Studies On Physiological And Ecological Characteristics Of Larrea Tridentata To Drought Stress

In this paper, we study the drought resistance ability of Larrea tridentata where planted in Yuanyang Hanan province from the seed germination, the form of anatomy, physiology and biochemistry indexes and other aspects, under the artificial simulation method of water stress used by PEG and natural water stress under natural conditions.The main results are listed as followes:The seed germination process of L. tridentata can complete in the arid habitats to some extent. But the scope of the soil moisture which the germination process adapted is not very wide. When the water potential reached -0.25 Mpa, the germination rate is very low. In the germination process, the seed reach the peak and the end period of germination quickly, this probably because L. tridentata can raise the germination speed to avoid the arid environment.The leave of L.tridentata is very thick. It has big epidermal cells and a thick cell wall and cuticle. Its fences organizations is developed. The ability of anti-dehydration of leave is almost as strong as conifers. L.tridentata has developed root system, the modality of root fit for absorbing water. All of which have shown a morphological characteristics of the ability to reduce water loss and showed its strong adaptability to drought resistance.Under four drought conditions, L.tridentata can make certain osmotic adjustments and maintain theΨp value mainly by improving the cell wall elasticity and retaining higher bound water proportion. It may also adapt to the drought stress with the ability of sarcode's dehydration- tolerating. With the increasing of drought stress, its tolerating degree of dehydration is enhanced while the maintaining degree of turgor is weakened.In the same soil moisture conditions, L. tridentata maintain a relatively high water potential and good moisture status more easily than other species.L.tridentata has a strong adaptability to water stress and high light. It reflected that the ability of reduce the moisture loss of L.tridentata is strong. With the increasing of water stress, photosynthesis is mainly adjusted by stoma, it showed that the ability of adapting the drought with the adjust of stoma of L.tridentata is strong. Water utilization efficiency was raised to some extent with the water stress. Water stress has little influence on leaf's actinic process. Photosynthetic apparatus were not harmed by drought.The inhibiting effect from the drought has been decreased with the elevated CO2. These findings suggest that elevated CO2 can promote photosynthetic activity and enhance the potential for L.tridentata to survive in extreme drought environment.The CO₂ concentration which saturated leaf RubisCO while could not cause stoma closed is 700-800μ? mol mol-1. The current CO2 concentration has not saturated the RubisCO of L.tridentata. The CO2 concentration increased in the future will promote the photosynthesis of L.tridentata, and may increase the drought resistance ability of L.tridentata.With the increase of soil moisture stress, the activity of enzyme and the content of MDA of L. tridentata increased at first then dropped when the soil water potential achieved at -2.415 MPa. The content of Proline take on a anabatic trend. Proline is an important osmotic regulator of L. tridentata. It showed that the protection of enzyme and osmotic adjustment has great help to improve the ability of drought resistance.The result showed that the contents of N, P, K, Ca, Mg in the leaves had the same tendency under the soil drought stress. The contents of the macronutrients decreased under light stress, then increased with the stress strengthened, except the contents of P decreased when the soil water potential reached -2.415MPa. All of the contents of the macronutrients remained at a high level when the soil moisture exceeded the witherd coefficient. The contents of the micronutrients did not change obviously under the drought stress. Under soil drought stress, L.tridentata can adjust its nutrition to improve its drought resisitance.From above, the ability of drought resistance of L. tridentata is strong. Its main mechanism of the drought-resistant is high water potential mechanism which delay dehydration. That is, L. tridentata delay dehydration and maintain a high water potential by limiting the loss of water or maintain the ability of absorbing water with the developed root. At the same time it has part of the low water potential mechanism which restrain itself from dehydration. Protoplasm and its main organ have very light injuries in the case of serious dehydration. The cell wall has good flexibility, it can maintain growth under severe water stress environment.Drought comprehensive evaluation results showed that under moderate water stress, L. tridentata showed the strongest ability to drought resistance. That is, because of its coordinating role, when the soil water potential within the scope of -2.415 MPa, L. tridentata itself was showed no symptoms from the drought, It showed that the ability of drought resistance of L.tridentata is strong.