Photosynthesis of an endolithic <i>Chlorococcum</i> alga (Chlorophyta, Chlorococcaceae) from travertine calcium carbonate rocks of a tropical limestone Spring

A green alga, Chlorococcum sp. (Chlorococcales, Chlorophyceae), was grown from scrapings of the travertine rocks outlet stream Emerald Pool, Khlong Thom Nuea, District Krabi province in Southern Thailand – a classic karstic habitat. It recalcitrant alga: organic solvents did not extract chlorophyll (Chl) algae very well but heated Dimethylsulphoxide (DMSO) effective. Rapid light curve PAM experiments were used to quantify photosynthetic parameters: Eopt = 275 ± 9.7 µmol photons m–2 s–1, ETRmax 277 5.99 e– g–1 Chl efficiency (Alpha, α0) 2.248 0.112 a. For deliberately low light, 290 4.89 s–1 109 0.97 Alpha (α0) 1.010 0.192 Overall, amount b compared with relatively for most + organisms (Chl b/a ≈ 0.21) ratio strongly affected by irradiance. The changes and α0 indicate that sp, responded irradiance increasing total as a, marginal decrease no substantial change far-red absorption. spectrum stripping technique confirmed is organism albeit content. Photosynthesis this species sensitive pH range 5–9 inhibited at 10, indicating it capable using HCO3– an inorganic carbon source. has concentrating mechanism (CCM), however based on its insensitivity depolarizing effects high [K+], unlikely be dependent membrane potential across cell membrane. alga homiochlorophyllous recovers rapidly dessication without synthesis new chlorophyll.