PARENT SESSION
Oral Session #40: Carbon sequestration and flux.
Presiding: G. Koch
Tuesday, August 6. 1:00 PM to 4:45 PM. Gila Meeting Room, TCC.
Canopy uptake of atmospheric nitrogen and potential carbon sequestration at a Colorado subalpine forest.
Sievering, Herman*,1,3, Tomaszewski, Timothy3, Torizzo, Jonathan2, Turnipseed, Andrew4, Boyce, Richard5, 1 Global Change & Environ. Qual. Prog. and INSTAAR, Denver/Boulder, CO3 INSTAAR and Environmental Sciences, Boulder, CO2 Global Change & Environ. Qual. Prog., Denver, CO4 Dept. of EPOB Biology, Boulder, CO5 INSTAAR, Boulder, CO
ABSTRACT- The Niwot Ridge, CO subalpine forest (3000m asl) is known to be an N-limited system that may receive a significant portion of its annual N requirement in the form of wet and dry deposition. Canopy (foliar+ twig) N uptake (CNU) of atmospheric N deposition was found to contribute 2-3.5 kgN ha-1 to the annual canopy growth N req. of 20-35 kgN ha-1. Reallocation of N and soil/root uptake each contribute about 10-15 kgN ha-1. Given atmospheric N deposition is readily taken up by this spruce-fir-pine forest at photosynthetically active canopy sites, the potential for CNU to influence carbon sequestration is high. A correlation analysis of CNU vs. net ecosystem exchange (NEE) across a range of timescales showed there to be a significant and strongest relation on the precipitation-event time base. Based on about 40 such time periods’ data obtained in 2000 and 2001, 10-15% of daytime-NEE variability during the May-Oct. growing season at this Niwot Ridge conifer forest is statistically explained by CNU. A substantial majority of CNU at this subalpine site may be attributed to anthropogenic N. Thus, it appears that: a) atmospheric N deposition is contributing to the annual N demand for photosynthesis at this spruce-fir-pine forest system; and b) the anthropogenic portion of this chronic atmospheric N deposition may, over time, cause for a perturbation of the N-cycle at this subalpine forest.
KEY WORDS: Nitrogen, Carbon, Atmospheric, Uptake