Leaf acclimation to soil flooding and light availability underlies photosynthetic capacity of , an endangered shrub of bottomland forests in the Mississippi Alluvial Valley, USA.

is an endangered shrub indigenous to the broadleaf forest of the Mississippi Alluvial Valley (MAV). In this region, extant colonies of the species are found in periodically ponded habitats where a diversity of broadleaf trees can form well-developed overstory and sub-canopies-these habitat characteristics suggest that soil flooding and light availability are primary drivers of ecophysiology. To understand how these two factors affect its photosynthetic capacity, we quantified leaf characteristics and photosynthetic response of plants grown in a large-scaled, field setting of three distinct soil flooding levels (no flood, 0 day; short-term flood, 45 days; and extended flood, 90 days) each containing three distinct light availability levels (high light, 30% shade cloth; intermediate light, 63% shade cloth; and low light, 95% shade cloth). leaves showed marked plasticity to interacting effects of flooding and light with lamina mass per unit area (L) varying 78% and total nitrogen content per unit area (N) varying 63% from the maximum. Photosynthetic capacity (A) ranged 123% increasing linearly with N from low to high light. Extended flooding decreased the slope of this relationship 99% through a reduction in N availability and metabolic depression of A relative to N. However, neither soil flooding nor light imposed an additive limitation on photosynthetic capacity when the other factor was at its most stressful level, and the A-N relationship for plants that experienced short-term flooding suggested post-flood acclimation in photosynthetic capacity was approaching the maximal level under respective light environments. Our findings provide evidence for wide plasticity and acclimation potential of . photosynthetic capacity, which supports active habitat management, such as manipulation of stand structure for improved understory light environments, to benefit long-term conservation of the species in the MAV.