Submitted by:S. Shaheda NasreenTAM/13- 25

Increased concentration of Co2 effects on crop

production

Effect of elevated carbon dioxide on crops

• Carbon dioxide is essential to plant growth. Rising CO2 concentration

in the atmosphere can have both positive and negative consequences.

• Increased CO2 is expected to have positive physiological effects by

increasing the rate of photosynthesis. ('carbon dioxide fertilisation‘). Currently, the amount of carbon dioxide in the atmosphere is 380 parts per million and oxygen is 210,000 ppm.

• Plant physiological and biochemical responses (Bowes 1993) to

elevated CO2, known as the CO2-fertilization effect (Dhakhwa et al.

1997), have been studied in plants with different photosynthetic pathways, mostly in C3 species, but also in C4

Effects of Rising Atmospheric Concentrations of Carbon Dioxide on Plants

• Atmospheric concentrations of carbon dioxide have been steadily rising, 315 ppm (parts per million) in 1959 to 385 ppm (Keeling et al.,2009).

• Rising CO2 concentrations are also likely to have profound direct effects on the growth, physiology, and chemistry of plants, independent of any effects on climate (Ziska 2008).

• Our knowledge of plant responses to future CO2 concentrations rests on the results of experiments that have experimentally increased CO2 and then compared the performance of the experimental plants with those grown under current ambient CO2 conditions.

Change in climate.

Physiological effects of plant due to elevated CO2

1. Behavior of stomata

2. Effects on the leaf

3. Effects on photosynthesis & photorespiration

4. Water use and water use efficiency

5. Changes in rooting pattern

6. Effect of CO2 on Nitrogen content

7. Germination

8. Decrease in crop duration

9. Effects on seed yields

10. Consequences on quality of food and forage

Effect of stomata • Elevated concentrations of CO2 –

partial stomatal closure.

• Reductions stomatal conductance in

crops would translate into reductions

of <10% in evapotranspiration, partly

because of increases in temperature

and decreases in humidity in the air

around crop leaves.

• Due narrowing the stomata has

additional benefit that a lesser amount

of pollutants in the air will make it

through the narrower openings.

Effects on the leaf• Growing plants at elevated concentration leads to increased

leaf area, leaf area index , leaf area duration and leaf thickness

as indicated by decreased specific leaf area (SLA) (Bowes

1993; Bray and Reid 2002), which is partly related to the

accumulation of non-structural carbohydrates (Lambers et al.

1998).

• Accumulation starch increased steadily at a rate of about 6

g/kg dry matter/hour.

• Elevated CO2 causes plants to produce more number of

mesophyll cells and chloroplasts

Effects on photosynthesis & photorespiration

• Photosynthesis :- 6CO2 + 6H2O → C6H12O6 + 6O2

• photosynthetic capacity per unit leaf area is increased under CO2 enrichment.

• The CO2 fertilization effect begins with enhanced photosynthetic CO2 fixation.

• Non-structural carbohydrates tend to accumulate in leaves and other plant

organs as starch, soluble carbohydrates or polyfructosans, depending on species.

• This may be because the CO2-enriched plants do not have an adequate sink

(inadequate growth capacity), or lack capacity to load phloem and translocate

soluble carbohydrates.

• Hence Improvement of photoassimilate utilization should be one goal of

designing cultivars for the future (Hall and Allen, 1993).

Photograph of representative plants that we carefully removed from each of our three experimental units.  The mid- and high-CO2 plants appear to have nearly identical root systems, while the root system of the low-CO2 plant is not much smaller.  In terms of aboveground growth, however, there are considerably larger differences.  The low-CO2 plant is much smaller than the others; and the plant from the high-CO2 unit is significantly larger than the plant from the mid-CO2 unit.

Water-use efficiency: effects of CO2

• Water-use efficiency is the ratio of the net gain in dry matter

over a given period, divided by the water loss (from the

vegetation alone or from soil and vegetation together) over the

same period.

• Stomatal conductance decreases with increasing

CO2 concentration which can cause a reduction of both leaf

and whole canopy transpiration.

• WUE increased with increasing CO2 due to the decline in ET

CO2 effect on Nitrogen content

• Plants with nitrogen-fixing symbionts (e.g., peas, beans, alfalfa), under favorable

environmental conditions for both symbiont and plant, tend to benefit more

• For most plants, growth under elevated CO2 can alter the internal balance between carbon

and nitrogen.

• The content of nonstructural carbohydrates generally increases under high CO2, while the

concentrations of mineral nutrients and proteins are reduced (Mooney and Koch, 1994;

Rogers et al., 1994 ).

Decrease in tissue nitrogen is likely due to several factors:

1. Dilution of nitrogen from increased carbohydrate concentrations;

2. Decreased uptake of minerals from the soil, as stomatal conductance decreases and

plants take up less water

3. Decreases in the rate of assimilation of nitrate into organic compounds

Changes in rooting pattern

• High carbon gain might increase root length, diameter and number (Lee-Ho

et al. 2007), and stimulate lateral root production in plants grown under

elevated CO2 (Pritchard and Rogers 2000). A shift in biomass allocation

from leaves to roots can occur under CO2 enrichment (Stulen and Den

Hertog 1993).

• longer stems and extended large roots with altered branching patterns

(Rogers et al. 1992; Bowes 1993).

• Root/shoot ratios often increase under elevated CO2 levels favouring root

crops and also contribute to soil organic matter build-up (Mauney et al.,

1992; Mitchell et al., 1993)

Decrease in crop duration

• Duration of crop growth cycles are above all, related to temperature. An

increase in temperature will speed up developmen.

• Sylvan Wittwer, quoted above, states that under most circumstances the

availability of CO2 is the factor which limits growth. Thus with a higher

level of CO2 in the air plants can grow faster with a higher temperature.

Germination• Increased CO2 concentration will decrease the rate of germination.

Effects on seed yields• Reproductive biomass growth as well as vegetative biomass growth are usually

increased by elevated CO2.

• However, the harvest index, or the ratio of seed yield to above-ground biomass

yield, is typically lower under elevated CO2 conditions (Allen, 1991; Baker et

al., 1989), which may also be evidence of the lack of capacity to utilize

completely the more abundant photoassimilate.

• C3 plants exhibit an increased production averaging about 30% at doubled (700

ppm) CO2 concentrations; both biomass and seed production show an increase

in almost all experiments under controlled conditions (Cure and Acock, 1986;

Rogers and Dahlmann, 1993).

• Plant growth and yield of soybean were increased by 45% with 1200ppm CO2.

Quality of food and forage• Protein concentrations in plant tissues are closely tied to plant

nitrogen status• Apart from an overall decrease in N and protein concentrations, as

shown under elevated CO2, the nutritional value and the quality of the edible products of most food and forage crops are largely unknown.

• For wheat, barley and rice, the reduction in grain protein ranged from 10% to 15% of the value of ambient CO2 (315–400 ppm).

• Overall decrease for most macronutrients and micronutrients such as Fe, Zn, Mn and Cu under high CO2, with nutrient concentrations more affected in straw than in grains, although the responses to elevated CO2 were species- and cultivar-dependent.

• Quality of forage crops decreases due higher c:n ratio

Rising atmospheric CO 2

may affect oil quality and seed yield of sunflower (Helianthus annus L.)

• Quality and yield in a sunflower hybrid DRSH 1 and variety DRSF 113, raised inside open top chambers and exposed to elevated CO 2 (550 ± 50 ). Elevated CO2 exposure significantly influenced the rate of photosynthesis, seed yield and the quality traits in both hybrid and variety.

• Plants grown under elevated CO2 concentration showed 61–68 % gain in bio-mass and 35–46 % increase in seed yield of both the genotypes, but mineral nutrient and protein concentration decreased in the seeds.

• Fatty acid compo-sition in seed oil contained higher proportion of unsatu-rated fatty acids (oleic and linoleic acid) under elevated CO 2 treatment, which is a desirable change in oil quality for human consumption.

Positive effects of CO2 on crop production• Elevated carbon dioxide increases the productivity and water use efficiency

of nearly all plants.• Higher levels of atmospheric CO2 improve, and sometimes fully compensate

for, the negative influences of various environmental stresses on plant growth.

• Health promoting substances found in various food crops and medicinal plants have been shown to benefit from rising atmospheric CO2.

• Elevated CO2 reduces, and frequently completely overrides, the negative effects of ozone pollution on plant photosynthesis, growth and yield.

• On the whole, CO2-enrichment does not increase the competitiveness of weeds over crops; higher atmospheric CO2 will likely reduce crop damage from insects and pathogenic diseases.

• In addition to enhancing forage productivity, atmospheric CO2-enrichment will likely not alter its digestibility by animals.

Negative effects

• CO2 is currently responsible for over 60% of the enhanced greenhouse effect.

• A new study, the first of its kind, performed by researchers at the University of California, Davis, demonstrated the inhibition of wheat crops to convert nitrate into a protein, due to increased CO2 levels, which affects its nutritional value.

• Increased CO2 concentration will decrease the rate of germination

• Food quality is declining under the rising levels of atmospheric carbon dioxide that we are experiencing

• The results showed that not only are amino acids like protein affected, but trace elements as well as, There was a 14 percent increase in lead and an eight percent drop in the iron content of the crop.

• If carbon dioxide levels continue to rise and negatively effect plants and crops, the amount of food proteins in the whole world could drop as much as three percent in just a few decades. There are already people all around the world without enough food or proper nutrition, especially protein.

Effect of CO2 on C3 and C4 plants

• Experiments concerning crop performance at elevated CO2 concentrations in general

show a positive but variable increase in productivity for annual crops (Kimball,

1983; Strain and Cure, 1985; Cure and Acock, 1986; Allen et al)

• C3 plants exhibit an increased production averaging about 30% at doubled (700

ppm) CO2 compaired to C4 plants

49% for C3 cereals,

20% for C4 cereals and

15% for CAM plants (Idso and Idso, 2000).

• The extent and occurrence of physiological adaptations of the photosynthetic

apparatus, particularly of perennial plants, to long-term exposure to high CO2

concentrations—which is more directly relevant to long-term climate change—are

still unreported.

Graph showing effect on photosynthesis

It is seen that the extra CO2 increases the optimum temperature for net photosynthesis by about 11o C: from 25o C in air of 325 ppm CO2 to 36oC in air of 1935 ppm CO2

The CO2 – Temperature- Growth interaction

IPCC (FACE)• The most widely used experimental system is the open-top chamber.

Free-air CO2 enrichment (FACE) experiments are more expensive but

attempt to create conditions close to those likely to be experienced in

an open field. Initial results from these experiments confirm the basic

positive response of crops to elevated CO2 but studies have been

conducted only for a few crops (Mauney et al., 1992).

• Crop traits are selected and bred into different varieties to produce

high yields for different climate and resource conditions.

• The separate and combined effects of elevated CO2 and high

temperature on plants have been studied, either in growth chambers, in

greenhouses or in the field

Free-air carbon dioxide enrichment(FACE) allows experiments with controlled atmospheric concentrations of carbon dioxide

to be conducted in the field

phytotrons

• Elevated CO2 also leads to changes in the chemical composition of plant tissues. Due to

increased photosynthetic activity, leaf nonstructural carbohydrates (sugars and

starches) per unit leaf area increase on average by 30–40% under FACE elevated

CO2 (Ainsworth 2008; Ainsworth & Long 2005).

• Leaf nitrogen concentrations in plant tissues typically decrease in FACE under elevated

CO2, with nitrogen per unit leaf mass decreasing on average by 13% (Ainsworth & Long

2005).

• Crop yield in FACE also appears to be enhanced by elevated CO2 to a lesser extent under

low-N than under high-N (Ainsworth & Long 2005; Ainsworth 2008; Long et al. 2006).

Estimated future level of CO2

year CO2 ppm 2015 389-3992050 463-6232100 700-1099

Adaptation / mitigation actions could include the following:

1. Selection of plants that can better utilize carbohydrates and produce less structural matter and more reproductive capacity under CO2 enrichment.

2. Search for germplasms that are adapted to higher day and night temperatures, and incorporate those traits into desirable crop production cultivars to improve flowering and seed set.

3. Change planting dates and other crop management procedures to optimize yields under new climatic conditions.

4. Shift to species that have more stable production under high temperatures or drought.

5. Determine whether more favourable N:C ratios can be attained in forage cultivars adapted to elevated CO2.

6. Where needed, and where possible, develop irrigation systems for crops.

7. Micro-algae can fix carbon dioxide from different sources, which can be categorised as:

• CO2 from the atmosphere.• CO2 from industrial exhaust gases (e.g., flue gas and flaring gas).• Fixed CO2 in the form of soluble carbonates (e.g., NaHCO3 and Na2CO3).• Can be grown in closed systems, which could result in savings of precious

freshwater resources.

Summary and conclusions

• Elevated CO2 increases the size and dry weight of most C3 plants and plant

components.

• The harvest index tends to decrease with increasing CO2 concentration and

temperature.

• Selection of plants that could partition more photoassimilates to

reproductive growth should be a goal for future research.

• C4 plants include most tropical and sub-tropical grasses and several

important crops, including maize (corn), sugar cane, sorghum, and the

millets. There has therefore been considerably more research on the

responses to elevated CO2 in C4 than in CAM plants.

• Rising CO2 over the next century is likely to affect both

agricultural production and food quality.

• Elevated CO2 concentration generally compensates for the

negative effects of warming temperatures on production.

Moreover, positive effects of elevated CO2 concentration on

grain yield increase with warming temperatures. The findings

could be critical for climate change-driven agricultural

production that ensures global food security.

Thank you....