Photosynthesis: The Effect Of Different Light Conditions And Different CO2 Concentrations On The Growth Of Eruca Sativa Plants Leaf

Introduction

Plants have developed highly sensitive and selective mechanisms that detect different aspects of their environment and respond to them. In plant production, light and temperature are two of the most commonly controlled environmental factors. Light is extremely important because plants rely on it for energy and survival. Several different photosensory systems perceive the quantity, quality and direction of light, which together regulate almost all phases of plant development, presumably to maintain photosynthetic efficiency (R.P. Hangarter, 1997). Light also provides the energy for photosynthesis which is the biochemical process that supports the food chain to convert carbon dioxide (CO2) and water into sugars and oxygen, Amane Makino’ and Tadahiko Mae (2002). Most biological growth depends on light and temperature however, the ‘optimal’ temperature for photosynthesis, is dependent on CO2 concentration. CO2 concentration also have a potentially dramatic effect on photosynthesis. Even though co2 has a negative impact on the environment it is a main component for photosynthesis and thus subtly increases plant growth. Photosynthesis increases as CO2 increases until a certain concentration is saturated. Enriching air with CO2 makes it easy for plants to use light more effectively. However, long-term CO2 enrichment reduces the initial stimulation of photosynthesis over a period of weeks to months and then frequently suppresses photosynthesis, Amane Makino’ and Tadahiko Mae (2002).. The way that each plant is affected by these factors differ from a plant another. This experiment was conducted to investigate on how different light conditions (high and low) and different CO2 concentrations (Ambient 400 ppm and elevated 1000ppm) affect the growth of Eruca Sativa plants.

In order to observe how different factors, affect the growth of an Eruca Sativa plant, a plant was taken from four different growth environments in regard to the amount of light and CO2 concentration with no water of nutrition limitation. Then, each plant from each environment was measured and results were recorded.

It was hypothesised that if the plant grew in high light and elevated CO2 concentration it will result in a larger leaf area. And plants that grew in low light and ambient amount of concentration will result in a smaller Leaf area.

Results

Results show that plants that grew up in an environment where they were exposed to elevated CO2 (1000 ppm) and high light were fairly large in regard to leaf area which was 48.2

cm2, and significantly larger than the leaf area of the plant that grew in an elevated CO2 (1000 ppm) and low light environment which was 33.0 cm2. Results also show that plants that grew in an ambient CO2 (400 ppm) and low light environment are slightly smaller in leaf area (31.5 cm2) than the plants that grew in elevated CO2 concentration (1000 ppm) and low light environment which had leaf area of 33.0 cm2.. T test results show that there is no significant different between Ambient CO2, Low Light and Elevated CO2, Low Light, as results are (t= 1.20, df=198, p=0.23). However, there appears to be a significant difference between Elevated CO2, Low Light and Elevated CO2, High Light as results are (t= 10.46, df=198, p=1.14293 x10-20).

Discussion

The plants of Eruca Sativa are typically grown as lettuce-like salad green in home gardens for culinary use. It grows in rich moist soils in full sun to part shade. It is best grown in the cooler spring and fall months of the year, not in the summer heat. In this study it was hypothesised that high light and elevated CO2 (1000 ppm) would result in a larger leaf area. Results show that the plant that grew in high light and elevated CO2 (figure 1) conditions were relatively larger in regard to leaf area compared to plants that grew in low light and ambient CO2 (figure 2). The results somehow support the hypothesis as there is a biological reason behind that but there are also limitations and other factors that might have influenced these results that weren’t tested in this study.

Both CO2 and light are key variables affecting plant growth whether it was positively or negatively. Light is the main source of energy for plant photosynthesis and an environmental signal for plant growth and structural differentiation. Plants grown in different light intensities from full sun to darkness show characteristic different in growth and development. Light doesn’t have a direct effect on plants instead its increased growth by raising temperature and increasing photosynthesis (H. F. Thut and W. E. Loomis). Plant growth is strongly affected by the quality of light that refers to the colours or wavelengths that reach the surface2 of a plant. Red (R) and blue (B) lights have the greatest impact on plant growth as they are the major sources of energy for plant photosynthetic CO2 assimilation (J.W. Hart ,1998). It also affects plant’s morphology, metabolism and photosynthesis as these are all factors that promote growth in plants (Res. J. Biotech, 2014). This explains why plants that were exposed to high light showed a larger growth in leaf size (Figure 1). The enrichment of CO2 stimulates photosynthesis and growth. It also enhances plants mass, Hendrick Porter and Marie Laure Navas (2003) . However, the effects on photosynthesis of long-term CO2 enrichment vary depending on the type of plant as Oecologia (1979). CO2 enrichment typically increases the productivity of C3 plants, but in C4 species the effect is minimal (G. BOWES) . Prolonged exposure to CO2 enrichment reduces initial photosynthesis stimulation in many species and often suppresses photosynthesis. These responses are related to secondary responses related to excess accumulation of carbohydrates rather than direct CO2 responses. Carbohydrate accumulation is sometimes associated with decreased net photosynthesis, which may cause feedback inhibition of RuBP / Pi regeneration capacities or disruption of chloroplast. Carbohydrate accumulation in leaves can lead to photosynthetic gene expression being repressed, and excess starch appears to impede CO2 diffusion. studies show that the effects of CO2 enrichment on photosynthesis are very complicated as they go down under two categories, short-term and long-term effects of CO2. However since this study didn’t test the effect of long term or excessive exposure of CO2 results weren’t able to support the negative impacts of it, as this study only showed that short term effects as it resulted in positive outcomes (figure 1) Conducting such study is a good way to observe how light intensity and CO2 concentration affect plant growth.

A previous study conducted by, Ainsworth et al (2002). Ainsworth and colleagues in the university of Illinois where they tested the effect of elevated CO2 on soybean plants. Their results show that the growth rate of soybean plant was increased by 12% which also happened in the Eruca Sativa plants study. Another study was made by H. F. THUT and W. E. LoomIs (1994) relating light to the growth of plants. This experiment was made on field grown plants were some were exposed to grow under sunlight, and some were covered. Their results show that plants made a greater growth during day time, when temperature and light was the limiting factor and made a greater growth during night time when moisture was limiting factor. The similarity between their results and this studies’ results is that light did seem to have a positive effect on plant’s growth. But, since water (moisture) was not recorded for this study results were not able to have complete explanation if whether moisture did have an effect on the growth of the of Eruca Sativa plants or not. H. F. Thut and W. E. LoomIs study also showed that excessive temperature and internal water deficits in plants under the combined effects of sunlight decreased growth in some plants. This was another limitation for this study as there were no plants exposed to excessive light to see what effect this would have on the Eruca Sativa. Even though H. F. THUT and W. E. LoomIs. study showed a biological reason behind light affecting plant growth but factors other than sunlight and moisture should be measured in order to get more accurate results as sunlight and moisture and not the only factors that affect plant growth. For this study temperature was another limitation as it is an important factor in plant, as increased temperature as an example can cause slow growth.

In conclusion this study found that light intensity and CO2 concentration have an effect on plant growth and leaf area of the Eruca Sativa plant. Plants that grew in high light and elevated conditions had a larger leaf area than those in low light and ambient CO2 concentration. Further research should be done as there were limitations for this study.

Reference list

1. Ainsworth et al, A meta-analysis of elevated CO2 effects on soybean (glycine max) physiology growth and yield, Globall changes biology ( 2002). 8, 695-709
2. Amane Makino’ and Tadahiko Mae, Department of Applied Plant Science, Graduate School of Agricultural Sciences, Tohoku University, Tsutsumidori-Amamiyamachi, Sendai, 981-8555 Japa, plant Cell Physiol. 40(10): 999-1006 (1999)
3. Chang-Chang Chen, Meng-Yuan Huang, Kuan-Hung Lin, Shau-Lian Wong , Wen-Dar Huang* and Chi-Ming Yang2 Vol. 9(4) April (2014) Res. J. Biotech
4. Hendrick Porter and Marie Laure Navas (2003) Plant growth and competition at elevated CO2: on winners, losers and functional groups, volume 157, issue 2, https://doi.org/10.1046/j.1469-8137.2003.00680.x
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