A direct and rapid leaf water extraction method for isotopic analysis

Abstract

Isotopic measurements of leaf water have provided insights into a range of ecophysiological and biogeochemical processes, but require an extraction step which often constitutes the major analytical bottleneck in large-scale studies. Current standard procedures for leaf water analysis are based on cryogenic vacuum or azeotrophic distillation, and are laborious, require sophisticated distillation lines and the use of toxic materials. We report a rapid technique based on centrifugation/filtration of leaf samples pulverised in their original sampling tubes, using a specifically adapted, simple apparatus. The leaf water extracts produced are suitable for isotopic analysis via pyrolysis gas chromatography isotope ratio mass spectrometry (PYR/GC/IRMS). The new method was validated against cryogenic vacuum distillation and showed an overall accuracy of +/-0.5 per thousand (nine grouped comparisons, n = 110) over a range of 21 per thousand. Effects due to the presence of soluble carbohydrates were near the detection limits for most samples analysed, and these effects could be corrected for (the extracted soluble organics could also be used for isotopic analysis). The extraction time for a routine eight-sample subset was reduced from 4 h (cryogenic distillation) to 45 min, limited only by the size of the centrifuge(s) used. This method provides a rapid, low-cost and reliable alternative to conventional vacuum and other distillation methods that can alleviate current restrictions on ecosystem- and global-scale studies that require high-throughput leaf water isotopic analysis.