Document: DAL-3-60-5

Effects of elevated CO2 on nutrient cycling in a sweetgum plantation.

JOHNSON, D.W.* 1, R.J.NORBY 4, W.CHENG 2, J.D.JOSLIN 3, D.E.TODD 4, N.T.EDWARDS 4 and E.G.O'NEILL 4

Desert Research Institute, Reno, NV 89512 USA 1
University of California-Santa Cruz, Santa Cruz, CA 95064 USA 2
University of Tennessee, Knoxville, TN 37901 USA 3
Oak Ridge National Laboratory, Oak Ridge, TN 37830 USA 4

Abstract:
The long-term effects of elevated CO2 on growth and carbon (C) sequestration are highly dependent upon the availability and cycling of nutrients. Elevated CO2 can mitigate nutrient deficiencies by facilitating increased uptake and/or biomass production per unit uptake or it could exacerbate nutrient deficiencies by introducing high-C/nutrient ratio litter and/or labile organic compounds into the soil. Many of these interactions have been studied in laboratory or in forests in the seedling to sapling stage; however, the feedbacks among these processes are numerous, complicated, and virtually impossible to predict outside an ecosystem context. Here we report the initial nutrient cycling results from a study on the effects of elevated CO2 in a closed-canopy sweetgum (Liquidambar styraciflua) plantation. Preliminary results (during the first year of fumigation) indicated a slight growth response (19% in basal area increment) and a downward trend in nutrient concentrations, resulting in little or no additional nutrient uptake. No significant effects of elevated CO2 on soil or soil solution nutrients have yet been detected, but lower decomposition rates of roots from CO2 - enriched plots (in a laboratory study), and a slight effect of elevated CO2 on soil microbial C have been detected. Thus, results at this early stage suggest that the growth increase with elevated CO2 was initially facilitated largely by increased biomass production per unit nutrient rather than by increased uptake or changes in soil availability. We await further data to determine whether this trend continues.

Keywords: Carbon dioxide, trees, nutrient cycling, soils

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This abstract is being presented at: 9:15 AM in session:
Oral Session #40: Elevated CO2 In Forest Systems.