Leaf water contains naturally occurring stable isotopes of oxygen and hydrogen in abundances that vary spatially and temporally. When sufficiently understood, these can be harnessed for a wide range of applications. Here, we review the current state of knowledge of stable isotope enrichment of leaf water, and its relevance for isotopic signals incorporated into plant organic matter and atmospheric gases. Models describing evaporative enrichment of leaf water have become increasingly complex over time, reflecting enhanced spatial and temporal resolution. We recommend that practitioners choose a model with a level of complexity suited to their application, and provide guidance. At the same time, there exists some lingering uncertainty about the biophysical processes relevant to patterns of isotopic enrichment in leaf water. An important goal for future research is to link observed variations in isotopic composition to specific anatomical and physiological features of leaves that reflect differences in hydraulic design. New measurement techniques are developing rapidly, enabling determinations of both transpired and leaf water δ(18) O and δ(2) H to be made more easily and at higher temporal resolution than previously possible. We expect these technological advances to spur new developments in our understanding of patterns of stable isotope fractionation in leaf water.

We compare vertebral microchemistry with previously described age-related movement patterns of bull sharks Carcharhinus leucas and pig-eye sharks C. amboinensis within coastal waters of north Australia. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) quantified the chemical signatures of nursery habitats within the vertebrae of juvenile and adult sharks. We examined evidence for adults returning to these habitats by applying LA-ICP-MS along a growth axis of their vertebrae. We transposed chemical signatures with growth increments in adult vertebrae to correlate with age estimates. Unique elemental signatures were identified in each of the freshwater nurseries, but we did not find them in adult vertebrae. Age-specific changes in vertebral microchemistry in mature female bull sharks correlate with periodic returns every 1 to 2 yr to less saline environments to pup. We were unable to discriminate among natal habitats of pig-eye sharks using elemental fingerprints, and age-specific changes in vertebral microchemistry were also absent. We conclude that changes in vertebral microchemistry correlate with known habitat use patterns of the bull and pig-eye sharks, showing the potential of vertebral microchemistry to discern movement patterns in sharks. KEY WORDS: Vertebral microchemistry · LA-ICP-MS · Movement · Long-term · Resource partitioning · CarcharhinidaeResale or republication not permitted without written consent of the publisher Mar Ecol Prog Ser 434: 133-142, 2011 Speed et al. 2010) that are critical to the maintenance of genetic diversity and replenishment of populations (Hueter et al. 2005).Studies tracking shark movements and identifying patterns of habitat use in coastal regions typically involve tagging with standard (numerical), satellite or sonar tags (Speed et al. 2010). Such an approach is often logistically difficult and expensive because it first involves the capture, tagging and release (in good condition) of the shark. Furthermore, the animals must either be recaptured (standard tags), or tags must report to satellites or arrays of listening stations (sonar tags) for data acquisition (Voegeli et al. 2001, Simpfendorfer & Heupel 2004. Rates of recapture are usually low, while failure of expensive satellite tags to report is commonplace (Hays et al. 2007). Arrays of listening stations require considerable effort to deploy, download and maintain, which can limit the duration and spatial extent of a study using this approach. Despite these problems, studies using these techniques have mapped fine-scale (25 km) movements of different-age cohorts of sharks in shallow coastal waters (Simpfendorfer et al. 2005, Yeiser et al. 2008, Heithaus et al. 2009, Ortega et al. 2009, but the logistics, cost and limited life span of tags have restricted the number of target individuals and species and, in the case of sonar tags, the spatial extent of the sampling area.To overcome the limitations associated with conventional tracking, natural chemical fingerprints are a developing ...

The process of evaporation results in the fractionation of water isotopes such that the lighter O isotope preferentially escapes the gas phase leaving the heavier O isotope to accumulate at the sites of evaporation. This applies to transpiration from a leaf with the degree of fractionation dependent on a number of environmental and physiological factors that are well understood. Nevertheless, the O enrichment of bulk leaf water is often less than that predicted for the sites of evaporation. The advection of less enriched water in the transpiration stream has been suggested to limit the back diffusion of enriched evaporative site water (Péclet effect); however, evidence for this effect has been varied. In sampling across a range of species with different vein densities and saturated water contents, we demonstrate the importance of accounting for the relative 'pool' sizes of the vascular and mesophyll water for the interpretation of a Péclet effect. Further, we provide strong evidence for a Péclet signal within the xylem that if unaccounted for can lead to confounding of the estimated enrichment within the mesophyll water. This has important implications for understanding variation in the effective path length of the mesophyll and hence potentially the δ O of organic matter.