Stable hydrogen isotopic compositions (deltaD) of compound-specific biomarkers, such as n-alkanes from plant leaf waxes, can be used as a proxy for paleoclimatic change. However, the relationship between hydrogen isotopes of plant leaf wax and plant ecological life forms is not well understood. Here, we report the deltaD of n-alkanes from 34 modern terrestrial plants, including twenty-one C(3) plants and thirteen C(4) plants from northwestern China, determined using gas chromatography/thermal conversion/isotope ratio mass spectrometry. Our data show that the stable hydrogen isotopes are poorly correlated with the plant photosynthetic pathway (C(3) vs. C(4)) and that they do not give clear regional precipitation signals. Together with a comparative analysis of published deltaD values from plant leaf waxes in other regions, we believe that the stable hydrogen isotope of plant leaf waxes is more closely related to ecological life forms of these terrestrial plants (i.e. tree, shrub, and grass). In general, the grasses have more negative deltaD values than the co-occurring trees and shrubs. Our findings suggest that the deltaD values of sedimentary leaf waxes from higher plants may record changes of a plant ecosystem under the influence of environmental alteration and imply that reconstruction of the paleoclimate using deltaD values from plant n-alkanes should be based upon specific plant taxa, and comparison should be made among plants with similar ecological life forms.

We performed a global scale analysis of available leaf wax n-alkane dD data compiled from our new results, as well as from the literature and expressed as average values of D/H ratios from three common lipids of n-alkanes with odd carbon numbers (n-C 27 , n-C 29 , and n-C 31 ) from living higher plants. Our results clearly indicate multiple controls of hydrogen isotope composition and its variability in plants leaf wax. (1) At the global scale, precipitation dD values play a dominating factor that exercises the first order of control for hydrogen isotopic compositions in plant leaf wax. The hydrogen isotopic composition of plant leaf wax tracks the decreasing trend of precipitation dD with increasing latitude. (2) Because of different water acquisition systems, plant life form influences the hydrogen isotopic composition of leaf wax n-alkanes with woody plants and grasses having different responses to the change of global precipitation dD. (3) Physiological difference, due to different photosynthesis pathways or different water usage strategies, can leave an imprint on dD patterns of plant leaf waxes, causing dD variations among plants using the same source water. While these results better explain the variability of hydrogen isotope composition in leaf wax, they also have important implications for the interpretation of n-alkane dD data from fossils and ancient sediments.

To identify Candidatus Neoehrlichia mikurensis infection in northeastern China, we tested blood samples from 622 febrile patients. We identified in 7 infected patients and natural foci for this bacterium. Field surveys showed that 1.6% of ticks and 3.8% of rodents collected from residences of patients were also infected.