Phd

The current experiment entitled “Evaluation of CO2 enrichment effects on resource utilization in cowpea (Vigna unguiculata L.) and amaranthus (Amaranthus tricolor L.)” was undertaken with the objective to study the impact of CO2 enrichment on cowpea and amaranthus under varying moisture, temperature and nutrient regimes. Four sets of pot culture experiments were conducted during 2015 to 2018 with two varieties of cowpea, Lola and Vellayani Jyothika and Arun variety of amaranthus. The technology used for CO2 enrichment was Open Top Chamber (OTC) system established under Department of Plant Physiology, College of Agriculture, Vellayani. Carbon dioxide was released from CO2 cylinders to one of the two OTC’s bringing the CO2 level to 600 ppm and the second OTC worked as control at ambient CO2 for chamber effect. The experiments were laid out in CRD factorial.
First experiment was conducted to study the varietal variation in cowpea in response to CO2 enrichment through OTC. Experimental plants were maintained in OTC from sowing to harvest. Observations were taken at biweekly intervals till 3 months. In this study highest values were recorded in variety Lola for number of leaves per plant (79.5), specific leaf area (208.78 cm2 g-1), root weight (14.91 g), shoot weight (65.05 g), root shoot ratio (0.229), total dry matter production (79.98g), single pod weight (12.88 g), number of seeds per pod (12.34) and early flowering was also observed under elevated CO2 condition. In Vellayani Jyothika, highest values were recorded for number of pods per plant (11.75), total yield (102.59 g/plant) and total chlorophyll content (0.897 mg g-1), stomatal frequency (2203.84 cm-2), starch (14.26 mg g-1) and reducing sugar (15.97 mg g-1), and fibre content (1.34 mg g-1) under elevated CO2 condition. Parameters like total soluble protein recorded lower values (8.75) under CO2 enrichment. Quality parameters were modified with a reduction in total protein content (15.76, 14.75 mg g-1) and increase in fibre content (1.34, 1.23 mg g-1). Among the two varieties of cowpea, Vellayani Jyothika was found to be the best



responding variety to elevated CO2 in terms of yield parameters and so was selected for further experiments.
In the second experiment evaluation of plant response to elevated CO2 under different soil moisture regimes were evaluated. Two weeks old potted plants were shifted to OTCs. All the three sets of plants were maintained at field capacity (FC) initially. Soil moisture levels were brought down to 80% and 70%, in the second and third sets 30 days after planting and were maintained for a period of 30 days at these soil moisture regimes in OTCs.
The result indicated an improvement in growth performances of cowpea and amaranthus under mild and severe moisture stress conditions (80% and 70% FC) in terms of increased number of leaves (46.82, 43.22), specific leaf area (360.43, 261.58 cm2 g-1) root weight (9.02, 8.51 g), shoot weight (30.56, 22.16 g), root shoot ratio (0.327, 0.216) and dry matter production (38.98, 29.67g) respectively. The same trend was found in the case of amaranthus for number of leaves per plant (41.00, 37.66), specific leaf area (171.25, 157.59 cm2 g-1), plant height (79.66, 72.32 cm), root weight (0.840, 0.416 g), shoot weight (4.740, 3.031 g), root shoot ratio (0.197, 0.130) and dry
matter production (4.82, 4.71 g).

In the case of cowpea CO2 enrichment induced early flowering in all the three soil moisture conditions. Significant increase in yield was also obtained under stress condition (78.51 and 77.08 g/plant) due to increase in number of pods per pod (8.67, 7.32), single pod weight (11.63, 10.36 g), number of seeds per pod (9.33, 8.75) both
under 80% and 70% FCs.

In cowpea, total chlorophyll content (1.671, 1.238 mg g-1), RWC (85.24, 77.97
%), stomatal frequency (2144.00, 1964.53 no cm-2), starch (6.12, 5.69 mg g-1),
reducing sugar (12.48, 12.09 mg/g), phenol content (0.943, 0.801 mg g-1) free amino
acid content (5.960, 4.823 mg/g), SOD activity (3.466, 4.230 g-1minute-1), ascorbic
acid content (6.87, 5.84 mg/100g). Reduction of transpiration rate (0.547, 0.335 mmol


water m-2 s-1) total soluble protein (6.02, 5.13 mg g-1), membrane integrity (% leakage) (37.80, 34.61%) under CO2 enrichment after stress. The same trend was found in the case of amaranthus total chlorophyll content (1.245, 1.206 mg g-1), RWC (84.98, 79.37%), stomatal frequency (691.16, 573.78 no cm-2), reducing sugar (17.61,
13.56 mg g-1), starch (2.66, 2.53 mg g-1), phenol content (6.20, 3.53 mg g-1) free amino acid content (1.071, 1.036 mg g-1), SOD activity (1.842, 1.526 g-1minute-1), ascorbic acid content (36.93, 28.40 mg/100g), reduction of transpiration rate (2.093, 1.410 mmol water m-2 s-1) total soluble protein (15.42, 15.06 mg g-1), membrane integrity (3.480, 3.017%) under elevated CO2.
Evaluation of plant responses to elevated CO2 under different soil nutrient regimes was carried out in the third experiment. Potted plants of cowpea and amaranthus (Variety Arun) were used for conducting the experiment. Plants were maintained at FC at four nutrient levels throughout the crop period. The best performance given by plants receiving nutrients as per POP recommendation along with 25% extra nitrogen In cowpea, the values were recorded as follows, number of leaves (76.00), specific leaf area (468.95 cm2 g-1), dry root weight (42.0%), dry shoot weight (0.5%), root shoot ratio (4.9%). total dry matter production (117.58 g), number of pods per plant (16.66), single pod weight (15.83 g), number of seeds per pod (13.33) and total yield (169.53 g/plant). In the case of physiological and biological parameters also this level of nutrient application recorded maximum values for total chlorophyll content (1.528 mg g-1), stomatal frequency (2782.01 no cm-2), total soluble protein (20.25 mg g-1), starch (13.88 mg g-1), reducing sugar (14.65 mg/g), total protein (15.25 mg g-1) and fibre content (1.18 mg g-1) and The highest number of root nodules per plant (45.26) and highest nutrient use efficiencies for N, P and K (1.013, 2.675, 0.293 g) were recorded under this treatment.
In amaranthus, higher values were recorded in for number of leaves per plant (52.11), specific leaf area (316.20 cm2 g-1), dry root weight (2.13 g), dry shoot weight


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(4.34 g), root shoot ratio (0.64 g) and total dry matter production (10.47 g). Total chlorophyll content (1.542 mg g-1), stomatal frequency (705.64 no cm-2), total soluble protein (20.25 mg g-1), starch (3.29 mg g-1), reducing sugar (23.14 mg g-1). Calcium content (23.69 mg g-1), Fe content (6.71 mg g-1) and ascorbic acid content (43.51 mg/100g), under elevated CO2 condition.

Though a C4 plant like amaranthus also responded to CO2 enrichment, extend of increase in growth and dry matter production was less compared to cowpea, which can be due to the innate CO2 enrichment mechanism present in C4 systems.

The fourth experiment was conducted to study the temperature and humidity interaction with CO2 enrichment. Potted plants of cowpea and amaranthus (variety Arun) were used for conducting the experiment. Plants were maintained at FC throughout the crop period as per POP recommendations of KAU. One set of plants were exposed to mist and the second set was maintained without exposure to mist.

In cowpea, highest values were recorded by plants exposed to mist for number of leaves per plant (76.14), specific leaf area (471.07 cm2 g-1), dry root weight (21.74 g), dry shoot weight (72.46 g), root shoot ratio (0.302), dry matter production (104.2 g), single pod weight (15.93 g), number of pods per plant (18.75), number of seeds per pod (14.00), total yield (175.36 g/plant), RWC (96.48%), total chlorophyll content (1.651 mg g-1), stomatal frequency (2724.83 no cm-2), starch (13.29 mg g-1), reducing sugar (15.71 mg g-1), phenol (1.128 mg g-1), Free amino acid (6.398 mg g-1), SOD activity (3.56 g-1minute-1) and ascorbic acid content (9.36 mg/100g), Early flowering was induced in this set of plants. Parameters like transpiration rate (1.394 mmol water m-2 s-1) total soluble protein (8.82 mg g-1), membrane integrity (43.92% leakage) recorded lower values under CO2 enriched treatments.
In amaranthus, higher values were recorded under mist condition for number of leaves (48.51), specific leaf area (327.68 cm2 g-1) dry root weight (2.160 g), dry


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shoot weight (6.74 g), root shoot ratio (0.517), dry matter production (8.90 g). RWC (95.38 %), Total chlorophyll content (1.382 mg g-1), stomatal frequency (694.02 no cm-2), starch (4.19 mg g-1), reducing sugar (23.02 mg g-1), phenol (7.92 mg g-1), Free amino acid (1.536 mg g-1), SOD activity (2.44 g-1minute-1) and ascorbic acid content (42.75mg/100g). Parameters like transpiration rate (12.36mmol water m-2 s-1), total soluble protein (19.05 mg g-1) (25.40 %) and membrane integrity (% leakage) (6.47 % leakage) recorded lower values. Significant improvement in plant performance and increase in yield are seen under CO2 enrichment with mist exposure in the cases of cowpea and amaranthus
The present study shows the existence of varietal variation in the crop responses under CO2 enrichment gives option for selection of varieties with better yield and quality under the changing climatic condition. Elevated CO2 concentration is found to be improve stress tolerance through better photosynthetic rate and activation of defence mechanism. Improved production technologies can be developed especially with mist facility with minimizing irrigation requirement. This can also be utilized for enhancement of antioxidant production which are economically valuable secondary metabolites. Exploitation of soils lacking sufficient nutrient and water can be done through the introduction of low cost CO2 enrichment methods. Since soil moisture and temperature are the primary determinants of nutrient availability and acquisition plant nutrition can strongly be influenced by global climate change. This necessitates site specific CO2 enrichment studies.
The present study showed the existence of varietal variation in the crop responses under CO2 enrichment which gives option for selection of varieties with better yield and quality under the changing climatic scenario. Elevated CO2 concentration is found to improve the performance of plants grown under low soil moisture levels by improving the performance of photosynthetic machinery and by activating defence mechanisms. Based on this, improved high-tech agriculture


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production technologies with mist facility can be developed with minimum irrigation requirement which will ensure maximum water use efficiency.
This also gives a possibility of utilizing the interactive effects of different cultivars, CO2 enrichment, and other abiotic factors for enhancing the production of antioxidants, many of which are economically valuable secondary metabolites.
The present programme also opens up possibilities of quality improvement of agricultural products based on the interaction of elevated CO2 with factors like cultivars, growth stages, light, nutrient and abiotic stress factors. Intensification of cultivation and quality improvement are equally important to address the new challenges of global health because many of the economically important crops, when grown under field conditions at the elevated atmospheric CO2were reported to have deleterious impacts on quality.
The present study indicated the improved performance of cowpea under CO2 enrichment with additional nitrogen input. This points towards the changing nutrient requirement of crop plants under the current scenario of increasing CO2 concentration and suggests for bringing out modifications in the nutrient recommendations with additional nutrients, especially nitrogen. Exploitation of soils lacking sufficient nutrient and water also can be done through the introduction of low cost CO2 enrichment methods. Since soil moisture and temperature are the primary determinants of nutrient availability and acquisition, plant nutrition can strongly be influenced by global climate change. So this study also points to the requirement of site specific CO2 enrichment studies.