Gas exchange and oxygen concentration in pneumatophores and prop roots of four mangrove species
We conducted in situ measurements of gas exchange and O2 concentration in pneumatophores of Sonneratia alba, Avicennia marina and Bruguiera gymnorrhiza and prop roots of Rhizophora stylosa. The mean rates of photosynthesis were 0.6 and 0.2 µmol CO2 m–2 s–1 in the raised pneumatophores of S. alba and A. marina, respectively, at a photosynthetic photon flux density of 100 µmol m–2 s–1. Photosynthetic activity was also detected in the prop roots of R. stylosa but the photosynthetic rate was lower than in A. marina. B. gymnorrhiza had no photosynthetic activity in knee pneumatophores. O2 concentrations in the pneumatophores of these four species decreased by 4–8% when the pneumatophores were submerged under water. The O2 concentrations in submerged pneumatophores of S. alba and A. marina were higher with higher solar radiation. Such photosynthetically generated O2 could diffuse down through the pneumatophores into the roots, particularly when sunlit pneumatophores were submerged by high tide. This may contribute to the success of S. alba and A. marina in zones where tidal inundation is common.
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