Assessing tree ring δ15N of four temperate deciduous species as an indicator of N availability using independent long-term records at the Fernow Experimental Forest, WV

Abstract

Nitrogen deposition in the northeastern US changed N availability in the latter part of the twentieth century, with potential legacy effects. However, long-term N cycle measurements are scarce. N isotopes in tree rings have been used as an indicator of N availability through time, but there is little verification of whether species differ in the strength of this signal. Using long-term records at the Fernow Experimental Forest in West Virginia, we examined the relationship between soil conditions, including net nitrification rates, and wood δ¹⁵N in 2014, and tested the strength of correlation between tree ring δ¹⁵N of four species and stream water NO₃⁻ loss from 1971 to 2000. Higher soil NO₃⁻ was weakly associated with higher wood δ¹⁵N across species, and higher soil net nitrification rates were associated with higher δ¹⁵N for Quercus rubra only. The δ¹⁵N of Liriodendron tulipifera and Q. rubra, but neither Fagus grandifolia nor Prunus serotina, was correlated with stream water NO₃⁻. L. tulipifera tree ring δ¹⁵N had a stronger association with stream water NO₃⁻ than Q. rubra. Overall, we found only limited evidence of a relationship between soil N cycling and tree ring δ¹⁵N, with a strong correlation between the wood δ¹⁵N and NO₃⁻ leaching loss through time for one of four species. Tree species differ in their ability to preserve legacies of N cycling in tree ring δ¹⁵N, and given the weak relationships between contemporary wood δ¹⁵N and soil N cycle measurements, caution is warranted when using wood δ¹⁵N to infer changes in the N cycle.

Citation

Burnham, Mark B.; Adams, Mary Beth; Peterjohn, William T. 2019. Assessing tree ring δ15N of four temperate deciduous species as an indicator of N availability using independent long-term records at the Fernow Experimental Forest, WV. Oecologia. 191(4): 971-981. https://doi.org/10.1007/s00442-019-04528-4.