PARENT SESSION
Poster Session 32: Biogeochemistry
Thursday, August 11, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal
Effect of nitrogen addition on fine roots in an oak forest.
Machona, Bruce1, Lovett, Gary1, 1 Wiley College, Marshall, TX, USA
ABSTRACT- Burning fossil fuels causes emission of nitrogen oxides, which can be deposited to ecosystems downwind of emission sources. Excess nitrogen deposition to forests can result in, changes in carbon allocation by the trees, and increased nitrate leaching, causing depletion of base cations such as calcium (Ca). Depletion of base cations may cause soil acidification and increased aluminum (Al) concentration and mobility. Aluminumin competes with base cations and inhibits their uptake by tree roots. Experimental addition of nitrogen to an upland oak-hickory forest near Millbrook, New York has resulted in increased tree mortality. I investigated two hypotheses: (1) increases in nitrogen might cause trees to produce fewer fine roots, causing water stress, and (2) nitrogen can cause soil acidification, possibly resulting in Al toxicity. I found that Ca concentration and Ca/Al ratio in roots were significantly lower in fertilized plots compared to unfertilized controls, but there was no significant difference in Al concentration. There was no significant difference in biomass of live or dead roots. There was no significant difference in foliage Ca/Al ratio in both fertilized and unfertilized plots in samples from 1996, but the ratio was significantly lower in fertilized plots in 2002. Thus, my study did not support the hypothesis that increased nitrogen caused changes in fine root biomass, but it did support the hypothesis that increased nitrogen led to potential Al toxicity, as evidenced by low Ca: Al ratios in roots and foliage, and perhaps to low Ca supply, as evidenced by lower Ca concentration in roots.
Key words: leaching, depletion, mobility, mortality