Variations in leaf morpho-anatomy and photosynthetic traits between sun and shade populations of Eurya japonica (Pentaphylacaceae) whose seeds are dispersed by birds across habitats

摘要

Eurya japonica occurs in diverse light environments through seed dispersal by birds. As the seed size is extremely small, we hypothesized that newly germinated seedlings with restricted depth of roots and length of the hypocotyl would suffer high mortality due to increased transpiration in sunny habitats and low light in shady habitats. We also expected that surviving seedlings would differ in leaf traits between habitats as a result of selection. We aimed to determine how photosynthetic traits differ between habitats and how leaf structure is related to this difference. We examined photosynthesis and leaf morpho-anatomy for plants cloned from cuttings collected from the forest understory (shade population) and neighboring roadsides and cut-over areas (sun population) and then grown under two irradiances (18.5% and 100% sunlight) in an experimental garden. Under growth in 100% sunlight, cloned plants from the sun population exhibited significantly greater area-based photosynthetic capacity compared to cloned plants from the shade population at a comparable stomatal conductance, which was attributable to a higher area-based leaf nitrogen concentration. On the other hand, mean values of photosynthetic capacity did not significantly differ between the two populations. Cloned plants from the sun population had significantly thicker leaf laminas and spongy tissue and lower stomatal density compared to cloned plants from the shade population. Thickened leaf lamina might have increased leaf tolerance to physical stresses in open habitats. The variation in leaf morpho-anatomy between the two populations can be explained in terms of the economy of leaf photosynthetic tissue.