Phytoplankton are more tolerant to UV than ­bacteria and viruses in the northern South China Sea

Abstract

In late summer of 2005, the effects of ultraviolet radiation (UVR) on primary production (PP), bacterial production (BP) and viral decay rates (VDR) were investigated along a salinity gradient in the northern South China Sea. The freshwater input increased the UVA diffuse attenuation coefficient (up to 2.7 m −1 ) near the Pearl River estuary and consequently influenced the UVR inhibitory effects, as VDR was significantly correlated with the UVA diffuse attenuation coefficient. UVR inhibition of PP was significantly higher in upwelled waters than downwelled waters, suggesting that the vertical mixing (i.e. upwelling and downwelling) was an important factor regulating microbial sensitivity to UVR. UVR inhibited PP and BP by ~15 and 25%, respectively, and the UVR inhibition of BP was significantly higher than that of PP in most of the samples; hence there was a competitive advantage for phytoplankton over bacteria under the relatively high UVR exposure. UVR increased VDR by ~30%, which decreased bacterial mortality by 0.12 to 0.3% h −1 and mitigated the inhibitory effects of UVR on bacteria. In general, phytoplankton were more tolerant than bacteria and viruses to UVR in the sub-tropical northern South China Sea.

Synergistic effects of UVR and simulated stratification on commensalistic phytoplankton–bacteria relationship in two optically contrasting oligotrophic Mediterranean lakes

“…In addition, a higher sensitivity to UVR was found for epilimnetic phytoplankton than for bacteria mainly under subsurface conditions, suggesting that photosynthetic processes are more sensitive under extreme conditions that mimic the global-warming scenario. This result contrasts with previous reports of greater UVR damage to bacterioplankton than to phytoplankton in oligotrophic waters of the Mediterranean Sea (Bertoni et al, 2011), the northern South China Sea (Yuan et al, 2011), high-mountain lakes (Sommaruga et al, 1997), and boreal lakes (Xenopoulos and Schindler, 2003).…”

Away from darkness: a review on the effects of solar radiation on heterotrophic bacterioplankton activity

“…For instance, bacterial production in oligotrophic marine waters was inhibited by sunlight to a greater extent than in coastal waters influenced by the discharge of less transparent nutrient-rich freshwater (Joux et al, 2009). By contrast, no clear patterns were observed in bacterial responses to UV exposure despite the differences in optical and chemical properties along a transect from estuarine to offshore waters (Yuan et al, 2011). …”

“…Despite a rising number of studies have shown that sunlight is a major cause of viral destruction (Suttle and Cheng, 1992; Noble and Fuhrman, 1997; Jacquet and Bratbak, 2003; Wilhelm et al, 2003; Yuan et al, 2011), to our knowledge no direct evidence is available for an associated enhancement of bacterial abundance or activity in natural waters. In contrast, exposure to surface UVR levels was shown to cause an increase in damaged prokaryotic cells and an accumulation of viruses, probably due to UVR induction of the lytic cycle in lysogenic bacteria (Maranger et al, 2002).…”

Consequences of UV‐enhanced community respiration for plankton metabolic balance

“…Predicting the effect of UV radiation (UVR) on plankton metabolic balance is cumbersome because, in addition to its direct effects on the inhibition and reduction of photosynthetic and community respiration rates, metabolic imbalances may derive from differential sensitivities to UVB among planktonic organisms within the community (De Lange et al 2003;Yuan et al 2011). Additionally, photochemical transformations of dissolved organic matter (DOM) mediated by UVR (Zepp et al 2007) can influence the availability of DOM to bacteria (Tranvik and Bertilsson 2001), potentially increasing respiration rates.…”