Manipulations of albedo and mortality of upper canopy leaves in a tropical forest diverge from Earth System model results

How tropical forest leaves respond to climate change has important
implications for the global carbon cycle and biodiversity. 
Climate change could impact the energy balance properties of tropical
forest canopies through 1) long-term trait changes and 2) abrupt
disruptions/damage to leaf/photosynthetic machinery.  We assessed
the radiative and evaporative impacts of two recently proposed impacts of
climate change on tropical forest canopies: 1) long-term leaf
darkening and 2) leaf death through high temperature extremes. 
We darkened leaves to absorb 138 Wm-2 more energy in the upper canopy of a
seasonally-dry tropical moist forest in Panama.  20% of this
energy went towards heating leaves by ~4°C, 3% went towards warming the
air, and 77% went towards evaporative cooling.  This leaf warming
led to the appearance of necrosis across 9±5 % of the leaf area on certain
species.   In contrast, brightening leaves decreased
energy absorbed by an average of 58 Wm-2, which mainly reduced evaporation
(88%) with only 12% reducing leaf temperatures (and no sensible heat
flux).  This asymmetrical result suggests leaves may be close to
hydraulic limitations towards the end of the dry season.  Similar
albedo increases in a model (CLM 4.0) did not diverge between brightening
and darkening leaves and generally showed sensible heat flux to dominate
although there were strong geographic trends.  Heat death in
leaves generally heated nearby leaves (by an average of ~1.35°C) and air
temperature (by 0.5°C), but less than hypothesized because leaf albedo
increased.  Overall, our canopy top experiments question
important potential climate feedbacks, but need further study.