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Mass balance of N in coniferous versus deciduous species in response to N deposition in two soil types.

Van Horn , Meghan *,1, Tuininga , Amy1, 1 Fordham University, Armonk, NY, 10504

ABSTRACT- Increased rates of nitrogen deposition from atmospheric pollutants can have large impacts on the N allocation patterns within species and in ecosystems. A greenhouse experiment was established using a sandy soil (Lebanon) and a loamy soil (Palisades) to address whether plant species or soil type affect N allocation. Intact soil cores were planted with either Pinus rigida (pitch pine) or Quercus alba (white oak) seedlings. A lysimeter was attached to each soil core to collect all water flow through. Two rates of N applications and a diH2O control (35, 17.5, 0 kg ha-1 yr-1) were made on a biweekly basis and seedlings were harvested after 12 weeks. Plant growth parameters, soil water and plant N chemistry were analyzed to compare N acquisition between species and flow through between soils under varying N treatments. Palisades soils under both pine and oak had higher levels of NO3-N and NH4-N in both the A and O horizon in all treatments, except for a large accumulation of NH4-N in the O horizon of Lebanon soils. Shoot mass was higher in the richer Palisades soils than in oligotrophic Lebanon soils for both species. Palisades oak total root N values are much higher than the Lebanon oak values. When comparing N treatments within a site, only Lebanon oak root N and shoot N concentrations increased, showing that there is increased N acquisition within the plant with increased N deposition. The lysimeter water NH4-N and NO3-N in the 0 and 17.5 kg treatments produced relatively equivalent results within soil type and species, but NO3-N leachate greatly increased in the highest N addition treatment. Within a soil type, oak leachate of NH4-N and NO3-N was lower than pine leachate in the two lower treatments, but not in the highest N treatment. Based on these results it is apparent theat there are different threshhold values for oak and pine. Critical loads are exceeded with pine at all levels of treatment, but only at the highest treatment level for the oaks. Oaks show that they can utilize increased N additions in oligotrophic soils. N allocation differences among species and soils could provide insights on future plant community composition as N deposition rates increase.

Key words: N deposition, mass balance

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