New Perspectives on Nitrogen Cycling in the Temperate and Tropical Americas: Rep

Publisher Description

Inputs of nitrogen to terrestrial and aquatic ecosystems have increased several-fold over the last one hundred and fifty years, with the steepest increases during the last four decades. The expansion of fertilizer manu­ facture and use, the increase in fossil fuel combustion, the intensification of animal husbandry, and widespread cultivation of N2 fixing crops have all contributed to the dramatic increase in N inputs. The increase has been most rapid in Northern Hemisphere (NH) temperate ecosystems, but presently subtropical and tropical regions of Asia are also experiencing an explosive increase in N inputs to terrestrial ecosystems (W. Chameides, pers. comm. ; Galloway et al. 1996). Projected increases in N deposition for these trop­ ical and subtropical regions, with a high natural background of N inputs, exceed increases projected for temperate and arctic regions (Cleveland et al. submitted; Galloway et al. 1994; Holland & Lamarque 1997a). Compared to biological N fixation, N deposition is becoming a proportionately greater source of N to terrestrial and aquatic ecosystems worldwide (Vitousek et al. 1997). 6 The nitrogen contained in the atmosphere as N , 3. 9 * 10 Tg (Tg = 2 12 10 g), is the largest reservoir of N in the Earth system (Warneck 1988). However, this paper focuses on the nitrogen emissions and deposition that have been transformed from N2 into reactive forms that are biologically avail­ able (e. g. Vitousek et al. 1997).

Table of Contents

N????? — An etymology of nitrogen and other related words.- Contemporary and pre-industrial global reactive nitrogen budgets.- Nitrogen stable isotopic composition of leaves and soil: Tropical versus temperate forests.- The globalization of N deposition: ecosystem consequences in tropical environments.- A nitrogen budget for late-successional hillslope tabonuco forest, Puerto Rico.- The impact of accelerating land-use change on the N-Cycle of tropical aquatic ecosystems: Current conditions and projected changes.- Nitrogen yields from undisturbed watersheds in the Americas.- Nitrogen cycling and anthropogenic impact in the tropical interamerican seas.- Ecosystem constraints to symbiotic nitrogen fixers: a simple model and its implications.- Do top-down and bottom-up controls interact to exclude nitrogen-fixing cyanobacteria from the plankton of estuaries? An exploration with a simulation model.- The presence of nitrogen fixing legumes in terrestrial communities: Evolutionary vs ecological considerations.- Nitrogen limitation in dryland ecosystems: Responses to geographical and temporal variation in precipitation.

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Inputs of nitrogen to terrestrial and aquatic ecosystems have increased several-fold over the last one hundred and fifty years, with the steepest increases during the last four decades. The expansion of fertilizer manu

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