COS 98-4 - American chestnut seedlings are more responsive to light than oaks and hickories: An assessment of growth and photosynthetic traits

Background/Question/Methods

The recent development of a blight-resistant transgenic American chestnut (Castanea dentata) provides the potential for reintroducing this species into forests it historically dominated. However, we lack an understanding of the environmental conditions most favorable to the growth and survival of American chestnut relative to species with which it historically co-existed. We examined effects of variable shelterwood densities the growth and physiology of 95 transgenic chestnut seedlings relative to sugar maple (Acer saccharum), and several oak (Quercus spp.) and hickory (Carya spp.) species across a range of light transmission (4-50%). To assess the hypothesis that American chestnuts are more physiologically plastic and responsive to light than oaks and hickories, we related measured seedling relative diameter and height growth rates and photosynthetic light-response curves to the gap-light index (GLI).

Results/Conclusions

The diameter and height growth of chestnut increased with light availability, while oaks and hickories did not (species * GLI interaction, P < 0.05). Species varied in maximum photosynthetic rate (P < 0.001), but not as a result of varying light availability. However, the dark respiration rate and light compensation point increased equivalently across species in response to increases in light availability. Thus, American chestnut demonstrated greater growth plasticity in response to light than sugar maple, oak, or hickory, suggesting chestnut is likely to outcompete its associates in higher light environments, but it is not clear that this was driven by differences in photosynthetic plasticity. Thus, relatively low residual shelterwood densities and correspondingly high understory light levels, may better promote the establishment of underplanted chestnut seedlings relative to associated tree species provided it does not result in detrimental increases in the productivity of competing understory species.