Parvin, S., Uddin, S.,
Bourgault, M., Roessner, U.,
Tausz-Posch, S., Armstrong, R.,
O'Leary, G., Fitzgerald, G.
and Tausz, M. 2018.
"Water availability moderates
N2 fixation benefit from elevated [CO2]:
A 2-year free-air CO2 enrichment study
on lentil (Lens culinaris MEDIK.)
in a water limited agroecosystem"
Plant, Cell & Environment 41: 2418-2434
Parvin et al. (2018)
recently investigated
the impact of plant nitrogen
acquisition on this
legume species that is
widely cultivated
as a grain food source
throughout the world.
Results of this study indicate that,
under adequate soil water conditions,
elevated CO2 will increase
both the quantity (grain yield)
and quality (grain N concentration)
of these two lentil cultivars.
Researchers exposed two
lentil cultivars to either
ambient (~400 ppm) or
elevated (~550 ppm)
levels of atmospheric CO2
during daylight hours only.
Results of the two-year experiment:
Elevated CO2 increased
the total biomass and grain yields
of cultivar PBA Ace by +23.8%
and +14.9% during 2015 and by
+27.1% and +55.4% during 2016.
Similarly, elevated CO2 enhanced
the total biomass and grain yields
of cultivar 05H010L-07HS3010
by +21.5% and +22.9% in 2015
and +31.4% and +55.8% in 2016.
Parvin et al. conclude that
"climate-adapted management
options that maintain soil water
later into the growing season
in a legume system
[such as irrigation]
would maximize N2 fixation
and contribute to maintaining
grain protein as well as add
more N into crop
rotation systems."
Symbiotic nitrogen-fixing bacteria
exist within specialized nodules
associated with leguminous plant roots.
These bacteria use the enzyme
nitrogenase to convert atmospheric
nitrogen (N2), which plants
cannot directly use, into
ammonium (NH4+), which is
readily utilized by plants.
Nitrogen acquired in this manner
can then be incorporated into
larger N-containing compounds
that are translocated
into various plant organs
to assist in their development
and growth.
The study included two lentil
(Lens culinaris)
genotypes
(PBA Ace
and 05H010L-07HS3010).
Their experiment was conducted
at the AGFACE free-air
CO2 enrichment facility
near Horsham, Victoria, Australia.
Over two full
growing seasons,
there were a
series of measurements
pertaining to their
growth response,
nodule metabolites,
tissue N concentration
and N2 fixation, soil N uptake,
and the allocation, partitioning
and remobilization of N
in plant organs.
Rainfall during the first
growing season (2015)
was very low (145.6 mm
below the long-term average),
The following year (2016)
rainfall was relatively high
at 110 mm above the
long-term mean.
An additional 96 mm of
irrigation water was added
during the 2015 growing season
to avoid drought-induced
crop failure.
Parvin et al. also found
elevated CO2 increased
the number of nodules (+27%),
the nodule mass (18%)
and nodule fixation activity
(+17% in each of the two lentil
cultivars, which combination
of changes resulted in an
overall CO2-induced stimulation
of N2 fixation that was greater
in the wet growing season of 2016
versus the dry growing season of 2015.
The researchers report stimulation
of N2 fixation under elevated CO2
during the wet year of 2016
"was more than sufficient
to meet the increased N demand
of stimulated biomass growth,
so that soil N uptake decreased
[in] absolute terms."
In contrast, they say that
"although N2 fixation
was still sufficiently increased
to meet (lower) additional demand
[in the dry growing season],
soil N uptake remained unaffected."
Parvin et al. observed
that "drought also changed
the effect of elevated CO2
on N allocation patterns
within the plants, and most
importantly, to the grains,
so that grain N concentration
decreased under elevated CO2
in the dry year but not in
the higher rainfall year"
(i.e., there was a 4% decline
in grain N concentration in 2015
versus a 3% increase in 2016).