Why do plant leaves turn yellow

Why do plant leaves turn yellow?

Usually known as chlorosis, it is caused by an inability to produce chlorophyll. Indeed, it can be determined by a number of factors, and not just lack of water or waterlogged soil, including nutrient deficiencies, pathogen infection, or unbalanced soil pH.

Many of these factors are related to the inability of the plant root system to properly absorb water. As you probably know, water gets into the root system to be transported into the shoot (through the xylem), mainly through transpiration, the water pressure caused by water loss through the leaves. This water contains the nutrients from the soil that the plant needs to synthesize substances that cannot be made by photosynthesis. So if you change the water balance (e.g. by drying the soil) it becomes difficult for plants to get the nutrients they need to make chlorophyll.

Usually this is mediated by a decreased intake of magnesium, iron or zinc. However, since the precursor to chlorophyll is an amino acid, it can also be caused by a lack of nitrogen. PH comes into play because plants use a delicate balance of acidic ions to mobilize (make available to the roots) the nutrients in the soil. If the pH of the soil is too different it becomes unsustainable.

In summary, it refers to both the lack of key nutrients or changes in the most important soil properties as well as the ability of the plant root system to absorb these key nutrients. It is mediated through these effects which result in insufficient chlorophyll being produced, resulting in the yellowed leaves you have observed.