TY - JOUR
T1 - Influence of physiology and climate on δD of leaf wax n-alkanes from C3 and C4 grasses
AU - Smith, Francesca A.
AU - Freeman, Katherine H.
N1 - Funding Information:
We thank Denny Walizer, Pratigya Polissar, Chris Lernihan, and David Beausang for their technical support. Heather Karsten, David Huff, Roy Knupp, and Paul Rebarchack kindly provided access to grass plants for sampling from the greehouses in at Penn State. Thank you to the researchers and staff at the USDA Northern Great Plains Research Laboratory, the Northern Prairie Wildlife Research Center, the SDSU Cottonwood Range and Livestock Research Station, the Shortgrass Steppe LTER, the Konza Prairie LTER, the Fort Hays College Farm, and the Sevilleta LTER for their assistance in the field. We thank the INSTAAR Stable Isotope Lab for analysis of water samples. The manuscript was greatly benefited from thoughtful reviews by Alex Sessions and two anonymous reviewers. This research was supported by an American Chemical Society Grant PRF# 38836-AC2, the Penn State Institutes of the Environment and the Penn State Biogeochemical Research Initiative for Education (BRIE) sponsored by NSF (IGERT) Grant DGE-9972759.
PY - 2006/3/1
Y1 - 2006/3/1
N2 - We measured hydrogen isotope compositions (δD) of high-molecular-weight n-alkanes (C27-C33) from grasses grown in greenhouses and collected from the US Great Plains. In both cases, n-alkanes from C4 grasses are enriched in D by more than 20‰ relative to those from C3 grasses. The apparent enrichment factor (εC29-GW) between C29 n-alkane and greenhouse water is -165 ± 12‰ for C3 grasses and -140 ± 15‰ for C4 grasses. For samples from the Great Plains, δD values of C29 n-alkanes range from -280 to -136‰, with values for C4 grasses ca. 21‰ more positive than those for C3 grasses from the same site. Differences in C3 and C4 grass n-alkane δD values are consistent with the shorter interveinal distance in C4 grass leaves, and greater back-diffusion of enriched water from stomata to veins, than in C3 grass leaves. Great Plains' grass n-alkane isotopic ratios largely reflect precipitation δD values. However, the offset or apparent fractionation between n-alkanes and precipitation is not uniform and varies with annual precipitation and relative humidity, suggesting climatic controls on lipid δD values. The dryer sites exhibit smaller absolute apparent fractionation indicative of D-enrichment of source waters through transpiration and/or soil evaporation. To explore the relationship between climate and n-alkane δD values, we develop three models. (1) The 'direct analog' model estimates δDC29 values simply by applying the apparent enrichment factors, εC29-GW, observed in greenhouse grasses to precipitation δD values from the Great Plains. (2) The 'leaf-water' model uses a Craig-Gordon model to estimate transpirational D-enrichment for both greenhouse and field sites. The transpiration-corrected enrichment factors between C29 and bulk leaf-water, εC29-GW, calculated from the greenhouse samples (-181‰ for C3 and -157‰ for C4) are applied to estimate δDC29 values relative to modeled bulk leaf-water δD values. (3) The 'soil- and leaf-water' model estimates the combined effects of soil evaporation, modeled by analogy with a flow-through lake, and transpiration on δDC29 values. Predictions improve with the addition of the explicit consideration of transpiration and soil evaporation, indicating that they are both important processes in determining plant lipid δD values. D-enrichment caused by these evaporative processes is controlled by relative humidity, suggesting that important climatic information is recorded in leaf wax n-alkane δD values. Calibration studies such as this one provide a baseline for future studies of plant-water-deuterium systematics and form the foundation for interpretation of plant wax hydrogen isotope ratios as a paleo-aridity proxy.
AB - We measured hydrogen isotope compositions (δD) of high-molecular-weight n-alkanes (C27-C33) from grasses grown in greenhouses and collected from the US Great Plains. In both cases, n-alkanes from C4 grasses are enriched in D by more than 20‰ relative to those from C3 grasses. The apparent enrichment factor (εC29-GW) between C29 n-alkane and greenhouse water is -165 ± 12‰ for C3 grasses and -140 ± 15‰ for C4 grasses. For samples from the Great Plains, δD values of C29 n-alkanes range from -280 to -136‰, with values for C4 grasses ca. 21‰ more positive than those for C3 grasses from the same site. Differences in C3 and C4 grass n-alkane δD values are consistent with the shorter interveinal distance in C4 grass leaves, and greater back-diffusion of enriched water from stomata to veins, than in C3 grass leaves. Great Plains' grass n-alkane isotopic ratios largely reflect precipitation δD values. However, the offset or apparent fractionation between n-alkanes and precipitation is not uniform and varies with annual precipitation and relative humidity, suggesting climatic controls on lipid δD values. The dryer sites exhibit smaller absolute apparent fractionation indicative of D-enrichment of source waters through transpiration and/or soil evaporation. To explore the relationship between climate and n-alkane δD values, we develop three models. (1) The 'direct analog' model estimates δDC29 values simply by applying the apparent enrichment factors, εC29-GW, observed in greenhouse grasses to precipitation δD values from the Great Plains. (2) The 'leaf-water' model uses a Craig-Gordon model to estimate transpirational D-enrichment for both greenhouse and field sites. The transpiration-corrected enrichment factors between C29 and bulk leaf-water, εC29-GW, calculated from the greenhouse samples (-181‰ for C3 and -157‰ for C4) are applied to estimate δDC29 values relative to modeled bulk leaf-water δD values. (3) The 'soil- and leaf-water' model estimates the combined effects of soil evaporation, modeled by analogy with a flow-through lake, and transpiration on δDC29 values. Predictions improve with the addition of the explicit consideration of transpiration and soil evaporation, indicating that they are both important processes in determining plant lipid δD values. D-enrichment caused by these evaporative processes is controlled by relative humidity, suggesting that important climatic information is recorded in leaf wax n-alkane δD values. Calibration studies such as this one provide a baseline for future studies of plant-water-deuterium systematics and form the foundation for interpretation of plant wax hydrogen isotope ratios as a paleo-aridity proxy.
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U2 - 10.1016/j.gca.2005.11.006
DO - 10.1016/j.gca.2005.11.006
M3 - Article
AN - SCOPUS:32944481316
SN - 0016-7037
VL - 70
SP - 1172
EP - 1187
JO - Geochimica et Cosmochimica Acta
JF - Geochimica et Cosmochimica Acta
IS - 5
ER -
