The response of tree ring δ¹⁵N to whole-watershed urea fertilization at the Fernow Experimental Forest, WV

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• 作者：Mark B. Burnham ; Brenden E. McNeil ; Mary Beth Adams…
• 关键词：δ15N ; Nitrogen deposition ; Nitrogen cycle ; Tree rings
• 刊名：Biogeochemistry
• 出版年：2016
• 出版时间：October 2016
• 年：2016
• 卷：130
• 期：1-2
• 页码：133-145
• 全文大小：638 KB
• 刊物类别：Earth and Environmental Science
• 刊物主题：Earth sciences
  Geochemistry
  Biochemistry
  Soil Science and Conservation
  Terrestrial Pollution
  
• 出版者：Springer Netherlands
• ISSN：1573-515X
• 卷排序：130

文摘

Plant tissue δ15N is frequently used as a proxy for N availability and N cycle dynamics, and the δ15N 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 δ15N 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 δ15N in recording a change in N availability, and whether its effectiveness differed by species or mycorrhizal type. Tree ring δ15N 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 δ15N tended to remain elevated throughout the measured time period (1967–2000), well past the pulsed fertilization response in stream water. This extended δ15N 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 δ15N levels beyond the direct fertilization effects. Collectively, these results confirm that tree ring δ15N from some species can document the onset of historical changes in the N cycle. We suggest that studies utilizing tree ring δ15N 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.