| Drought, which is one of the common natural calamities, has a strong destructive force. The losses caused by drought are more than all the other natural calamities. With the rigorous trend of global warming, rainfall capacity is changing regionally. While the environmental temperature increased, it would make the water evaporation increasing and cause a great change in air humidity. Global warming intensified the frequency of extreme climates (drought, flood, freeze, high-temperature, and so on) at the same time. The potted-plant experiments were conducted by using soybean’YUDOU19’as tested material. Temperature, fluorescent light intensity and relative air humidity (RH) factors were controlled in plant growth chamber to simulate the natural drought condition. After a period of drought and re-watering treatments, physiological and photosynthesis characteristics (samples of the soybean seedling’s leaves) were measured and analyzed. The conclusions were shown as follows:(1) With the rate of drought aggravating, the longer it lasted, the more damage plants would endure. The severe drought stress resulted in the decrease of leaf relative water content (LRWC), soluble sugar and free proline contents. Furthermore, the reduction of superoxide dismutase (SOD) and the raised of peroxidase (POD) could clean away accumulated reactive oxygen species (ROS). Mild drought treatment didn’t cause harmful effect to plant growth, whose conditions approached nearly the controlled group. Moderate group’s condition was much worse, significant difference to controlled group. Soybean had some tolerance to drought stress in a short period.(2) Improving air humidity contributed to weaken the soil drought harm. While LRWC was increasing, soluble sugar and free proline contents were slightly decreasing, which indicated that drought damage had been reduced. In addition, the reduction of malondialdehyde (MDA) content could indicate that higher humidity resisted some drought damage, inhibiting lipid peroxidation and antagonism reduction of membrane fluidity. As a result, high humidity played an important role in the process of resisting water stress. Giving it adequate water, soybeans would gradually bring back to life. Mild drought group quickly reached the controlled state, not suffering seriously. Severe drought group deserved more time to gradually remit the damage and recover, which meant that drought didn’t coursed irreversible damage. After re-watering, they could recover and make up the growth losses. The higher air humidity could weaken the damage if drought stress was not so serious.(3) With the air humidity rising, LRWC showed a significant growth, and the photosynthetic condition increased simultaneously. In addition, it was found that a negative correlation existed between LRWC and chlorophyll (Chl), while a positive relation existed between evaporation rate (Tr) and stomatal conductance (Gs). While raising RH, it could only relieve the injuries caused by drought stress to a certain extent. The stomatal limitation was dominant under drought stress. Re-watering experiments made all the treatments recovering from the risk of drought, whose results were finally close to the level of the controlled groups.(4) Soil moisture deficit was more significant than air humidity by largely affecting plant’s growth condition. Although air humidity could not replace the role of soil moisture, its improvement would weaken the damage of drought and promote its drought resistance. |
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