Effect of waterlogging on carbon isotope discrimination during photosynthesis in Larix gmelinii.

Soil moisture is a major factor controlling carbon isotope discrimination (ΔC), which has been demonstrated to decrease under dry conditions in many studies; however, few studies on ΔC under waterlogging condition have been conducted. In this study, a pot experiment was conducted with Larix gmelinii, a major larch species in the east Siberian Taiga, to investigate the effect of waterlogging on ΔC during photosynthesis. Assimilation rate and ΔC (instantaneous ΔC calculated with Rayleigh distillation equation) decreased drastically soon after waterlogging, followed by recovery in their values, which was caused by a change in stomatal conductance. Thereafter, assimilation rate decreased gradually, whereas ΔC decreased more gently. These results were thought to be caused by the decrease in both stomatal conductance and carboxylation. Our results indicate that extreme wet events may cause a decrease in ΔC, which is important information for detecting flooding events in the past using tree-ring isotope analyses and for studying impacts of flooding on plants in areas where waterlogging might occur.