Ecosystem N distribution and δ15N during a century of forest regrowth after agricultural abandonment

Ecosystems
By: , and 

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Abstract

Stable isotope ratios of terrestrial ecosystem nitrogen (N) pools reflect internal processes and input–output balances. Disturbance generally increases N cycling and loss, yet few studies have examined ecosystem δ15N over a disturbance-recovery sequence. We used a chronosequence approach to examine N distribution and δ15N during forest regrowth after agricultural abandonment. Site ages ranged from 10 to 115 years, with similar soils, climate, land-use history, and overstory vegetation (white pine Pinus strobus). Foliar N and δ15N decreased as stands aged, consistent with a progressive tightening of the N cycle during forest regrowth on agricultural lands. Over time, foliar δ15N became more negative, indicating increased fractionation along the mineralization–mycorrhizal–plant uptake pathway. Total ecosystem N was constant across the chronosequence, but substantial internal N redistribution occurred from the mineral soil to plants and litter over 115 years (>25% of ecosystem N or 1,610 kg ha−1). Temporal trends in soil δ15N generally reflected a redistribution of depleted N from the mineral soil to the developing O horizon. Although plants and soil δ15N are coupled over millennial time scales of ecosystem development, our observed divergence between plants and soil suggests that they can be uncoupled during the disturbance-regrowth sequence. The approximate 2‰ decrease in ecosystem δ15N over the century scale suggests significant incorporation of atmospheric N, which was not detected by traditional ecosystem N accounting. Consideration of temporal trends and disturbance legacies can improve our understanding of the influence of broader factors such as climate or N deposition on ecosystem N balances and δ15N.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Ecosystem N distribution and δ15N during a century of forest regrowth after agricultural abandonment
Series title Ecosystems
DOI 10.1007/s10021-007-9087-y
Volume 10
Issue 7
Year Published 2007
Language English
Publisher Springer
Contributing office(s) Forest and Rangeland Ecosystem Science Center
Description 12 p.
Larger Work Type Article
Larger Work Subtype Journal Article
Larger Work Title Ecosystems
First page 1197
Last page 1208