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High nitrogen (N) accumulation in terrestrial ecosystems can shift patterns of nutrient limitation and deficiency beyond N toward other nutrients, most notably phosphorus (P) and base cations (calcium [Ca], magnesium [Mg], and potassium [K]). We examined how naturally high N accumulation from a legacy of symbiotic N fixation shaped P and base cation cycling across a gradient of nine temperate conifer forests in the Oregon Coast Range. We were particularly interested in whether long-term legacies of symbiotic N fixation promoted coupled N and organic P accumulation in soils, and whether biotic demands by non-fixing vegetation could conserve ecosystem base cations as N accumulated. Total soil N (0-100 cm) pools increased nearly threefold across the N gradient, leading to increased nitrate leaching, declines in soil pH from 5.8 to 4.2, 10-fold declines in soil exchangeable Ca, Mg, and K, and increased mobilization of aluminum. These results suggest that long-term N enrichment had acidified soils and depleted much of the readily weatherable base cation pool. Soil organic P increased with both soil N and C across the gradient, but soil inorganic P, biomass P, and P leaching loss did not vary with N, implying that historic symbiotic N fixation promoted soil organic P accumulation and P sufficiency for non-fixers. Even though soil pools of Ca, Mg, and K all declined as soil N increased, only Ca declined in biomass pools, suggesting the emergence of Ca deficiency at high N. Biotic conservation and tight recycling of Ca increased in response to whole-ecosystem Ca depletion, as indicated by preferential accumulation of Ca in biomass and surface soil. Our findings support a hierarchical model of coupled N-Ca cycling under long-term soil N enrichment, whereby ecosystem-level N saturation and nitrate leaching deplete readily available soil Ca, stimulating biotic Ca conservation as overall supply diminishes. We conclude that a legacy of biological N fixation can increase N and P accumulation in soil organic matter to the point that neither nutrient is limiting to subsequent non-fixers, while also resulting in natural N saturation that intensifies base cation depletion and deficiency. [ABSTRACT FROM AUTHOR]

The article discusses the effects of atmospheric nitrogen (N) deposition on ecosystems and the empirical N critical loads in the U.S. The ecosystem impacts include biogeochemical responses which involve increased N mineralization and nitrification, and individual species, population and community responses which involve increased tissue N and changes in species richness. It is noted that the empirical critical loads for N increase in life forms including diatoms, lichens and trees.

The article presents an isotropic evidence for in-lake production of accumulating nitrate in Lake Superior. The authors employ stable isotope ratios of oxygen and nitrogen in nitrate to examine its sources in this lake. Results show that isotropic evidence indicates strongly that the accumulating nitrate is almost entirely derived from nitrification occurring within the lake. While increases in atmospheric deposition of nitrate may have downplayed a role in its buildup in the lake, other factors must also be considered as potential drivers of rising nitrate. Other significant results relative to the matter are discussed.

The article presets a study that examines the long-term effects of logging and fire on aboveground biomass, foliar N, soil C and N pools, net N mineralization and nitrification, and NO3 leaching in northern hardwood forests in the White Mountain National Forest, New Hampshire. It uses historical land-use maps to identify five areas each containing previously logged, burned, and relatively undisturbed (old-growth) forests. The results show that forest N cycling is affected by disturbances.

The article presents a paper that analyses nitrogen saturation and retention in forested watershed in Catskill Mountains in New York. Topics discussed include high rates of atmospheric nitrogen (N) and nitric oxide deposition found in Catskill Mountains that has increased since the late 1960s, use of concentration of nitric oxide stream water as indices of nitrogen saturation in the survey of Catskill watersheds and study of seasonal fluctuations of nitric oxide concentration in stream water.