Photosynthesis Physiology And Water Metabolism Of Robinia Pseudoacacia And Amorpha Fruticosa Under Drought And Lead Stress

In order to repeal effect of soil water, Pb and interaction between the two on photosynthesis physiology, leaf water potential, leaf relative water saturation deficit and cell membrane permeability of Robinia pseudoacacia and Amorpha fruticosa. With the one-year-old seedlings of Robinia pseudoacacia and Amorpha fruticosa as material, a potted experiment was conducted respectively in simulating different water condition (the soil relative water content with 40%, 60%, 80% and 100%) to measure the change of water and Pb stress(Pb content with 0, 300, 500, 1 000, 2 000 and 3 000 mg/kg) on photosynthesis physiology, leaf water potential, leaf relative water saturation deficit and cell membrane permeability of Robinia pseudoacacia and Amorpha fruticosa seedlings. To study the two trees on the adaptability of lead pollution, the main results as follow:1. The chlorophyll of Robinia pseudoacacia and Amorpha fruticosa was increased with the increase of drought stress. The chlorophyll of Robinia pseudoacacia and Amorpha fruticosa was first decreased and then increased again decreased with the increase of the soil Pb content. Slight lead stress (soil lead content with 300 and 500 mg/kg) could decrease the chlorophyll of Robinia pseudoacacia and Amorpha fruticosa. The chlorophyll of Robinia pseudoacacia and Amorpha fruticosa could be increased under severe lead stress (soil lead content with 1 000, 2 000 and 3 000 mg/kg).2. The net photosynthetic rate, stomatal conductance, intercellular CO₂ concentration and transpiration rate of Robinia pseudoacacia and Amorpha fruticosa decreased significantly under severe drought stress (the soil relative water content with 40%), but slight drought stress could increase them. The same soil water content, the net photosynthetic rate, stomatal conductance, intercellular CO₂ concentration and transpiration rate of Robinia pseudoacacia and Amorpha fruticosa decreased significantly under soil lead content with 300, 500, 3 000 mg/kg. Soil content of soil 2 000 mg/kg treatment was signigicantly higher than the other lead treat. The net photosynthetic rate Robinia pseudoacacia and Amorpha fruticosa increased with the trend of soil lead content as same as chlorophyll content.3. The water use efficiency is the net photosynthetic rate and transpiration rate of the ratio between, so changes in water use efficiency is closely related with net photosynthetic rate and transpiration rate. The same soil lead content, the soil water use efficiency of Robinia pseudoacacia and Amorpha fruticosa Severe under severe water stress (soil water content is 40% and 60%) was higher than that slight water stress (soil water content is 80%) and adequate water supplied. The lead stress could reduce soil water use efficiency of Robinia pseudoacacia and Amorpha fruticosa.4. The leaf water potential of Robinia pseudoacacia and Amorpha fruticosa was significantly correlated with water stress level, when the soil water content is 40%, the leaf water potential minmum, the leaf water potential of Robinia pseudoacacia in soil water content is 60% maximum, while the leaf water potential of Amorpha fruticosa in soil water content is 80% maximum. The leaf water potential of Robinia pseudoacacia was no significant under lead stress. When soil water content is 40%, the leaf water potential of Robinia pseudoacacia was first decreased and then increased again decreased with the decrease of the soil lead content. The leaf water potential of Amorpha fruticosa significantly affected under soil lead stress. When the soil water content is 40%, the leaf water potential of Amorpha fruticosa was first increased and then decreased with increase of soil lead content. Soil water content is 60%, 80% and 100%, the leaf water potential of Amorpha fruticosa was overall upward trend with increase of soil lead content.5. Leaf relative water saturation deficit of Robinia pseudoacacia and Amorpha fruticosa was significant effect with water stress, the severe water stress (soil water content is 40%), Robinia pseudoacacia and Amorpha fruticosa had large relative leaf relative water saturation deficit. Slight water stress (soil water content is 80%), leaf relative water saturation deficit was small. Leaf relative water saturation deficit had no significant effect under lead stress. By compared the results obtained, the same water stress, Leaf relative water saturation deficit of Amorpha fruticosa leaves less than Robinia pseudoacacia, we could indicate that Robinia pseudoacacia water-retention capacity than Amorpha fruticosa.6. In the different lead content, the locust basically the maximum cell membrane permeability of Robinia pseudoacacia in the soil water content is 100%, the minimum in 80%. And the maximum value of cell membrane permeability of Amorpha fruticosa is basically in the soil water content is 40%, the minimum in 100%. In all water conditions, Robinia pseudoacacia and Amorpha membrane cell membrane permeability wsa first decreased and then increased and then decreased with increase of lead content.7. Under the same conditions of soil Pb, leaf water potential of Robinia pseudoacacia as the growth phase decreased first and then increased, and the third growth phase, leaf water potential was significantly higher than the first growth phase and the second growth phase. Amorpha fruticosa opposite changes in leaf water potential. The leaf relative water deficit of Robinia pseudoacacia and Amorpha fruticosa was different change with the growth phase in all the Pb treatments. Robinia pseudoacacia and Amorpha fruticosa cell membrane permeability was increased and then decreased with the growth time, the first growth phase cell membrane permeability of Robinia pseudoacacia was less than the third growth phase and the second growth phase.