In many wetlands the primary determinant of environmental patterning and species distributions is the spatial and temporal variation in water levels. In the Florida Everglades, wetland species with low tolerance to inundation are restricted by their physiological and growth responses to areas with low water levels or short inundation periods, such as ridges and short-hydroperiod marshes. However, less is known about the responses of Everglades wetland species that tolerate high water levels and long inundation periods. Furthermore, soil type complicates understanding of species responses to inundation, as short-hydroperiod sites tend to develop marl soils and long-hydroperiod sites develop peat soils. We asked whether biomass allocation, emergent leaf length, and assimilation rates of two common wetland graminoids change in response to water level/soil type. Using a mesocosm experiment, we examined the responses to water level and soil type of two coexisting Everglades plant species, Cladium jamaicense, a C3 sedge that is more common at sites with high water levels and long hydroperiods, and Muhlenbergia capillaris, a C4 grass that is more common at sites with low water levels and short hydroperiods. Plants were grown in three water levels (+20, 0, -20cm), and in two common soil types, marl and peat.
Results/Conclusions
After one year, we found that C. jamaicense developed more and shorter leaves in low water level and longer and fewer leaves in high water level, especially in peat soil. M. capillaris presented the longest leaves at low water level regardless of soil type. In C. jamaicense, photosynthetic capacity was lowest under inundated conditions (+20cm) and highest under soil-saturated conditions (0cm). M. capillaris exhibited a strong reduction in photosynthetic capacity with inundated (+20cm) and saturated soils (0cm). In general, total biomass decreased as water level increased for the both species. Changes in biomass allocation with water level were only significant for M. capillaris, for which below:aboveground ratios increased with water depth, suggesting a considerable decrease in leaf growth. Our results indicate that for short-hydroperiod marshes, where M. capillaris and C. jamaicense are co-dominant, an increase of the period of inundation or saturated soils would have a disproportional negative effect on M. capillaris, which in the long term will result in a change in ecosystem structure where C. jamaicense becomes the dominant species.