An in situ study of photosynthetic oxygen exchange and electron transport rate in the marine macroalga Ulva lactuca (Chlorophyta).

摘要: Direct comparisons between photosynthetic O2 evolution rate and electron transport (ETR) were made in situ over 24 h using the benthic macroalga Ulva lactuca (Chlorophyta), growing measured at a depth of 1.8 m, where midday irradiance rose to 400–600 μmol photons m−2 s−1. exchange was with 5-chamber data-logging apparatus ETR submersible pulse amplitude modulated (PAM) fluorometer (Diving-PAM). Steady-state quantum yield ((Fm′−Ft)/Fm′) decreased from 0.7 during morning 0.45 midday, followed by some recovery late afternoon. At low medium irradiances (0–300 s−1), there significant correlation ETR, but higher irradiances, continued increase steadily, while tended towards an asymptote. However high levels (600–1200 s−1) significantly lowered. Two methods measuring based on either diel ambient light fluorescence yields or rapid curves, gave similar results moderate levels. Nutrient enrichment (increases [NO3 −], [NH4 +] [HPO4 2-] 5- 15-fold concentrations) resulted increase, within hours, rates both techniques. approximately 6.5 8.2 electrons passed through PS II one molecule O2, i.e., up twice theoretical minimum number four. However, nutrient-enriched treatments this ratio dropped 5.1. The indicate that PAM can be used as good indication only irradiances.