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Moisture Stress
Moisture stress is a form of abiotic stress that occurs when the moisture of plant tissues is reduced to suboptimal levels. Water stress occurs in response to atmospheric and soil water availability when the transpiration rate exceeds the rate of water uptake by the roots and cells lose turgor pressure. Moisture stress is described by two main metrics, water potential and water content. Moisture stress has an effect on stomatal opening, mainly causing a closure in stomata as to reduce the amount of carbon dioxide assimilation. Closing of the stomata also slows the rate of transpiration, which limits water loss and helps to prevent the wilting effects of moisture stress. This closing can be trigged by the roots sensing dry soil and in response producing the hormone ABA which when transported up the xylem into the leaves will reduce stomatal conductance and wall extensibility of growing cells. This lowers the rates of transpiration, photosynthesis and leaf expansion. ABA also increa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Abiotic Stress
Abiotic stress is the negative impact of non-living factors on the living organisms in a specific environment. The non-living variable must influence the environment beyond its normal range of variation to adversely affect the population performance or individual physiology of the organism in a significant way. Whereas a biotic stress would include living disturbances such as fungi or harmful insects, abiotic stress factors, or stressors, are naturally occurring, often intangible and inanimate factors such as intense sunlight, temperature or wind that may cause harm to the plants and animals in the area affected. Abiotic stress is essentially unavoidable. Abiotic stress affects animals, but plants are especially dependent, if not solely dependent, on environmental factors, so it is particularly constraining. Abiotic stress is the most harmful factor concerning the growth and productivity of crops worldwide. Research has also shown that abiotic stressors are at their most harmful ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Transpiration
Transpiration is the process of water movement through a plant and its evaporation from aerial parts, such as leaves, stems and flowers. Water is necessary for plants but only a small amount of water taken up by the roots is used for growth and metabolism. The remaining 97–99.5% is lost by transpiration and guttation. Leaf surfaces are dotted with pores called stomata (singular "stoma"), and in most plants they are more numerous on the undersides of the foliage. The stomata are bordered by guard cells and their stomatal accessory cells (together known as stomatal complex) that open and close the pore. Transpiration occurs through the stomatal apertures, and can be thought of as a necessary "cost" associated with the opening of the stomata to allow the diffusion of carbon dioxide gas from the air for photosynthesis. Transpiration also cools plants, changes osmotic pressure of cells, and enables mass flow of mineral nutrients and water from roots to shoots. Two major factors i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Turgor Pressure
Turgor pressure is the force within the cell that pushes the plasma membrane against the cell wall. It is also called ''hydrostatic pressure'', and is defined as the pressure in a fluid measured at a certain point within itself when at equilibrium. Generally, turgor pressure is caused by the osmotic flow of water and occurs in plants, fungi, and bacteria. The phenomenon is also observed in protists that have cell walls. This system is not seen in animal cells, as the absence of a cell wall would cause the cell to lyse when under too much pressure. The pressure exerted by the osmotic flow of water is called turgidity. It is caused by the osmotic flow of water through a selectively permeable membrane. Movement of water through a semipermeable membrane from a volume with a low solute concentration to one with a higher solute concentration is called osmotic flow. In plants, this entails the water moving from the low concentration solute outside the cell into the cell's vacuole. Mec ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Water Potential
Water potential is the potential energy of water per unit volume relative to pure water in reference conditions. Water potential quantifies the tendency of water to move from one area to another due to osmosis, gravity, mechanical pressure and matrix effects such as capillary action (which is caused by surface tension). The concept of water potential has proved useful in understanding and computing water movement within plants, animals, and soil. Water potential is typically expressed in potential energy per unit volume and very often is represented by the Greek letter ψ. Water potential integrates a variety of different potential drivers of water movement, which may operate in the same or different directions. Within complex biological systems, many potential factors may be operating simultaneously. For example, the addition of solutes lowers the potential (negative vector), while an increase in pressure increases the potential (positive vector). If the flow is not restricte ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Water Content
Water content or moisture content is the quantity of water contained in a material, such as soil (called soil moisture), rock, ceramics, crops, or wood. Water content is used in a wide range of scientific and technical areas, and is expressed as a ratio, which can range from 0 (completely dry) to the value of the materials' porosity at saturation. It can be given on a volumetric or mass (gravimetric) basis. Definitions Volumetric water content, θ, is defined mathematically as: :\theta = \frac where V_w is the volume of water and V_\text = V_s + V_w + V_a is equal to the total volume of the wet material, i.e. of the sum of the volume of solid host material (e.g., soil particles, vegetation tissue) V_s, of water V_w, and of air V_a. Gravimetric water content is expressed by mass (weight) as follows: :u = \frac where m_w is the mass of water and m_s is the mass of the solids. For materials that change in volume with water content, such as coal, the gravimetric water content, ''u' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stoma
In botany, a stoma (from Greek ''στόμα'', "mouth", plural "stomata"), also called a stomate (plural "stomates"), is a pore found in the epidermis of leaves, stems, and other organs, that controls the rate of gas exchange. The pore is bordered by a pair of specialized parenchyma cells known as guard cells that are responsible for regulating the size of the stomatal opening. The term is usually used collectively to refer to the entire stomatal complex, consisting of the paired guard cells and the pore itself, which is referred to as the stomatal aperture. Air, containing oxygen, which is used in respiration, and carbon dioxide, which is used in photosynthesis, passes through stomata by gaseous diffusion. Water vapour diffuses through the stomata into the atmosphere in a process called transpiration. Stomata are present in the sporophyte generation of all land plant groups except liverworts. In vascular plants the number, size and distribution of stomata varies widely. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Carbon Fixation
Biological carbon fixation or сarbon assimilation is the process by which inorganic carbon (particularly in the form of carbon dioxide) is converted to organic compounds by living organisms. The compounds are then used to store energy and as structure for other biomolecules. Carbon is primarily fixed through photosynthesis, but some organisms use a process called chemosynthesis in the absence of sunlight. Organisms that grow by fixing carbon are called autotrophs, which include photoautotrophs (which use sunlight), and lithoautotrophs (which use inorganic oxidation). Heterotrophs are not themselves capable of carbon fixation but are able to grow by consuming the carbon fixed by autotrophs or other heterotrophs. "Fixed carbon", "reduced carbon", and "organic carbon" may all be used interchangeably to refer to various organic compounds. Chemosynthesis is carbon fixation driven by chemical energy, rather than from sunlight. Sulfur- and hydrogen-oxidizing bacteria often use the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Wilting
Wilting is the loss of rigidity of non-woody parts of plants. This occurs when the turgor pressure in non-lignified plant cells falls towards zero, as a result of diminished water in the cells. Wilting also serves to reduce water loss, as it makes the leaves expose less surface area. The rate of loss of water from the plant is greater than the absorption of water in the plant. The process of wilting modifies the leaf angle distribution of the plant (or canopy) towards more erectophile conditions. Lower water availability may result from: * drought conditions, where the soil moisture drops below conditions most favorable for plant functioning; * the temperature falls to the point where the plant's vascular system cannot function; * high salinity, which causes water to diffuse from the plant cells and induce shrinkage; * saturated soil conditions, where roots are unable to obtain sufficient oxygen for cellular respiration, and so are unable to transport water into the plant; or ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stomatal Conductance
Stomatal conductance, usually measured in mmol m−2 s−1 by a porometer, estimates the rate of gas exchange (i.e., carbon dioxide uptake) and transpiration (i.e., water loss as water vapor) through the leaf stomata as determined by the degree of stomatal aperture (and therefore the physical resistances to the movement of gases between the air and the interior of the leaf). The stomatal conductance, or its inverse, stomatal resistance, is under the direct biological control of the leaf through its guard cells, which surround the stomatal pore. The turgor pressure and osmotic potential of guard cells are directly related to the stomatal conductance. Stomatal conductance is a function of stomatal density, stomatal aperture, and stomatal size. Stomatal conductance is integral to leaf level calculations of transpiration. Multiple studies have shown a direct correlation between the use of herbicides and changes in physiological and biochemical growth processes in plants, particularly n ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nonlimiting Water Range
The non-limiting water range (NLWR) represents the range of water content in the soil where limitations to plant growth (such as water potential, air-filled porosity, or soil strength) are minimal. John Letey (1985) from UC Riverside introduced the NLWR concept in an attempt to integrate several physical properties associated with plant or root growth to refine the concept of available water capacity. Alvaro Pires da Silva, Bev Kay. and Ed Perfect (University of Guelph, Ontario) (1994) refined the concept and termed it ''least limiting water range'' (LLWR). The upper limit (wet end) of LLWR is determined not only at water content at field capacity (FC), but also the capability of providing adequate aeration for plant roots (usually taken as a minimum air filled porosity of 10%). The upper limit is then defined as: min q . Rather than air-filled porosity at 10%, LaoSheng Wu from UC Riverside proposed moisture content where Oxygen gas diffusion rate ODR value of 0.2 micro-g/cm2/mi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Permanent Wilting Point
Permanent wilting point (PWP) or wilting point (WP) is defined as the minimum amount of water in the soil that the plant requires not to wilt. If the soil water content decreases to this or any lower point a plant wilts and can no longer recover its turgidity when placed in a saturated atmosphere for 12 hours. The physical definition of the wilting point, symbolically expressed as or , is said by convention as the water content at of suction pressure, or negative hydraulic head. History The concept was introduced in the early 1910s. Lyman Briggs and Homer LeRoy Shantz (1912) proposed the wilting coefficient, which is defined as ''the percentage water content of a soil when the plants growing in that soil are first reduced to a wilted condition from which they cannot recover in approximately saturated atmosphere without the addition of water to the soil''. See pedotransfer function for wilting coefficient by Briggs. Frank Veihmeyer and Arthur Hendrickson from University of Ca ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Soil Plant Atmosphere Continuum
The soil-plant-atmosphere continuum (SPAC) is the pathway for water moving from soil through plants to the atmosphere. Continuum in the description highlights the continuous nature of water connection through the pathway. The low water potential of the atmosphere, and relatively higher (i.e. less negative) water potential inside leaves, leads to a diffusion gradient across the stomatal pores of leaves, drawing water out of the leaves as vapour. As water vapour transpires out of the leaf, further water molecules evaporate off the surface of mesophyll cells to replace the lost molecules since water in the air inside leaves is maintained at saturation vapour pressure. Water lost at the surface of cells is replaced by water from the xylem, which due to the cohesion-tension properties of water in the xylem of plants pulls additional water molecules through the xylem from the roots toward the leaf. Components The transport of water along this pathway occurs in components, variously de ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
