Trade-off between light interception efficiency and light use efficiency: Implications for species coexistence in one-sided light competition

Taller plant species can pre-empt solar energy and suppress growth of subordinate species in vegetation stands, which is described through one-sided competition. Yet, in much of the world's vegetation species of different statures coexist. This study aims to clarify the mechanisms underlying this apparent paradox. We quantified how co-occurring species and individuals intercepted and used light for growth in a mature, warm-temperate evergreen forest. This was performed by determining the 3D distribution of foliage and light with a ground-based lidar system in combination with nondestructive measurements of plant growth. Taller trees intercepted light more efficiently per unit of above-ground biomass than shorter trees did (=higher light interception efficiency, LIE). However, taller trees tended to have lower biomass production per unit light interception (=lower light use efficiency, LUE). Reduced LUE in taller trees was associated with their higher biomass allocation to nonphotosynthetic organs and probably with over-saturated light intensity for photosynthesis at high canopy positions. Due to the increased LIE and decreased LUE with tree heights, a trade-off between LIE and LUE was found, and this trade-off resulted in trees of different statures having similar relative growth rates. Synthesis. Light competition drives trees to grow taller, and the light interception efficiency is higher in taller trees; however, this benefit comes at a cost of decreased efficiency of light use for growth. This trade-off allows trees of different statures to grow at proportionally comparable rates and may promote coexistence of tree species in one-sided light competition. Taller plants can pre-empt light and suppress growth of subordinate plants, yet in many vegetation species of different statures coexist. We explored the mechanisms underlying this apparent paradox using a novel combined analysis of tree growth and light interception. Taller trees were more efficient in light interception but less efficient in light utilization than shorter trees, resulting into similar relative growth rates across different tree heights. This mechanism may help to explain species coexistence under one-sided light competition.