Changes in leaf hydraulic conductance during leaf shedding in seasonally dry tropical forest

Abstract

• The hydraulic conductance of leaves ( k leaf ) was examined to determine whether this little understood component of the water transport pathway plays a role in governing leaf phenology of two deciduous dry forest trees ( Calycophyllum candidissimum and Rhedera trinervis ). • k leaf was monitored in parallel with stem hydraulic conductivity (K stem ) during the transition from wet to dry season. The relationships between declining photosynthetic quantum yield during senescence and declining k leaf and K stem were compared. • Divergent patterns were observed in the response of K stem to seasonal drying; however, the behaviour of k leaf was essentially similar in both species. Large (five- to ten-fold) decreases in leaf hydraulic conductance occurred before, and during the later stages of leaf senescence. During senescence, declining k leaf , which continued until leaves were ultimately shed, was associated with a concomitant decline in quantum yield. • We conclude that, in these species, the loss of hydraulic conductance of the leaf vascular system is linked to, and possibly responsible for, the loss of photosynthetic capacity during leaf senescence.