Variation in photoinhibition among Sasa senanensis, Quercus mongolica, and Acer mono in the understory of a deciduous broad-leaved forest exposed to canopy gaps caused by typhoons

Abstract

To elucidate mechanisms for tolerating sudden increases in light intensity following canopy gap formation, we investigated susceptibility to photoinhibition in the evergreen clonal plant bamboo, Sasa senanensis, and two deciduous broadleaf woody plants, Quercus mongolica, and Acer mono. We measured pre-dawn photochemical efficiency of photosystem II (Fv/Fm) in plants exposed to canopy gaps and in shade-grown plants through the month following gap formation. Photoinhibition (indicated by decreased Fv/Fm) was smallest in S. senanensis and largest in A. mono. S. senanensis had the highest area-based net CO2 assimilation rate (Aarea) and electron transport rate (ETR) under high light conditions. This species also had the highest leaf mass per area (LMA) and leaf nitrogen content per area (Narea). Higher values of LMA and Narea under shade conditions probably contribute to circumvent photoinhibition through maintenance of a higher ETR capacity. Q. mongolica, a gap-dependent species, had properties intermediate between S. senanensis and A. mono; it appeared less susceptible to photoinhibition than the shade-tolerant A. mono. None of the species examined had increased photosynthetic capacity 1 month after gap formation, indicating that shade-grown leaves were unable to fully acclimate to increased light.