February 28, 2007
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A Guide to Information on Greenhouse Gases and Ozone Depletion
Published July 1988 through June 1999
FROM VOLUME 12, NUMBER 3, MARCH 1999
Carbon Balance of Young Birch Trees Grown in Ambient and Elevated
Atmospheric CO2 Concentrations, Y.-P. Wang, A. Rey, and
P. G. Jarvis, Global Change Biology 4 (8), 797-807 (1998).
Birches grown in elevated CO2 had 43% more leaves and a 110%
increase in their net leaf photosynthesis. However, those same trees grew
only 59% more biomass, and their maximum rate of carboxylation per unit of
leaf nitrogen was decreased by 21%. The majority of the rest of the fixed
carbon probably was lost by fine-root production and mycorrhiza growth.
Integration of Photosynthetic Acclimation to CO2 at the
Whole-Plant Level, D. W. Wolfe et al., Global Change Biology
4 (8), 879-893 (1998).
A broad review of the literature indicates that plants responses
to the concentration of CO2 in the atmosphere depend largely
on genotypic and environmental factors that affect the plants
abilities to develop new carbon sinks and to acquire enough nitrogen and
other resources to support additional growth. That growth generally
increases nitrogen- use efficiency because photosynthesis can be
maintained with less nitrogen investment in photosynthesis enzymes. The
resulting accumulation of carbohydrates in the leaves under elevated CO2,
however, leads to the repression of the genes that produce those enzymes.
Elevated Atmospheric CO2 Increases Fine Root Production,
Respiration, Rhizosphere Respiration and Soil CO2 Efflux in
Scots Pine Seedlings, I. A. Janssens et al., Global Change
Biology 4 (8), 871-878 (1998).
Elevated CO2 increased Scots pines mean total root
length and biomass more than 100% over that of the ambient samples. The
elevated-CO2 samples also accumulated more starch, had lower
C/N ratios, and had higher root- respiration rates, probably because of
increased nitrogen concentrations in the roots.
Growth, Loss, and Vertical Distribution ofPinus radiata Fine
Roots Growing at Ambient and Elevated CO2 Concentration,
Global Change Biology 5 (1), 107-121 (1999).
The seasonal increase in root growth began 6 weeks earlier for
elevated-CO2 pines than for ambient ones, and maximum growth
rate was attained 10 weeks earlier. After 2 years, the fine-root growth of
the elevated-CO2 trees was 36% greater, although the
subsequent die-off rate of those roots was also greater (14 vs. 9%), and
fine roots that were grown under elevated CO2 in the latter
part of the growing season experienced an even greater die-off than those
grown under ambient CO2 (62 vs. 18%). For both cases,
root-length density decreased exponentially with depth.
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