Factors affecting the distribution and oxygen consumption of Nymphaea odorata and Nuphar variegata among wetlands of northern Michgian.

Abstract

Plant species have adapted to their diverse environments through various physiological and chemical modifications in order to grow and reproduce efficiently. For instance, the diversity of plant life that contributes to the ecosystems of wetlands must adapt to saturation, fluctuation of water levels, and anaerobic soil conditions. The degree of adaptation of aquatic plants from their terrestrial ancestors, however, varies from slightly modified to specialized forms owing to the level of plant submergence (Riemer, 1984). Aquatic plant species have developed specialized leaves, stems, roots, and lacunar systems in order to obtain oxygen and store nutrients. Aquatic leaves can be submerged, floating, or emergent; stems also display similar adaptations to their aquatic environment; rhizomatous root systems allow plants to reproduce vegetatively as well as store nutrients for yearly regeneration; and the lacunar system consists of interconnecting gas-filled chambers that permeate all submerged stems, petioles, and floating leaves (Riemer, 1984). Two particular aquatic species of the same family, Nymphaeaceae, display interesting structural characteristics which they have evolved in order to transport oxygen to and carbon dioxide away from their rhizomatous root system which is anchored in an otherwise anaerobic environment. The petioles of Nymphaea odorata Aiton (White water-lily) contain four large air passages and many smaller chambers to transport gases (Newmaster et at., 1997). The petioles of Nuphar variegata Durand (Yellow pond-lily; Spatterdock) contain a less specialized gas transport system composed of small, randomly arranged lacunae (Padgett et al., 1999). Previous research by Sinden-Hempstead on Nymphaea odorata investigated the relationship among water depth, substrate nitrogen, and leaf surface area. This study showed that water depth and substrate nitrogen content are instrumental in limiting the growth of N. odorata (Sinden-Hempstead, 1996). A study by Grosse examined the process by which members of Nymphaeaceae transported gas to and from their roots. This study showed that the ventilation systems of different species operate via different structural features (Grosse 1996). Overall their research prompted our curiosity about how environmental factors influence distribution of N. odorata and N. variegata as well as how their structural differences affect gas transportation ability. In light of these differences, we studied the effect that both species exhibited on the amount of dissolved oxygen present in the water column when growing together and were taking their required oxygen from the water. It was our hypothesis that the more specialized lacunar structure of N. odorata would allow the plant to obtain more oxygen, thus having a greater influence on the amount of dissolved oxygen in the water column than N. variegata. After observing many different types of wetlands during field work in northern Michigan, it became apparent that both Nymphaea odorata and Nuphar variegata rarely occurred in the same body of water, and when they coexisted, they were in separate locations. This observation led us to believe that the two species had different environmental tolerances, while simultaneous occurrences were a product of a narrow overlap in these tolerances. Factors that might be responsible for the separation of the two species were temperature, pH, water disturbance, and oxygen content of the water column. It was our hypothesis that each species would have a distinct range of tolerances for these factors, with an overlap in tolerances explaining their coexistence.