The spectral sensitivity of phytoplankton communities to ultraviolet radiation‐induced photoinhibition differs among clear and humic temperate lakes

Abstract

We determined the spectral sensitivity of phytoplankton communities to photoinhibition in six temperate lakes spanning a transparency gradient due to variation in dissolved organic carbon (DOC) content. Changes in variable fluorescence (F V : F M ) were monitored during experimental irradiance exposures and used to estimate spectral weighting functions for damage by ultraviolet radiation (UVR) and recovery rates. DOC explained a high proportion of the variation in UVR sensitivity, with clear-water phytoplankton communities showing greater resistance to UVR-induced photoinhibition than those of browner waters. These differences were greater when assessed in September, after clear-sky conditions, than in July, after several days of overcast skies, especially in the long-wavelength UVA spectral region. Surprisingly, the most UVR-sensitive phytoplankton communities were dominated by filamentous cyanobacteria, a putatively UVR-resistant taxon, whereas small unicellular eukaryotes were common in the most UVR-tolerant assemblages. Model estimates of in situ photoinhibition after 2 h exposure to an incident solar spectrum were only slightly higher in the clear lakes than browner ones, despite appreciably higher UVR exposure in the former. Phytoplankton in clear lakes can maintain values of F V : F M comparable to communities protected from UVR by high concentrations of DOC.

Direct and indirect effects of vertical mixing, nutrients and ultraviolet radiation on the bacterioplankton metabolism in high-mountain lakes from southern Europe

“…3). This result is in agree- ment with previous studies that showed less acclimation of algae to cope with fluctuating UVR in high-DOC ecosystems (Villafane et al, 2004;Harrison and Smith, 2011;Helbling et al, 2013). However, by assuming that mixed conditions represented the most realistic climate of light affecting HBP in each lake (Ruiz-Gonzalez et al, 2013), bacteria of the opaque lake were the most protected as no UVR inhibition was observed.…”

“…Thus, high DOM contents can absorb UVR in upper water layers, therefore biota would receive less solar radiation (Williamson and Rose, 2010) and so they would reduce damage caused by these wavelengths. However, recent studies (Harrison and Smith, 2011;Helbling et al, 2013) showed that shade-adapted algae from ecosystems with high DOM content are more vulnerable to UVR under increased or fluctuating levels. Moreover, photochemical processes might influence organic C availability for bacteria (Ruiz-Gonzalez et al, 2013).…”

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

“…This result agrees with the findings of higher UVR damage to primary producers in low-UVR lakes than in high-UVR lakes as reported by Helbling et al (2013), although in their study this response was found only under fluctuating irradiances. The results presented here indicate increased susceptibility to UVR of bacteria and phytoplankton communities relatively less exposed to UV-B during their life cycles (Pakulski et al, 2007;Harrison and Smith, 2011a). Interestingly, the UVR effect on %EOC was only significant in the high-UVR lake; the release of C has been described as a protective mechanism to prevent photosystem damage from reducing power excess under high irradiance of PAR (Wood and Van Valen, 1990) as well as UVR (Carrillo et al, , 2008.…”

Interactive effects of vertical mixing, nutrients and ultraviolet radiation: in situ photosynthetic responses of phytoplankton from high mountain lakes in Southern Europe

“…Surprisingly, relatively few studies clearly addressed this topic: the higher sensitivity of phytoplankton from opaque lakes as compared with clear ones was observed when evaluating UVB-induced DNA damage in several Andean lakes (Villafañe et al, 2004). Recent studies using model simulations (Harrison and Smith, 2011) indicated that phytoplankton from opaque lakes were less resistant as compared with those from clear environments, as the latter have slightly higher photoinhibition in spite of the higher UVR exposure; this resulted in less inhibition per unit energy in clear lakes. Likewise, Ayoub et al (2012) in doing a transect along the shoreline, showed that the content of mycosporine like amino acids (MAAs) in surface samples increased with decreasing concentration of CDOM in the water, suggesting the photoacclimation to high irradiance in the clear environment.…”