@misc{SachseBillaultBowenetal.2012, author = {Sachse, Dirk and Billault, Isabelle and Bowen, Gabriel J. and Chikaraishi, Yoshito and Dawson, Todd E. and Feakins, Sarah J. and Freeman, Katherine H. and Magill, Clayton R. and McInerney, Francesca A. and van der Meer, Marcel T. J. and Polissar, Pratigya and Robins, Richard J. and Sachs, Julian P. and Schmidt, Hanns-Ludwig and Sessions, Alex L. and White, James W. C. and West, Jason B. and Kahmen, Ansgar}, title = {Molecular Paleohydrology interpreting the Hydrogen- Isotopic Composition of Lipid Biomarkers from Photosynthesizing Organisms}, series = {Annual review of earth and planetary sciences}, volume = {40}, journal = {Annual review of earth and planetary sciences}, number = {1}, editor = {Jeanloz, R}, publisher = {Annual Reviews}, address = {Palo Alto}, isbn = {978-0-8243-2040-9}, issn = {0084-6597}, doi = {10.1146/annurev-earth-042711-105535}, pages = {221 -- 249}, year = {2012}, abstract = {Hydrogen-isotopic abundances of lipid biomarkers are emerging as important proxies in the study of ancient environments and ecosystems. A decade ago, pioneering studies made use of new analytical methods and demonstrated that the hydrogen-isotopic composition of individual lipids from aquatic and terrestrial organisms can be related to the composition of their growth (i.e., environmental) water. Subsequently, compound-specific deuterium/hydrogen (D/H) ratios of sedimentary biomarkers have been increasingly used as paleohydrological proxies over a range of geological timescales. Isotopic fractionation observed between hydrogen in environmental water and hydrogen in lipids, however, is sensitive to biochemical, physiological, and environmental influences on the composition of hydrogen available for biosynthesis in cells. Here we review the factors and processes that are known to influence the hydrogen-isotopic compositions of lipids-especially n-alkanes-from photosynthesizing organisms, and we provide a framework for interpreting their D/H ratios from ancient sediments and identify future research opportunities.}, language = {en} } @article{KahmenDawsonViethetal.2011, author = {Kahmen, Ansgar and Dawson, Todd E. and Vieth, Andrea and Sachse, Dirk}, title = {Leaf wax n-alkane delta D values are determined early in the ontogeny of Populus trichocarpa leaves when grown under controlled environmental conditions}, series = {Plant, cell \& environment : cell physiology, whole-plant physiology, community physiology}, volume = {34}, journal = {Plant, cell \& environment : cell physiology, whole-plant physiology, community physiology}, number = {10}, publisher = {Wiley-Blackwell}, address = {Hoboken}, issn = {0140-7791}, doi = {10.1111/j.1365-3040.2011.02360.x}, pages = {1639 -- 1651}, year = {2011}, abstract = {The stable hydrogen isotope ratios (delta D) of leaf wax n-alkanes record valuable information on plant and ecosystem water relations. It remains, however, unknown if leaf wax n-alkane delta D values record only environmental variation during the brief period of time of leaf growth or if leaf wax n-alkane delta D values are affected by environmental variability throughout the entire lifespan of a leaf. To resolve these uncertainties, we irrigated Populus trichocarpa trees with a pulse of deuterium-enriched water and used compound-specific stable hydrogen isotope analyses to test if the applied tracer could be recovered from leaf wax n-alkanes of leaves that were at different stages of their development during the tracer application. Our experiment revealed that only leaf wax n-alkanes from leaves that had developed during the time of the tracer application were affected, while leaves that were already fully matured at the time of the tracer application were not. We conclude from our study that under controlled environmental conditions, leaf wax n-alkanes are synthesized only early in the ontogeny of a leaf. Our experiment has implications for the interpretation of leaf wax n-alkane delta D values in an environmental context, as it suggests that these compounds record only a brief period of the environmental variability that a leaf experiences throughout its life.}, language = {en} } @article{KahmenSachseArndtetal.2011, author = {Kahmen, Ansgar and Sachse, Dirk and Arndt, Stefan K. and Tu, Kevin P. and Farrington, Heraldo and Vitousek, Peter M. and Dawson, Todd E.}, title = {Cellulose delta O-18 is an index of leaf-to-air vapor pressure difference (VPD) in tropical plants}, series = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {108}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, number = {5}, publisher = {National Acad. of Sciences}, address = {Washington}, issn = {0027-8424}, doi = {10.1073/pnas.1018906108}, pages = {1981 -- 1986}, year = {2011}, abstract = {Cellulose in plants contains oxygen that derives in most cases from precipitation. Because the stable oxygen isotope composition, delta O-18, of precipitation is associated with environmental conditions, cellulose delta O-18 should be as well. However, plant physiological models using delta O-18 suggest that cellulose delta O-18 is influenced by a complex mix of both climatic and physiological drivers. This influence complicates the interpretation of cellulose delta O-18 values in a paleo-context. Here, we combined empirical data analyses with mechanistic model simulations to i) quantify the impacts that the primary climatic drivers humidity (e(a)) and air temperature (T-air) have on cellulose delta O-18 values in different tropical ecosystems and ii) determine which environmental signal is dominating cellulose delta O-18 values. Our results revealed that e(a) and T-air equally influence cellulose delta O-18 values and that distinguishing which of these factors dominates the delta O-18 values of cellulose cannot be accomplished in the absence of additional environmental information. However, the individual impacts of e(a) and T-air on the delta O-18 values of cellulose can be integrated into a single index of plant-experienced atmospheric vapor demand: the leaf-to-air vapor pressure difference (VPD). We found a robust relationship between VPD and cellulose delta O-18 values in both empirical and modeled data in all ecosystems that we investigated. Our analysis revealed therefore that delta O-18 values in plant cellulose can be used as a proxy for VPD in tropical ecosystems. As VPD is an essential variable that determines the biogeochemical dynamics of ecosystems, our study has applications in ecological-, climate-, or forensic-sciences.}, language = {en} } @article{SachseDawsonKahmen2015, author = {Sachse, Dirk and Dawson, Todd E. and Kahmen, Ansgar}, title = {Seasonal variation of leaf wax n-alkane production and delta H-2 values from the evergreen oak tree, Quercus agrifolia}, series = {Isotopes in environmental and health studies}, volume = {51}, journal = {Isotopes in environmental and health studies}, number = {1}, publisher = {Routledge, Taylor \& Francis Group}, address = {Abingdon}, issn = {1025-6016}, doi = {10.1080/10256016.2015.1011636}, pages = {124 -- 142}, year = {2015}, abstract = {In order to understand the timing of leaf wax synthesis in higher plants, we analysed the variability in leaf wax n-alkane concentration, composition (expressed as average chain length (ACL)), and delta H-2(wax) values as well as plant source water delta H-2 values (xylem and leaf water) in the evergreen tree Quercus agrifolia over a period of 9 months, beginning with leaf flush. We identified three distinct periods of leaf development with the first month following leaf flush being characterized by de novo synthesis and possibly removal of n-alkanes. During the following 3 months, n-alkane concentrations increased sevenfold and delta H-2(wax) and ACL values increased, suggesting this period was the major leaf wax n-alkane formation period. During the remaining 4 months of the experiment, stable values suggest cessation of leaf wax n-alkane formation. We find that n-alkane synthesis in Q. agrifolia takes place over 4 months, substantially longer than that observed for deciduous trees.}, language = {en} }