Abiotic stresses are the main limiting factors of plant performance, and they limit the amount of photosynthesis and reduce the ability to convert plant energy into biomass and byproducts. The reactions of plants to stress are different, but in general, abiotic stresses cause disturbances in the production of chlorophyll pigments and photosynthesis. During their growth, plants face many environmental stresses. Each of these stresses can have different impacts on their growth, metabolism, and performance. Drought and salinity are the most important environmental factors that reduce the growth and performance of plants, especially in arid and semi-arid regions of the world. Generally, when drought and salinity stresses increase, the chlorophyll content and photosynthetic pigment of plants decrease significantly. One of the most important reasons for photosynthetic pigment reduction is the destruction of the chloroplast structure and the prevention of chlorophyll synthesis. The disruption of enzyme activities involved in the biosynthesis of photosynthetic pigments has been reported as other harmful impacts of salinity and drought stresses. These changes ultimately reduce stomatal conductance and plant photosynthesis. Moreover, heavy metals have been added to soils because of the increased consumption of chemical fertilizers, irrigation with wastewater, and industrialization of societies, which have harmful consequences on soil and plant systems. Studies indicate a decrease in photosynthesis in plants grown in soils contaminated with heavy metals. Moreover, heavy metals prevent the synthesis of chlorophyll by disrupting the absorption of essential elements such as magnesium and iron. The decrease in chlorophyll content due to stress caused by heavy metals may be the result of inhibiting the enzymes responsible for chlorophyll biosynthesis. In addition to the inhibition of chlorophyll biosynthesis by heavy metals, these metals also cause chlorophyll biodegradation.
