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Briefly analyze the effect of water change on plant internal environment

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In each growth period, the three stages of sufficient water supply-water stress-rehydration are successively experienced
In each growth period, the three stages of sufficient water supply-water stress-rehydration are successively experienced: (1) the cotton plant is fully irrigated to 80 in the field, and the water is fully balanced (about 4 to 5 hours) for observation; On the basis of the above soil moisture, the slow water stress is carried out. After about 2 to 3 days, the soil moisture is reduced to 40±5 in the field, and the parameters are determined when the leaves show obvious wilting; (3) rehydration after stress The water holding capacity of the field is 80, and the parameters are determined after the water is sufficiently uniform. During the moisture treatment, the moisture dynamics were monitored with a Time Domain-Reflectometer (TDR, USA). The light intensity treatment is based on natural light and passes two different shading densities (one is 40, that is, the light transmittance is 60; the other is 75, that is, the light transmittance is 25; the shading area is 4m×3m), respectively The black nylon mesh fixed on the outdoor 2 m high steel frame reaches the processing light intensity. There are 5 repetitions for each water treatment stage, and the total of 10 shade levels is 10 pots. The test observations were carried out on a sunny day at 11:40 to 14:30, and the respective water treatment stages were measured in the order of sufficient light-shading-full illumination. For example, in the full water supply stage, the plants are fully illuminated, and the functional leaves of the same leaf position and leaf age in the upper part of the main stem are selected. The net photosynthetic rate (Pn), transpiration rate (E), and temperature of the leaves are determined by a CO2 analyzer produced by American CID Company. Ta), leaf temperature (Tl), photosynthetically active radiation (PAR), relative humidity (RH) for about 10min, and then quickly placed under the shading net for 5min, and finally remove the shading net to fully restore the light to determine the above indicators for about 10min, and use The small liquid flow method was used to track the water potential (LWP) of the noon leaf.
A total of 3 measurements were taken for each moisture treatment stage. The experimental results were analyzed and plotted using EXCEL data processing software. From the seedling stage to the bud stage, the cumulative net photosynthetic rate and accumulated water loss during the light-shadow-light period were calculated from the measured data. The effect of water treatment and short-term shading on the photosynthetic rate and transpiration rate of cotton leaves decreased rapidly, and then Pn gradually increased. Shading also reduces E, but slows down more slowly than Pn. After the sunshade net is removed, Pn and E return to the level before shading, but the rate of Pn recovery is faster than E. Under short-term shading conditions, water stress reduced LWP, Pn and E at noon. Under sufficient light conditions, the Pn and E of cotton under water stress decreased by 41 and No149, respectively, compared with the case of sufficient water supply. During water stress, the average Pn of the leaves of shading 75 was only 71 of the shading 40, and E was also decreased. During the whole stress period, the accumulated Pn and accumulated water loss of the shading 75 were reduced; the water stress after rehydration The effect of the residual negative effect on the shading 75 is greater than that of the shading 40, so that the blade Pn of the shading 75 cannot be fully restored to the level at the time of full water supply, and the photosynthetic recovery rate also lags behind that of the shading 40. In the first minute of illumination, the blade Pn of the shade 75 is only 78 of the shade 40. Effect of water treatment and short-term shading on cotton leaf WUE Cotton single-leaf WUE is represented by Pn/E. For the treatment of shading 40, the WUE change during full illumination during the water treatment treatment was 2.80-3.45 Lmol/mmol, and the WUE change during shading was 1.60-2.60 Lmol/mmol, which was the highest under stress. From full illumination to shading, PAR decreased by 53.65 to 70.81, and WUE decreased by 24.6 to 42.8.