Soil pH, also known as “soil reaction”, is an acid-base reaction of soil solutions, an important chemical property of the soil. The activities of soil microbes, the decomposition of soil organic matter, the release and transformation of soil nutrients, and the migration of elements during soil formation are closely related. Soil pH depends mainly on the concentration of hydrogen ions in the soil solution, expressed as pH. The solution having a pH of 7 is a neutral solution; the pH is less than 7, which is an acidic reaction; and the pH is greater than 7 is an alkaline reaction. Soil pH not only has a great impact on soil fertility, soil nutrients, plant growth, but also changes the color of flowers. In the nature, all kinds of flowers are colorful, red and blue, but some flowers have a magical color change reaction, which will show different colors with different soil pH, which is the role of soil pH. The most typical example is the hydrangea.
The common colors of hydrangea are red, pink, blue and white. Generally, in the natural state, the white variety is initially greenish and then turned white. When the soil pH is 5, the flowers are blue; when the pH is 7, the flowers are pink; acid The base value is between 5 and 7, and the flower is lavender. In the range of tolerable acid and alkali, the stronger the acidity, the more blue, and the stronger the alkalinity, the more red. The pink and red varieties also show different colors in different acid-alkaline soils.
Then why does the pH of the soil affect the color of the flowers? Why do some flowers change color, and some flowers do not? How to adjust the soil pH to let the flowers bloom the color we want, what flowers? With such a magical color change ability?
The color of the flowers is mainly derived from the two pigments of anthocyanins and carotenoids. The orange and yellow flowers are mainly due to the carotenoids, and the red, blue and purple flowers such as hydrangea are mostly caused by the inclusion of anthocyanins in the vacuoles. Anthocyanins are water-soluble pigments with a wide variety of substitutions and glycosylation at different positions in the mother nucleus to produce different colors, and at different pHs, the same anthocyanin can change color with the acidity and alkalinity of the cell fluid. The cell liquid is acidic when it is acidic, and the cell liquid is alkaline, which is blue, that is, acid red alkali blue, which is like the acid-base indicator in chemical experiments. Therefore, when the soil pH changes, the nutrients that the plant absorbs from the soil through the roots and other transport tissues are changed, so that the cells in the plant change, affecting the acid-base conditions in the vacuole, and the color change reaction occurs. Morning glory follows this rule. In acidic soil, the flowers are purple-red and the alkaline soil is blue. Then why hydrangea does not follow such rules, but acid blue alkali red. This is because the color of hydrangea is controlled by a pigment belonging to the anthocyanins, the delphinidin pigment, which is different from other kinds of anthocyanins. This pigment combines with aluminum ions to form a barrier during biosynthesis, which in turn is affected by pH. These complex biochemical effects ultimately lead to a unique color change reaction of hydrangea.
Color change reaction of anthocyanins with pH:
Anthocyanins with different substituents have different colors:
So why do some flowers change color with pH, and some don't?
This is because the types of pigments contained in flowers vary and the range of variation varies. In short, the premise that the color of the flower changes with pH is that the plant can survive in such a pH environment. Some pigments must undergo a color change reaction in an extreme pH environment. At this time, the plant has already "discolored and died first," so naturally there is no color change reaction. For example, azaleas must be grown under acidic conditions. There are also some flowers that do not have visible color-changing pigments, such as white flowers.
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