Successional and physical controls on the retention of nitrogen in an undisturbed boreal forest ecosystem.

Floristic succession in the boreal forest can have a dramatic influence on ecosystem nutrient cycling. We predicted that a decrease in plant and microbial demand for nitrogen (N) during the transition from mid- to late-succession forests would induce an increase in the leaching of dissolved inorganic nitrogen (DIN), relative to dissolved organic nitrogen (DON). To test this, we examined the chemistry of the soil solution collected from within and below the main rooting zones of mid- and late-succession forests, located along the Tanana River in interior Alaska.

Soil carbon and nitrogen in a pine-oak sand plain in central Massachusetts: Role of vegetation and land-use history.

Over the last 150 years much of the landscape of eastern North America has been transformed from predominantly agricultural lands to forest. Although cultivation strongly affects important ecosystem processes such as biomass accumulation, soil organic matter dynamics, and nitrogen cycling, recovery of these processes after abandonment is insufficiently understood. We examined soil carbon and nitrogen pools and nitrogen dynamics for 16 plots on a central Massachusetts sand plain, over 80% of which had been cultivated and subsequently abandoned at least 40 years ago.

Plant and Soil Responses to Chronic Nitrogen Additions at the Harvard Forest, Massachusetts.

Data are presented on changes in plant and soil processes in two forest types (red pine plantation and oak-maple forest) at the Harvard Forest, Petersham, Massachusetts, in response to 3 yr of chronic N fertilization. The hardwood stand exhibited greater N limitation on biological function than the pine stand prior to fertilization as evidenced by a lower net N mineralization rate, nearly undetectable rates of net nitrification, and very low foliar N content. N additions were made in six equal applications throughout the growing season, and consisted of 5 and 15 g°m °yr of N as ammonium nitrate.

Factors Controlling Nitrogen Cycling and Nitrogen Saturation in Northern Temperate Forest Ecosystems.

An analysis of the factors controlling rates of nitrogen cycling in northern temperate forest ecosystems is presented based on a quantitative analysis of an extensive data set for forests in Wisconsin and Massachusetts as those data are synthesized in a computer model (VEGIE) of organic matter and nutrient dynamics. The model is of the "lumped-parameter," nutrient-flux-density type, dealing with major components of forest ecosystems rather than stems or species. It deals explicitly with the interactions among light, water, and nutrient availability in determining transient and equilibrium rates of primary production and nutrient cycling.