HR: 1340h
AN: PP43B-1246    [Abstracts]
TI: Relationship between Leaf Water and Leaf Waxes in Growing Pine Needles
AU: * Majumdar, S
EM: Shreoshi.Majumdar@dartmouth.edu
AF: Dartmouth College, Department of Earth Science, 6105 Fairchild, Hanover, NH 03755, United States
AU: Feng, X
EM: xiahong.feng@dartmouth.edu
AF: Dartmouth College, Department of Earth Science, 6105 Fairchild, Hanover, NH 03755, United States
AU: Hou, J
EM: Juzhi_Hou@Brown.edu
AF: Brown University, Department of Geological Sciences, Box 1846, Providence, RI 02912, United States
AU: Faiia, A M
EM: Anthony.M.Faiia@dartmouth.edu
AF: Dartmouth College, Department of Earth Science, 6105 Fairchild, Hanover, NH 03755, United States
AU: Huang, Y
EM: Yongsong_Huang@brown.edu
AF: Brown University, Department of Geological Sciences, Box 1846, Providence, RI 02912, United States
AB: There has been an increasing interest in reconstruction of paleoclimate and paleo-environment using hydrogen isotopic ratios of plant lipids extracted from sediments. It has been shown that δD of plant lipids is related to the δD of leaf water, which in turn is related to the δD of precipitation and relative humidity. However, the δD of leaf water changes significantly through the life of a leaf, it is not clear how the leaf water dynamics affects the bulk isotopic composition of lipids that are synthesized throughout the life of the leaf. This work is a detailed study of the relationship between δD values in leaf water and in leaf wax n-acids for two species of pine needles, red pine ( Pinus resinosa) and white pine ( Pinus strobus). In an earlier investigation we found that the δD of leaf water in pine needles increased as they were elongated through the needle-growing season. The leaf water of red pine needles has higher δD values than that of white pine needles at each comparable stage of growth. In addition, for a given needle, the leaf water δD also increased from the base to the tip of the needle. To examine the variation of lipid δD in relation to that of leaf water δD, we collected 4 sets of needles during their elongation period, obtained the bulk leaf water, then sectioned them into smaller segments along the length, and measured δD values of n-acids with 24 to 32 carbons. We test how the measured D/H ratios of leaf waxes vary with time, between two species, and with the position in the needle (relative distance from the tip, 0-1). A multiple regression analysis shows the following results. 1) The δD values of all types of n-acids are significantly correlated with the position of the sample; δD is lower near the base and higher near the tip. This result is consistent with the along-needle isotopic distribution of leaf water. 2) Leaf waxes of red pine needles are significantly more enriched in D than white pine needles, also consistent with leaf water δD variation between the two species. 3) Regardless of temporal increases of leaf water δD, the δD of 4 out of 5 wax n-acids shows a decreasing trend with time, although only two (C-24, 32) are statistically significant. This may reflect use of stored hydrogen (from stored carbohydrates) at earlier stages of growth. 4) The significance of the overall regression of δD against time, species and relative position increases from low carbon to high carbon number lipids (for C-24, 26, 28, 30, and 32, r²=0.34, 0.31, 0.56, 0.61, and 0.83), suggesting that longer wax n-acids are more influenced by local leaf water.
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 1055 Organic and biogenic geochemistry
DE: 3344 Paleoclimatology (0473, 4900)
DE: 4900 PALEOCEANOGRAPHY (0473, 3344)
DE: 4914 Continental climate records
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting