© 1997 Heron Publishing—Victoria, Canada
Effects of atmospheric CO2 on longleaf pine: productivity and allocation as influenced by nitrogen and water
S. A. Prior (1), G. B. Runion (2), R. J. Mitchell (3), H. H. Rogers (1) and J. S. Amthor (4)
1. USDA-ARS National Soil Dynamics Laboratory, P.O. Box 3439, Auburn, AL 36831-3439, USA / 2. School of Forestry, 108 M. White Smith Hall, Auburn University, AL 36849, USA / 3. Joseph W. Jones Ecological Research Center, P.O. Box 2324, Newton, GA 31770, USA / 4. Health and Ecological Assessment Division and Global Climate Research Division, L-256, Lawrence Livermore National Laboratory,
P.O. Box 808, Livermore, CA 94550-9900, USA / Received June 21, 1996
Summary
Longleaf pine (Pinus palustris Mill.) seedlings were exposed to two concentrations of atmospheric CO2 (365 or 720 µmol mol–1) in combination with two N treatments (40 or 400 kg N ha–1 year–1) and two irrigation treatments (target values of –0.5 or –1.5 MPa xylem pressure potential) in open-top chambers from March
1993 through November 1994. Irrigation treatments were imposed after seedling establishment (i.e., 19 weeks after planting).
Seedlings were harvested at 4, 8, 12, and 20 months. Elevated CO2 increased biomass production only in the high-N treatment, and the relative growth enhancement was greater for the root system
than for the shoot system. In water-stressed trees, elevated CO2 increased root biomass only at the final harvest. Root:shoot ratios were usually increased by both the elevated CO2 and low-N treatments. In the elevated CO2 treatment, water-stressed trees had a higher root:shoot ratio than well-watered trees as a result of a drought-induced increase
in the proportion of plant biomass in roots. Well-watered seedlings consistently grew larger than water-stressed seedlings
only in the high-N treatment. We conclude that available soil N was the controlling resource for the growth response to elevated
CO2 in this study. Although some growth enhancement was observed in water-stressed trees in the elevated CO2 treatment, this response was contingent on available soil N.
Keywords:
biomass partitioning, carbon dioxide, Pinus palustris, resource limitations.
