The response of tree ring d15N to whole-watershed urea fertilization at the Fernow Experimental Forest, WV

Author

• Burnham, Mark B.
• McNeil, Brenden E.
• Adams, Mary Beth
• Peterjohn, William T.

Year Published

2016

Source

Biogeochemistry. 130(1-2): 133-145.

Abstract

Plant tissue d¹⁵N is frequently used as a proxy for N availability and N cycle dynamics, and the d¹⁵N 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 d¹⁵N 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 d¹⁵N in recording a change in N availability, and whether its effectiveness differed by species or mycorrhizal type. Tree ring d¹⁵N 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 d¹⁵N tended to remain elevated throughout the measured time period (1967-2000), well past the pulsed fertilization response in stream water. This extended d¹⁵N 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 d¹⁵N levels beyond the direct fertilization effects. Collectively, these results confirm that tree ring d¹⁵N from some species can document the onset of historical changes in the N cycle. We suggest that studies utilizing tree ring d¹⁵N 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.

Keywords

• 15N
• Nitrogen deposition
• Nitrogen cycle
• Tree rings

Citation

Burnham, Mark B.; McNeil, Brenden E.; Adams, Mary Beth; Peterjohn, William T. 2016. The response of tree ring d¹⁵N to whole-watershed urea fertilization at the Fernow Experimental Forest, WV. Biogeochemistry. 130(1-2): 133-145.

For further details log on website :
https://www.nrs.fs.fed.us/pubs/53178