Plant water relations in lychee: diurnal variations in leaf conductance and leaf water potential

Abstract

Diurnal variations in leaf conductance and leaf water potential were investigated in 6-year-old lychee trees (Litchi chinensis sonn. cv. Bengal) during the dry season in subtropical Queensland, Australia. Leaf conductance and leaf water potential fell from 0.56 mol m−2 s−1 and -0.1 MPa in the morning to 0.08 mol m−2 s−1 and -1.0 MPa, respectively, in the middle of the day and then recovered slowly during the afternoon. Most of the variation in leaf conductance and leaf water potential could be attributed to a negative response to leaf-air water vapour concentration gradient (r ≈ 0.90, P < 0.01).
The marked sensitivity of lychee stomata to relative humidity suggests that CO2 assimilation could be reduced dramatically at high vapour concentration gradient and is one of the possible explanations for the poor fruit retention of lychee in dry environments. It is possible that the productivity of lychee at low humidities could be improved by techniques which decrease leaf-air vapour concentration gradient, such as overhead intermittent misting.