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 9, NUMBER 12, DECEMBER 1996
IMPACTS OF ELEVATED CO2
"System-Level Adjustments to Elevated CO2 in
Model Spruce Ecosystems," S. Hättenschwiler
(Botanisches Inst., Univ. Basel, Schönbeinstr. 6, CH-4056
Basel, Switz.), C. Körner, Global Change Biology, 2(4),
377-387, Aug. 1996.
Predictions that atmospheric CO2 enrichment and
increasing N deposition will increase forest productivity are
often based on data for isolated forest tree seedlings or their
leaves. This study looked at the effects of these gases on whole
stands of 4-yr-old spruce trees (Picea abies). One tree
from each of six clones, together with two herbaceous understory
species, were established in each of nine 0.7 m2 model ecosystems
in nutrient-poor soil and grown in a simulated montane climate,
with increasing CO2 and N, for two years. The observed
lack of above-ground growth response to elevated CO2
is due to several effects, including increasing strength of
below-ground carbon sinks. The non-linearity of treatment
suggests that major responses of coniferous forests may already
be under way and future responses may be smaller.
"Forest Canopy Productivity Index," R.J. Norby
(Environ. Sci. Div., Oak Ridge Natl. Lab., Oak Ridge TN 37831), Nature, 381(6583),
564, June 13, 1996.
Results of the few field experiments that have investigated
tree responses to increased CO2 are difficult to
generalize and extrapolate, possibly because plant dry mass is
used as the primary indicator of response. Proposed here is a
more robust and conceptually more useful measure: the annual
production of wood per unit of leaf areathe canopy
productivity index (CPI), formerly called growth efficiency. It
provides a useful construct for organizing existing data and
"Elevated CO2 Decreases Seed Germination in Arabidopsis
thaliana," C. Andalo,..I. Till-Bottraud (Biol. des
Populations d'Altitude, URA 1946 Univ. Joseph Fourier, Bât
76, BP 53, F-38041 Grenoble Cedex 9, France; e-mail
firstname.lastname@example.org), Global Change Biology, 2(2),
129-135, Apr. 1996.
Studied two generations of seed from different genotypes of an
annual herb. The maternal generation was produced in the
greenhouse (present-day conditions); the offspring generation was
produced in chambers where the CO2 was either 350 ppm
or 700 ppm. Elevated CO2 during maturation of seeds on
the mother plants decreased germination, but elevated CO2
during germination had no effect on the proportion of germinated
seeds. However, germination for seeds produced and
germinated under elevated CO2 was both low and slow.
Since responses varied strongly among genotypes, there is ample
genetic variance for selection.
"Leaf Senescence and Decline of End-of-Season Gas Exchange
in Five Temperate Deciduous Tree Species Grown in Elevated CO2
Concentrations," K.D.M. McConnaughay (Dept. Biol., Bradley
Univ., Peoria IL 61625; e-mail: email@example.com), S.L.
Bassow et al., ibid., 2(1), 25-33, Feb. 1996.
Seedlings from these species were studied: grey birch (Betula
populifolia), ash (Fraxinus americana), red maple (Acer
rubrum), yellow birch (Betula alleghaniensis), and
striped maple (Acer pennsylvanicum). For current and
elevated atmospheric CO2 levels, parameters measured
included leaf-level photosynthetic rates, canopy area per unit
time, leaf level transpiration rates, and water use efficiency.
Results suggest that whole canopy end-of-season gas exchange may
be altered significantly under elevated CO2, resulting
in reduced carbon gain and water use efficiency. Seedling growth
and survival, and ultimately temperate forest regeneration, could
be reduced under higher levels of CO2 in the future.
"Effects of Elevated CO2, Nitrogen Supply and
Tropospheric Ozone on Spring Wheat. I. Growth and Yield," A.
Fangmeier (Inst. Pflanzenökol., Heinrich-Buff-Ring 38,
D-35392 Giessen, Ger.), U. Grüters et al., Environ.
Pollut., 91(3), 381-390, 1996.
The wheat cultivar Minaret was exposed to three CO2
levels, in combination with two N fertilizer levels and two
levels of tropospheric O3. Plants were harvested at various
growth stages to gain information about biomass partitioning. CO2
enrichments drastically increased the biomass of organs serving
as long-term carbohydrate pools; average yield increased 34%.
Elevated N application was most effective on the biomass of green
tissues, and yield was increased from 150 to 270 N ha-1.
Significant interactions were observed between CO2
enrichment and N application. The cultivar was insensitive to O3.
"Growth Responses of an Alpine Grassland to Elevated CO2,"
B. Schäppi, C. Körner (Botanisches Inst., Univ. Basel,
Schönbeinstr. 6, CH-4056 Basel, Switz.), Oecologia, 105(1),
Plots of narrow alpine grassland were exposed for three
seasons to ambient and elevated CO2; some plots also
received moderate additions of N in a complete fertilizer mix.
Results do not support the hypothesis that alpine plants, due to
their higher carbon uptake efficiency, will increase biomass
production under future atmospheric CO2 enrichment, at
least not in such late successional communities. However, because
the subdominant generalistic species, Poa alpina, strongly
increased shoot growth, altered community and perhaps ecosystem
structure may occur in the longer term. Even under moderate
climate warming or enhanced atmospheric nitrogen deposition,
positive biomass responses to CO2 enrichment of the
currently dominating species are unlikely.
"Comparison of Radiative and Physiological Effects of
Doubled Atmospheric CO2 on Climate," P.J.
Sellers, (Biospheric Sci., MC 923, NASA-Goddard, Greenbelt MD
20771), L. Bounoua et al., Science, 271(5254),
1402-1406, Mar. 8, 1996.
A coupled biosphere-atmosphere model indicates that under
doubled CO2, evapotranspiration will drop and air
temperature will increase over the tropical continents,
amplifying the changes resulting from atmospheric radiative
Issue: Wheat Growth Under Global Environmental Change, J.I.L.
Morrison, S.P. Long, Eds., Global Change Biology, 1(6),
Dec. 1995. Request single issues from Subscription Dept., Marston
Book Services, POB 87, Oxford OX2 0DT, UK (tel: 44 1865 791 155;
fax: 44 1865 791 927).
Globally, as a food crop, wheat provides 19% of dietary energy
and 20% of protein. The world wheat crop will respond to global
change, and it has the potential to modify global change because
it occupies such a large area of the globe. The latter could
occur through changes in the fluxes of C, N, and water, in
genotypes and agronomic practices, or through crop substitution.
This special issue brings together contributions from six of the
leading international laboratories that have investigated the
topic, first presented as invited lectures to a conference
organized by the Society for Experimental Biology (St. Andrew's,
Scotland, April 1995). Some of the studies include the impact of
altered temperature as well as elevated CO2.
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