Abstract:
• A technique for measuring
in vitro
respiration was investigated to understand
why rates were higher than those reported
in vivo
and to elucidate trends within
mature
Pseudotsuga menziesii
(Douglas-fir) trees.
• Extracted increment cores were divided into 3–4 radial depths and a gas chromatograph
was used to compare respiration rates radially and vertically within stems.
• Respiration of inner bark was 2–3 times greater than sapwood, and 50–70%
higher in outer than inner sapwood. Inner bark and outer sapwood released > 40%
more CO
2
at treetops than at bases. Trends were robust for CO
2
production on a
core dry-mass, volume, or total carbon basis. By contrast, CO
2
production on a nitrogen
basis showed almost no significant variation.
• This
in vitro
technique provided an effective index for relative differences in respiration
within tree stems. Discrepancies between
in vitro
and
in vivo
measurements
might be related to the gaseous environment in stems. The estimated within-stem
gradients in respiration were possibly determined by enzyme quantity and availability
and could be useful in scaling to whole-trees.
