Age-based Variation Of Drought-resistance For Juniperus Sabina

This paper presents a comprehensive review and analyses on identification indexes andmethods of trees drought resistance. The current situation, existent problems and the future ofthe drought-resistance indicators and methods were set forth in the paper. We made astatistical comparison of every drought-resistance indicator and figure out their appliedfrequency because the applied frequency not only can reflect the workers' approbation tothem but can suggest their practicability, facility and validity. At the same time, severalphysiological characteristics of Juniperus Sabina at three ages were measured in this paper inorder to make out whether the ages of the plants can influence the result of theirdrought-resistance ability. Main results obtained are as following:Plant water potential is used most frequently at present. Its applied frequency reaches47.22%. All drought-resistance indicators of woody plants in common use are classified intofive levels according to their applied frequency.Water-losing rate of Juniperus Sabina is significantly different among seedling ages.Older seedlings have lower water-losing rate than young seedlings. The relative permeabilityof membrane of Juniperus Sabina depresses as the age grows. Significant difference appearsamong these three ages. But there is no significantly difference on RWD whether under thewater stress or not. This shows that RWD is more age-stable than Water-losing rate andrelative permeability of membrane.Results indicate that while the soil water gradient has a significant effect on stomataconductance, transpiration rate, it has no significant influence on the net photosynthesis rate,CO₂ concentration inside the cell, apparent light use efficiency, and the enzyme RuBP.activity of Juniperus Sabina. Net photosynthesis rate don't respond sensitively to soil watercontent under water stress. This result evidently indicated that Juniperus Sabina has an extrasensitive stomata regulation. In addition to it's drought-resistance structures in evidence,Juniperus Sabina is a drought tolerance species in nature, and exhibited a saving water-use strategy in a sandy land ecosystem.There is no significant difference on net photosynthesis rate, stomata conductance, CO₂concentration inside the cell, apparent light use efficiency, water-use efficiency andtranspiration rate among 1-year old seedlings, 3-year old seedlings and 5-year old seedlingsof Juniperus Sabina accept the activity of enzyme RuBP when there is no water stress. As theage of the seedlings grows, net photosynthesis rate, activity of enzyme RuBP and apparentlight use efficiency become low under water stress. Significant difference appears amongthese three seeding ages. This indicates that the younger Juniperus Sabina seedlings are morevital than older ones. In contrast, the 5-year old seedlings have higher CO₂ concentrationinside the cell than 3-year old seedlings and 1-year old seedlings. At the same time, the 5-yearold seedlings have the largest changing range on stomata conductance and transpiration rateas the soil water content grows down. This may indicates that while the 3-year old seedlingsand 1-year old seedlings are more vital than the 5-year seedlings, the 5-year old seedlings aremore adaptive than the 3-year old seedlings and 1-year old seedlings.Therefore, we'd better choose the materials at the same age as the test sample when wedo some drought resistance appraisal. Sensitivity and stability of drought resistance appraisalto seedling age must be considered. If the ages of the test sample are different, we'd betterchoose more age-stable drought-resistant indicators.