Global change factors derived from anthropogenic activities such as increased CO2 and ultraviolet radiation (UVR) have direct impacts on the physiological responses of organisms in both terrestrial and aquatic ecosystems. We assessed in this work the mechanistic, physiological and molecular response of the unicellular chlorophyte Dunaliella tertiolecta exposed to combinatorial present (390 ppmv, LC) and future CO2 levels predicted for the year 2100 (900 ppmv, HC) and different UVR doses. Growth rates, cell esterase activity, reactive oxygen species accumulation (ROS), and 14C fixation decreased under HC compared to LC. The deleterious effects of UVR were attenuated in HC, except for decreased photosynthetic capacities. Transcriptome analysis showed different expression patterns depending on UVR and CO2 levels. PsbA, LhcII and eCA gene expression was downregulated at HC compared to LC. However, photolyase (PL) gene expression was upregulated at HC with respect LC in UVR. This suggests that HC (as opposed to LC) promoted a "low-metabolic steady state", decreasing UVR exposure-activated repair by means of protein replacement. Only PL photoreactivation was active under HC. Our data add evidence on D. tertiolecta possibly becoming more resilient to UVR exposure under future CO2 regimes, and maybe other marine unicellular chlorophytes, warranting serious considerations on the consequent ecological implications.

In order to allow full comparability with other ocean acidification data sets, the R package seacarb (Gattuso et al, 2016) was used to compute a complete and consistent set of carbonate system variables, as described by Nisumaa et al. (2010). In this dataset the original values were archived in addition with the recalculated parameters (see related PI). The date of carbonate chemistry calculation is 2017-03-16.

Supplement to: García-Gómez, Candela; Mata, M T; Van Breusegem, Frank; Segovia, María (2016): Low-steady-state metabolism induced by elevated CO2 increases resilience to UV radiation in the unicellular green-algae Dunaliella tertiolecta. Environmental and Experimental Botany, 132, 163-174