Stomatal conductance indicates the extent of stomatal opening, affecting photosynthesis, respiration, and transpiration. Main factors affecting stomatal opening and closing: At present, there are two main methods for measuring the measured porosity of the air hole: First, according to the principle of cyclic diffusion, the measurement is calculated from the change of the surface humidity of the plant leaf. The representative instrument is the British AP4 plant stomata meter, which can measure the stomatal conductance and stomatal resistance of the plant; The other is that the US SC-1 steady-state porometer uses a channel clip with a known diffusivity to clamp the blade, and the water vapor flux is obtained by measuring the water vapor pressure gradient on the surface of the blade, thereby utilizing the water vapor flux and known. The channel diffusivity gives the leaf stomatal conductance. Both measuring instruments are light and easy to carry, and can be used for field measurements for a long time. They are the right assistants for researchers and agricultural producers. It has a very high application value in crop yield increase and irrigation improvement. Guangzhou Zhongzhinan Supply Chain Co.,Ltd. , https://www.gzzhongzhinan.com
Porosity is the main channel for gas exchange between plant leaves and the outside world. The gas diffused through the pores has O2, CO2 and water vapor. Plant photosynthesis under light, CO2 absorption through the pores, so the pores must be opened, but the stomata opening will inevitably occur transpiration, the pores can adjust the size of their opening according to changes in environmental conditions, so that plants lose moisture Get the most CO2 under less conditions. Stomatal opening has a direct impact on transpiration. It is now generally expressed in terms of stomatal conductance, the unit of which is mmol·m-2·s-1, also expressed by stomatal resistance, which are all quantities describing the stomatal opening. Stomatal conductance is more convenient to use in many cases because it is directly proportional to transpiration and inversely proportional to stomatal resistance.
Effect of leaf stomatal conductance on plant growth and measurement methods
Stoma is one of many small openings in the epithelium of leaves, stems and other plant organs, and is a structure unique to the epidermis of plants. The stomata are usually present in the aerial parts of the plant body, especially on the leaf epidermis, and are also visible on young stems and petals. In the narrow sense, a convex lens-like small hole formed between guard cells is often referred to as a pore. The guard cells are distinguished from the epidermal cells by the fact that they contain chloroplasts in the structure, but the volume is small, the number is small, and the lamellar structure is poorly developed, but photosynthesis can be used to synthesize saccharides. Sometimes accompanied by 2-4 guard cells adjacent to guard cells. Including these cells is a generalized stomata (or stomata). There is a wide cell gap (air chamber) immediately below the stomata. In the gas metabolism such as carbon assimilation, respiration, and transpiration, the pores become channels of air and water vapor, and the amount of the pores is regulated by the opening and closing action of the guard cells, which is physiologically important.
Illumination: The chloroplast of the guard cells is photosynthesized under illumination, and the pH value of the cells is increased by using CO2. The starch phosphorylase hydrolyzes the starch to phosphate glucose, and the intracellular water potential decreases. The guard cells swell and swell open; the CO2 produced by breathing in the dark reduces the pH of the guard cells, and the starch phosphorylase synthesizes glucose into starch, the concentration of the cell fluid decreases, the water potential rises, the guard cells lose water, and the stomata close. .
Carbon dioxide affects stomatal movement : low concentrations of CO2 promote stomatal opening, and high concentrations of CO2 cause the pores to close quickly, regardless of light or darkness. The inhibition mechanism may be that the guard cell pH drops, the water potential rises, and the guard cells lose water. The stomata must be opened rapidly after the light is consumed for a period of time.
Temperature affects stomatal movement: stomatal opening generally increases with temperature, reaching maximum at around 30 °C, low temperature (such as below 10 °C), although long-term illumination, the pores are still not open well, mainly starch phosphorylase activity If it is not high, too high a temperature will cause the transpiration to be too strong, and the guard cells will lose water and the pores will be closed.
The water content of the leaves affects the movement of the stomata: if the transpiration is too strong during the day, the deflated pores of the guard cells are closed, the leaves are saturated with water during the rainy days, the water content of the epidermal cells is high, and the cells are squeezed, so the white weather holes are also closed.
Wind: The breeze promotes the opening of the pores because the breeze can appropriately reduce the humidity around the blades. Strong winds cause the pores to close.
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