Small understorey trees have greater capacity than canopy trees to
adjust hydraulic traits following prolonged drought in a tropical forest
Abstract
The future of tropical forests is dependent on the capacity of young
trees to adjust to drought. We evaluated multiple hydraulic traits
indicative of the drought tolerance of small trees across nine common
genera at the world’s longest-running tropical throughfall exclusion
experiment and compared their responses with surviving large canopy
trees. Small understorey trees increased specific hydraulic conductivity
by 56.3% and leaf:sapwood area ratio by 45.6% in response to the
drought treatment. However, understorey trees in both a control and the
throughfall exclusion treatment had significantly lower minimum stomatal
conductance and maximum hydraulic leaf-specific conductivity relative to
the large trees, as well as significantly greater hydraulic safety
margin (HSM) and PLC and embolism resitance, occupying a distinctly
different hydrualic niche. The greater HSM of small understorey trees
relative to large canopy trees likely enables them to adjust other
aspects of their hydraulic systems to take advantage of increases in
light availability in the understorey, driven by drought-induced
mortality of canopy trees. Our results suggest that small understorey
trees can adjust their hydraulic systems in response to changes in water
and light availability and this has major implications for the
regeneration potential of tropical forests following droughts.