title: Multiyear fate of a15N tracer in a mixed deciduous forest: retention, redistribution, and differences by mycorrhizal association.
abstract: The impact of atmospheric nitrogen deposition on forest ecosystems depends in large part on its fate. Past tracer studies show that litter and soils dominate the short-term fate of added15N, yet few have examined its longer term dynamics or differences among forest types. This study examined the fate of a15N-NO3- tracer over 5-6 years in a mixed deciduous stand that was evenly composed of trees with ectomycorrhizal and arbuscular mycorrhizal associations. The tracer was expected to slowly mineralize from its main initial fate in litter and surface soil, with some15N moving to trees, some to deeper soil, and some net losses. Recovery of added15N in trees and litterfall totaled 11.3% both 1 and 5-6 years after the tracer addition, as15N redistributed from fine and especially coarse roots into cumulative litterfall and small accumulations in woody tissues. Estimates of potential carbon sequestration from tree15N recovery amounted to 12-14 kg C per kg of N deposition. Tree15N acquisition occurred within the first year after the tracer addition, with no subsequent additional net transfer of15N from detrital to plant pools. In both years, ectomycorrhizal trees gained 50% more of the tracer than did trees with arbuscular mycorrhizae. Much of the15N recovered in wood occurred in tree rings formed prior to the15N addition, demonstrating the mobility of N in wood. Tracer recovery rapidly decreased over time in surface litter material and accumulated in both shallow and deep soil, perhaps through mixing by earthworms. Overall, results showed redistribution of tracer15N through trees and surface soils without any losses, as whole-ecosystem recovery remained constant between 1 and 5-6 years at 70% of the15N addition. These results demonstrate the persistent ecosystem retention of N deposition even as it redistributes, without additional plant uptake over this timescale.
authors: Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, NY, 14853, USA.
authors: Christine L
authors: CL
authors: Goodale
mesh_terms: D017753:Ecosystem; D065928:Forests; D038821:Mycorrhizae; D009584:Nitrogen; D012987:Soil; D014197:Trees
chemical_list: D012987:Soil; D009584:Nitrogen
keywords: 15N tracer; arbuscular mycorrhizae; ectomycorrhizae; nitrogen deposition; nitrogen fate; nitrogen retention; nitrogen uptake