The greenhouse is a semi-closed system. Crops interact through transpiration and greenhouse environmental factors. During this process, crops in the greenhouse form a unique pattern of transpiration. The external solar radiation warms the greenhouse, the relative humidity of the air decreases, and the transpiration of the crops in the greenhouse causes the liquid water absorbed by the crop from the roots to absorb the heat on the surface of the leaves and turn into vaporous water, which is emitted into the air in the form of water vapor. The sensible heat generated by solar radiation is converted into latent heat, which eases the upward trend of the indoor temperature and increases the humidity of the air. While the transpiration of crops is affected by the greenhouse environment, it also changes the environmental factors in the greenhouse. Therefore, the transpiration of crops is an important basis for water irrigation of greenhouse fertilizers and greenhouse environment control. Photosynthesis is also an important life course of crop production. Photosynthesis instruments can be used for effective measurement research.
The transpiration rate of cucumber on sunny days showed a single peak curve. It began to rise from sunrise, reached a maximum around 13 o'clock, then began to decline, and was very small by night. In sunny days, from the beginning of the morning, as the solar radiation gradually strengthens, the greenhouse temperature increases, the indoor humidity decreases, the cucumber transpiration rate begins to increase, reaches a maximum around 13 o'clock, and thereafter, as the solar radiation decreases, As the temperature in the greenhouse decreases and the humidity rises, the transpiration rate of cucumber begins to decrease, and the transpiration of cucumber is less than 1.0 at night.
When there is wind in the multi-span greenhouse (wind speed greater than 0.4m/s), the correlation coefficient between the two is only 0.64. This is because the transpiration rate measured in this experiment is performed in the leaf chamber of the photosynthetic apparatus and the indoor environment of the leaf is not affected by the greenhouse. The effect of wind speed inside. This resulted in poor correlation between the two. In the greenhouse, in order to reduce the use of pesticides and improve the quality of crops, ventilation holes in multi-span greenhouses are equipped with insect nets to block flying insects. This increases the ventilation resistance of the greenhouse. During the entire experiment period, the indoor wind speed is generally less than 0.4 m/s except for a few days. Therefore, in most production time, the change of transpiration rate can be used to reflect the variation of transpiration rate in real time. At the same time, the real-time measurement of crop sap flow is more convenient than direct transpiration measurement. Therefore, sap flow variation values ​​can be used in actual production. Reflect changes in transpiration.
The experimental results of instruments such as photosynthetic apparatus showed that the transpiration rate of cucumber in greenhouses in summer showed a clear single-peak curve in sunny weather conditions. On cloudy days, the peak values ​​were small and varied; solar radiation was the main factor affecting cucumber transpiration, and air The second is temperature, and the relative humidity of air is the least. The stomatal conductance is similar to the change of transpiration rate, and leaf stomata has a strong regulation effect on leaf transpiration. The sap flow of cucumber is significantly related to transpiration, and the change trend of transpiration can be expressed by the change trend of stem flow.
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