Plant Life In Anaerobic Environments PDF Download

Wetlands are productive ecosystems known as areas of biogeochemical diversity. This diversity comes from nutrient transformations and gas fluxes that are caused by adjoining aerobic and anaerobic environments. Nitrogen is an important part of the nutrient transformations and gas fluxes in wetlands. Aquatic plants are also important to the nitrogen cycle of lotic wetlands. These plants grow at key interfaces within lotic wetlands, giving them the ability to have significant effects on nutrient cycling. They typically sequester large amounts of nitrogen from the soil and water during their growing season, affecting the amounts of ammonium available to neighboring plant species. Different emergent species sequester different amounts of nitrogen from the soil into aboveground biomass; therefore, different species have more or less nitrogen available to put back into the system through decomposition. Other species growing at the junction between anaerobic and aerobic environments, such as actinorhizal plants, are also important to the nitrogen cycle of lotic wetland ecosystems. Actinorhizal plants are woody angiosperms that have a symbiotic relationship with the nitrogen-fixing actinorhizae, Frankia. Because of the plant's relationship with Frankia, it has the potential to supply nitrogen to the surrounding environment. Actinorhizal plants accomplish this by increasing the local soil nitrogen pools and through decomposition of the leaves that typically have higher foliar nitrogen content than other wetland and terrestrial plants. Alder is an example of an actinorhizal shrub that dominates many wetlands and forested watersheds of eastern North America. Wetlands dominated by alder are regarded as significant areas for transport of nitrogen into watersheds, because wetland alder zones occupy critical interface regions between upslope, forested regions and down-gradient streams. Thus, the presence of alder can contribute large amounts of nitrogen to the watershed as a whole by the addition of nitrogen to the local environment, the acceleration of nitrification processes, and the use of little soil-derived nitrogen. Because these different types of wetland plants can influence nitrogen cycling in different ways, it is important to understand how dominant species differ in their foliar chemistry, and how this relates to differences in water and soil chemistry among vegetation zones over a growing season. In on-going studies at a beaver-impounded, wetland pond in the southeastern U.S., differences in nitrogen (N) composition among three dominant wetland plants: actinorhizal hazel alder (Alnus serrulata), fragrant water lily (Nymphaea odorata), and soft rush (Juncus effusus) were investigated. Also investigated were how foliar N in these plants changes across a growing season, and whether there were discernible relationships between plant N content, proximate water chemistry, and sediment chemical composition within the pond zones in which the plants grew. Results showed highest N content in water lily leaves and associated sediments (foliar N increased over growing season), closely followed by alder leaves (foliar N decreased over growing season), and lowest N content in rush culms (foliar N increased over growing season). Juncus plants located near alder had higher foliar N than Juncus not near alder. Ammonium was the dominate form of inorganic N in overlying pond-water with highest levels in pools within alder stands and close to the dam where alder mixed with rush occurred. Highest levels of dissolved organic carbon (DOC) also occurred in alder pools. Results suggested that alder subsidized N content in nearby plants, contributed to inorganic N and DOC content in the overlying water, and that alder-derived N and C were likely exported to down-gradient streams and rivers.