Ecophysiological responses of five emergent-wetland plants to diminished water supply: an experimental microcosm study

Freshwater wetlands are fundamentally tied to hydrology as they are often found along the boundaries between terrestrial uplands and open waters. Although wetland systems are frequently prone to extended periods of flooding and exposure, the degree of water deprivation may intensify during periods of low precipitation or drought. Therefore, the purpose of this study was to evaluate plant–water relations in five emergent macrophytes (Carex alata, Juncus effusus, Peltandra virginica, Saururus cernuus, and Justicia americana) to simulated drought conditions. Weekly evaluations of tissue water content and xylem water potential (free energy of water in xylem tissues) were conducted on plants grown in experimental microcosms over a 9-week period. Plant performance was also evaluated in each species by monitoring the changes in plant biomass, leaf area, and survival. The results indicate that J. effusus and P. virginica performed better in both flooded and moderately dry conditions, and plants that maintained higher water content in water logged soils (i.e., J. americana) were less tolerant to drying conditions. This study also illustrates the importance of periodic water withdrawal on plant performance. In general, plants that were subjected to both flooded and dry conditions responded better physiologically than plants that were either continuously flooded or received extended droughts (≥4 weeks). Therefore, provided the duration of water deficit is not extensive, short periods of water withdrawal can enhance the performance and water relations in some emergent-wetland plant species.