No abstract

The extent to which both water source and atmospheric humidity affect δ(2)H values of terrestrial plant leaf waxes will affect the interpretations of δ(2)H variation of leaf waxes as a proxy for hydrological conditions. To elucidate the effects of these parameters, we conducted a long-term experiment in which we grew two tree species, Populus fremontii and Betula occidentalis, hydroponically under combinations of six isotopically distinct waters and two different atmospheric humidities. We observed that leaf n-alkane δ(2)H values of both species were linearly related to source water δ(2)H values, but with slope differences associated with differing humidities. When a modified version of the Craig-Gordon model incorporating plant factors was used to predict the δ(2)H values of leaf water, all modelled leaf water values fit the same linear relationship with n-alkane δ(2)H values. These observations suggested a relatively constant biosynthetic fractionation factor between leaf water and n-alkanes. However, our calculations indicated a small difference in the biosynthetic fractionation factor between the two species, consistent with small differences calculated for species in other studies. At present, it remains unclear if these apparent interspecies differences in biosynthetic fractionation reflect species-specific biochemistry or a common biosynthetic fractionation factor with insufficient model parameterization.

The use of hydrogen isotope ratios (δ(2)H) of sedimentary n-alkanes from leaf waxes has become an important tool for reconstructing paleoenvironmental and ancient hydrologic conditions. Studies of modern plant waxes can elucidate driving ecological mechanisms behind geologic deposits. Here, we used a transect across the North American Monsoon region of the western USA from Tucson, Arizona to Salt Lake City, Utah to study variations in leaf wax δ(2)H among co-occurring plants. Three co-occurring life forms were selected: perennial shrub (rabbit brush, Chrysothamnus nauseosus; sagebrush, Artemisia tridentata); tree (Gambel's oak tree, Quercus gambelii); and annual (sunflower, Helianthus annuus). Our results showed that the distributions and abundances of n-alkanes in perennial plants were similar across all sites and generally did not vary with environmental conditions (e.g., precipitation and temperature). In contrast, variations in n-alkane δ(2)H were significantly correlated with the fraction of the annual precipitation coming during the summer monsoon period. We use a modified Craig-Gordon model to speculate on the possible drivers of the δ(2)H values of leaf wax n-alkanes of plants across the region. The model results suggest that the most likely explanation for variation in wax δ(2)H values was a combination of seasonal source water usage and subsequent environmental conditions.

Submarine canyons are regarded as a sink for pollutants. In order to determine if this theory applied to deep-sea species from an important fishing ground (the Blanes submarine canyon) located in the NW Mediterranean, we sampled the commercial fish Phycis blennoides and Micromesistius poutassou and the crustacean Aristeus antennatus. Specimens were sampled inside and outside (in the open continental slope) the submarine canyon; both are regarded as potentially affected by exposure to different anthropogenic chemicals. Several pollution biomarkers in muscle (activity of cholinesterases) and liver/hepatopancreas (catalase, glutathione S-transferases, carboxylesterases, ethoxyresorufin O-deethylase in fish or mixed function oxygenase (MFO)-related reductases in crustacean, and lipid peroxidation levels) were measured. Chemical analysis of the persistent organic pollutants, namely polychlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethanes (DDTs) and hexachlorocyclohexanes (HCHs) was also performed on the fish and crustacean muscle. Biomarker activities and levels were discussed in relation to pollutant exposure, habitat, and parameters including sex, size, and species. Biochemical responses and chemical analysis of PCBs evidenced interspecies differences as well as sex and size-related ones, mainly in A. antennatus. An indication of higher exposure to pollutants inside the canyon was observed, which was more clearly reflected in the fish than in the crustacean. However, further research is required to confirm this observation.