The impacts of leaf damage on the isotopic composition of leaf transpiration

Stable isotopes of water are useful tracers to study water cycling between the subsurface, plants, and the atmosphere. The development of water vapor based isotope methods has facilitated the direct and continuous measurements of plant transpiration isotopic composition, which is often used to determine plant water sources and partition evapotranspiration. The assumption that isotopic composition of transpiration is equal to the source water is fundamental in such applications. However, it is possible that leaf damage may obscure the transpiration isotopic signature violating this key assumption. We hypothesized that leaf damage would expose isotopically enriched lamina water to the chamber environment resulting in more enriched measurements. We compared the isotopic compositions of transpiration for un-damaged, artificially damaged, and recovered leaves using a leaf chamber and laser isotope analyzer. Our results showed significant enrichment in the transpiration isotope signature after leaf damage and the signature returned to pre-damage values after a few days. This study is the first to evaluate the consequences of damaged leaves on the isotopic composition of transpiration using chamber based methods and has direct applications for source water