Nitrogen Translocation to Fresh Litter in Northern Hardwood Forest
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Nitrogen immobilization in fresh litter represents a significant N flux in forest ecosystems, and changes in this process resulting from atmospheric N deposition could have important implications for ecosystem responses. We conducted two leaf decay experiments, using 15N-labeled sugar maple leaf litter, to quantify N transport from old litter and soil to fresh litter during early stages of decomposition, and we examined the influence of litter N concentration and soil N availability on upward N transfer in a northern hardwood forest. After one year of decay, the average N transfer from soil to fresh litter (2.63 mg N g−1 litter) was much higher than the N transfer from older litter (1- to 2-years-old) to fresh litter (0.37 mg N g−1 litter). We calculated the ratio of annual N transfer per unit of excess 15N pool for these two N sources. The ratio was not significantly different between old litter and soil, suggesting that fungi utilize N in the old litter and mineral soil pools for transport to decaying fresh litter with similar efficiency. Initial litter N concentration had a significant effect on upward N flux into decaying leaf litter, whereas no effect of soil N fertilization was observed. Reduction in the flux from soil to fresh litter owing to anthropogenic N inputs probably contributes significantly to changing soil N dynamics. Future work is needed on fungal N acquisition and transport as well as the fungal taxa involved in this process and their responses to changing environments.
Keywordsfungi isotope tracer litter decay nitrogen immobilization nitrogen saturation sugar maple
We appreciate Alexis Heinz and Ruth Sherman for their assistance in field experiments and Teresa Pawlowska for reviewing the manuscript. This research was supported by the Biogeochemistry and Environmental Biocomplexity Program from Cornell University.
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