Li, P., Li, B.,
Seneweera, S.,
Zong, Y., Li, F.Y.,
Han, Y. and Hao, X.
2019
Photosynthesis and
yield response
to elevated CO2,
C4 plant foxtail millet
behaves similarly
to C3 species.
Plant Science 285: 239-247
NOTE:
C4 photosynthesis
crops were expected
to be unresponsive
to CO2 enrichment,
because they have
a CO2 concentrating
mechanism, unlike
the C3 photosynthesis
plants ( C3 includes
most plants that people
and animals eat ).
https://en.wikipedia.org/wiki/C3_carbon_fixation
https://en.wikipedia.org/wiki/C4_carbon_fixation
https://en.wikipedia.org/wiki/C3_carbon_fixation
https://en.wikipedia.org/wiki/C4_carbon_fixation
But many
recent studies
have revealed
that assumption,
about C4 plants,
and CO2 endichment,
was wrong.
Many studies
are finding
significant CO2
enrichment growth
enhancements
in C4 plants,
including this study,
which tested a +205 ppm
CO2 level increase.
Foxtail millet
( Setaria italica ),
is a nutrient-rich crop,
usually grown in arid
and semi-arid regions,
due to its high drought
tolerance level.
SUMMARY:
This C4 plant,
benefits from a rise
in atmospheric CO2,
similar to C3 plants.
Net photosynthesis
increased from
elevated CO2
at all stages of
plant development,
up +21%, +73%
and +123% at the
heading, anthesis
and grain-filling stages
in 2014,
and by +7%
and +19%
at anthesis and
grain-filling in 2015
( heading stage not measured in 2015 ).
Also, there were
Increases in plant water
use efficiency, at the
heading (+77%),
anthesis (+8%) and
grain-filling (+41%)
stages in 2014, and
at anthesis (+45%) and
grain-filling (+56%)
in 2015.
Elevated CO2
increased
the tiller number,
stem diameter,
seed number,
leaf weight,
panicle weight,
aboveground biomass,
and total yield by
+27%, +16%, +25%,
+20%, +18%, +19%
and +32% in 2014,
respectively,
and by
+14%, +12%, +8%,
+4%, +19%, +8%
and +14% in 2015,
respectively.
DETAILS:
The plants were grown
in pots in open-top
chambers at Shanxi
Agricultural University
in Taigu, Shanxi, China,
There were two
growing seasons
( 2104 and 2015 )
There were two CO2 levels,
ambient ( 385 ppm )
and elevated ( 590 ppm ).
Fertilizer was added
to the soil ,and irrigation
was added, to supplement
rainfall and ensure
no water stress.
Photosynthetic measurements
were made multiple times
during the growing season,
and at the end of each season
the plants were harvested,
and growth characteristics
measured.
Transcriptomic analyses
identified genes that might
explain the observations.
In all, 66 differentially
expressed genes
were noted.
"Changes in
these genes
reduced plant height,
increased stem
diameters,
and promoted
CO2 fixation,"
which
"suggest
that under
increasing CO2
concentration
in the future,
foxtail millet,
a C4 species,
will not forfeit
its advantage
to C3 crops."
Chart Below:
Percent change
in total yield,
aboveground
biomass,
panicle weight,
leaf weight,
seed number,
stem diameter
and tiller number of
Foxtail Millet plants
due to a +205 ppm
increase in their
atmospheric CO2.
