Hasegawa, T., Sakai, H.,
Tokida, T., Usui, Y.,
Nakamura, H., Wakatsuki, H.,
Chen, C.P., Ikawa, H., Zhang, G.,
Nakano, H., Matsushima, M.Y.
and Hayashi, K. 2019.
"A high-yielding
rice cultivar "Takanari"
shows no N constraints
on CO2 fertilization."
Frontiers in Plant Science 10:
Article 361,
doi: 10.3389/fpls.2019.00361.
SUMMARY:
Takanari
"could be a useful
genetic resource
for improving
N use efficiency
[in other cultivars]
under elevated CO2,"
which will ensure
that future rice yields
will increase in quantity
without a sacrifice to quality.
Great news
for a planet
where rice is
an important
food crop !
DETAILS:
Hasegawa et al. (2019)
note uncertainty in projecting
the positive effects
on CO2 fertilization effect
because the strength
of the CO2 fertilization
response also depends on
water, nutrients, temperature,
crop species and genotypes.
They say to "exploit the
positive effects of elevated CO2
on crop production in the future,
the mechanisms by which
the CO2 fertilization effects vary
must be better understood."
They studied the
interactive effects
of elevated CO2 and
nitrogen (N) supply
on two rice cultivars:
Koshihikari,
a standard
japonica cultivar,
and Takanari,
a high-yielding
indica cultivar.
Researchers grew
both cultivars outdoors
in a free-air CO2
enrichment (FACE)
environment for
three consecutive
growing seasons (2012-2014)
at the Tsukuba FACE facility
in Tsukubamirai, Ibaraki, Japan.
Ambient and enriched CO2 levels
across the three years varied little
and averaged 382 ppm and 578 ppm,
respectively.
Nitrogen supply
included treatments
of no N added,
8 g m-2 added and
12 g m-2 added.
Aboveground biomass increased
in both cultivars under elevated CO2
at all N treatment levels.
The increase in this parameter
(relative to ambient CO2 levels)
diminished in the lower-yielding
Koshihikari cultivar as the amount
of N applied decreased.
For higher-yielding Takanari,
the greatest relative CO2
biomass response was observed
in the treatment with no added N.
Similar findings were observed for
paddy (unhulled grain) yield
and brown rice yield, where the
greatest relative CO2-induced
increases for Takanari were observed
in the no N added treatment,
followed by that obtained in the
12 and 8 g N m-2 added treatments.
For Koshihikari, under elevated CO2
the highest paddy and brown rice
yield enhancements occurred
at the highest level of N application,
diminishing slightly in the 8 g N m-2
treatment and then turning negative
when no N was applied.
Hasegawa et al. say the N-limiting influence
of the CO2 fertilization effect on Koshihikari
resulted from a reduction in the allocation
of biomass into its grains.
In contrast, they confirm that
"the N-limited CO2 fertilization effect
does not hold for [the] high-yielding
indica cultivar [Takanari]."
This is because of enhanced crop
N uptake that occurs in Takanari,
even without the application
of N fertilizer.
Hasegawa et al. also examined
the percent of grain chalkiness
present in the two cultivars,
used as an indicator of grain
appearance quality.
Lower-yielding Koshihikari
had consistently higher levels
of grain chalkiness
( reduced grain appearance quality )
than Takanari.
The twelve scientists conclude that,
as the air's CO2 content rises
in the future, the Takanari cultivar
will likely "retain its high yield advantage
over Koshihikari with limited increase
in chalkiness even under limited N conditions."
