Intensity and mode of Lindera melissifolia reproduction are affected by flooding and light availability.

We studied the impact of flooding and light availability gradients on sexual and asexual reproduction in Lindera melissifolia (Walt.) Blume, an endangered shrub found in floodplain forests of the Mississippi Alluvial Valley (MAV), USA. A water impoundment facility was used to control the duration of soil flooding (0, 45, or 90 days), and shade houses were used to control light availability (high = 72%, intermediate = 33%, or low = 2% of ambient light) received by L. melissifolia established on native soil of the MAV. Sexual reproductive intensity, as measured by inflorescence bud count, fruit set, and drupe production, was greatest in the absence of soil flooding. Ninety days of soil flooding in the year prior to anthesis decreased inflorescence bud counts, and 45 days of soil flooding in the year of anthesis lessened fruit set and drupe production. Inflorescence bud development was the greatest in environments of intermediate light, decreased in high-light environments, and was absent in low light environments. But low fruit set diminished drupe production in intermediate light environments as compared to high light environments. Asexual reproduction, as measured by development of new ramets, was greatest in the absence of soil flooding and where plants were grown in high or intermediate light. Plants exhibited plasticity in reproductive mode such that soil flooding increased the relative importance of asexual reproduction. The high light environment was most favorable to sexual reproduction, and reproductive mode transitioned to exclusively asexual in the low light environment. Our results raise several implications important to active management for the conservation of this imperiled plant.

Photosynthate distribution patterns in cherrybark oak seedling sprouts.

We used 14C tracers to determine photosynthate distribution in cherrybark oak (Quercus pagoda Raf.) seedling sprouts following release from competing mid-story vegetation. Fall acquisition of labeled photosynthates by seedlings followed expected source-sink patterns, with root and basal stem tissues serving as the primary sinks. Four months after the seedlings had been labeled with 14C, they were clipped to induce sprouting. First-flush stem and leaf tissues of the resulting seedling sprouts were the primary sinks for labeled photosynthates stored in root tissues. Second-flush stem and leaf tissues, and first-flush stem and leaf tissues the following growing season, were not primary sinks for labeled photosynthates stored in root tissues despite the high radioactivity in root tissues. Root tissues appeared to deposit photosynthates in a layering process whereby the last photosynthates stored in new xylem were the first to be depleted during the initiation of a growth flush the following spring. There were more labeled photosynthates in roots of released seedling sprouts compared with non-released seedling sprouts, indicating increased vigor of released seedling sprouts in response to greater light availability. In contrast, stem and source leaf tissues of non-released seedling sprouts contained greater percentages of labeled photosynthates compared with released seedling sprouts, indicating either greater sink strength or poorly developed xylem and phloem pathways that created inefficiencies in distribution to root tissues. The 14C distribution coefficients confirmed the distribution patterns and provided additional information on the important sinks in released and non-released cherrybark oak seedling sprouts.