Color is found everywhere in nature, ranging from flowers to the vibrant colors of autumn leaves. However, this phenomenon has never been ventured into. What determines nature’s colors, and can this be altered? Does color change with levels of pH? pH is the measure of how alkaline or acidic a substance is. It is measured out of a scale of 14, 7.0 being neutral, anything lower than 7.0 being more acidic, and anything higher than 7.0 being more basic. pH impacts the lives of people more than imagined, ranging from which brand of bottled water is better, to health and diseases. Cadmium poisoning is caused by the heavy amounts of cadmium, which is becoming more common due to pollution. Tamrix leaves can remove cadmium, but this depends on the pH level, demonstrating how pH impacts a leaf’s properties (Zaggout, Al-Subu & El-Ghoti, 2006). On the other hand, plants get their color from specific types of pigments. Most plants get their green leaves from chlorophyll, a pigment is found in chloroplasts. They absorb solar energy, and convert it into chlorophyll, making plants green. This color of green changes to yellow, orange and red, eventually leading to leaves falling down when autumn arrives. During this length of time, the amount of days will become shorter, and therefore, limit the amount of sunlight chloroplasts can absorb in order to produce more chlorophyll. Less chlorophyll is produced, and this makes leaves lose their vibrant green colors. Temperature drops can also play a role in how plants function. However, there may be a deeper reason to color changes in plants. Although it was always thought to be just because of the lack of chlorophyll and chloroplasts, this might be related to many other outside aspects, including camouflaging insects and aposematic reasons (defense, used to warn predators to stay away) (Lev-Yadon & Gould, 2007). The relationship between acidity and color in nature is apparent in many plants, and can lead to future artificial manipulation in pH in order to change a leaf’s physical appearance.
One major influential aspect in a plant’s pH is soil acidity. Lower pH levels in soil can lead to negative influences in a plant’s function, cellular structure, chlorophyll, and more. It limits crop harvest, and can also greatly change how a plant grows, how fast it grows, as well as its health and height. An experiment conducted on the impact of soil acidity on plants has supported that soil acidity has many impacts on how a plant grows as well as its characteristics, and its way of functioning. Citrus plants were chosen to experiment with due to its wide range of pH and its ability to tolerate highly acidic soils. Two citrus plants, Citrus Sinensis and C. grandis, were planted in soil with a pH of 2.5. Both plants had large decreases in stomatal conductance as well as leaf carbon dioxide intake/assimilation. Low pH of 2.5 also changed leaf photosynthesis by increasing the accumulation of non structural carbohydrates. This supports the fact that at the pH level of 2.5, the amount of proteins involved with both carbohydrates and energy metabolism can be altered (Zhang et al., 2018). Soil acidity also can impact the acidity of a plant, and the quality of the soil. In addition to this concept, pH depends on location and minerals already in the soil (de Caritat, Cooper & Wilford, 2011).
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Soil near a coastal fringe will have a lower pH (more acidic), while soil isolated from water will have a higher pH. Soils near coastal areas will be more acidic because this is where high leaching takes place (de Caritat, Cooper & Wilford, 2011). Soil pH is decreasing due to soil leaching (the action of certain harmful substances dissolving in water sinking in the soil), acid rain, bad nutrient cycling, nitrogen fertilizer, and intense agriculture (Zhang et al., 2018). Organic acids will also make soil more acidic. On instances in which basic rocks that provide base cations to soils are not present, soil acidity would lower, making it more acidic. Minerals like calcrete will give the soil a higher pH (more basic), and if the soil is above a limestone bedrock, then the pH will be higher as well. Distinct alkaline areas will also have carbonate lithologies, like marble. Meanwhile, if there is an abundance in organic matter, the pH of the soil will be lower (more acidic). In addition, pH can vary from where you measure, like topsoil (0.10 m) and subsoils (0.16-0.80 m) (de Caritat, Cooper & Wilford, 2011).
In terms of color, there have been many advances on genetic engineering on how to regulate and control petal pigment. Methods usually depend on the “biochemical control of plant pigments and cell acidity” (Becker, 1996). There are three main pigments: chlorophyll, carotenoids and flavonoids. Carotenoids give a bright orange, yellow and red color, while flavonoids can range from purple to blue, or even red, and chlorophyll gives a green color. These pigments can mix together in different amounts to form many different colors for a flower’s petals. The pH of a petal with anthocyanins can be altered and from this, the color can be changed. Anthocyanins are a type of flavonoids that give out a purple/blue color. Cellular pH determines the distance between copigments with metal ions and anthocyanins. Changing the distance results in changes of the color of a flower’s petals (Becker, 1996). However, the theory of color has been elaborated when it comes to red and yellow leaves. It is thought that red and yellow leaves can have a deeper meaning to the change of color rather than the loss of chlorophyll in chloroplasts during autumn. A few theories are to signal ripe fruits, signal aphids that trees are defended, for camouflage, defense, to show herbivores that they are low in resources and for other aposematic reasons. In addition to this, they could also be changing colors to signal insects to not occupy the leaves due to the fact that it will soon shed and fall. More specifically, it can signal aphids about nutrients. The color yellow indicates the presence of nitrogen amino acids, and the color also attracts aphids. Contrary to these theories, red and yellow leaves may not be adaptive or defensive, and may instead be a variation. These changes can be a result of the position of leaves on trees, water supply, mineral nutrition, geographical limitations, and insect attacks (Lev-Yadon & Gould, 2007).
Furthermore, one experiment is performed on petunias, a type of flower that can range from many colors of purple, pink and blue. When the pH in a petunia is changed by 1/10, the color completely changed from blue to red. This show small changes in a cell’s pH are responsible for the changing colors of flowers. Another experiment based on color and the change of pH is performed on hydroangeas, another type of flower. When the soil pH is 6.0 (meaning it is acidic), it produces pink flowers. However, with a 0.5 change to 5.5, the flower produced will be blue. This is explained with the fact that when a soil is acidic, aluminum is more soluble (meaning it is easier to dissolve), allowing it to be absorbed from the plant. After being absorbed, aluminum binds and connects to anthocyanin, and then the petal changes color. In addition to this experiment, it is further observed that light and temperature impacts the color of flowers. Research has shown that bright light and cool temperatures make colors more vibrant while blooming (Becker, 1996). Another example of changing pH having an impact on a leaf’s characteristics is when the pH of Tamrix leaves were changed to see if changing the acidity/alkalinity would impact the amount of cadmium it can absorb from water. It was observed that at the pH level of 5.0, the maximum amount of cadmium ions are removed. However, the amount of metal ions removed is decreased at any pH higher or lower than 5.0. Increasing or decreasing the leaf’s pH from 5.0 would limit the amount of cadmium ions removed, in addition to the speed and rate the ions are removed (Zaggout, Al-Subu & El-Ghoti, 2006).
In conclusion, the relationship between color and pH in nature is apparent. Soil acidity is a major aspect in a plant’s pH. It impacts the quality of the soil as well as changing the plant’s pH. The pH of soil depends on the location and materials already inside the soil. Soil leaching would lower the pH, while the presence of limestone or marble would increase the pH. The pH can vary as well depending on whether you measure the topsoil or subsoils. Many experiments are also conducted, testing the impact of soil acidity on plant growth, and/or its distinctive characteristics. These experiments range from using citrus leaves and planting them in a soil with a specific pH to using Tamrix leaves to extract cadmium ions from water. There have also been other experiments involving color, and why it changes. There are three main pigments: chlorophyll, carotenoids and flavonoids. These pigments are what determines the color of flowers. They mix with one another to create a variety of different colors. However, acidity also plays a role in this. The pH of petunias and hydroangeas are altered in order to demonstrate how the pH of plants impacts the color. Both pH’s of the flowers slightly changed, yet both resulted in significant changes of color. This show even small changes in pH can change color drastically. It is also observed that light and temperature impacts the color of plants. However, it is thought that the change of color in leaves goes deeper than just the loss of chlorophyll, or change in pigment and pH. A few theories are for aposematic/defense reasons, signaling aphids or herbivores the status of their resources, as well as signaling ripe fruit. On the contrary, these theories may just be a variation. These changes can be a result of many aspects, including position of leaves on trees, water supply, mineral nutrition, geographical limitations, and insect attacks. The correlation between pH and color in nature can be a minor thing, like the interest of how pH can change color, but this correlation between these two aspects can be greater as well. It can lead to future artificial manipulation of leaves in order to fit a person’s needs, or it can help with health, and prevent cadmium poisoning worldwide.
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