2.3 | Dark respiration
We assessed mitochondrial respiration in darkness, as there are
inconsistencies among the different methods used to estimate respiration
in the light (Way et al. 2019). At ~5 a.m. we covered
leaves with thin aluminum foil to keep them darkened after dawn, and
measured dark respiration rates at several different temperatures during
the morning with the LI-6400XT. Dome temperatures were set to match the
target leaf temperatures. Measurements were made at the
[CO2] of the measurement domes to minimize
diffusion-related measurement errors. The flow rate was set to 250 µmol
s–1. Respiration rates were logged for 2 minutes and
the logged values were averaged prior to further analyses to reduce the
effects of random fluctuations on the respiration estimates caused by
the relatively low signal-to-noise ratio when measuring low flux rates
on a small leaf area (e.g., the 6 cm2 of the standard
cuvette of the LI-6400XT). The temperature sensitivity of respiration
was expressed as the Q10, calculated as:
\(Q_{10}=e^{\left(10\times b\right)}\), Eqn. 1
where b is the slope of the natural log-transformed respiration
rates versus leaf temperature:
ln(RDark) = a + b \(\times\)TLeaf Eqn. 2
From this, we calculated respiration rates at a set temperature of 30°C
(R30) and at the mean nighttime temperatures of the two
domes.