Effects of light acclimation on the photosynthesis, growth, and biomass allocation in American chestnut ( Castanea dentata) seedlings

American chestnut ( Castanea dentata) is currently regarded as functionally extinct because of chestnut blight. To reintroduce blight-resistant American chestnut back to its historic range, it is imperative to understand the silvics and silviculture of the species. In an outdoor rainout shelter, we grew American chestnut seedlings at four levels of irradiance (4, 12, 32 and 100% of full sunlight) to examine how light intensity affects photosynthesis, growth, and biomass allocation. Net photosynthetic rate increased linearly with increasing irradiance while instantaneous water use efficiency peaked at 32% full sunlight, when seedlings were measured at their acclimated irradiance level. Height and diameter increased with increasing irradiance. However, seedlings only grew laterally under 4% full sunlight. Total biomass increased linearly with increasing irradiance and root to shoot ratio was lowest under 4 and 12% full sunlight. Regardless of irradiance level, >70% of total biomass was allocated to shoot growth. With increasing shade, specific leaf area significantly increased. These observed physiological and morphological light acclimation characteristics indicate that American chestnut is shade tolerant, which partially explains why the species has persisted in the understory for almost a century. The shade-tolerance and fast growing characteristics suggest that an underplanting-and-release or gap-phase regeneration approach would be a suitable silvicultural alternative to a clearcut-and-planting approach for the reintroduction of blight-resistant American chestnut.