Journal of Experimental Botany, Vol 49, 885-895, Copyright © 1998 by Oxford University Press
C Reid and E Fiscus
Soybean (Glycine max) was grown in open-top field
chambers at ambient (360
ARTICLES
Effects of elevated [CO2] and/or ozone on limitations to CO2 assimilation in soybean (Glycine max)
Department of Crop Science, Agricultural Research Service, Box 7632, North Carolina State University, 1509 Varsity Drive, Raleigh, NC 27695, USA; US Department of Agriculture, Agricultural Research Service, and Department of Crop Science, North Carolina State University, 1509 Varsity Drive, Raleigh, NC 27695, USA; Corresponding author; e-mail: chantal_reid@ncsu.edu
mol
mol-1) or doubled [CO2] either in charcoal-filtered
air (20 nmol mol-1 [O3]) or in non-filtered air
supplemented to 1,5 x ambient [O3] (70 nmol mol-1)
to determine the major limitations to assimilation under conditions of
elevated [CO2] and/or [O3]. Through plant ontogeny, assimilation versus
intercellular CO2 concentration (A/Ci) responses were
measured to assess the limitations to assimilation imposed by the capacity
for Rubisco carboxylation, RuBP regeneration, and stomatal diffusion.In the
vegetative stages, no significant treatment effects of elevated [CO2]
and/or [O3] were observed on Rubisco carboxylation efficiency
(CE), light and CO2-saturated assimilation capacity
(Amax), and chlorophyll content
(Chl). However, for plants grown in elevated [CO2],
the assimilation rate at growth [CO2] (A) was 60%
higher than at ambient [CO2] up to the seed maturation stage, and the
potential rate of assimilation by Rubisco capacity
(Ap) was increased. Also in elevated [CO2]:
A was 51% of Ap; the relative
stomatal limitation (%Stomata) was 5%; and the
relative RuBP regeneration limitation (%RuBP) was 44%.
In ambient [CO2], O3 gradually decreased A per unit
leaf area, but had little effect on Ap and the
relative limitations to assimilation where A remained
51% of Ap, %Stomata was 27%, and
%RuBP was 22%.During reproduction,
CE declined for plants grown in elevated [CO2] and/or
[O3]; Ap was unaffected by elevated [CO2], but was
reduced by [O3] at ambient [CO2]; A increased to 72%
of Ap in elevated [CO2] and/or [O3]-fumigated air; the
%Stomata increased; and the %RuBP
decreased, to become non significant in elevated [CO2] from the beginning
of seed growth on, and in O3-fumigated air at ambient [CO2] at the seed
maturation stage. The decrease in %RuBP occurred
concomitantly with an increase in Amax and
Chl. Significant [CO2] x [O3] interactions support the
lack of an O3 effect on assimilation and its limitations at elevated [CO2]
during seed maturation. These data suggest that elevated [CO2] alleviated
some of the effects of O3 on photosynthesis.Keywords:
CO2 by O3 interactions, elevated [CO2], O3 fumigation, Rubisco
carboxylation efficiency, RuBP regeneration.
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