Gas exchange measurements
The RACiR technique was used according to Stinziano et al . (2017,
2019a). Briefly, we used a Licor 6800 portable photosynthesis machine
equipped with a fluorescence head (Licor Biosciences, Lincoln, Nebraska,
USA), and tailored chamber and RACiR parameters to each species (Table
1). RACiR range was selected after initial analyses to ensure that we
captured part of the inflection region of theA-Ci response as required by the curve fitting
procedure we used. Initial light responses were measured to determine
saturating light intensity for each species. Note that the overpressure
(ΔP) controls and accounts for chamber leaks. Starting at Zeitgeiber
Time (ZT, also photoperiod time; the time since sunrise) of 1 hour (1
hour after meteorological sunrise) on October 31st,
2016, RACiR curves were run every hour until ZT10 for P opulusdeltoides , while for Populus trichocarpa , RACiR curves
were run on November 30th, 2016 every 1.5 hours from
ZT1.5 until ZT9. For Capsicum annuum , RACiR curves were run every
two hours from ZT0 until ZT12. Malus domestica were measured in
the field every two hours from ZT2.5 until ZT8.5 on October
9th, 2016. Asclepias speciosa , Quercus
muehlenbergii , and Rosa grandiflora were measured on June
28th, 2018 from ~ZT1.5 until
~ZT12. Pinus ponderosa were measured on October
26th, 2017 from observed ~ZT0.5 to
~ZT8.5 (meteorological ZT1.5 to ZT9.5). Due to issues
with low gs (which can interfere with Cicalculations), sample size for each time point for P. ponderosavaries from 1 to 4. Cedrus deodar and Ginkgo biloba were
measured from ZT2.5 until ZT12 on August 24th, 2018.
All measurements were performed on the same area of leaf tissue for
broad leaf species and the same branch for each needle leaf species.
Note that due to external environmental temperatures, Asclepias
speciosa , Quercus muehlenbergii , Rosa grandiflora ,Cedrus deodar , and Ginkgo biloba were all measured at 30
°C. Dark respiration (R ) was measured in each species by letting
the leaf equilibrate to dark cuvette conditions for 30 min prior to
measurements (note: chamber conditions are outlined in Table 1).
RACiR data were corrected using the R package {racir} (Stinziano,
2018) and were analyzed for Vcmax andJmax using the {plantecophys} package (Duursma,
2015) in R v3.5.1 (R Core Team, 2018), and default parameters were used
as in Stinziano et al . (2017), which correspond to Rubisco
kinetics and thermal coefficients as in Bernacchi et al . (2001).