Figure 6: Oscillations are not seen following a spike in
CO2 in plants that have acclimated to elevated
CO2 for 30 h. The hallmark reduction of
Qa, measured here as qL , is not
seen, and so more energy is not diverted into non-photochemical
quenching (φNPQ ).
Figure Legends
Figure 1: Plants were exposed to elevated (1500 ppm) ambient (400 ppm)
or low (150 ppm) CO2 for 30 h, including an 8-hour dark
period during the typical night hours, with A/Cicurves performed every 2.5 hours. The A/Ci curves
were fit according to Gregory et al. , (2021) and the three
primary fit parameters, Vcmax , J , andTPU relative to an A/Ci curve run before
treatment began are plotted.
Figure 2: CO2 assimilation and optical measurements from
an A/Ci curve before and after a 30 h elevated
CO2 treatment. After 30 h in elevated
CO2, parameters show acclimation to TPU-limiting
conditions, including reduced response of assimilation,φII , NPQt , andECSt to increasing CO2. The
clouds are LOESS fitting (LOcal Estimation of Scatterplot Smoothing)
95% CI n=5.
Figure 3: TPU limitation causes reduced rubisco activation state that
persists for an extended period. Rubisco activation state remains low
over the course of adaptation (a), and the total rubisco activity
declines (b). Rubisco activation state decreases quickly after adding
CO2 initially (c) and remains recoverable over 10 min
for at least the first several hours (d).
Figure 4: Plants are given a spike in CO2, which induces
oscillations in electron transport. In the first phase, photosynthesis
is unlimited by TPU and PSI becomes more oxidized by the addition of
extra CO2, while proton conductivity remains high. The
second phase (blue) is the earliest effect of TPU limitation and is
primarily described by PSI and Qa quickly become reduced
(measured as PSI ox and qL ), along with
constriction of proton flow across the thylakoid membrane
(gH+ ) and electron flow to PSI
(ket ) blue-shaded region). The third phase
(green) begins when slower regulations, which depend on proton-motive
force (measured as ECSt ), energy dependent
quenching (NPQt ) and photoprotection at
cytochrome b6f complex, relieve reduction of the electron
transport chain. Finally, the electron transport chain enters a new
steady-state (red).
Figure 5: Three traces of PSI measurements from oscillations in PSI
reduction induced by spike in CO2, which demonstrate
varying levels of re-reduction during saturating flashes. Typically, a
saturating flash should fully oxidize PSI, but kinetics in electron
transport can change this. (a) Extreme re-reduction of PSI can be seen
during a saturation flash when PSI is most reduced, 40 s after beginning
an elevated CO2 pulse. This demonstrates a high level of
PSI-acceptor side limitation. (b) Less re-reduction of PSI during a
saturation flash is seen when PSI is less limited by electron acceptors
60 s after beginning a CO2 pulse. (c) After returning to
a new steady-state 100 s after beginning an elevated CO2pulse, PSI acceptor-side limitation is much diminished, and PSI
re-reduction is minimal.
Figure 6: Oscillations are not seen following a spike in
CO2 in plants that have acclimated to elevated
CO2 for 30 h. The hallmark reduction of
Qa, measured here as qL , is not
seen, and so more energy is not diverted into non-photochemical
quenching (φNPQ ).