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Saturday, May 18, 2019

Parvin et al. (2018) A 2-year free-air CO2 enrichment study on lentils in a water limited agro-ecosystem

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) 
(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).