Uptake and Distribution of Nitrogen from Acidic Fog within a Ponderosa Pine (Pinus ponderosa Laws.)/Litter/Soil System

Abstract

The magnitude and importance of wet deposition of N in forests of the South Coast (Los Angeles) Air Basin have not been well characterized. We exposed 3-yr-old ponderosa pine (Pinus ponderos Laws.) seedlings growing in native forest soil to acidic fog treatments (pH 3.1) simulating fog chemistry from a pine forest near Los Angeles, California. Fog solutions contained either ¹⁵NH⁺₄, ¹⁵NO^-₃ or unlabeled N. The fog treatments were applied in open-top chambers in six 5-hr exposures. Soil treatments within each of the fog exposures were bare soil, soil overlain with L- and F-litter, and soil covered with plastic during the fog events to preventfogwaterfrom contacting soil. Seedlings were harvested and samples were collected 15 wk after the fog treatments. Uptake of ¹⁵N by roots was by farthe dominant pathway for plant assimilation of fog-deposited ¹⁵N. Deposition of N in fog supplied 9.4% and 8.7% of the total N in current-year crown biomass in the litter-overlay and bare-soil treatments, respectively. Total N concentrations in every plant fraction except current-year stems were significantly higher in the bare-soil treatment than in the plastic-covered soil treatment. Less than 5% of the ¹⁵N deposited directly to the seedling crowns was retained by the plants in the covered-soil treatment, whereas 57% of the ¹⁵N deposited to the seedling/litter/soil systems was incorporated into plant biomass. The litter layers retained ¹⁵NH⁺₄ more effectively than ¹⁵NO^-₃. Data from this study suggest that N deposited from fog may be an important source of N for plant growth in forests of the SCAB where fog occurrence and pollution exposure coincide. FOR. SCI. 41(4):645-663.

Citation

Fenn, Mark E.; Leininger, Theodor D. 1995. Uptake and Distribution of Nitrogen from Acidic Fog within a Ponderosa Pine (Pinus ponderosa Laws.)/Litter/Soil System. Forest Science, Vol. 41, No. 4, November 1995. pp 645-663.