Publication Date:
2017-06-29
Description:
Marine phytoplankton such as bloom-forming, calcite-producing coccolithophores, are naturally exposed to solar UV radiation (UVR, 280–400nm) in the ocean's upper mixed layers. Nevertheless, effects of increasing CO2-induced ocean acidification and warming have rarely been investigated in the presence of UVR. We examined calcification and photosynthetic carbon fixation performance in the most cosmopolitan coccolithophorid, Emiliania huxleyi, grown under high (1000μatm, HC; pHT: 7.70) and low (400μatm, LC; pHT: 8.02) CO2 levels, at 15°C (LT), 20°C (MT) and 24°C (HT) with or without UVR. The HC treatment didn't affect photosynthetic carbon fixation at 15°C, but significantly enhanced it with increasing temperature. Exposure to UVR inhibited photosynthesis, with higher inhibition by UVA (320–395nm) than UVB (295–320nm), except in the HC and 24°C-grown cells, in which UVB caused more inhibition than UVA. Reduced thickness of the coccolith layer in the HC-grown cells appeared to be responsible for the UV-induced inhibition, and an increased repair rate of UVA-derived damage in the HCHT-grown cells could be responsible for lowered UVA-induced inhibition. While calcification was reduced with the elevated CO2 concentration, exposure to UVB or UVA affected it differentially, with the former inhibiting and the latter enhancing it. UVA-induced stimulation of calcification was higher in the HC-grown cells at 15 and 20°C, whereas at 24°C, observed enhancement was not significant. The calcification to photosynthesis ratio (Cal/Pho ratio) was lower in the HC treatment, and increasing temperature also lowered the value. However, at 20 and 24°C, exposures to UVR significantly increased the Cal/Pho ratio, especially in HC-grown cells, by up to 100%. This implies that UVR can counteract the negative effects of the greenhouse treatment on the Cal/Pho ratio, and so may be a key stressor when considering the impacts of future greenhouse conditions on E. huxleyi.
Print ISSN:
1810-6277
Electronic ISSN:
1810-6285
Topics:
Biology
,
Geosciences
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