重水分胁迫下苹果树茎、叶水势的变化

对田间生长的3年生苹果树(红富士/M26/八棱海棠)在土壤干旱和湿润条件下的茎及叶片水势、气孔导度和净光合的日变化进行了测定。茎水势的测定采用外围新梢的直接取样测定法,以便同剪口处叶片的水势进行比较。测定结果表明,干旱土壤条件下的叶片水势稍低于土壤湿润的树,一般仅相差0.3MPa。而二个处理之间午间茎水势的差别则高达1～1.2MPa,表现出该指标对土壤干旱十分敏感。干旱条件下叶片气孔导度和净光合与土壤湿润的树也有明显差异。研究还发现,在水分严重亏缺条件下存在茎水势低于叶水势及一定压力下枝条木质部漏气现象。对这些现象的发生条件和可能原因进行了讨论。

Variations of Leaf and Stem Water Potentials in Field Grown Apple Trees Under Severe Water Stress

Diurnal variations of leaf and stem water potentials,stomatal conductance and net photosynthesis of3-year old ap-ple trees(Fuji/M 26 /Malus micromalus seedling)grown in field were measured under wet and drought soil conditions in a high air evapora tion day.The stem water potentials were measured directly on the sunlit shoot after it was cut down and the leaves were detached.The results showed that the difference of leave water potential between the trees under wet and drought con ditions was about 0.3MPa.However,the difference of midday stem water potential between two treatments was1.0～1.2MPa.This confirms that the midday stem water potential is a very sensitive indi cator of water stress in orchard trees.The vari-ation of stomatal conductance and net photosynthesis of water stressed trees were differ from nonstressed ones.The mid day stem water poten tial was lower than leaf water potential on stressed trees and gas leached from xylem during measurement were also observed.The factors related to the phenomenon are discussed.