Trait coordination at leaf level explains the resistance to excess light stress in shade-tolerant tropical tree species.

Plant functioning in response to the environment is an important issue for vegetation reassembly of degraded lands because of both low and excessive sunlight influence the performance of young plants. However, how shade-tolerant tree species deal with excess of light energy remains unclear due to the contrasting results among studies and the subjective classifications of species shade tolerance. From a quantitative classification of shade tolerance of 12 tropical tree species planted in the field under contrasting light conditions, we hypothesized that shade-tolerant species are capable of effective long-term acclimation to high-light conditions. Plant size and survival of species were measured at the beginning and 38 months after planting. We also measured functional traits associated with carbon economy and non-photochemical energy dissipation. Under high-light condition, more light-demanding species showed higher growth rates associated with higher values of functional traits that improve the CO2 assimilation capacity. By contrast, more shade-tolerant species showed higher survival that was associated with higher values of qN, leaf K contents and leaf thickness. The concomitant increase in these traits, as well as their greater plasticity to light in WUEi, Fv/Fm and qN, confers on these species strong photoprotection to avoid high-light stress and to persist under open field conditions. The results challenge the common assumption that only fast-growing and light-demanding tree species are suitable for vegetation reassembly in full sunlight conditions and to improve the environmental conditions for other species.