Stomata regulate convective flow within the gas canals of the sacred lotus, Nelumbo nucifera

Lotus, Nelumbo nucifera, posses a specialised efflux organ in the centre of their leaves, which connects the gas canals in the leaves and stems with the atmosphere through the apertures of large stomata. The role of these large central plate stomata in regulating air flow through the gas canals were examined on excised leaves and on intact plants in situ. The stomata show a diurnal cycle, closing at midday then opening during the evening and night. They act as exhaust valves, releasing pressurised air from the adjacent leaf blade and gas canals when open, preventing efflux while closed. Measurements of air flow within the petiolar gas canals of the lotus leaves show different patterns in the canals connected with the central plate stomata compared with those that only connect with the leaf blade. Flow begins in the morning, flowing up the petiole to the atmosphere through the canals connected with the central plate, and down to the rhizome through those connecting only with the leaf blade. But near midday these flow patterns change abruptly, coincident with stomatal closure, and can stop or even reverse direction. This constitutes the first evidence of stomata regulating convective air flow. Possible benefits gained from this behaviour are considered.