Relationship of growth and photosynthesis with colony size in an edible cyanobacterium, Ge-Xian-Mi Nostoc (Cyanophyceae)

Growth and photosynthesis of an edible cyanobacterium, Ge-Xian-Mi (Nostoc), were investigated with differently sized colonies. Both photosynthesis and growth were dependent on the colony size. Compared with larger ones, smaller colonies grew faster regardless of the levels of light and temperature for culture and showed higher values of maximal net photosynthetic rate, apparent quantum yield, light-saturating and compensating points, and dark respiration. The ratios of chl a content and mass to surface area of a colony increased and that of chl a to mass or mass to volume of a colony decreased with increased colonial sizes. A Ge-Xian-Mi colony appeared to increase its chl a content per surface area, enhancing the light-shading effect; however, at the same time it decreased its mass density on a volume basis, minimizing the enhanced effects of shading and diffusion barrier caused by the thickening outer layer with increasing colony size during growth.