Coping with branch excision when measuring leaf net photosynthetic rates in a lowland tropical forest

Measuring leaf gas exchange from canopy leaves is fundamental for
our understanding of photosynthesis and for a realistic representation of
carbon uptake in vegetation models. Since canopy leaves are often difficult
to reach, especially in tropical forests with emergent trees up to 60
meters at remote places, canopy access techniques such as canopy cranes or
towers have facilitated photosynthetic measurements. These structures are
expensive and therefore not very common. As an alternative, branches are
often cut to enable leaf gas exchange measurements. The effect of branch
excision on leaf gas exchange rates should be minimised and quantified to
evaluate possible bias. We compared light-saturated leaf net photosynthetic
rates measured on excised and intact branches. We selected branches
positioned at three canopy positions, estimated relative to the top of the
canopy: upper sunlit foliage, middle canopy foliage, and lower canopy
foliage. We studied the variation of the effects of branc...