Document: JIL-3-33-22

N-deposition does not explain increased cottonwood growth in urban compared to rural environments in the vicinity of NYC.

GREGG, J.W.* ¹ and G.M.LOVETT ²

US EPA, Corvallis, OR, USA ¹
Institute of Ecosystem Studies, Millbrook, NY USA ²

Abstract:
Previously, we grew a cottonwood phytometer (Populus deltoides, clone ST109) adjacent to air pollution monitoring stations in urban and rural sites in the vicinity of NYC and found that the phytometer grew twice as large in urban compared to rural sites for three consecutive growing seasons. Here, we provide detailed N-budget calculations to determine whether increased N-deposition could account for the increased phytometer growth in NYC. Specifically, we calculated the total N-assimilated by each plant before bud set and leaf senescence at the end of the season (calculated as total biomass x %N). N-assimilation was then compared to the total nitrogen deposited to each plant via wet and dry nitrogen deposition. Wet deposition to each pot was calculated from that deposited per m² ground area. Dry deposition was calculated from atmospheric pollutant concentrations, stomatal conductance, and tri-weekly measurements of leaf area. We found that phytometers grown in soils transplanted from eight different forests assimilated 140 mg more N per plant in our urban sites than those grown in the same soils in the country. N deposited to the urban-grown phytometers via wet (2 mg) and dry (25 mg) N-deposition, could only account for 19% of the additional N-assimilation. Phytometers grown in fertilized potting soils had a larger difference in N-assimilation between urban and rural sites (430 mg). Increased leaf area led to a larger difference in N dry deposition (urban rural difference = 50.2 mg), but total deposition (52.2 mg) was still nearly an order of magnitude less than assimilated N, and more than two orders of magnitude less than N already available from the fertilizer (5800 mg). We conclude that N-deposition was not the primary factor influencing phytometer growth in urban and rural sites in the vicinity of NYC.

Keywords: nitrogen deposition, wet deposition, dry deposition, nitrogen assimilation, urban, rural, multiple factors, cottonwood, phytometer,

This abstract is being presented at: 3:30 PM in session:
Poster Session #15: Nutrient Cycling.