Description:
<p>Foliar nitrogen isotope (δ 15 N) composition patterns have been linked to soil N, mycorrhizal fractionation, and within-plant fractionations. However, few studies have examined the potential importance of the direct foliar uptake of gaseous reactive N on foliar δ 15 N. Using an experimental set-up in which the rate of mycorrhizal infection was reduced using a fungicide, we examined the influence of mycorrhizae on foliar δ 15 N in potted red maple (Acer rubrum) seedlings along a regional N deposition gradient in New York State. Mycorrhizal associations altered foliar δ 15 N values in red maple seedlings from 0.06 to 0.74 ‰ across sites. At the same sites, we explored the predictive roles of direct foliar N uptake, soil δ 15 N, and mycorrhizae on foliar δ 15 N in adult stands of A. rubrum, American beech (Fagus grandifolia), black birch (Betula lenta), and red oak (Quercus rubra). Multiple regression analysis indicated that ambient atmospheric nitrogen dioxide (NO 2 ) concentration explained 0, 69, 23, and 45 % of the variation in foliar δ 15 N in American beech, red maple, red oak, and black birch, respectively, after accounting for the influence of soil δ 15 N. There was no correlation between foliar δ 13 C and foliar %N with increasing atmospheric NO 2 concentration in most species. Our findings suggest that total canopy uptake, and likely direct foliar N uptake, of pollution-derived atmospheric N deposition may significantly impact foliar δ 15 N in several dominant species occurring in temperate forest ecosystems.</p>