Stress from low light availability and flooding can reduce photosynthesis and growth rates of trees, contributing to possible regeneration challenges in bottomland hardwood forests. This study investigated the photosynthetic light responses of pin oak (Quercus palustris Muenchh.) and swamp white oak (Quercus bicolor Willd.) seedlings growing in two light environments and across a hydrological gradient. Our findings revealed that neither light environment nor soil moisture availability had a significant impact on leaf mass per area, light compensation point, dark respiration rate, or apparent quantum yield. However, light availability strongly affected photosynthetic rates of the oak seedlings, with greatest photosynthetic rates observed in high light environments. The more light-demanding pin oak exhibited lower rate of photosynthesis in response to decreased light availability compared to swamp white oak. The different light requirements of these oak species could directly influence the length of time seedlings can remain in the understory before they can be released. Additionally, the effect of soil moisture stress on foliar nitrogen and photosynthesis was more pronounced in low light environments. We observed a direct relationship between foliar nitrogen and light availability, as well as a positive correlation between photosynthetic rate and foliar nitrogen. Thus, any decrease in foliar nitrogen resulting from low light environments and soil inundation could adversely affect photosynthetic capacity and subsequent development of oak seedlings in bottomland hardwood forests.
Hayford et al. (Sat,) studied this question.