The Fate of 15NO-2 Tracer in Soils under Different Tree Species of the Catskill Mountains, New York

摘要

The incorporation of nitrite (NO-₂) into soil organic matter (SOM) has received little attention as a mechanism contributing to the retention of atmospherically deposited N in forest ecosystems, despite previous studies in agricultural systems showing that NO-₂ fixation by SOM is enhanced in soils with high acidity and organic matter content, characteristics commonly found in forest soils. Given previous studies showing that nitrification and nitrate (NO-₃) leaching may vary significantly in soils under different tree species, the primary objectives of this study were to determine if the incorporation of NO-₂ into SOM was quantitatively significant and if the incorporation varied among soils under different tree species from the Catskill Mountains in New York State. A pulse-chase laboratory experiment was performed, where 15NO-₂ was added to organic soils from three tree species (American beech [Fagus grandifolia], northern red oak [Quercus rubra], sugar maple [Acer saccharum]), and 15N recoveries were determined in total soil, extractable inorganic, readily mineralizable, microbial biomass, dinitrogen (N₂), and nitrous oxide (N₂O) pools. Results from our experiment demonstrate that the incorporation of NO-₂ into SOM can occur rapidly, at time scales of 1 d or shorter, and that NO-₂ incorporation into SOM is the dominant fate of the 15NO-₂ tracer, suggesting that the incorporation of NO-₂ into SOM is a potentially important N sink in forest soils. The incorporation of NO-₂ into SOM did not vary significantly among tree species. Our results suggest that models of the N cycle in forest ecosystems should include considerations of NO-₂ incorporation into SOM.