PHOTOINHIBITION OF PHOTOSYNTHESIS IN THE SURF DIATOM, ANAULUS-AUSTRALIS DREBES ET SCHULZ

The surf diatom, Anaulus australis Drebes et Schulz, exhibited photoinhibition in response to high light despite the fact that the cells which are frequently exposed to full sunlight would be expected to be adapted to photosynthesize optimally under these conditions. Photosynthesis-irradiance curves showed post-saturation inhibition when samples were incubated for 3 hours at saturating irradiances, but not when incubated for 10 minutes. High cell concentrations resulted in shading, so that even at high irradiances, photoinhibition did not occur. In Anaulus australis samples, Pmax typically showed a three-phase time response to illumination: a photoinduction phase (during which Pmax increased), an optimum phase (when Pmax remained nearly constant) and a decreasing phase (during which Pmax decreased gradually when the cells were held in sub-saturating light and rapidly when held in saturating light). The photoinduction phase was always about 1 hour, irrespective of the quantum dose received. However, the time taken for photoinhibition to occur varied; shorter times being recorded when cells were held at higher irradiances. Anaulus australis exhibits the same three phases in the field, with a mean of 80% photoinhibition of photosynthesis occurring on cloudless days. © 1990, Walter de Gruyter. All rights reserved.