Leaf Stomatal
Density and Carbon Isotope Responses to CO2 Variations during
the Past 40,000 years (NSF GRANT #EAR-9418269 Investigators: Steven W. Leavitt, Julio L. Betancourt, Peter K.
Van de Water and Lisa C. Pedicino
Stomatal density
and d13C were measured in southwestern
leaves from herbarium collections representing the last 150 years of
atmospheric CO2 rise since industrialization, and from packrat
middens representing the Late Pleistocene to Holocene CO2
increase during deglaciation. Several gas-exchange parameters such as discrimination
(D), intercellular-to-external CO2
ratios (Ci/Ca), and water-use efficiency (A/g)
were derived from the d13C values. Additionally, modern samples
from elevational transects in 1) shifts
in d13C in modern
populations along steep environmental gradients seldom exceed inter-plant
variability at a given site, 2) inter-plant and intra-site d13C variability in modern and historic herbarium collections
of the C4 halophytes Atriplex canescens and A.
confertifolia and packrat midden
macrofossils of A. canescens
excludes their use as a reliable proxy for atmospheric d13C without large numbers of samples, 3)
calcium-oxalate crystals are common component in plant tissue and can
have a significantly different d13C value
that increases inter-plant variability, especially in C4 plants such
as Atriplex canescens and
A. confertifolia, 4) carbon isotope and stomatal density/index measurements of macrofossils from packrat
middens show species- specific adaptation
in ecophysiological processes as atmospheric CO2 rose
from the full-glacial concentrations, 5) herbarium sample analysis (after
smoothing the time series data) indicates homeostasis strategies differ
among the species, but there was also high and unsystematic variability
for individual analyses, and 6) the greatest adaptation to low atmospheric
CO2 during the last ice age was seen in the C3 species, whereas
the C4 and CAM plants showed few changes in their discrimination against
13C or in the number of stomata on leaf surfaces during deglaciation CO2 changes. Publications and Presentations: Betancourt,
J.L., Rylander, K.A., Whitham,
T., Leavitt, S.W., Van de Water, P.K. and Pedicino,
L., 1996. Stand-level variations
in d13C of pinyon pine leaf cellulose at Sunset Crater,
Pedicino, L.C.,
1997. Carbon Isotopic Variations in 7
Pedicino, L.C., Betancourt, J.L., Leavitt,
S.W., Van de Water, P.K., 1997. Leaf
d13C responses
of seven southwestern plant species to climate and CO2 enrichment
during the last 100 years. 82nd Annual Meeting of the Ecological Society of Pedicino, L.C., Leavitt, S.W., Betancourt, J.L. and Van de Water,
P.K., 2002. Historical
variations in d13Cleaf
of herbarium specimens in the southwestern Terwilliger, V.J., Betancourt, J.L., Leavitt, S.W. and Van de Water,
P.K., 2002. Leaf cellulose dD and d18O trends
with elevation differ in direction among co-occurring, semi-arid plant
species. Geochimica et Cosmochimica Acta 66: 3887-3900. Van de Water, P.K., 1999. d13C
and Stomatal Density Variability in Modern
and Fossil Leaves of Key Plants in the Van de Water, P.K., Leavitt,
S.W. and Betancourt, J.L., 1996. d13C variability in modern Atriplex; Implications for reconstructing d13C of past atmospheres. American Quaternary Association, Annual Meeting, Van de Water, P.K., Leavitt, S.W. and Betancourt, J.B., 1997. Inter- and intra-plant variability
of carbon isotopes and the packrat midden
record. 82nd
Annual Meeting of the Ecological Society of Van de Water, P.K., Leavitt, S.W. and Betancourt, J.B., and Pedicino, L., 1997. d13C variability in modern Atriplex communities; implications for reconstruction
d13C of past atmospheres. 14th annual Pacific
Climate Workshop (PACLIM), 6-9 April, Van de Water, P. K. 1997. Carbon
isotopic analysis of modern plant transects from Van de Water, P.K., 2002. The effect of chemical processing
on the d13C value of plant tissue.
Geochimica et Cosmochimica et
Acta 66: 1211–1219. Van
de Water, P.K., Leavitt, S.W., Betancourt, J.L., 2002. Leaf d13C variability
with elevation, slope aspect, and precipitation in the U.S. Southwest. Oecologia 132: 332-343. Van de Water, P.K., Leavitt, S.W., Betancourt, J.L. and
Pedicino, L.C., d13C of C4
halophytes (Atriplex canescens
and A. confertifolia) as a proxy of
d13Cair. In preparation. Van de Water, P.K., Leavitt, S.W. and Betancourt, J.L.,
Late Quaternary d13Cleaf
variations from the packrat midden record
of the southwestern Van
de Water, P.K., Leavitt, S.W. and Betancourt, J.L., Stomatal density
and index variations in space, time and species from the southwestern
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