Chavan, S.G., Duursma, R.A.,
Tausz, M. and Channoum, O.
2019
Elevated CO2 alleviates
the negative impact
of heat stress
on wheat physiology
but not on grain yield.
Journal of Experimental
Botany 70: 6447-6459.
NOTE:
Chavan et al. (2019)
write that
"developing
wheat varieties
ready for
future climates,
calls for improved
understanding of
how elevated CO2
and heat stress
interactively impact
wheat yields."
SUMMARY:
In the future,
elevated CO2 levels
may be able to eliminate
a large portion of the
negative impact of
high temperature stress
on wheat grain yields.
Chavan et al. state that
"heat stress
caused
irreversible
photosynthetic
damage at
ambient CO2,
while growth
at elevated CO2
mitigated the
negative impact
of heat stress
on photosynthesis."
"Plant biomass
completely
recovered
from
heat stress,
under both
CO2 treatments,
due to the
development
of additional
late tillers
and ears;
yet these
did not
fully develop
and fill grains,"
which explains
the drop
in grain yield
observed under
heat stress.
DETAILS:
Chavan et al.
report that
elevated CO2
enhanced net
photosynthesis
by 36%
in non-heat
stressed plants,
whereas
high temperature
stress reduced
this parameter
by 42%.
In the combined
elevated CO2 and
heat stress treatment,
net photosynthesis
was not reduced
because,
"elevated CO2
protected
photosynthesis
by increasing
ribulose
biphosphate
regeneration
capacity
and reducing
photochemical
damage
[caused by]
heat stress."
The experiment
was conducted
in controlled-
environment
glasshouses at the
Hawkesbury campus
of Western Sydney
University, Richmond,
New South Wales,
Australia.
The authors used
a commercial
wheat cultivar,
Scout, which they
describe as a
"high yielding
variety with
very good
grain quality
[that] contains
a putative
high transpiration
efficiency gene
which can increase
water use efficiency."
CO2 concentrations
examined in the study
included ambient
( 419 ppm )
and elevated
( 654 ppm ).
Temperatures
were
maintained
at 22/15 °C
( day / night )
in the
control
treatment.
Then,
thirteen weeks
after planting
heat stress
was enacted
on half
the plants
in each CO2
treatment
by raising
the day/night
temperatures
to 40/24 °C
for five days.
Thereafter, the
heat-stressed
plants were
returned to
the control
temperatures.
Adequate water
was supplied
to all treatments
throughout the
experiment
so as to avoid
confounding
effects of
water stress.
CHART BELOW:
With respect to
biomass and yield,
elevated CO2
stimulated these
two parameters
by 36% and 31%,
respectively,
in the control
treatment.
Heat stress
alone,
in contrast,
induced a small
non-significant
reduction in
total biomass
and a
44% reduction
in grain yield.
When
elevated CO2
and heat stress
were combined,
total biomass
increased by 46%
over the
control
treatment
( ambient CO2 and
non-heat stress )
and by 58%
relative to the
heat stress
treatment under
ambient CO2.
Grain yield
experienced
a 23% decline
in the combined
elevated CO2 and
heat stress
treatment
relative to control
conditions, but a
positive 37%
increase relative to
heat stress alone
at ambient CO2.
Total biomass (a)
and grain yield (b)
of wheat plants
at harvest
in response to
elevated CO2
and heat stress (HS).
Values represent
means ± SE using
two-way ANOVA.
Means sharing
the same letter
in the
individual panels
are not significantly
different
according to
Tukey's HSD test
at the 5% level.
Statistical
significance
levels (t-test)
for eCO2 effect
are shown
as follows:
** P < 0.01:
*** P < 0.001.
The percentages
in red text
indicate
indicate
the change
in biomass
or grain yield
due to
elevated CO2
under control
or heat stress
conditions.