LIGHT REQUIREMENTS FOR PHOTOSYNTHESIS AND GROWTH IN SEVERAL MACROALGAE FROM A SMALL SOFT-WATER STREAM IN THE SPESSART MOUNTAINS, GERMANY

Fluence rate-response curves (P vs I curves) were measured in several species of stream macroalgae from laboratory culture and from a small soft-water stream. Photosynthesis of laboratory-grown algae was light saturated at 24 mu mol photons m(-2) s(-1) of white light in Klebsormi dum vivulare (Kutzing) Morison et Sheath, at 25.5 mu mol m(-2) s(-1) i n Batrachospermum helminthosum Bory emend. Sheath et al, at 35 mu mol m(-2) s(-1) in Balbiania investiens (lenormand) Sirodot (cultivated at 4 mu mol m(-2) s(-1)), at 42 mu mol m(-2) s(-1) in Microspora quadrat a Hazen, at 67 mu mol m(-2) s(-1) in Cladophara glomerata (Linnaeus) K utzing. Photosynthesis of algae taken from the Bieber stream was light saturated at significantly higher photon irradiances of 115 mu mol m( -2) s(-1) in Batrachospermum helminthosum and Vaucheria bursata and at 190 mu mol m(-2) s(-1) in Cladophora glomerata. I-k-values (photon fl uence rate at which the linear branch of the P vs I curves and the sat uration plateau intersect) ranged from 12.5 to 29.4 mu mol m(-2) s(-1) in algae from laboratory cultures and from 13.3 to 32.5 mu mol m(-2) s(-1) in algae taken from the Bieber stream. P vs I curves of Vaucheri a bursata and Cladophora glomerata collected directly from the stream proved to have the lowest alpha-values (initial slopes). Growth in the laboratory was light saturated at 20 mu mol m(-2) s(-1) of white fluo rescent light in Batrachospermum helminthosum and at 20-50 mu mol m(-2 ) s(-1) in Vaucheria bursata. In Cladophora glomerata growth was not s aturated at photon fluence rates up to 100 mu mol m(-2) s(-1). The dif ferent light requirements for growth and photosynthesis reflect the li ght conditions at the locations in the Bierber stream where the specie s studied are growing.