Soil water uptake by trees using water stable isotopes (delta H-2 and delta O-18)-a method test regarding soil moisture, texture and carbonate

摘要

Stable isotopes of oxygen and hydrogen are often used to determine plant water uptake depths. We investigated whether and to what extend soil moisture, clay content, and soil calcium carbonate influences the water isotopic composition. In the laboratory, dried soil samples varying in clay content were rewetted with different amounts of water of known isotopic composition. Further, we removed soil carbonate from a subset of samples prior to rewetting. Water was extracted from samples via cryogenic vacuum extraction and analysed by mass spectrometry. The isotopic composition of extracted soil water was similarly depleted in both O-18 and H-2 with decreasing soil moisture and increasing clay and carbonate content. Soil carbonate changed the delta O-18 composition while delta H-2 was not affected. Our results indicate that soil carbonate can cause artifacts for O-18 isotopic composition of soil water. At low soil moisture and high carbonate content this could lead to conflicting results for delta O-18 and delta H-2 in plant water uptake studies.