Proc. Natl. Acad. Sci., India, Sect. B Biol. Sci. DOI 10.1007/s40011-015-0615-9
RESEARCH ARTICLE
Growth, Physiology and Biochemical Responses of Two Different Brassica Species to Elevated CO2 K. Chakraborty1,2 • D. C. Uprety1 • D. Bhaduri2
Received: 28 January 2015 / Revised: 29 March 2015 / Accepted: 3 July 2015 The National Academy of Sciences, India 2015
Abstract In an open top chamber study, two contrasting Brassica cultivars from two different species were grown under two distinct levels of CO2 concentration, 550 lmol mol-1 (elevated) and 390 lmol mol-1 (ambient). CO2 enrichment showed significant increase in growth, leaf area and dry matter production in both the species. The continuous higher rate of photosynthesis (36.2 % in RH-30 and 27.3 % in Pusa Gold) under elevated CO2 condition attributed to the increased generation of foliage and enhancement in stem and root growth which is also evidenced by higher net assimilation and relative growth rate. The increase was highest at flowering stage with a concomitant increase in net photosynthetic rate but showed reduction in respiration rate and stomatal conductance. The increase in net photosynthesis further resulted in higher accumulation of sugars, non-structural carbohydrates and starch in leaves in elevated CO2 grown plants. Larger accumulation of biomass was observed in root as compared to other plant parts. However, the species specific differences were reflected in the accumulation of biomass, grain yield and gas exchange phenomena, wherein the greater response was invariably found in RH30 (Brassica juncea) as compared to Pusa Gold (Brassica campestris). The present study may prove beneficial to understand crop responses to future climatic conditions and suggest efficient adaptive strategies from crop management perspectives. & K. Chakraborty
[email protected] 1
Division of Plant Physiology, Indian Agricultural Research Institute, New Delhi, India
2
Present Address: ICAR-Directorate of Groundnut Research, Junagadh, Gujarat 362001, India
Keywords Biomass C-assimilation Climate change Crop stages Mustard
Introduction The Brassicas are one of the most important oilseed crop worldwide, cultivated in tropical and sub-tropical part of India. Globally, India contributes 28.3 and 19.8 % in world acreage and production of rapeseed-mustard [1]. But, like other C3 crops, the vulnerability of Brassica to climate change and its species level variability in response to elevated CO2 is an important area of study in today’s context in order to identify suitable cultivars responsive to higher level of atmospheric CO2. As observed in the last decade, the rate of increase in atmospheric CO2 concentration has been 1.8 lmol mol-1 year-1 and is predicted to be as high as 550 lmol mol-1 by 2050 [2]. The obvious impact of this phenomenon towards agricultural ecosystems cannot be ignored anymore. The commonly cultivated C3 plant like rice, wheat, pulses etc. respond to elevated CO2 since they reduce oxygenase activity of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) enzyme in plants [3]. Unlike C4 plants whose photosynthetic responses are completely saturated by CO2, C3 plants lack the CO2 concentrating mechanism in them and thus the enzyme Rubisco operates well below its saturation level and usually show significant positive response under elevated CO2 concentration [4]. Hence, a number of physiological and biochemical parameters are likely to change under elevated CO2 condition for Brassica. Elevated CO2 brought about significant increase in the size of stomatal guard cells, stroma and epidermal cells and such acclimation involves in the regulation of photosynthesis in rice [5]. Decrease in Rubisco
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protein content as much as 60 % was also observed in some plants indicating that nitrogen is being reallocated under elevated CO2 condition [6]. A few studies were attempted to understand the response of Brassica species to elevated CO2 mostly in growth chamber or with short term exposure to elevated level of CO2. Hence, it is considered important to understand the sustenance of CO2 induced stimulation of plant responses in Brassica cultivars up to the seed formation stage and also to observe the species specific differences in their response pattern. With this objective the present study was carried out to characterize the responses of two species of Brassica viz. B. juncea (RH-30) and B. campestris (Pusa Gold) under elevated and ambient CO2 condition in terms of physiological and biochemical parameters, along with growth and yield attributes in three different plant growth stages.
Material and Methods Plant Material and Growing Condition For the present investigation two Brassica cultivars viz. ‘Pusa Gold’ (B. campestris 2n = 20; AA) and ‘RH-30’ (B. juncea 2n = 36; AABB) were selected from two most common species of Brassica having significant variation at genomic level (one having diploid genome, whereas the other with tetra-ploid genomic configuration) with a possibility of behaving differentially under elevated CO2 condition. The earlier reports from this laboratory suggested that differential response under elevated CO2 could well be associated with genomic configuration of a species as found in case of different species of Triticum [7]. The present study was carried out in open top chambers (OTC) of Division of Plant Physiology, Indian Agricultural Research Institute, New Delhi following standard package of practices. The plants were grown in soil of alluvial origin, sandy clay loam in texture, alkaline in reaction, non-calcareous with low cation exchange capacity with a pH 7.8 and EC 0.45 dS m-1 and having 0.48 % organic C, 102 mg kg-1 available N, 9.91 mg kg-1 P and 160 mg kg-1 K. During the crop growth period the mean maximum and minimum temperatures were 25.2 and 11.3 C, respectively along with 80–85 % RH and 28 mm of rainfall. The experiment was a (2 9 2) factorial experiment of two cultivars of Brassica (Pusa Gold, RH-30) and two different CO2 level (ambient: 390 lmol mol-1; elevated CO2: 550 lmol mol-1). The plants were sampled for observations of growth, physiological and biochemical parameters at (a) vegetative/pre-flowering (20 days after
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sowing), (b) flowering (50 days after sowing) and (c) postflowering (70 days after sowing) stages and for each observations the mean value(s) of at least 5-plants were taken into consideration.
Growth and Yield Parameters Plant height, root length, number of branches and leaves were recorded at vegetative, flowering and post flowering stages of growth. The allometry of root growth with respect to shoot growth was expressed by root: shoot ratio at different stages of growth. Leaf area was measured using leaf area meter (LICOR 3100). For measuring plant biomass (root, stem, leaves, siliqua), samples were dried in an oven at 80 C and dry weight(s) of plant parts were measured subsequently and growth analysis was done. The dry matter partitioning of different parts of the plant i.e. leaf, stem, root, shoot and pods were studied according to the method of Thurling [8]. The net assimilation rate (NAR) was calculated based on increase in dry weight of plant per unit leaf area per unit time using the following formula. NAR ¼ ðW2 W1 = A2 A1 Þ ðlnA2 lnA1 Þ= t2 t1 and expressed as mg cm-2 day-1, where A1 and A2 were leaf area and W1 and W2 were total dry weight for time t1 and t2 respectively. Relative growth rate (RGR) expressed as g g-1 day-1 was measured as under. RGR ¼ ðlnW2 lnW1 Þ=t2 t1 where W1 and W2 were total dry weight of plant for time t1 and t2 respectively, ln = natural logarithmic base [9]. Yield components like (a) 1000 seed weight, (b) pod dry weight per plant, (c) seed yield (g m-2) were recorded at the time of harvest. The harvest index (in percentage) was calculated as the ratio of economic yield to biological yield [8]. Physiological Parameters The rate of photosynthesis was measured on leaves using a portable Infrared Gas Analyzer (IRGA, LICOR 6200). The photosynthesis, respiration and stomatal conductance were estimated by the method of Centritto et al. [10] using IRGA. Biochemical Parameters Total soluble protein [11] and sugar content [12] were estimated from leaf samples. The reducing sugar content was estimated from 80 % ethanol extracted samples
Growth, physiology and biochemical responses of two different Brassica…
whereas acid hydrolyzed samples were estimated for total sugar estimation. Starch content was determined by Anthrone Method [13] and absorbance was measured at 620 nm in UV–Vis spectrophotometer. Difference between means of treatments in terms of CD (p = 0.05) values of investigated growth, physiological, and biochemical parameters was statistically analyzed by using SPSS 16.0.
Results and Discussion Plant Growth Parameters and Changes in Phenological Behaviour Elevated CO2 brought significant change in plant vigour (Fig. 1a). Due to sustained growth under elevated CO2 condition significant increase was observed in all the plant
Fig. 1 Changes in a different plant parts (leaf, root, stem) and b biomass distribution of Brassica spp. under elevated (E) and ambient CO2 (A) environment; CD(P=0.05) (V 9 T) are 1.39, 6.30 and 8.08 for vegetative, flowering, and post flowering stages respectively; ‘RH’ and ‘PG’ imply cultivars RH-30 and Pusa Gold, respectively
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K. Chakraborty et al. Table 1 Effect of Elevated CO2 on plant height, root length, branch number and leaf area in Brassica spp. under elevated CO2 (E) and ambient CO2 (A) conditions Conditions
Plant height (cm)
Root length (cm)
Branch no. (plant-1)
Leaf area (cm2)
PF
V
F
PF 1776.0
V
F
PF
V
F
PF
V
F
RH-E
39.7
165.3
248.0
15.2
26.0
30.7
8.3
12.0
13.0
1258.7
2695.8
RH-A
35.3
138.0
219.3
11.8
20.7
25.3
6.7
9.3
10.7
882.6
2035.9
1430.9
PG-E PG-A
36.7 31.0
132 112
187.3 155.0
11.5 8.7
19.7 16.3
20.7 17.3
7.7 6.3
10.3 8.7
12.0 11.3
1037.4 697.3
1973.2 1646.1
1621.9 1408.4
CD0.05 Var.
2.03
3.41
6.95
1.3
2.2
1.9
0.32
0.47
0.71
135.3
221.8
199.9
CD0.05 CO2
1.90
10.09
19.91
1.6
3.4
2.2
0.98
1.71
3.02
109.7
146.4
187.3
CD0.05 (Var. 9 CO2)
3.52
5.91
12.04
1.8
3.7
3.3
0.82
0.81
1.24
198.6
384.1
346.2
V vegetative, F flowering, and PF post flowering stages; ‘RH’ and ‘PG’ imply cultivars RH-30 and Pusa Gold, respectively Table 2 Effect of elevated CO2 on crop growth period in Brassica spp. under elevated CO2 (E) and ambient CO2 (A) conditions Conditions
Vegetative stage (DAS)
Reproductive stage (DAS)
Seed to maturity (DAS)
Seed filling period (days)
RH-E
54.7
85.6
152.4
56.8
RH-A
51.1
80.3
142.8
52.5
PG-E
45.5
72.4
138.2
55.8
PG-A
43.6
69.1
132.4
53.3
CD0.05 Var.
1.55
9.86
10.97
4.92
CD0.05 CO2
2.42
5.09
5.38
2.73
CD0.05 (Var. 9 CO2)
1.42
3.20
5.63
2.80
‘RH’ and ‘PG’ imply cultivars RH-30 and Pusa Gold, respectively
parts viz. leaf, stem and root. Further the effect can also be evidenced from increased plant height of elevated CO2 grown plants at flowering and post flowering stages in both the species. The increase in plant height were 19.6 and 16.1 % at flowering and post flowering stages, respectively in RH-30, while it showed comparatively less increase in Pusa Gold (17.8 % at flowering stage, and 14.8 % at post flowering stage) over ambient chamber (Table 1). The CO2 enrichment significantly increased the number of primary branches in both RH-30 (44.1 %) and in Pusa Gold (28.6 %), but the increase was more in RH-30 at flowering stage (Table 1). Similar to that of plant height and branch number elevated CO2 significantly increased leaf area in both the species. The highest increase in leaf area was observed in RH-30 (32.4 %) at flowering stage under elevated CO2 condition (Table 1). Elevated CO2 induced increase in plant growth in terms of fresh weights of shoots in Brassica [14] and plant height, stem thickness, total dry weight in tomato seedling is also reported by Juan et al. [15]. Primarily under elevated CO2 condition the overall morphological promotion of plant growth is through increased photosynthetic rates [16, 17] which ultimately resulted in increase in plant height, leaf area development and altered shoot to root ratio [17]. Like that of shoot growth significantly higher proliferation in root growth was also observed under elevated CO2.
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The increase varied from 25.8 % (flowering stage) to 21.9 % (post flowering stage) in RH-30 over ambient chamber; while the increase was 20.4 % (flowering stage) and 19.2 % (post flowering stage) in Pusa Gold (Table 1). Significant increase in root growth in the elevated CO2 grown rice plants was observed by Senewara [18]. Increased C supply under elevated CO2 condition is often found to induce root growth in crop plants than shoot growth [19]. Elevated CO2 brought about significant changes in phenological parameters in both the species (Table 2). The plants of RH-30 and Pusa Gold grown in elevated level of CO2 had taken almost 10 and 6 days, respectively, in total crop growth period from seed to maturity. Although the CO2 mediated increase in crop duration was observed in both vegetative and reproductive stages, but the effect was more in the duration of total reproductive phase and seed filling period. The delay in completion of reproductive phase as well as maturation of the soybean crop under elevated CO2 was also noticed [20]. Changes in Biomass Production and its Partitioning Changes in dry matter partitioning of different plant parts varied with both cultivars and crop growth stages under elevated CO2 condition (Fig. 1b). With respect to ambient CO2 condition, the root biomass increased about 17–28 and
Growth, physiology and biochemical responses of two different Brassica…
Net Assimilation Rate (NAR), Relative Growth Rate (RGR) and Net Photosynthesis Rate NAR was significantly higher under elevated CO2 condition; however the increase was higher in RH-30 (23.2 %) than Pusa Gold (19.2 %) (Fig. 2a). The increased level of CO2 also significantly enhanced the RGR in both the Brassica species (19.1 % in RH-30 and 17.4 % in Pusa Gold) (Fig. 2b). Similarly, rate of photosynthesis increased under elevated CO2 in both the Brassica species. The increase was maximum at flowering stage viz. 36.2 and 27.3 % followed by the vegetative stage (27.9 and 26.2 %) and post flowering stage (23.3 and 23.9 %) in RH-30 and Pusa Gold, respectively over ambient chambers (Fig. 3a). The photosynthetic rate was significantly higher in RH-30 in all three stages of growth irrespective of the CO2treatment imposed. Similar enhancement of photosynthetic rate under elevated CO2 was also observed in wheat cultivars [24]. Long et al. [25] reported that CO2 being an essential plant nutrient has tremendous potential to enhance crop growth and productivity when it is present in elevated level in the atmosphere. It can significantly increase the quality and quantity of produce by increasing net photosynthesis and water use efficiency [26]. Apart from increasing the net photosynthesis rate in the plants per se, elevated CO2 has proven to increase thermo-tolerance in C3 plants, which gives an indication towards better
a NAR (g cm-2 day-1)
19–24 % for RH-30 and Pusa Gold, respectively, spanning from vegetative to flowering stage. Similarly, significant increase in above-ground biomass i.e. stem and leaf was also observed under elevated CO2 in both the species. Highest percentage increase in root biomass was found at post-flowering stage which was significantly higher in magnitude than above-ground plant parts for both RH-30 (32.6 %) and Pusa Gold (30.9 %). Partitioning of dry matter between leaves, stems and roots is an important phenomenon when there is additional supply of C-substrate as observed in case of plants grown under elevated CO2 level [21]. In fact, without a concomitant increase in root biomass, greater aboveground biomass theoretically could alter key processes like water and nutrient uptake. Apart from stimulating the total photosynthetic rate and increment of above ground biomass, elevated CO2 can alter C partitioning/allocation of biomass more towards root tissue [22]. The increase in dry matter partitioning to roots at elevated CO2 could be an adaptive mechanism to control the efficiency of carbon gain [18]. More so, the plants having limited capacity to increase above ground canopy when there is extra supply of carbohydrate produced at elevated CO2 condition, tend to show greater partitioning of biomass to root as the below ground part possess higher elasticity in growth than above ground part [23].
0.00045 0.00040 0.00035 0.00030 0.00025 0.00020 0.00015 0.00010 0.00005 0.00000
b
Fig. 2 Changes in a net assimilation ratio (NAR) and b relative growth rate (RGR) under elevated CO2 (E) and ambient CO2 (A) conditions of Brassica. CD(P=0.05) (V 9 T) are 0.023 for (a) and 0.0012 for (b) respectively; V vegetative, F flowering, and PF post flowering stages; ‘RH’ and ‘PG’ imply cultivars RH-30 and Pusa Gold, respectively
adaptability in the crop species having greater ability to respond to elevated CO2 for future climate change scenario [27]. Stomatal Conductance and Respiration In contrast to photosynthetic rate measured, elevated CO2 significantly reduced the stomatal conductance in both the species. Reduction was observed to be highest at vegetative stage viz. 36.9 and 35.7 % in RH-30 and Pusa Gold, respectively. While at flowering and post flowering stages the stomatal conductance reduced at 18.7 and 19.8 % in RH-30, and 20.5 and 11.9 % in Pusa Gold (Fig. 3b). The stomatal conductance was greater in Pusa Gold than RH-30 irrespective of treatments. Reduction in stomatal conductance under elevated CO2 condition had been reported by many workers. There may be two possible mechanisms behind reduced stomatal conductance either by reducing the stomatal aperture per se under elevated CO2 condition [16] or it may be due to increase in boundary wall resistance of guard cells when there is high level of external CO2 [5]. Generally it is found that with doubling of external CO2 level stomatal conductance is found to decrease by 20–40 % [16].
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workers suggest increased rate of total respiration in elevated CO2 grown plants as they are supposed to have more respiratory substrate than ambient CO2 grown plants [29]. Biochemical Traits Reducing, Non-reducing and Total Sugar Content
Fig. 3 Changes in physiological parameters (a photosynthesis, b stomatal conductance, c respiration) under elevated and ambient CO2 environment over three growth stages of Brassica. CD(P=0.05) (V 9 T) are 1.53, 0.56 and 0.49 for (a); 0.43, 0.42 and 0.67 for (b) and 0.93, 1.20 and 0.85 for (c) for vegetative, flowering and pod development stages, respectively; V vegetative, F flowering, and PF post flowering stages; ‘RH’ and ‘PG’ imply cultivars RH-30 and Pusa Gold, respectively
Carbon dioxide enrichment significantly reduced the rate of respiration, as a complimentary factor of increased photosynthesis rate. Higher reduction was accounted in Pusa Gold at flowering and post flowering stages (18.9 and 22.3 %, respectively) as compared to that of RH-30 at flowering and post flowering stages (11.5 and 16.4 %, respectively) (Fig. 3c). Gifford [28] reported that elevated CO2 reduced the growth as well as maintenance respiration in wheat plants, especially when they were exposed to higher level CO2 for a longer period of time. But other
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Elevated CO2 significantly increased the non-structural carbohydrates in terms of reducing and non-reducing sugar content in the leaves. In RH-30 the increase in reducing sugar content were observed as 26.6, 36.1 and 23.1 % at vegetative, flowering and post flowering stages, respectively. However, in Pusa Gold the same was increased only at flowering (30.4 %) and post flowering (18.4 %) stages with a lesser magnitude (Table 3). Overall the content of reducing sugar was more in RH-30 than Pusa Gold. Nonreducing sugar content also showed the similar trend under elevated CO2, whereas CO2-induced increases were 34.5 and 22.6 % in RH-30 and 29.7 and 19.9 % in Pusa Gold at flowering and post flowering stages, respectively (Table 3). The total sugar content significantly increased at vegetative (12.5 %), flowering (35.3 %) and post flowering (22.9 %) stages in RH-30 under elevated CO2, whereas Pusa Gold showed the increase only at flowering (30.0 %) and post flowering stages (19.4 %) (Table 3). The increase in soluble carbohydrate level in the leaf of elevated CO2 grown plants has been reported long back [30]. But, often it is found that differential control in relative distribution of these mesophyllic cytosolic carbohydrate levels ultimately determine the photosynthetic acclimation and overall response of a particular species to elevated CO2 [31]. In the present study too, we found relatively higher increase in leaf sugar level in more responsive B. juncea species than B. campestris under elevated CO2 condition. Starch Content Similar to that of leaf sugar content, CO2 enrichment significantly increased the leaf starch content in both the species. The increase was 39.4, 46.0 and 30.8 % in RH-30 and 36.7, 44.5 and 26.5 % in Pusa Gold at vegetative stage, flowering stage and post flowering stages, respectively (Table 3) which again suggest an average elevated CO2 mediated change in leaf carbohydrate level was invariably higher in B. juncea than B. campestris. Hogy and Fangmeier [32] reported higher accumulation of starch content in elevated CO2 grown wheat plants which finally resulted in increased grain starch content due to efficient translocation from the source (leaves and stem) to sink (grain) tissue.
Growth, physiology and biochemical responses of two different Brassica… Table 3 Changes in biochemical traits in leaves of Brassica spp. under elevated CO2 (E) and ambient CO2 (A) conditions Conditions
Reducing sugar (mg g-1 DW) V
F
PF
Non-reducing sugar (mg g-1 DW)
Total sugar (mg g-1 DW)
V
V
F
PF
F
Starch (mg g-1 DW) PF
V
F
Protein (mg g-1 DW) PF
F
PF
RH-E
10.92
23.51
14.83
13.19
25.44
18.26
24.12
48.90
33.12
231.4
301.5
240.2
16.73
9.21
RH-A
8.69
17.28
12.06
12.70
18.91
14.89
21.44
36.20
26.95
166.0
206.5
183.6
21.79
12.09
PG-E PG-A
6.82 6.48
17.50 13.39
11.50 9.61
9.43 9.27
23.69 18.27
13.87 11.57
16.28 15.72
41.13 31.65
25.34 21.24
173.8 127.1
240.8 166.7
182.9 144.6
12.39 16.86
6.28 7.78
CD0.05 Var.
0.71
0.77
0.85
0.23
0.40
0.29
1.18
4.68
1.05
16.1
15.5
12.6
0.87
0.62
CD0.05 CO2
1.30
3.57
1.46
0.36
0.30
0.28
2.25
3.97
1.25
14.7
28.0
23.8
1.32
0.94
CD0.05 (Var. 9 CO2)
1.23
1.34
1.47
0.40
0.69
0.50
2.04
8.12
1.82
27.8
26.9
21.8
1.52
1.08
V vegetative, F flowering, and PF post flowering stages; ‘RH’ and ‘PG’ imply cultivars RH-30 and Pusa Gold, respectively
Total Soluble Protein Content Unlike the leaf carbohydrate level, the total soluble protein content in the leaves significantly reduced due to elevated CO2 treatment. The reduction was 23.2 % in RH-30 and 26.5 % in Pusa Gold at flowering stages over the ambient chamber. However, at the post flowering stages the reduction was 23.8 % in RH-30 and 19.3 % in Pusa Gold (Table 3). The excessive accumulation of carbohydrates in leaves often alter the C:N balance of the elevated CO2 grown plants resulting in lower level of soluble protein content (when calculated per unit biomass basis) in the leaf mostly due to dilution effect [7, 24]. Studies showed that not only in leaves but the grain protein concentration also gets reduced in the magnitude of 5–15 % due to elevated CO2 depending upon time and method of exposure [33]. Change in the activity of C- and N-metabolizing enzymes was reported under both increased level of CO2 and temperature. Balancing of C and N metabolism could well be the important regulatory adaptation strategy to Brassica in future climatic conditions [34].
Yield and Yield Attributes The elevated CO2 significantly increased seed yield in both RH-30 (13.2 %) and Pusa Gold (12.2 %). The CO2 enrichment brought significant increase in the seed weight and harvest index of both RH-30 and Pusa Gold (Fig. 4). However, the 1000 seed weight of Pusa Gold was more irrespective of the treatments. Elevated CO2 brought about substantial increase in grain yield in other crops too [18]. Similarly, change in the thousand grain weight in wheat was reported under elevated CO2 which further increased the yield, based on the development of the number of grains (more ears per m2) rather than heavier kernels [35]. The present study showed excess carbohydrates produced during vegetative and early reproductive phases helped in
Fig. 4 Effect of elevated CO2 on a 1000 seed weight and b yield under elevated CO2 (E) and ambient CO2 (A) conditions of Brassica; CD(P=0.05) (V 9 T) are 0.39 and 87.3 respectively for (a, b). V vegetative, F flowering, and PF post flowering stages; ‘RH’ and ‘PG’ imply cultivars RH-30 and Pusa Gold, respectively
generation and development of more new sinks which ultimately contribute to the higher productivity of the crop.
Conclusion It can be concluded that elevated CO2 helped to sequester more carbon in plant parts leading to the accumulation of greater carbohydrate contents in Brassica leaves.
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Differential responses in growth, gas exchange behavior and carbohydrate accumulation in two Brassica species characterizes their overall response to elevated level of atmospheric CO2. The present investigation, outlining the growth, physiological and biochemical responses clearly showed better relative performance of B. juncea species (RH-30) to the elevated CO2. The effect of elevated CO2 in crop growth duration and life cycle may prove to be crucial from agricultural perspective with more focus on per day productivity of the crop. On the other hand, significant change in C and N balance (with higher carbohydrate and lower protein concentration) in the plants may attract special attention to altered nutritional management in crop plants especially regarding the use of nitrogenous fertilizer to reduce the elevated CO2 induced widened C:N ratio in these two species. The information generated in the present study would definitely prove useful in future crop improvement programme and development of efficient agronomic package of practices under changing global climate scenario. Acknowledgments First author is grateful to ICAR, New Delhi for receiving financial support during the period of study. Compliance with Ethical Standards Conflict of interest There is no conflict of interest regarding the content of the paper and all the authors agreed to publish.
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