Kaufmann M R
Department of Botany, Duke University, Durham, North Carolina.
Plant Physiol. 1968 Feb;43(2):281-8. doi: 10.1104/pp.43.2.281.
The effects of water stress on growth and water relations of loblolly and white pine seedlings were studied during series of drying cycles. As mean soil water potential decreased, growth of roots, needles, and buds decreased. Growth of roots during successive severe drying cycles was not uniform, however. A study of needle and root extension showed that of the total growth of roots for 3 7-day drying cycles, only 6% occurred during the third cycle, while needle extension was uniform for the 3 cycles. The difference in response of needles and roots to drying cycles may be attributed primarily to the effect of water stress on the growing region. When subjected to a severe stress, roots matured toward the tip and became dormant, resulting in less growth during subsequent drying cycles. The intercalary growing region of needles, however, was not altered seriously enough by the stress to cause a difference in amount of growth during each drying cycle.Transpiration of loblolly pine was lower in the second drying cycle than in the first. Needle water potential after rewatering was as high as that of control plants watered daily; root resistance was apparently not important in restricting transpiration during a second drying cycle. Needle diffusion resistance of loblolly pine, measured with a low-resistance diffusion porometer, was slightly higher during the second drying cycle than during the first. In addition, many primary needles were killed during the first period of stress. These factors contributed to the reduction of transpiration during the second drying cycle. Diffusion resistance of Coleus increased and transpiration ceased during the first drying cycle while water potential remained relatively high. After rewatering, both leaf resistance and transpiration returned to the control level, presumably because the stress during the first period of drying was not severe. The diffusion resistances observed for well-watered plants were 30 to 50 sec.cm(-1) for loblolly pine, 3 to 5 sec.cm(-1) for Coleus, and 4 to 6 sec.cm(-1) for tomato. These values agree closely with those reported by other workers.
在一系列干燥周期中，研究了水分胁迫对火炬松和白松幼苗生长及水分关系的影响。随着土壤平均水势降低，根、针叶和芽的生长均减少。然而，在连续的严重干燥周期中，根的生长并不均匀。一项对针叶和根伸长的研究表明，在3个7天干燥周期的根总生长中，只有6%发生在第三个周期，而针叶伸长在这3个周期中是均匀的。针叶和根对干燥周期反应的差异可能主要归因于水分胁迫对生长区域的影响。当受到严重胁迫时，根向尖端成熟并进入休眠状态，导致在随后的干燥周期中生长减少。然而，针叶的居间生长区域并未因胁迫而严重改变，以至于在每个干燥周期中生长量没有差异。火炬松在第二个干燥周期的蒸腾作用低于第一个周期。复水后针叶水势与每日浇水的对照植株一样高；在第二个干燥周期中，根阻力显然对限制蒸腾作用并不重要。用低阻力扩散气孔计测量，火炬松在第二个干燥周期的针叶扩散阻力略高于第一个周期。此外，许多初生针叶在胁迫的第一阶段死亡。这些因素导致了第二个干燥周期蒸腾作用的降低。彩叶草在第一个干燥周期中扩散阻力增加且蒸腾作用停止，而水势仍相对较高。复水后，叶片阻力和蒸腾作用均恢复到对照水平，可能是因为第一个干燥阶段的胁迫并不严重。对于水分充足的植株，观察到的扩散阻力分别为：火炬松30至50秒·厘米⁻¹，彩叶草3至5秒·厘米⁻¹，番茄4至6秒·厘米⁻¹。这些数值与其他研究者报道的数值非常接近。
