Bassman J H, Zwier J C
Department of Natural Resource Sciences, Washington State University, Pullman, WA 99164-6410, USA.
Tree Physiol. 1991 Mar;8(2):145-59. doi: 10.1093/treephys/8.2.145.
Responses of net photosynthesis, dark respiration, photorespiration, transpiration, and stomatal conductance to irradiance, temperature, leaf-to-air vapor density difference (VDD), and plant water stress were examined in two Populus trichocarpa clones (one from a moist, coastal climate in western Washington and one from a dry, continental climate in eastern Washington), one P. deltoides clone, and two P. trichocarpa x P. deltoides clones. Light saturation of photosynthesis in greenhouse-grown trees occurred at about 800 micromol m(-2) s(-1) for P. deltoides, P. trichocarpa x P. deltoides, and the eastern Washington ecotype of P. trichocarpa, but at about 600 micromol m(-2) s(-1) for the western Washington ecotype of P. trichocarpa. Average net photosynthesis (at saturating irradiance and the optimum temperature of 25 degrees C) was 20.7, 18.8, 18.2 and 13.4 micromol CO(2) m(-2) s(-1) for P. deltoides, P. trichocarpa x P. deltoides, and the eastern and western Washington clones of P. trichocarpa, respectively. In all clones, net photosynthesis decreased about 14% as VDD increased from 3 to 18 g H(2)O m(-3). Stomatal conductance decreased sharply with decreasing xylem pressure potential (XPP) in all clones except the western Washington clone of P. trichocarpa. Stomata in this clone were insensitive to changes in XPP and did not control water loss. Complete stomatal closure (stomatal conductance < 0.05 cm s(-1)) occurred at about -2.0 MPa in the eastern Washington clone of P. trichocarpa and around -1.25 MPa in the P. deltoides and P. trichocarpa x P. deltoides clones. Transpiration rates were highest in the P. trichocarpa x P. deltoides clone and lowest in the western Washington clone of P. trichocarpa. The P. deltoides clone and eastern Washington clone of P. trichocarpa had the highest water use efficiency (WUE) and the western Washington clone of P. trichocarpa had the lowest WUE. The hybrids were intermediate. It was concluded that: (1) gas exchange characteristics of eastern and western Washington clones of P. trichocarpa reflected adaptation to their native environment; (2) crossing the western Washington clone of P. trichocarpa with the more drought resistant P. deltoides clone produced plants better adapted to the interior Pacific Northwest climate, although the stomatal response to soil water deficits in the hybrid was conservative compared with that of the eastern Washington clone of P. trichocarpa; and (3) introducing eastern Washington clones of black cottonwood into breeding programs is likely to yield lines with favorable growth characteristics combined with enhanced WUE and adaptation to soil water deficits.
在两个毛果杨无性系（一个来自华盛顿州西部湿润的沿海气候区，另一个来自华盛顿州东部干燥的大陆性气候区）、一个三角叶杨无性系以及两个毛果杨×三角叶杨无性系中，研究了净光合作用、暗呼吸、光呼吸、蒸腾作用和气孔导度对光照、温度、叶 - 气蒸汽密度差（VDD）以及植物水分胁迫的响应。温室种植树木中，三角叶杨、毛果杨×三角叶杨以及华盛顿州东部生态型的毛果杨光合作用的光饱和点约为800微摩尔·平方米⁻²·秒⁻¹，而华盛顿州西部生态型的毛果杨光饱和点约为600微摩尔·平方米⁻²·秒⁻¹。在饱和光照和25℃的最适温度下，三角叶杨、毛果杨×三角叶杨以及华盛顿州东部和西部的毛果杨无性系的平均净光合作用分别为20.7、18.8、18.2和13.4微摩尔二氧化碳·平方米⁻²·秒⁻¹。在所有无性系中，随着VDD从3克·立方米⁻³增加到18克·立方米⁻³，净光合作用下降约14%。除华盛顿州西部的毛果杨无性系外，所有无性系的气孔导度都随着木质部压力势（XPP）的降低而急剧下降。该无性系的气孔对XPP的变化不敏感，无法控制水分流失。华盛顿州东部的毛果杨无性系在约 -2.0兆帕时气孔完全关闭（气孔导度 < 0.05厘米·秒⁻¹），三角叶杨和毛果杨×三角叶杨无性系在约 -1.25兆帕时气孔完全关闭。蒸腾速率在毛果杨×三角叶杨无性系中最高，在华盛顿州西部的毛果杨无性系中最低。三角叶杨无性系和华盛顿州东部的毛果杨无性系水分利用效率（WUE）最高，华盛顿州西部的毛果杨无性系WUE最低。杂种处于中间水平。研究得出以下结论：（1）华盛顿州东部和西部的毛果杨无性系的气体交换特征反映了对其原生环境的适应；（2）将华盛顿州西部的毛果杨无性系与更耐旱的三角叶杨无性系杂交，培育出的植株更适应太平洋西北部内陆气候，尽管杂种气孔对土壤水分亏缺的响应比华盛顿州东部的毛果杨无性系保守；（3）将华盛顿州东部的黑杨无性系引入育种计划可能会培育出具有良好生长特性、更高WUE且适应土壤水分亏缺的品系。
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