Interactive effects of salinity, flooding, and soil type on Panicum hemitomon

It is well documented that Louisiana is experiencing wetland loss at rates greater than any other locale in the world. High rates of relative sea-level rise, a combination of eustatic sea-level rise and subsidence, is anticipated to compound this problem further in the future through increased flooding and encroachment of saline water into freshwater wetlands. The research presented in this paper examines the interactive effect of increased salinity level, flooding depth, and soil type on the growth responses of a dominant Louisiana fresh-water marsh plant, Panicum hemitomon, whose prevalence in Louisiana is currently in decline. This study was conducted under greenhouse conditions and employed a factorial design consisting of three salinity levels (0, 1.5, 3.0 ppt), three hydrologic regimes (0, 10, 20 cm), and two soil types (high organic content, low organic content). Panicum hemitomon productivity was significantly reduced even under the relatively small increases in salinity level (1.5 and 3.0 ppt) imposed in this study. Interestingly, moderate flooding tended to increase productivity, although this relationship was not statistically significant. Significantly greater productivity was observed for plants grown in mineral soil compared with organic soil. These results indicate that any degree of saline influx into P. hemitomon-dominated wetlands will result in decreased vigor and localized decline of this species. Moderate increases in the degree of freshwater inundation may not be as damaging as originally expected and, in fact, may actually stimulate production. However, if increased flooding is accompanied by increased salinity levels, which is anticipated to occur, then the overall effect on this species will be detrimental.