Note Evidence for water use efficiency as an important factor in determining the dD values of tree leaf waxes Juzhi Hou, William J. D’Andrea, Dana MacDonald, Yongsong Huang * Department of Geological Sciences, Brown University, Providence, RI 02912, USA Received 8 January 2007; received in revised form 22 March 2007; accepted 22 March 2007 Available online 2 April 2007 Abstract D/H ratios of sedimentary leaf waxes can provide useful information about past climate change. However, factors con- trolling dD values of higher plant leaf waxes (dD wax ) are poorly understood. Here we show that dD wax values are negatively correlated with d 13 C values of leaf waxes (d 13 C wax ), based on a study of 35 leaf samples of 11 tree species around Blood Pond, Massachusetts (USA). Our data suggest that plant water use efficiency exerts an important control on the dD wax variation among tree species. Ó 2007 Elsevier Ltd. All rights reserved. 1. Introduction Hydrogen isotope ratios of plant leaf waxes (dD wax ) from lake and ocean sediments track dD values of environmental waters and have potential for paleoclimate reconstruction (e.g., Schefuß et al., 2005; Liu and Huang, 2005; Sachse et al., 2004; Shuman et al., 2006; Pagani et al., 2006). However, values of dD wax show considerable varia- tion among different plants from a single site receiv- ing the same precipitation (Hou et al., 2007). While existing data suggest plant water use strategies may affect dD values of plant leaf waxes (Smith and Freeman, 2006; Sachse et al., 2006; Hou et al., 2007), there have been no data directly linking plant water use efficiency to hydrogen isotope ratios of leaf waxes. Carbon isotope ratios are well estab- lished indicators of plant water use efficiency (WUE), defined as the ratio of carbon assimilation, A, to the transpiration water loss from the plant, E (Farquhar et al., 1989; Bacon, 2004): WUE ¼ A E ¼ ð1  /Þp a 1:6vðb  aÞ ðb  D 13 CÞ¼ k 0 ðb  D 13 CÞ ð1Þ where / is the respired proportion of assimilated carbon; p a is the atmospheric CO 2 pressure; v is the difference between intercellular and atmospheric water vapor pressure; the factor 1.6 is the ratio of diffusivity of water vapor and CO 2 in air; a is the fractionation occurring due to diffusion in air and b is the net fractionation caused by carboxylation; D 13 C is the carbon isotopic discrimination of plant material relative to ambient CO 2 ; D 13 C is defined as (d 13 C a  d 13 C p )/ (1 + d 13 C a ), where d 13 C a and 0146-6380/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.orggeochem.2007.03.011 * Corresponding author. Tel.: +1 401 863 3822; fax: +1 401 863 2058. E-mail address: Yongsong_Huang@brown.edu (Y. Huang). Organic Geochemistry 38 (2007) 1251–1255 www.elsevier.com/locate/orggeochem Organic Geochemistry