Plant responses to hydrology are central to understanding the structure of wetland plant communities and to informing restoration efforts. The objectives of this study were to examine ecological responses of emergent plant species to water depth in a freshwater wetland in south-central New York (USA) and to test growth responses and associated nutrient relations for emergent species exposed to controlled water depths without interspecific competition in a greenhouse experiment. Field observations quantified the distribution of wetland plants in relation to water depth at Harpur Pond in the Binghamton University Nature Preserve. Presence or absence of plant species was noted in 0.25-m2 quadrats, along 11 transects extending from the upland limit of emergents to their greatest depth in the pond. Ten of the 12 most frequent taxa showed significantly nonrandom distributions (P < 0.05). For example, Boehmeria cylindrica and Persicaria sagittata were more frequent > 0.2 m above the median water level, whereas Sparganium americanum and Leersia oryzoides were more frequent near it. In contrast, Eleocharis palustris was evenly distributed across the approximately 0.6-m elevational range. Species richness decreased significantly from the upper and middle ends to the lower end of the hydrological gradient, and plant community composition at the highest elevation was 80% dissimilar to that below the median water level. The greenhouse experiment was conducted to examine the effects of small-scale differences in water depth (−11 cm, −8 cm, −2 cm, and 3 cm in relation to the soil surface) on the growth and nutrient concentrations of transplanted ramets of five common wetland plant species: Juncus effusus, Scirpus cyperinus, L. oryzoides, Glyceria grandis, and S. americanum. After 45 days of growth, S. americanum had accumulated 96% greater biomass at 3 cm below the water level than at 11 cm above (P = 0.03 from one-way ANOVA), showing that minor differences in water depth can be important to plant success. Water depth did not significantly affect growth for the other four species. Greater biomass was correlated with lower tissue nitrogen concentration for S. americanum, L. oryzoides, and G. grandis and with lower phosphorus concentration for L. oryzoides and G. grandis, indicating that growth may result in nutrient dilution within tissues.
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