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Plant water physiology
This is a mind map about the water physiology of plants in Chapter 2. The main contents include: 2.6 Water absorption by plant roots, 2.7 Transpiration, 2.8 Water transport in plants, 2.9 Physiological basis of reasonable irrigation, 2.5 Soil water and soil water potential, 2.4 transmembrane transport of water, 2.3 plant absorption of cell water, 2.2 chemical potential, water potential, 2.1 role of water in plant life activities.
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Plant water physiology
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Chapter 2 Water Physiology of Plants
2.1 The role of water in plant life activities
2.1.1 Water content and water existence status in plants
Bound water: Any water that is attracted by the colloidal particles of plant cells or the hydrophilic groups (such as -COOH, -OH) of osmotic substances, and is tightly bound around it and cannot move freely.
Free water: water that is not attracted by colloidal particles or hydrophilic groups of osmotic substances or has little attraction and can move freely
2.1.2 The physiological role of water in plant life activities
①Water is the main component of cell protoplasm
②Water directly participates in the metabolic process in plants
③Water is a good medium for various biochemical reactions and substance absorption and transportation
④Water can keep plants in their original posture
⑤ Cell division and extension growth require sufficient water.
2.1.3 The ecological role of water in plant life activities
①Water is a plant temperature regulator (water molecules have high vaporization heat and specific heat, which can lower body temperature through transpiration, making plants less susceptible to high temperature damage)
②The regulating effect of water on the microenvironment of plant survival (increasing atmospheric humidity, improving the temperature of soil and soil surface atmosphere)
2.2 Chemical potential, water potential
Water potential: Water potential is the difference between the chemical potential of partial molar volume of water in a system and the chemical potential of pure water at the same temperature and pressure.
Partial molar volume: refers to the effective volume occupied by 1 mol of the substance in the mixed system under the conditions of constant temperature, constant pressure and the concentration of other components.
2.3 Plants’ absorption of cellular water
2.3.1 Osmotic water absorption of plant cells
2.3.1.1 Plasmolysis and plasmolysis recovery
2.3.2 Water potential composition of plant cells
solute potential
pressure potential
Gravitational potential (negligible at cellular level)
Substrate potential (cells with large vacuoles are generally ignored)
2.3.1.3 Water movement between cells (water potential gradient)
2.3.2 Plant cells absorb water (vacuoles are not formed)
2.3.3 Metabolism of plant cells and water absorption
2.4 Transmembrane transport of water
2.4.1 Diffusion
Diffusion is the movement of material molecules (including gas molecules, water molecules, and solute molecules) from one point to another, that is, the random and progressive movement of molecules from a higher chemical potential area to a lower chemical potential area, which usually results in diffusion of molecules. Evenly distributed.
2.4.2 Convergence
In the presence of a pressure difference, the collective movement of a large number of molecules in a liquid is called collective flow.
2.5 Moisture in soil and soil water potential
Permanent wilting point: For most plants, when the soil moisture content reaches the permanent wilting coefficient (the amount of water remaining in the soil when the plant has just wilted permanently), its water potential is about -1.5MPa, which is called the permanent wilting point.
Field water capacity: the soil moisture content when all gravity water in the soil is removed and all capillary water and irreducible water are retained.
2.9 Physiological basis of reasonable irrigation
Plant water balance: the harmonious and dynamic relationship between plants’ water absorption, water use, and water loss
Moisture critical period: The period when plants are most sensitive to insufficient water and most vulnerable to damage.
Soil moisture content: generally 60%-80% of field water capacity
crop indicators
Shape indicators: Growth rate decreases wilting of young leaves Stems and leaves turn red in color
Physiological indicators: Leaf water potential Cell juice concentration or osmotic potential Stomatal condition
Plant water use efficiency (used to describe the relationship between plant yield (biological yield or economic yield) and water consumption, usually refers to the biological yield or economic yield or economic value produced per unit of water consumption)
2.8 Water transport in plants
Transport pathway: soil water → root hairs → root cortex → root pericycle → root vessels → stem vessels → petiole vessels → vein vessels → mesophyll cells → mesophyll cell spaces → stomatal subspace → stomata → in the atmosphere (soil-plant-atmosphere continuous System SPAC)
Cohesive mechanics theory: Water can be transported over long distances in plants without directly consuming plant metabolic energy.
2.7 Transpiration
2.7.1 Transpiration: refers to the process in which water in plants is lost from the surface of the plant to the outside world in a gaseous manner. |Physiological meaning:
① The transpiration pull caused by the water potential gradient caused by water loss through transpiration is the main driving force for plants to passively absorb and transport water.
②Transpiration relies on the high heat of vaporization of water to reduce the temperature of plants and leaves, preventing them from being burned by high temperature and strong light.
③The updraft caused by transpiration helps the roots transport inorganic ions and organic matter absorbed from the soil and organic matter synthesized in the roots to various parts of the plant to meet the needs of life activities.
2.7.2 Methods and measurement of transpiration
① Transpiration rate (TR): The amount of water lost by a plant through transpiration per unit leaf area in unit time is called the transpiration rate, also known as transpiration intensity. ②Transpiration efficiency: the mass of dry matter produced by the plant per kilogram of water consumed (g) ③Transpiration coefficient: The amount of water (g) consumed by plants to produce 1g of dry matter. It is the reciprocal of transpiration efficiency.
Stomatal transpiration (guard cells: kidney-shaped, dumbbell-shaped) (open during the day and closed at night)
Pore diffusivity: The diffusion rate of gas through a porous surface is not proportional to the pore area, but proportional to the circumference of the pore
Characteristics of guard cells: ① The cells are small in size and have a special structure with thin outer walls and thick inner walls, which is conducive to rapid and significant changes in turgor pressure; ② There are transverse radial microfiber bundles on the outer wall of the cell connected to the inner wall, which facilitates the application of effects on the inner wall; ③There is a complete set of organelles in the cytoplasm, and the number is large
Five hypotheses: ①Starch and sugar conversion hypothesis ②Potassium ion accumulation hypothesis ③Malic acid production hypothesis ④ Zeaxanthin hypothesis ⑤The hypothesis that sucrose regulates stomatal movement
Factors regulating stomatal movement: ①Carbon dioxide ②Light ③Temperature ④Moisture ⑤Wind ⑥Plant hormones
overall transpiration
Factors affecting transpiration
Internal factors: structural characteristics of stomata
Environmental factors: light, atmospheric humidity, atmospheric temperature, wind, soil conditions
2.6 Water absorption by plant roots
2.6.1 The area where roots absorb water (root hair area)
① There are many root hairs in the root hair area, which increases the absorption area.
②The outside of the root hair cell wall is covered with pectin material, which makes it highly sticky and hydrophilic.
③The conductive tissue in the root hair area is well developed and has little resistance to the movement of water.
④The root hairs are long and slender and can enter the soil capillaries.
2.6.2 Methods, pathways and motivation for water absorption by roots
① Passive water absorption (the transpiration pulling force generated by transpiration is the driving force)
② Actively absorb water (relying on root pressure as power)
apoplastic pathway
symplast pathway
transmembrane pathway
2.6.3 Root water absorption resistance
soil resistance
Root-soil interface resistance
Root radial and axial resistance
2.6.4 Factors affecting root water absorption
2.6.4.1 Root system factors
Root density: refers to the length of roots per unit volume of soil
2.6.4.2 Soil conditions
available water in soil
Available water: only soil moisture above the permanent wilting coefficient
Soil aeration status
soil temperature
soil solution concentration