EXAMINING THE METHODS OF PLANT WATER EXTRACTION AND STABLE ISOTOPES ANALYSIS FOR ECOHYDROLOGICAL STUDIES.

The stable isotope ratios of hydrogen and oxygen (2H/1H (δ2H) and 18O/16O (δ18O)) are an important, and widely applied set of tracers, used to trace water movement through the soil-plant-atmosphere continuum. They are employed in a variety of physiological, ecohydrological, and biogeochemical studies. An accurate understanding of the global water balance will be critical in a world undergoing rapidly changing climatic conditions. Specifically, understanding how, where, and when plants get their water from the soil is crucial to our management of water resources, especially considering a future where the availability of fresh water for irrigation may be limited. For studies investigating plant water use via stable isotopes, water (analyte) extraction and analysis are a critical step. Several methods exist to extract and analyze plant and soil analytes for stable isotope composition. However, new work has called into question the validity of using these methods interchangeably when extracting soil bound analytes. Within this thesis work, I began by inter-comparing six methods of plant analyte extraction for stable isotope analysis of δ2H and δ18O values, to determine if these extraction systems return accurate, interchangeable results. I then examined how the presence of co-extracted organic contaminants like methanol and ethanol effected stable isotope results returned by the Los Gatos Research off axis-integrated cavity output spectroscopy (OA-ICOS) system. Additionally, I assessed the effectiveness of the Absorption plot and the Spectra Fit Residuals plot, sub components of the OA-ICOS system, at detecting organic contamination during vapour-mode analysis. Key findings of this work are: (1) The tested methods of plant analyte extraction returned significantly different (p≤ 0.05) results; (2) Direct vapour equilibration may be a useful approach for plant analyte extraction-analysis due to potential limited interference from organic compounds, rapid sample throughput and field portability; (3) I confirm that methanol and ethanol drastically impact returned stable isotope results during analysis by spectrometric methods (OA-ICOS), but contrary to the findings of previous work, methanol caused OA-ICOS results to skew positively, while ethanol caused OA-ICOS result to skew negatively, relative to the control water isotopic composition; and (4) the Spectra Fit Residuals plot is a useful tool for the detection of organic contamination during vapour-mode analysis. These findings will have direct implications for studies utilizing stable isotope data generated from plant extracted water