Leaf Stomatal Density and Carbon Isotope Responses to CO₂ Variations during the Past 40,000 years

(NSF GRANT #EAR-9418269 1 Dec. 1994 to 31 Nov. 1998)

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 New Mexico and Utah were collected to quantify natural variability and any relationships of parameters with climate/elevation. The project concentrated on species that are major floral components of modern and fossil communities. Key findings include:

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, Arizona: Implications for the fossil record. American Quaternary Association, Annual Meeting, Flagstaff, AZ, 20-22 May.

Pedicino, L.C., 1997. Carbon Isotopic Variations in 7 Southwestern U.S. Plants from Herbarium Collections of the Last 150 Years, MS Thesis, U. of Arizona, 93 pp.

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 America, 10-14 August. Albuquerque.

Pedicino, L.C., Leavitt, S.W., Betancourt, J.L. and Van de Water, P.K., 2002. Historical variations in d¹³C_leaf of herbarium specimens in the southwestern U.S. Western North American Naturalist 62: 348-359.

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 Western United States, PhD Dissertation, U. of Arizona, 328 pp.

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, Flagstaff, AZ, 20-22 May.

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 America, 10-14 August. Albuquerque.

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, Santa Catalina Island, CA.

Van de Water, P. K. 1997. Carbon isotopic analysis of modern plant transects from Utah and New Mexico; Preliminary results. Tumamoc Hill Investigator Lecture Series, 24 Sept, Desert Laboratory, University of Arizona, Tucson.

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 d¹³C_air. In preparation.

Van de Water, P.K., Leavitt, S.W. and Betancourt, J.L., Late Quaternary d¹³C_leaf variations from the packrat midden record of the southwestern USA. In preparation.

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 United States. In preparation.