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Natural abundance 15N in soil and litter across a nitrate-output gradient in New Hampshire
Forest Ecology and Management. 251: 217-230.
Stable isotopes of nitrogen are potentially a valuable tool for regional assessments of nitrogen saturation because they provide an integrated measure of the past nitrogen cycling history of a site. We measured d15N of soil and litter, as well as net nitrification potential, at three sites across a nitrate-loss gradient in the White Mountains, New Hampshire to test the hypotheses: (1) that d15N in soil and litter increase across a spatial gradient of nitrate loss; and (2) that d15N in soil and litter is elevated when nitrification is elevated. d15N was found not to vary significantly among the three sites. Patterns of leaf litter and forest floor d15N, however, were strongly influenced by species composition in individual plots. Beech litter had significantly higher d15N than yellow birch, sugar maple, and red maple. The conifer-dominated plots had significantly lower d15N in both the organic soil horizons and in litter than did the hardwood-dominated plots. When we adjusted for spatial heterogeneity in mineral soil d15N values by using an enrichment factor, d15Nfoliar - d15NBs, in place of absolute soil d15N values, a positive relationship was found with net nitrification for hardwoods. d15N may also be a useful tool for evaluating species differences in nitrogen cycling and nitrogen uptake. The distinct pattern we observed of decreasing d15N across the continuum from hardwood-dominated to conifer-dominated sites may suggest that local drivers (for example, nitrification rate) regulate the absolute value of foliar d15N, while species-driven factors (e.g., timing and type of uptake) control the foliar d15N value of one species relative to another in the same plot.
Pardo, L.H.; Hemond, H.F.; Montoya, J.P.; Pett-Ridge, J. 2007. Natural abundance 15N in soil and litter across a nitrate-output gradient in New Hampshire. Forest Ecology and Management. 251: 217-230.
Last updated on: October 11, 2007