Physio-biochemical and metabolomic analyses of the agarophyte Gracilaria salicornia indicates its tolerance to elevated pCO₂ levels

Gracilaria salicornia is an agar-producing red macroalga commonly found growing in the intertidal and upper subtidal on various substrates with distribution across the Indo-Pacific. The ability of G. salicornia to survive under harsh conditions suggests potential use as a candidate for sustainable farming and alternative source of livelihood for the local coastal communities under future climate conditions. An earlier study investigated the effects of future predicted pCO(2) level on the photosynthesis and respiration of G. salicornia but studies on the metabolomic responses of this alga to constant elevated pCO(2) level is lacking. Here, elevated pCO(2) level was simulated on G. salicornia for 14 days to compare its growth, photosynthetic efficiency, pigment content, agar properties and metabolite composition under current pCO(2) level (similar to pH 8.1) and end-of-century future-predicted (similar to pH 7.8) pCO(2) level. The observed biomass growth, coupled with unaffected photosynthetic parameters and agar-related properties underscore G. salicornia's ability to adapt to higher pCO(2) levels. The modulation of metabolites showcases the alga's adaptive strategies at elevated pCO(2) whereby stress-mediating compounds such as gallic acid and oxalic acid were increased while stress-indicating metabolites such as serine, glycine, and ascorbic acid did not show significant changes. Interestingly, the metabolome profile imply that the alga regulates its metabolism according to culture duration rather than the pCO(2) level.