PARENT SESSION
Poster Session #42: Carbon Storage.
Thursday, August 9, 2001. Presentation from 3:30 PM to 5:00 PM. Exhibition Hall

Decadal scale movements of ¹⁵N tracers into bolewood at the Harvard Forest Chronic N Study.

COLMAN, BENJAMIN¹, NADELHOFFER, KNUTE¹, CURRIE, WILLIAM², ^{1 2}

ABSTRACT- Wood is posited to be an important carbon sink in the North Temperate Zone, and elevated nitrogen deposition on temperate forests could contribute to carbon storage by stimulating wood production. At the Harvard Forest LTER Chronic N Amendment Study, ¹⁵N-tracers were added to control (ambient deposition) and fertilized (50kg N ha^-1yr^-1 since 1988) plots in 1991 and 1992. In both forest types studied (oak and red pine), ambient and fertilized plots received NH₄¹⁵NO₃ tracer on one half and ¹⁵NH₄NO₃ on the other. Previous work showed that ¹⁵N tracer recovery in bolewood at the end of the two-year tracer addition ranged from 0.1% to 4.4% when averaged across tracer forms. Tracer recovery varied with forest type, N-input rate, and ionic form of ¹⁵N added. Overall, more ¹⁵N accumulated in wood when ¹⁵NO₃^- was applied, oaks accumulated more tracer than pines, and the percent recoveries increased with N input rate. In 1999, seven years after the end of tracer application, recoveries were larger in bolewood than at the end of the two-year tracer addition, ranging from 0.8% to 5.1% averaged across tracer forms. As in 1992, tracer recovery depended on forest type, rate of N-input, and form of tracer addition. Although tracers continued to accumulate in wood for almost a decade after being added to plots, low recoveries show that N deposition has a small influence on C sequestration in these forests.

KEY WORDS: nitrogen deposition, temperate forest, carbon sink, ¹⁵N tracer