The response of tree ring delta super(15)N to whole-watershed urea fertilization at the Fernow Experimental Forest, WV

Plant tissue delta super(15)N is frequently used as a proxy for N availability and N cycle dynamics, and the delta super(15)N signature of tree rings could potentially be used to reconstruct past changes in the N cycle due to forest disturbance or anthropogenic N deposition. However, there are subst...

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Veröffentlicht in:Biogeochemistry 2016-10, Vol.130 (1-2), p.133-145
Hauptverfasser: Burnham, Mark B, McNeil, Brenden E, Adams, Mary Beth, Peterjohn, William T
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Sprache:eng
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Zusammenfassung:Plant tissue delta super(15)N is frequently used as a proxy for N availability and N cycle dynamics, and the delta super(15)N signature of tree rings could potentially be used to reconstruct past changes in the N cycle due to forest disturbance or anthropogenic N deposition. However, there are substantial uncertainties regarding how effectively tree ring delta super(15)N records N cycle dynamics. We used increment tree cores from a forested watershed that received a one-time application of urea, along with the long-term stream water chemistry record from that watershed and a nearby reference watershed, to determine the effectiveness of tree ring delta super(15)N in recording a change in N availability, and whether its effectiveness differed by species or mycorrhizal type. Tree ring delta super(15)N of three species increased rapidly (within ~1 to 3 years) following fertilization (Quercus rubra, Fagus grandifolia, and Prunus serotina), while that of Liriodendron tulipifera did not respond to fertilization but increased ~10 years later. Tree ring delta super(15)N tended to remain elevated throughout the measured time period (1967-2000), well past the pulsed fertilization response in stream water. This extended delta super(15)N response may be partially caused by chronic atmospheric N deposition in the region, which also contributed to greater losses of nitrate in stream water by ~1980. Additionally, local recycling of N compounds, and retranslocation of N within the trees, may account for the persistence of elevated tree ring delta super(15)N levels beyond the direct fertilization effects. Collectively, these results confirm that tree ring delta super(15)N from some species can document the onset of historical changes in the N cycle. We suggest that studies utilizing tree ring delta super(15)N as a proxy for long-term N cycle dynamics should look for a consistent pattern of change among several species rather than relying on the record from a single species.
ISSN:0168-2563
1573-515X
DOI:10.1007/s10533-016-0248-y