Pulse amplitude modulated fluorescence in the green macrophytes, Codium adherens, Enteromorpha muscoides, Ulva gigantea and Ulva rigida, from the Atlantic coast of Southern Spain

The effect of ambient and enhanced solar radiation on the photosynthetic ap paratus in four marine green macroalgae on the Southern coast of Spain (Str ait of Gibraltar) was investigated using pulse amplitude modulation (PAM) f luorescence. The dependence of the fluorescence parameters on the irradianc e of the actinic light was determined for all four species. It showed that maximal fluorescence after light adaptation (F'(m)) photochemical quenching (q(P)) and the photosynthetic quantum yield decreased in Enteromorpha musc oides with irradiance while non-photochemical quenching (q(N)) rose continu ously. In Ulva rigida the photosynthetic quantum yield dropped at irradianc es above 4 W m(-2) but q(P) did not decrease with increasing light. q(N) qu enching rose sharply above 37 W m(-2), and maximal fluorescence dropped abo ve 1 W m(-2). In Ulva gigantea the yield dropped to zero at irradiances of 37 W m(-2), as did q(P) at 53 W m(-2). q(N) started from an intermediate le vel and increased to a maximum at the highest irradiances. In Codium adhere ns, the yield and q(P) behaved similarly as in U. rigida, while q(N) rose a t much lower irradiances. All investigated algae suffered from photoinhibit ion even at their natural sites of growth when the sun is at high angles. T he hypothesis that algae with flat thalli suffer more than those with massi ve ones was confirmed. Photoinhibition was less pronounced in U. rigida and C. adherens than in the other two species. After 1 h of exposure to solar radiation at the surface, the photosynthetic quantum yield decreased substa ntially in the surface algae E. muscoides and U. rigida. In both macroalgae , recovery of the photosynthetic quantum yield was almost complete after 2- 3 h in the shade. Two other green algae from shaded habitats (U. gigantea a nd C. adherens) did not show complete recovery of the yield from photoinhib ition. This confirms the second hypothesis that sun-adapted algae recover f aster from photoinhibition than those adapted to shaded sites. (C) 1999 Els evier Science B.V. All rights reserved.