研究了PEG模拟干旱胁迫环境下的火力楠(Michelia macclurel)、尾叶桉(Eucalyptus urophylla)、枫香(Liquidambar formosana)、荷木(Schima superba)幼苗的生理变化。结果表明,干旱胁迫下,4种幼苗叶片的相对含水量小于对照,其中,尾叶桉和枫香下降明显;不同干旱胁迫条件下,4种树种幼苗叶片的相对电导率均显著大于对照,其中尾叶桉和枫香上升幅度大;干旱胁迫下的火力楠和荷木幼苗叶片的脯氨酸含量呈现波动,尾叶桉和枫香幼苗则显著大于对照;不同干旱胁迫时间下的幼苗叶片的叶绿素含量小幅波动;4个树种幼苗的过氧岐化酶(SOD)活性随胁迫时间增加而呈现先升后降的趋势,其中火力楠和荷木的幼苗的SOD活性持续维持在较高水平;荷木叶片的丙二醛(MDA)含量先升后降,最后和对照水平相近,其余幼苗的MDA含量均大于对照;干旱胁迫下4种幼苗叶片的可溶性糖含量增加幅度较大。主成分分析表明,4种幼苗的抗旱能力排序为荷木>火力楠>尾叶桉>枫香。
The amount and seasonality of rainfall varies strongly in South China, so that drought is a very obvious ecological factor limiting tree growth in drought season, whereas drought stress of tree species in this region has received less attention. Understanding how tree physiological characteristics respond to drought is a key element for a deeper understanding of sustainable management of forest ecosystems. Tree species with relatively high water requirements are very sensitive to periodical soil drought because of low rainfall level during the drought season, whereas those with relatively low water requirements have evolved a wide variety of physiological tolerance mechanisms in response to drought. A deficiency of water often results in physiological changes of tree species, which depends on the drought severity and duration of the drought stress. Michelia macclurel, Eucalyptus urophylla, Liquidambar formosana and Schima superba are important tree species in South China. To develop a drought stress response function in these tree species, efficient laboratory tests were used to analyze the effect of drought on their physiological characteristics under varying degrees of stress and different stress duration time. Different responses among four seedlings were observed, and the physiological differences that confer drought resistance or susceptibility are well explained. Experiment of seedlings of Michelia macclurel, Eucalyptus urophylla, Liquidambar formosana, Schima superba was conducted under drought stress using treatments of different PEG6000 concentrations (mild stress, moderate stress, severe stress) and different stress duration time (12 hours, 24 hours, 36 hours). The results showed that relative water content of four seedlings decreased after being treated with drought stress, and decrement of the E. urophylla and L. formosana was greater than M. macclurel and S. superba. Relative conductivity of the four seedlings significantly was greater than the controls, and increment of the E. urophylla and L. formosana was greater than M. macclurel and S. superba. Under drought stress, complex carbohydrates and proteins can be broken down by enzymes into soluble compounds simpler sugars and amino acids, such as proline, respectively, and accumulation of soluble compounds in cells increase osmotic potential and reduce water loss from cells. The content of free proline of M. macclurel and S. superba fluctuated after being treated with drought stress, whereas that of E. urophylla and L. formosana increased significantly compared to the controls. With increasing stress intensity and prolonging duration, chlorophyll content of the four seedlings slightly fluctuated. With increasing stress intensity and prolonging duration, the activity of super oxide dismutase (SOD) of the four seedlings increased and then decreased, and that of M. macclurel and S. superba remained relatively high level. The content of malondidehyde (MDA) of S. superba increased and then declined to level of the control, whereas that of other seedlings was greater than the controls. The content of soluble sugar of four seedlings increased obviously under drought stress. Principal component analysis can provide a quantitative evaluation of the different physiological indices for the seedlings under drought, which indicated that the order of drought resistance of the four seedlings was S. superba﹥M. macclurel﹥E. urophylla﹥L. formosana.