Photosynthetic characteristics of the terrestrial blue-green alga, Nostoc flagelliforme

Abstract

Photosynthetic responses of rewetted Nostoc flagelliforme to CO₂, desiccation, light and temperature were investigated under emersed conditions in order to characterize its ecophysiological behaviour in nature. Net photosynthesis increased to a maximum rate at about 30% water loss, then decreased, while dark respiration always decreased with the progress of desiccation. Light-saturated photosynthesis and dark respiration were significantly reduced at 8 °C, but remained little affected by changes of temperature within the range of 15–35 °C. Photosynthetic efficiency (α) was maximal at the beginning of desiccation and then reduced with increased water loss. Saturating irradiance for photosynthesis was about 194–439 μmol quanta m⁻² s⁻¹, being maximal at about 30% water loss. No photoinhibition was observed at irradiances up to 1140 μmol m⁻² s⁻¹. Light compensation points were about 41–93 μmol m⁻² s⁻¹. Photosynthesis of N. flagelliforme was CO₂-limited at the present atmospheric CO₂ level. The CO₂-saturated photosynthesis increased with increase of irradiance (190–1140 μmol m⁻² s⁻¹) and temperature (8–25 °C) and decreased significantly with water loss (0–75%). Photosynthetic affinity for CO₂ was sensitive to temperature and irradiance. The CO₂ compensation point (Γ) increased significantly with increased temperature and was insensitive to irradiance. Desiccation did not affect Γ values before water loss exceeded 70%. Photorespiratory CO₂ release did not occur in N. flagelliforme at the current atmospheric CO₂ level.