Photosynthesis is significantly affected by various abiotic stresses such as salinity, drought, and high temperature. These stresses alter physiological, biochemical, and molecular processes in plants, particularly impacting photosynthesis. The photosynthetic process involves multiple components, including photosynthetic pigments, photosystems, the electron transport system, and CO₂ reduction pathways. Stress-induced damage to any of these components can reduce the overall photosynthetic capacity of plants. Stress factors such as salinity, drought, and high temperature can lead to the degradation of photosynthetic pigments like chlorophyll (Chl) and carotenoids (Car), which are essential for light absorption and photoprotection. Salt stress, for example, can cause the breakdown of Chl, while drought stress can lead to the deterioration of thylakoid membranes and reduced Chl content. High temperatures can damage the photosystem II (PSII) and reduce the efficiency of photosynthesis. Stomatal closure is a common response to stress, which limits CO₂ diffusion into leaves and reduces photosynthetic rates. Stomatal closure is often triggered by abscisic acid (ABA), a plant hormone that accumulates under stress conditions. The accumulation of ABA can lead to increased cytosolic Ca²+ levels and the activation of plasma membrane-localized anion channels, resulting in potassium efflux and guard cell depolarization. Salt stress can also affect the structure and function of PSII, leading to reduced photosynthetic efficiency. The xanthophyll cycle, which involves the conversion of violaxanthin to zeaxanthin, plays a crucial role in photoprotection and energy dissipation under high light intensity. The de-epoxidation of violaxanthin to zeaxanthin helps protect the photosynthetic apparatus from oxidative damage. Drought stress can lead to reduced photosynthetic capacity by impairing the photosystems and reducing the efficiency of electron transport. The photosynthetic rate is often limited by stomatal limitations, and the availability of CO₂ in the chloroplast is a key factor in determining photosynthetic efficiency. High temperatures can damage the thylakoid membrane and reduce the activity of PSII, leading to a decrease in photosynthetic capacity. The heat-induced damage to the oxygen evolving center (OEC) of PSII can result in significant reductions in photosynthetic efficiency. Gas-exchange characteristics, such as CO₂ assimilation rate and stomatal conductance, are also affected by various stresses. Salinity stress can lead to a reduction in these characteristics, while drought stress can cause stomatal closure and reduced CO₂ uptake. The association between photosynthetic capacity and drought tolerance varies among plant species, and photosynthetic capacity may not always be a reliable indicator of salt or drought tolerance. The activities of key photosynthetic enzymes, such as Rubisco, are also affected by various stresses. Stress-induced changes in enzymePhotosynthesis is significantly affected by various abiotic stresses such as salinity, drought, and high temperature. These stresses alter physiological, biochemical, and molecular processes in plants, particularly impacting photosynthesis. The photosynthetic process involves multiple components, including photosynthetic pigments, photosystems, the electron transport system, and CO₂ reduction pathways. Stress-induced damage to any of these components can reduce the overall photosynthetic capacity of plants. Stress factors such as salinity, drought, and high temperature can lead to the degradation of photosynthetic pigments like chlorophyll (Chl) and carotenoids (Car), which are essential for light absorption and photoprotection. Salt stress, for example, can cause the breakdown of Chl, while drought stress can lead to the deterioration of thylakoid membranes and reduced Chl content. High temperatures can damage the photosystem II (PSII) and reduce the efficiency of photosynthesis. Stomatal closure is a common response to stress, which limits CO₂ diffusion into leaves and reduces photosynthetic rates. Stomatal closure is often triggered by abscisic acid (ABA), a plant hormone that accumulates under stress conditions. The accumulation of ABA can lead to increased cytosolic Ca²+ levels and the activation of plasma membrane-localized anion channels, resulting in potassium efflux and guard cell depolarization. Salt stress can also affect the structure and function of PSII, leading to reduced photosynthetic efficiency. The xanthophyll cycle, which involves the conversion of violaxanthin to zeaxanthin, plays a crucial role in photoprotection and energy dissipation under high light intensity. The de-epoxidation of violaxanthin to zeaxanthin helps protect the photosynthetic apparatus from oxidative damage. Drought stress can lead to reduced photosynthetic capacity by impairing the photosystems and reducing the efficiency of electron transport. The photosynthetic rate is often limited by stomatal limitations, and the availability of CO₂ in the chloroplast is a key factor in determining photosynthetic efficiency. High temperatures can damage the thylakoid membrane and reduce the activity of PSII, leading to a decrease in photosynthetic capacity. The heat-induced damage to the oxygen evolving center (OEC) of PSII can result in significant reductions in photosynthetic efficiency. Gas-exchange characteristics, such as CO₂ assimilation rate and stomatal conductance, are also affected by various stresses. Salinity stress can lead to a reduction in these characteristics, while drought stress can cause stomatal closure and reduced CO₂ uptake. The association between photosynthetic capacity and drought tolerance varies among plant species, and photosynthetic capacity may not always be a reliable indicator of salt or drought tolerance. The activities of key photosynthetic enzymes, such as Rubisco, are also affected by various stresses. Stress-induced changes in enzyme