Effect of submergence and shading of hypocotyls on leaf conductance in young seedlings of the mangrove Rhizophora stylosa

Abstract.

Effects of submergence and shading of hypocotyls on leaf conductance were examined in 12- to 18-month-old seedlings of Rhizophora stylosa. The net photosynthetic rates of hypocotyls increased with increase in incident photosynthetic photon flux density (PPFD) to a maximum of 2.7 µmol CO₂ m^–2 s^–1 at a PPFD of about 300 µmol m^–2 s^–1. This maximal photosynthetic rate was 80% of the dark respiration rate in the hypocotyls. The leaf conductance was suppressed by 20% when hypocotyls were submerged and by 40% when hypocotyls were both submerged and shielded from incident sunlight. Thus, extended submergence or shading of hypocotyls adversely affected photosynthetic carbon gain by leaves, which could, in turn, retard growth of young seedlings.