Leaf anatomical responses to periodical waterlogging in simulated semidiurnal tides in mangrove Bruguiera gymnorrhiza seedlings

Abstract

Leaf anatomical changes of Bruguiera gymnorrhiza (L.) Lamk seedlings grown in experimental equipment that simulated semidiurnal tides with salinities of 15‰ under greenhouse conditions were studied. Compared with the 0 h treatments, leaf thickness, palisade parenchyma thickness, spongy parenchyma thickness, palisade–spongy thickness ratio, xylem length of the vascular system and number of vessels and vessel lines under the 12 h treatments declined 31.9%, 59.1%, 21.7%, 47.1%, 48.9%, 67.1% and 51.6%, respectively. However, the upper and lower epidermis to leaf thickness ratio, upper and lower hypodermis to leaf thickness ratio and stomatal density of 12 h treatments showed increases of 47.9%, 50.9%, 14.3%, 21.4% and 104.3% over those of 0 h treatments, respectively. The cuticle to leaf thickness ratio (inundated for 0–6 h) decreased significantly with waterlogging duration at first and then increased. Moreover, the percentage of intercellular spaces in spongy tissue decreased from 4 to 10 h treatment and then tended to increase by nearly 20% in the 12 h treatment. Tannin cells that were distributed in the vascular tissue, crystalliferous cells and phloem fibers were more abundant in the short-duration waterlogging treatments than in the long-duration waterlogging treatment. It was concluded that significant changes in the leaf anatomical features as a result of periods of immersion would have come at the cost of reduction of photosynthesis and water transport when waterlogging duration was longer than 2 h. These anatomical characteristics further proved that B. gymnorrhiza had a relatively low tolerance to waterlogging at the seedling stage.