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NITROGEN DISTRIBUTION AND 15N IN A 115-YEAR CHRONOSEQUENCE OF OLD-FIELD WHITE PINE
Citation:
Compton, J E., T. D. Hooker, S. S. Perakis, AND R B. McKane. NITROGEN DISTRIBUTION AND 15N IN A 115-YEAR CHRONOSEQUENCE OF OLD-FIELD WHITE PINE. Presented at ESA Annual Meeting, Tucson, AZ, August 5-9, 2002.
Description:
Regrowing forests of the northeastern US are expected to serve as an important sink for carbon and nitrogen as they recover from extensive clearing and agriculture. We used a chronosequence approach to examine the changes in ecosystem N pools during the first 115 years after agricultural abandonment in Rhode Island, USA. The sites differed in time since abandonment, but had similar soils, climate, land-use history, and overstory white pine (Pinus strobus). Total ecosystem N did not change over time. Instead, N accumulated in the forest floor (11.6 kg N ha-1 yr-1) and plant biomass (4.1 kg N ha-1 yr-1), and these increases were roughly balanced by a significant decrease in mineral soil N content (-12.4 kg N ha-1 yr-1). In young white pine stands, the d15N of foliage was very similar to the mineral soil (+2 to +3 per mil), while as the stands aged, foliar d15N decreased, and became isotopically similar to the developing O horizon (-1 to -2 per mil). The d15N of plants and mineral soil diverged over time, with the soil becoming more enriched in 15N. Our findings indicate that soil N cycling and availability to regrowing forests changes dramatically over time, and that O horizon development may play a key role in these changes.