Drought And Heat Stress – How It Is Affecting Crop Production In Changing Climate
Drought and heat stress are the most significant restrictions to the planet's agricultural output and food security. Global food security is threatened by fast population growth and extreme climate change. Due to climate change, drought and heat stress have become the major limiting factors to agricultural growth and food security. Droughts are becoming more common across the planet as precipitation levels decline and rainfall patterns shift. Drought stress decreases photosynthetically active radiation absorption, radiation usage efficiency, and harvest index. Plants adjust their growth patterns and physiological processes in response to the severe impacts of drought stress.
Plant responses to drought stress vary by species and rely on plant development stage and other environmental conditions.
The first consequence of dryness on plants is poor germination and seedling establishment. Several studies have shown that drought stress has a harmful influence on germination and seedling development. Drought stress has been shown to reduce germination potential, early seedling development, root and shoot dry weight, hypocotyl length, and vegetative growth in major field crops such as pea, alfalfa, and rice. Cell division, expansion, and differentiation are the primary mechanisms by which plants grow. Drought inhibits mitosis and cell elongation, resulting in slow growth. Drought inhibits cell development primarily via the loss of turgor. Water scarcity impairs cell elongation, owing to insufficient water transport from the xylem to neighboring cells. Drought reduces the number of leaves and the size of individual leaves. The leaf's expansion is generally determined by the turgor pressure and the availability of assimilates. Under dry circumstances, reduced turgor pressure and a sluggish rate of photosynthesis primarily restrict leaf elongation. Under water-limiting circumstances, both fresh and dry weights are drastically decreased. Plant height, leaf size, and stem girth drastically reduce when water is scarce.
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Drought stress in plants
Yield is essentially the complicated integration of several physiological systems. Drought stress hurts the majority of these physiological functions. The adverse effects of drought on yield are determined mainly by the degree of stress and the stage of plant development. Drought stress has resulted in significant output reductions in key field crops. Drought-induced before anthesis delayed the time to anthesis, whereas drought-induced after anthesis shortened the length of grain filling in cereals. Sucrose Synthase, Starch Synthase, Starch Branching Enzyme, and Adenosine Diphosphate Glucose Pyrophosphorylase are the four primary enzymes that govern the grain filling process in cereals. Drought circumstances have been shown to reduce the activity of these enzymes, which has a detrimental influence on grain output. Drought stress during blooming may cause total sterility in pearl millet, mainly caused by disrupted assimilate transport to the growing ear.
Excessive radiation and high temperatures are other critical limiting factors for plant growth and development in tropical areas. High temperatures may induce blistering of the twigs and leaves, as well as visual indications of sunburn, leaf senescence, growth restriction, and fruit and leaf discoloration. Elevated temperatures may impair seed germination potential, resulting in poor germination and stand establishment. The adverse effects of high temperatures on grain crops vary depending on the heat stress's timing, length, and severity. High temperatures decreased the number of spikes and florets per plant in rice, while seed-set in sorghum was similarly reduced under comparable circumstances. Anthers and pollen within florets were more sensitive to high temperatures than ovules. Floret sterility has been linked to decreased anther dehiscence, poor pollen shedding, poor germination of pollen grains on the stigma, decreased elongation of pollen tubes and decreased in vivo pollen germination at high temperatures (>30°C). Under heat stress, maize and sugarcane growth and net absorption rates were significantly reduced.
High-temperature shocks during the reproductive period of major cereals may cause significant yield reductions in temperate locations. Heat stress has a detrimental impact on the quality of the final product in grains and oilseed crops because it significantly decreases the oil, starch, and protein levels. Temperature stress decreased rice production by lowering the performance of many rice development and yield features. A drop in individual grain weight resulted in a considerable fall in rice grain yield per unit area under high night temperatures. Heat stress reduced production significantly in common beans and peanuts. Heat stress substantially impacts tomato meiosis, fertilization, and the development of fertilized embryos, resulting in a substantial drop in output.
Specific parameters, like leaf water potential, leaf and canopy temperature, transpiration rate, and stomatal conductance, impact water relations. Drought stress disrupts all of these processes in plants. Under drought conditions, efficient wheat cultivars utilize water more efficiently. Plants extend their roots' length and surface area to acquire fewer mobile nutrients and modify their architecture. Root-microbe interactions are vital in plant nutrient connections.
Heat stress is often associated with water constraints in the field, particularly in tropical and subtropical areas. Drought and heat stress impact plants' nutrient cycle, absorption, and availability by interfering with many physiological systems. Heat and drought stress's critical impacts on photosynthetic processes are described here. Drought causes damage to photosynthetic pigments and thylakoid membranes. It has also been noted that dryness reduces chlorophyll content.
High temperature generally leads to a decrease in chlorophyll production. To minimize water loss via transpiration, practically all plants' first and predominant reaction to moisture stress is stomatal closure. Photosynthesis is hampered by poor Rubisco enzyme action in drought circumstances. Elevated amounts of solutes in the cytoplasm may potentially have a negative influence on the functioning of photosynthetic enzymes. Drought and heat stress have an impact on the photosynthesis of certain crops.
The significant sources of damage are light-dependent chemical processes in the thylakoid and metabolism in the stroma. The photosynthetic activities of two rice cultivars were lowered by high day and night temperatures. Drought upsets the assimilate balance since most of them are translocated to the roots to promote water intake. Drought reduces acid invertase activity by interfering with phloem loading and unloading under moisture stress.
Most abiotic stressors in plants result in oxidative damage as a secondary step. Drought stressors induce oxidative damage in plants by causing the creation of reactive oxygen species (ROS). These ROS endanger cell function by causing lipid and protein damage. Drought stress enhanced lipid and protein peroxidation in pea fourfold compared to noreverydayrcumstances.
Heat stress in a plant will often manifest as wilting, which indicates that water loss has occurred. If this is not addressed, the situation will deteriorate, with the plants ultimately drying out and becoming a crispy brown before dying. Yellowing of the leaves may occur in certain circumstances.
Drought stress is multifaceted and affects plant physiological, morphological, biochemical, and molecular properties. Many plants have improved their drought resistance mechanisms, although these vary depending on the type.
Drought stress is an unavoidable element that appears in various habvariouso discernible bounds and no prominent warning, hindering plant biomass output, quality, and energy. The most severe environmental stress is drought and heat stressors reactions caused by temperature dynamics, light intensity, and inadequate rainfall.
Drought stress is caused by human climate change, which reduces agricultural output and global dispersion. Among the several strategies used to counteract drought-induced plant damage, the use of nanoparticles is showing promise.
Drought and heat stress are significant constraints affecting agricultural yield globally. Plants have a broad spectrum, usually shown by plant development and morphology changes. Although drought and heat stress may harm overall plant growth and development, reproductive growth is the most affected. A little stress during anthesis or grain filling might significantly diminish crop output. Damaged photosynthetic machinery, oxidative damage, and membrane instability are also visible side consequences of these pressures.
Drought and heat stress significantly reduce crop development and output; however, the level of damage varies depending on the crop growth stage and intensity of the stress. In general, the reproductive period is more vulnerable to stressors, resulting in a significant loss in output.