Growth, yield and nitrogen uptake in rice crop grown under elevated carbon dioxide and different doses of nitrogen fertilizer

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Indian Journal of Experimental Biology
Vol. 57, March 2019, pp. 181-187
Growth, yield and nitrogen uptake in rice crop grown under elevated
carbon dioxide and different doses of nitrogen fertilizer
Amita Raj1*, B Chakrabarti1, H Pathak3, SD Singh1, U Mina1 & TJ Purakayastha2
1Centre for Environment Science and Climate Resilient Agriculture; 2Soil Science and Agricultural Chemistry,
ICAR-Indian Agricultural Research Institute, New Delhi-110 012, India
3National Rice Research Institute, Cuttack, Odisha-753 006, India
Received 08 March 2017; revised 09 February 2018
Climate change associated with rising atmospheric carbon dioxide (CO2) concentration may have impact on crop
production and soil health. Increase in atmospheric CO2 concentration may enhance crop growth with higher demand for
nutrients by the crop. An experiment was conducted during July-October, 2013 using Free Air Carbon Dioxide Enrichment
facility at the Indian Agricultural Research Institute, New Delhi to study the impact of elevated CO2 and nitrogen (N) dose
on growth, yield and nitrogen uptake in rice crop. Four doses of N, i.e., control, 0.6 g N pot-1 (75% recommended dose of
N), 0.8 g N pot-1 (100% recommended dose of N) and 1.0 g N pot-1 (125% recommended dose of N) were applied in both
ambient (395 ppm) and elevated CO2 (550±20 ppm) conditions. Grain and biomass yield of rice was significantly higher
under elevated CO2 condition. Plant growth and yield parameters also increased with increased N doses in both elevated and
ambient CO2 conditions. Nitrogen concentration of grain and straw decreased under high CO2 level but N uptake increased
under elevated CO2 condition. Agronomic efficiency of N was higher under elevated CO2 while recovery efficiency of N
remained unaffected. The study showed that although yield of rice increases under elevated CO2 condition, to maintain plant
nitrogen concentration, application of additional dose of N is required.
Keywords: Climate change, Elevated CO2, Paddy, Oryza sativa
Climate change due to rising concentrations of
greenhouse gases (GHGs) in the atmosphere may
possibly affect crop production and soil health. The
Inter-Governmental Panel on Climate Change1 in its
5thAssessment Report (AR5) mentioned about the
adverse consequences of climate change on
agriculture, human health, settlements and natural
resources. According to the Inter-Governmental Panel
on Climate Change report, baseline scenarios (those
without additional mitigation), result in increase in
global mean surface temperature by 3.7 to 4.8°C by
2100 compared to the pre-industrial levels1.
Atmospheric CO2 concentration increased from
280 µmol mol-1 in 1750 to 400 µmol mol-1 in 20152.
The food grain production of tropical and subtropical
countries including India is likely to be severely
affected under changing climatic scenario3. Climate
change can affect rice production mainly
through increased atmospheric CO2 concentration,
temperature and changes in rainfall pattern4. Increase
in atmospheric carbon dioxide concentration has a
fertilization effect enhancing the growth and yield of
crops5. It has been reported that C3 grain and legume
crops show lower concentrations of zinc and iron
when grown under elevated CO2 concentration
conditions. Also, C3 crops other than legumes
reported to have lower concentrations of protein,
whereas C4 crops seem to be less affected6. The
fertilization effects of CO2 on crop production will be
necessary in future climate change scenarios to offset
the anticipated negative impacts of high temperature7.
Rice is a major food crop in Asia in particular and
in the world in general, providing a significant
proportion of the people’s dietary needs. It is a staple
diet of more than 2 billion people in Asia and millions
of people in Africa and South America and is a main
source of calories for about 60% of the world
population8. With the likely growth of world's
population, the demand for rice will increase. Climate
change will pose a significant challenge to meet this
demand and future food security9. It is, therefore,
important to assess the response of rice to elevated
atmospheric CO2 level. Reports on yield enhancement
—————
*Correspondence:
E-mail: amitaraj09@gmail.com
]Supplementay data available only online in NOPR]

INDIAN J EXP BIOL, MARCH 2019
182
in rice under elevated CO2 condition varies widely
due to different experimental methods adopted by
different researchers. Canopy level studies showed
10–20% yield enhancement at +200 ppm CO2
concentration under non-stress conditions9. Reports
also showed that average grain yield of rice increased
by an average of 13% grown inside free air carbon
dioxide enrichment (FACE) facility10.
Increased growth of crops under elevated CO2
condition will require higher nutrient uptake and
assimilation. The demand for nutrients by crops might
also get changed in future under increased CO2
concentration. Numerous studies suggested that
nitrogen could be a key factor in regulating the
response of ecosystem to elevated CO211. Lenka &
Lal12 reported that elevated CO2 condition increases
recalcitrant carbon fractions in plant biomass
causing progressive decline in availability of soil N
which necessitates application of supplemental N.
Besides this, increased N uptake under high CO2
condition also induces a negative feedback in
soil N dynamics. Hence, the management of nitrogen
will play crucial role in future climate change
scenarios for enhancing yield and nutrient uptake in
rice crop. Only limited reports are available on the
effect of elevated CO2 on yield as well as nutrient
dynamics in rice crop in Indian condition. The
following study was conducted to assess the impacts
of elevated CO2 on yield, plant nitrogen concentration
and nitrogen uptake in rice crop under varying
nitrogen doses.
Materials and Methods
Site
The experiment was carried out during the
kharif (June-October) season of 2013 in a Free Air
Carbon Dioxide Enrichment (FACE) facility, at the
Indian Agricultural Research Institute farm,
New Delhi, India. The site is located at 28°35'N
and 77°12'E. The climate of Delhi is subtropical,
semi-arid. The region receives about 750 mm annual
rainfall, 80% of which occurs from June to September.
The mean annual maximum temperature is 35C while
the mean annual minimum temperature is 18C.
Meteorological condition
During the entire growing season of the rice crop
the average temperature ranged from 25.4C to
30.2C (Fig. 1). A total rainfall of 112.2 mm was
reported during the entire crop growth period.
Maximum rainfall (28 mm) was observed during the
33rd standard meteorological week.
Treatments and experimental design
The experiment was conducted by growing rice
crop (variety Pusa 44) in pots filled with 15 kg soil,
under elevated CO2 in FACE rings and ambient
condition. The soil was sandy loam in texture with pH
of 7.6. Two rice seedlings (30 days old) were
transplanted in each pot in July, 2013. The CO2
concentration in the FACE ring was set at 550±20
ppm at crop canopy level using the supervisory
control and data acquisition (SCADA) software-based
FACE facility13. In control, the ambient CO2
concentration was around 395 ppm. Four different
nitrogen (N) doses were applied in both ambient and
elevated CO2 conditions (Table 1) in 3 split doses
(50% as basal dose, and rest at 25 days intervals). The
recommended dose of N was 120 kg N ha-1 which was
supplied through urea and diammonium di-
ammonium phosphate (DAP). In total there were 8
treatments with 4 replications each. Basal dose of
phosphorous and potassium was applied through DAP
and muriate of potash (MOP). Irrigation was provided
on every alternate day to maintain the saturation level
and 3-4 cm standing water throughout the cropping
period.
Fig.1 —
Variation in air temperature and rainfall during the crop
growth period
Table 1 — Treatment details for the experiment
CO2 level Treatment N (g pot
-
1
)
Ambient
(395 ppm) N0 0 (No nitrogen)
N1 0.6 (75 % recommended dose)
†
N2 0.8 (100 % of recommended dose)
N3 1.0 (125% of recommended dose)
Elevated
(550±20 ppm)
N0 0 (No nitrogen)
N1 0.6 (75 % recommended dose)
N2 0.8 (100 % of recommended dose)
N3 1.0 (125% of recommended dose)
†Recommended dose of N: 120 kg ha
-
1

IMPACT OF ELEVATED CO2 & N ON GROWTH, YIELD AND NITROGEN UPTAKE IN RICE
183
Plant sampling and analysis
At harvesting stage of the crop grains were
separated from the straw, dried, and weighed.
Subsamples were dried in an oven at 65°C for 48 h for
further chemical analysis. Growth parameters like
plant height was recorded at flowering stage, number
of tillers at maximum tillering stage and aboveground
biomass of the crop at maturity. Roots were collected
from the pot using water and khurpi. The soil was
removed from the root by placing the root in a water
flow. Oven dry weight of root was recorded. Yield
parameters like panicle number, number of grains per
panicle, number of filled and unfilled grains per
panicle, grain biomass, and thousand grain weights
(test weight) were recorded. Oven dried grain and
straw samples were analysed for nitrogen content
using micro-Kjeldahl method14.
Partitioning coefficient
Partitioning coefficient of root, shoot and grain was
calculated by dividing root, shoot and grain dry
biomass to the total dry biomass of the crop.
Plant N use efficiencies
Nutrient uptake was calculated as given below.
Grain N uptake (g pot-1) = Grain weight (g pot-1) ×
Grain N concentration (%) /100 …(1)
Straw N uptake (g pot-1) = Straw weight (g pot-1) ×
Straw N concentration (%) /100 …(2)
Aboveground N uptake (g pot-1) = Grain N uptake
(g pot-1) + Straw N uptake (g pot-1) ...(3)
Agronomic efficiency (AE) was calculated as given
below15.
AE (g grain g-1 N applied) =




 
1 1
1
Grain wt. in N treatment g pot Grain wt.
in no N treatment g pot
N dose g pot
 


...(4)
Recovery efficiency (RE) was calculated as given
below16.
RE (%) =




 
1 1
1
Plant N in N treatment g pot plant N in no N treatment g pot
100
N dose g pot
 

(5)
Statistical analysis
Design of the experiment was factorial Completely
Randomised Design (CRD). Statistical analysis of the
data was done using ANOVA (analysis of variance)
technique recommended for the design17 to test whether
the differences between means were statistically
significant or not. Unless indicated otherwise,
differences were considered significant at P <0.05.
Results
Impact of elevated CO2 on rice growth
Plant height significantly increased under elevated
CO2 condition. In elevated CO2 treatment, height of
rice plants was 81.7 cm while in ambient condition
plant height was 76.9 cm with recommended dose of
N fertilizer (Table 2). Similarly, tiller number also
increased under elevated CO2 condition. Number of
Table 2 — Effect of different nitrogen (N) levels on yield and its components of rice crops grown under
ambient and elevated CO2 condition
N dose CO2 level
Plant
height
(cm)
No. of
tillers
pot-1
Root
weight
(g pot-1)
Above
ground
biomass
(g pot-1)
Panicle
length (cm)
No. of
panicles
pot-1
No. of
grains
panicle-1
Grain yield
(g pot-1) Harvest
index
1000
grain
weight
(g)
N0 Ambient 72.3 52.0 20.7 107.2 22.3 38.0 93.0 43.7 38.0 15.6
Elevated 80.9 56.0 38.2 142.6 24.3 39.0 103.0 51.2 38.0 15.5
% Change
11.9 7.7 84.3 33.0 9.0 2.6 10.8 16.9 0 -0.6
N1 Ambient 75.0 56.0 32.6 131.1 21.5 43.0 104.0 51.5 39.3 14.5
Elevated 81.7 62.0 55.0 162.8 24.8 46.0 111.0 60.5 37.2 14.9
% Change
8.9 10.7 68.6 24.2 15.3 7.0 6.7 17.6 -5.3 2.8
N2 Ambient 76.9 65.0 42.3 135.65 24.3 50.0 108.0 54.5 40.2 14.5
Elevated 81.7 72.0 69.6 163.9 23.7 54.0 118.0 68.4 41.7 15.6
% Change
6.2 10.8 64.7 20.8 -2.5 8.0 9.3 25.5 3.9 7.6
N3 Ambient 78.3 71.0 49.0 136.8 24.0 56.0 114.0 57.0 41.7 15.2
Elevated 83.3 80.0 76.9 170.9 24.0 62.0 125.0 71.9 41.5 15.1
% Change
6.4 12.7 56.9 24.9 0.0 10.7 9.6 26.1 -0.5 -0.7
ANOVA
(P = 0.05)
N
CO2
N x CO2
NS 7.0 2.6 25.8 NS 8.0 5.0 8.6 NS NS
3.5 5.0 3.7 18.2 1.0 6.0 9.0 6.1 NS NS
NS 9.0 5.2 36.4 NS 11.0 NS 12.2 NS NS

INDIAN J EXP BIOL, MARCH 2019
184
tillers per pot was maximum in N3 treatment under
both ambient (71) and elevated (80) CO2 conditions
(Table 2). The productive tiller fraction ranged
0.73–0.79 under ambient condition and from 0.70 to
0.78 under elevated CO2 condition, across all N levels
(Fig. 2). Higher crop growth in elevated CO2
treatment was reflected in higher biomass of rice crop.
Elevated CO2 level increased above ground biomass
by 20.8% and 24.9% in N2 and N3 treatments,
respectively (Table 2). Higher N doses along with
elevated CO2 level significantly increased biomass
yield of the crop (suppl. Table 1).
Root dry weight also increased significantly under
elevated CO2 condition. Elevated CO2 level along
with higher N doses further increased root weight of
the crop significantly (suppl. Table 1). Root biomass
was found to be maximum (76.9 g pot-1) in N3
treatment under high CO2 level (Table 2). Partitioning
of biomass to root and shoot got altered in elevated
CO2 treatment. Partitioning of biomass to rice roots
significantly increased in elevated CO2 treatment
while that for shoots, it remained unaffected by CO2
level (Table 3).
Impact of elevated CO2 on yield parameters of rice crop
Grain yield of rice crop increased significantly
under elevated CO2 concentration as compared to
ambient condition irrespective of N doses (Table 2).
Elevated CO2 level increased grain yield by 25.5%
over ambient treatment with recommended dose of N.
Maximum grain yield was obtained in N3 treatment
both under ambient (57 g pot-1) and elevated (71.9 g
pot-1) CO2 condition (Table 2). Although grain yield
increased at elevated CO2 level but partitioning of
total biomass to grains decreased under high CO2
concentration (Table 3).
Number of grains per panicle was found to be
maximum in N3 treatment in both ambient (114) and
elevated (125) CO2 level (Table 2). Harvest index (HI)
of rice crop ranged from 38.0% to 41.7%. Test weight
of rice grains varied from 14.5 g to 15.6 g under
ambient and from 14.9 g to 15.6 g at elevated CO2
condition (Table 2).
Impact of elevated CO2 on nitrogen content in rice
Grain as well as straw nitrogen (N) concentration
significantly decreased under elevated CO2 condition.
On the other hand, application of N fertilizer
significantly increased N concentration in grain as
well straw in both ambient and elevated CO2
treatment (suppl. Table 1). Grain N concentration was
1.31% in elevated CO2 treatment while in ambient
condition N concentration in rice grains was 1.46%
(Table 4). Application of nitrogen significantly
increased grain N concentration over control.
Maximum N content in rice grains (1.66%) was
observed in N3 treatment under ambient CO2
condition. Maximum N content in straw was observed
in N3 treatment under both ambient (0.82%) as well
as elevated CO2 condition (0.78%) (Table 4).
Grain as well as total nitrogen (N) uptake in rice
crop significantly increased under elevated CO2
condition (suppl. Table 1). N uptake in grains was
found to be positively correlated (r = 0.88) with grain
yield of rice crop (suppl. Table 2). Application of
nitrogen fertilizer also significantly increased N
uptake over control. Maximum N uptake in rice grains
(0.97 g pot-1) was observed in N3 treatment under
elevated CO2 condition (Fig. 3). Total N uptake was
also highest in N3 treatment in both ambient
(1.57 g pot-1) and elevated (1.79 g pot-1) CO2
conditions. Significant positive correlation (r = 0.86)
Fig. 2 —
Effect of different nitrogen (N) levels on the productive
tiller ratio of rice crop grown under ambient and elevated CO2
condition. [N0, 0.0 g N pot-1 (control); N1, 0.6 g N pot-
1 (75% of
recommended dose); N2, 0.8 g N pot-
1 (100% of recommended
dose); and N3, 1.0 g N pot-1 (125% of recommended dose)]
Table 3 — Partitioning coefficient in rice as affected by elevated
carbon dioxide condition and N levels
Partitioning coefficient
N dose
CO2 level Root Shoot Grain
N0
Ambient 0.16 0.50 0.34
Elevated 0.21 0.51 0.28
N1
Ambient 0.20 0.49 0.31
Elevated 0.25 0.47 0.28
N2
Ambient 0.24 0.46 0.31
Elevated 0.30 0.41 0.29
N3
Ambient 0.26 0.43 0.31
Elevated 0.31 0.40 0.29
ANOVA
(P = 0.05)
N
CO2
N x CO2
0.02
0.02
NS
0.05
NS
NS
NS
0.03
NS

IMPACT OF ELEVATED CO2 & N ON GROWTH, YIELD AND NITROGEN UPTAKE IN RICE
185
was observed between total N uptake and
aboveground biomass of the crop (suppl. Table 2).
Nitrogen use efficiency in rice as affected by CO2 level
Agronomic efficiency (AE) of N application in rice
was higher under elevated CO2 condition (Fig. 4A).
AE of rice was found to be maximum (17.8 g grain
per g N applied) in N2 treatment under elevated CO2
condition. Recovery efficiency of rice crop was at par
in both ambient and elevated CO2 treatment (Fig. 4B).
Recovery efficiency ranged from 56 to 57.3% in
ambient CO2 treatment while it varied from 57 to 58%
in elevated CO2 treatment.
Discussion
Crop growth significantly increased under elevated
CO2 condition which was reflected in more number of
tillers, higher aboveground and belowground biomass
of rice crop. The interactive effect of high CO2 along
with high N doses further improved number of tillers
in rice (suppl Table 1). It was found that although
total number of tillers increased under elevated CO2
condition but the fraction of productive tillers (i.e.
panicle bearing) got reduced under elevated CO2
condition. Increased N doses helped in increasing the
productive tiller count. Similar result has been
reported by Baker et al.18 showing reduced fraction of
productive tillers under high CO2 condition. This
decrease in productive tiller ratio across all N levels
was possibly due to a greater response of the
vegetative tissues to elevated CO2 condition compared
to the reproductive parts5.
Earlier studies have also shown that elevated CO2
increased photosynthesis rate and plant biomass in
different crops19-21. Increased biomass under high CO2
condition is primarily attributed to increased
photosynthetic rates22,23, which subsequently leads
increased carbon assimilation and more partitioning
of assimilates to plant parts24 causing morphological
changes, such as leaf area development, tiller
production and changes in shoot to root ratios25,26.
Increased translocation of biomass to roots and
decreased amount of biomass partitioning to grains
was observed in the present study under high CO2
condition. There are similar reports, that root growth
of crop plants is often stimulated to a greater extent
than other plant parts due to greater C allocation
under increased CO2 concentration27-29. It has been
Fig. 3 —
Impact of elevated carbon dioxide and N levels on N
uptake (g pot-1) in rice crop. [N0, 0.0 g N pot-
1 (control); N1,
0.6 g N pot-1 (75% of recommended dose); N2, 0.8 g N pot-
1
(100% of recommended dose); and N3, 1.0 g N pot-
1 (125% of
recommended dose)]
Fig. 4 —
Impact of elevated carbon dioxide and N levels on (A)
agronomic efficiency; and (B) recovery efficiency of rice crop.
[N0, 0.0 g N pot-1 (control); N1, 0.6 g N pot-
1 (75% of
recommended dose); and; N2, 0.8 g N pot-
1 (100% of
recommended dose]
Table 4 — Impact of elevated CO2 and N doses on grain and straw N concentration
N dose
(g pot-1) Grain N (%) Straw N (%)
Ambient
CO2 Elevated
CO2 Mean CO2 fertilization
effect (% change)
Ambient CO2
Elevated CO2
Mean CO2 fertilization
effect (% change)
0 1.09 1.00 1.05 -8.3 0.53 0.49 0.51 -7.5
0.6 1.49 1.39 1.44 -6.7 0.74 0.69 0.72 -6.8
0.8 1.61 1.45 1.53 -9.9 0.81 0.73 0.77 -9.9
1.0 1.66 1.48 1.57 -10.8 0.82 0.78 0.80 -4.9
Mean 1.46 1.31 0.73 0.67
LSD
(P = 0.05)
N: 0.14
CO2: 0.10
N x CO2: NS
N: 0.06
CO2: 0.05
N x CO2: NS

INDIAN J EXP BIOL, MARCH 2019
186
observed that the fraction of biomass partitioned to
rice grains under elevated CO2 condition did not
exceed than ambient condition30. Some researchers
reported that in maize grown under elevated CO2 level
relative growth rate of roots was increased compared
to the relative shoot growth rate due to increased
translocation of carbon to the roots31.
Studies with rice have shown that elevated CO2
level increases grain yield of the crop19. Some
scientists reported 15% increase in rice yield grown
under high CO2 condition32. In a study, 50% increase
in biomass and 24 to 30% increase in seed yield has
been reported33. High CO2 concentration and
increased N doses synergistically helped in increasing
panicle number of rice crop (suppl. Table 1). Similar
results have been reported for rice crop grown under
elevated CO2 where increased grain yield was found
to be associated with increase in tiller number and
subsequent increase in number of panicles34,35.
Although N concentration in grains decreased
under elevated CO2 condition but application of
higher doses of nitrogen increased grain N
concentration to certain extent. Increased biomass
under elevated CO2 condition resulted in dilution
effect which has lowered N concentration. Several
researchers have also reported decrease in N
concentration in plants grown under elevated CO2
condition36,37. Reduction in N and crude protein
content in Maize has also been reported under
elevated CO2 condition38. Higher grain as well as
biomass yield under high CO2 treatment has resulted
in higher N uptake of the crop. Earlier workers also
reported that in rice crop total nitrogen (N) uptake for
the whole plant get increased under elevated CO2
condition39,40.
Higher AE of N application under elevated CO2
shows that yield enhancement with increased N dose
was more at higher CO2 treatment. Earlier results also
showed that nutrient use efficiency of N, P, K, and
Mg in all organs of rice plant significantly increased
in elevated CO2 condition41.
Conclusion
Increase in atmospheric CO2 concentration
increased both grain and biomass yield of rice crop.
Application of nitrogen significantly increased
various growth and yield parameters of rice in both
ambient and increased CO2 treatment. Nitrogen
concentration in grain as well as straw got decreased
under elevated CO2 condition due to the dilution
effect of more carbohydrate accumulation at increased
CO2 level. Nitrogen uptake by rice plants increased
under elevated CO2 condition and was more with
increased N doses. Agronomic efficiency of N
application was higher under elevated CO2 condition
while recovery efficiency was not affected much by
the CO2 level. From the current study it is evident that
under elevated CO2 condition growth and yield of rice
crop will increase but the quality of grains might get
affected. In order to increase grain nitrogen
concentration of rice there may be a need to apply
higher N doses at elevated CO2 level.
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