Transition of stable isotope ratios of leaf water under simulated dew formation

Dew formation, a common meteorological phenomenon, is expected to intensify in the future. Dew can influence the (H2O)-O-18 and HDO isotopic compositions of leaf water (delta(L)), but the phenomenon has been neglected in many experimental and modelling studies. In this study, the dew effect on delta(L) was investigated with a dark plant chamber in which dew formation was introduced. The (H2O)-O-18 and HDO compositions of water vapour, dew water and leaf water of five species were measured for up to 48 h of dew exposure. Our results show that the exchanges of (H2O)-O-18 and HDO in leaf water with the air continued in the darkness when the net (H2O)-O-16 flux was zero. Our estimates of the leaf conductance using the isotopic mass balance method ranged from 0.035 to 0.087 mol m(-2) s(-1), in broad agreement of the night-time stomatal conductance reported in the literature. In our experiments, the conductance of the C-4 species was 0.04 +/- 0.01 mol m(-2) s(-1) and that of the C-3 plants was 0.10 +/- 0.04 mol m(-2) s(-1). At the end of 16 h dew exposure, 72 (+/- 17) and 94 (+/- 11)% of the leaf water came from dew according to the O-18 and D tracer, respectively.