Study On Drought Resistance Of5Different Shrubs

Specific to the trend of global warming and drought, it is of great importance to select and breeding species with strong drought resistance to mitigation global climate. In this study, five common shrubs in Sichuan (Pyracantha fortuneana, Pyracantha angustifolia, Pyracantha fortuneana’Harlequin", Photinia glabra×Photinia serrulata, Ligustrum japonicum’Howardii’) were tested by greenhouses moisture management, conducted a control and three treatments (CK, T1, T2, T3), the relative soil water content of85±5%FC,65±5%FC,45±5%FC and25±5%FC four moisture gradient, respectively. Start from the drought stress impact on plant physiology, the study systematic analysis water physiology, active oxygen metabolism, osmotic adjustment, photosynthetic physiology and morphological index of five species’response mechanism to water deficit in order to provide the basis for selecting appropriate trees in large scale cultivation in arid, semi-arid regions. The findings are as follows:(1)The water status of five shrubs in response to drought stressThe leaf water retention capacity of five shrubs increased significantly with the degree of aridity. Severe drought caused an obvious reduction about20%of the leaf relative water content. In the water shortage environment, five shrubs mainly by reducing the leaf water potential, enhancing tissue water retention capacity in order to maintain the cells’water absorbing and normal water metabolism.(2) Active oxygen metabolism of five shrubs in response to drought stressModerate and severe drought induced Pyracantha fortuneana, Pyracantha angustifolia and Ligustrum japonicum’Howardii’SOD activity increased; which was2.07,1.70and1.29times of CK under severe treatment, respectively; Pyracantha fortuneana’Harlequin’SOD activity was always suppressed in each treatment. Severe drought inhibited Pyracantha fortuneana and Pyracantha fortuneana’Harlequin’POD activity; Ligustrum japonicum’Howardii’POD activity gradually increased with the intensification of aridity, rose by48.78%relative to CK under severe treatment. Pyracantha fortuneana’Harlequin’and Photinia glabra×Photinia serrulata CAT activity increased in mild drought, CAT activity of remaining species were induced surge under moderate drought. Drought did not significantly change the MDA content of Ligustrum japonicum’Howardii’, while the MDA content of Pyracantha fortuneana ’Harlequin’up to1.90times that of CK under mild drought. Soil drought had little effect on relative conductivity of Pyracantha fortuneana and Ligustrum japonicum’Howardii’; relative conductivity of remaining species visibly increased under severe drought.(3) Osmotic adjustment of five shrubs in response to drought stressAs the drought intensified the Pyracantha fortuneana’Harlequin’SS content increased gradually, the highest increase by54.09%that of CK; severe drought resulted in a sharp rise of SS content in remaining species. Under different stress treatments Pyracantha angustifolia SP content evidently increased; Pyracantha fortuneana SP content increased significantly in mild and moderate drought; Ligustrum japonicum ’Howardii’ SP content increased by21.51%than that of CK in severe drought; Pyracantha fortuneana’Harlequin’and Photinia glabra×Photinia serrulata SP content was not affected by soil water content. With the intensification of soil aridity, Pyracantha fortuneana, Pyracantha angustifolia, Ligustrum japonicum’Howardii’Pro content soared; the Pro content of other two species increased significantly in mild and moderate drought.(4) Photosynthetic physiology of five shrubs in response to drought stressPigment content of Ligustrum japonicum’Howardii’ changed little under all treatments; severe drought seriously hindered the pigment accumulation of other trees, Pyracantha fortuneana’Harlequin’only59.70%of CK. Drought stress led to the reduction of Pn, Gs, Tr,Pn max, light intensity and CO2available range as well as solar energy utilization. Pyracantha fortuneana Rd raised in T2treatment; no great change in Ligustrum japonicum’Howardii’Rd. Severe drought led to a significant restrain of RuBP in Pyracantha fortuneana; Ligustrum japonicum’Howardii’RuBP apparently improved in each treatment. Pyracantha fortuneana and Ligustrum japonicum ’Howardii’ Rp gradually increased with moisture dropped; Pyracantha fortuneana ’Harlequin’Rp speeded up under mild and moderate drought. Visibly, Ligustrum japonicum’Howardii’showed suitable adaptability to light environment, and its drought tolerance was relatively strong. (5) Morphological index of five shrubs in response to drought stressUnder drought stress, seedling height and diameter growth of each plant was severely inhibited, especially Pyracantha fortuneana’Harlequin’, while the impact on Ligustrum japonicum’Howardii’was relatively slight. Maybe under water deficit, plant roots unable to absorb enough water and nutrients from soil which limited the growth and development of organs to prevent excessive water consumption of aerial parts.Comprehensive analysis showed that drought stress resulted in the usage water decreased, respiration weakened, photosynthesis severely inhibited, which reflected the reduction in the amount of plant height and diameter growth. But they could resist drought environment through their own osmotic adjustment mechanism, antioxidant protection systems, and photorespiration in order to maintain the normal operation of life activities. On the whole, Ligustrum japonicum’Howardii’owned strong adaptability to water stress and abled to adjust physiological metabolic processes orderly under severe drought stress, so drought tolerance among the five species in descending order was:Ligustrum japonicum’Howardii’> Pyracantha fortuneana> Pyracantha angustifolia> Photinia glabra×Photinia serrulata> Pyracantha fortuneana’Harlequin’.