that in-situ PAR values would not photoinhibit these DDA strains. However, damaging effects by solar UV wavelengths (Zhu et al, 2020) require further examination. Follett et al (2018) and Inomura et al (2020) utilized H. hauckii DDA growth rates extracted from Pyle (2011) for modeling applications.…”

“…Thus, it seems possible that in-situ PAR values would not photoinhibit these DDA strains. However, damaging effects by solar UV wavelengths ( Zhu et al, 2020 ) require further examination.…”

Effects of Ocean Acidification on Marine Photosynthetic Organisms Under the Concurrent Influences of Warming, UV Radiation, and Deoxygenation

“…In the marine diazotroph Trichodesmium, UV radiation reduces rates of photosynthesis, N 2 fixation, and growth (Cai X. et al, 2017), though moderate or low levels of UV-A may be stimulating. Another recent study showed that growth, N 2 fixation, and CO 2 fixation rates of the Trichodesmium strain IMS 101 and Crocosphaera WH0005 were both negatively affected by UV-B exposure (Zhu et al, 2019). This inhibition was much greater for Trichodesmium IMS 101, which fixes N 2 during the day, than for Crocosphaera, which fixes N 2 only during the night; however, another Trichodesmium isolate (GBR) was much more resistant to UV-B inhibition (Zhu et al, 2019).…”

“…Another recent study showed that growth, N 2 fixation, and CO 2 fixation rates of the Trichodesmium strain IMS 101 and Crocosphaera WH0005 were both negatively affected by UV-B exposure (Zhu et al, 2019). This inhibition was much greater for Trichodesmium IMS 101, which fixes N 2 during the day, than for Crocosphaera, which fixes N 2 only during the night; however, another Trichodesmium isolate (GBR) was much more resistant to UV-B inhibition (Zhu et al, 2019). To the best of our knowledge, however, nothing has been documented on the interactive effects of OA and UV radiation on marine diazotrophs.…”

Interactions Between Ultraviolet B Radiation, Warming, and Changing Nitrogen Source May Reduce the Accumulation of Toxic Pseudo-nitzschia multiseries Biomass in Future Coastal Oceans

“…Modified F/2 medium (100 µM total nitrogen, 100 µM silicate, 6 µM phosphate; Guillard and Ryther, 1962;Guillard, 1975) was made using natural seawater filtered through an ultrafiltration water purifier (MUF1580-2T, Midea, China), autoclaved, and bubbled with air filtered through a 0.22 µm PVD syringe filter (Membrane Solutions, Nantong) to equilibrate with ambient atmospheric gas concentrations. Quartz culture bottles were used to allow UVB wavelengths to pass through (Zhu et al, 2020).…”