The elements organisms require for development, maintenance, and reproduction are called nutrients. Ecologists refer to the use, transformation, movement, and reuse of nutrients in ecosystems as nutrient cycling. Nutrient cycling is one of the most ecologically significant processes studied by ecosystem ecologists. The carbon, nitrogen, and phosphorus cycles have played especially prominent roles in studies of nutrient cycling. Decomposition rate is influenced by temperature, moisture, and chemical composition of litter and the environment. The rate of decomposition affects the rate at which nutrients, such as nitrogen and phosphorus, are made available to primary producers. Rates of decomposition in terrestrial ecosystems are higher under warm, moist conditions. The rate of decomposition in terrestrial ecosystems increases with nitrogen content and decreases with the lignin content of litter. The chemical composition of litter and the availability of nutrients in the surrounding environment also influence rates of decomposition in aquatic ecosystems.Plants and animals can modify the distribution and cycling of nutrients in ecosystems. The dynamics of nutrients in streams are best represented by a spiral rather than a cycle. The length of stream required for an atom of a nutrient to complete a cycle is called the spiraling length. Stream macroinvertebrates can substantially reduce spiraling length of nutrients in stream ecosystems. Animals can also alter the distribution and rate of nutrient cycling in terrestrial ecosystems. Some experiments have shown a positive correlation between shredder species richness and leaf mass loss. Nitrogen-fixing plants increase the quantity and rates of nitrogen cycling in terrestrial ecosystems.Disturbance increases nutrient loss from ecosystems. Vegetation exerts substantial control on nutrient retention by terrestrial ecosystems. Vegetative controls on nutrient loss from forest ecosystems appear to be most important in environments that are warm and moist during the growing season. Vegetative controls appear to be less important in cold and/or dry environments. Nutrient loss by stream ecosystems is highly pulsed and associated with disturbance by flooding.
Nutrient enrichment by humans is altering aquatic and terrestrial ecosystems. Nitrate concentration and export by the earth’s major rivers correlate directly with human population density. Human disturbance also increases export of phosphorus from aquatic catchments. Nutrient enrichment appears to be reducing the diversity of plants and fungi in terrestrial ecosystems. Land managers around the world use nutrient loading models to predict and manage the impact of land use on aquatic ecosystems.
