Elevated CO2 increases sensitivity to ultraviolet radiation in lacustrine phytoplankton assemblages

Abstract

This study tests the effects of elevated CO 2 and ultraviolet radiation (UVR) on phytoplankton photosynthesis through in situ incubations in Lake Giles, Pennsylvania. In a first experiment, CO 2 was supplied from a tank to simulate atmospheric CO 2 concentrations predicted in scenarios of future global change. In a second experiment, elevated CO 2 conditions were obtained by the mineralization of added colored dissolved organic matter (CDOM) of terrestrial origin (400 mmol L 21 final concentration). The results demonstrated that for natural assemblages from Lake Giles, atmospheric CO 2 concentrations similar to those predicted for the end of the century can increase primary productivity up to 23% in the absence of photoinhibition. However, elevated CO 2 concentrations also increased sensitivity of phytoplankton to UVR, making cells more susceptible and increasing photoinhibition. Increased sensitivity was observed in samples incubated with the artificial CO 2 supply as well as with the CDOM addition, the latter resulting in CO 2 partial pressures close to three times present atmospheric levels. Photosynthetic rate modeled for elevated CO 2 and midday solar exposure just below the lake surface was 17% of potential production compared with 21% under usual CO 2 levels in the lake, resulting in similar rates between phytoplankton assemblages grown under high and low CO 2 levels. Understanding the effect on primary productivity of the interaction between factors that may be affected by global change is essential to predict future changes in ecosystems and climate.

Algal evolution in relation to atmospheric CO 2 : carboxylases, carbon-concentrating mechanisms and carbon oxidation cycles

“…UV-B radiation causes damage to Rubisco and to photosystem II, but has less effect on photosystem I. The limited data available suggest that UV-B has little effect on CCM activity in the green alga Dunaliella tertiolecta [122] but elevated CO 2 can increase the sensitivity of microalgae to UV-B [123,124]. There is no information about the possibility of a differential impact of UV-B on the various forms of Rubisco, though it would be interesting to know if changes in UV-B in the past relate to the evolution of different Rubiscos.…”

UV effects on the primary productivity of picophytoplankton: biological weighting functions and exposure response curves of <i>Synechococcus</i>

“…Compared to the E model, this model was significantly better at fitting observations at high E * inh in several studies of cultures and natural assemblages (Sobrino and Neale, 2007;Sobrino et al, 2005;Sobrino et al, 2009). However, the imposition of a threshold in the T model has the disadvantage of ignoring the modest, but still evident, effects of UV and PAR at low exposures.…”

Algal and aquatic plant carbon concentrating mechanisms in relation to environmental change

“…Following the pioneering work of there have been a number of studies with a variety of algae on the effects of UVB on CCMs, with a range of results (Song and Qiu 2007;Sobrino et al 2008Sobrino et al , 2009Beardall et al 2009a,c;Gao et al 2009;Xu and Gao 2009). There seem to be no data on how UVB influences inorganic C affinity of algae with diffusive CO 2 entry.…”