Dickmann D. I., Michael D. A., Isebrands J. G., Westin S.
Department of Forestry, Michigan State University, East Lansing, MI 48824-1222, USA.
Tree Physiol. 1990 Dec;7(1_2_3_4):7-20. doi: 10.1093/treephys/7.1-2-3-4.7.
Effects of the contrasting leaf display of poplar cultivars Eugenei (Populus x euramericana) and Tristis (P. tristis x P. balsamifera) on light interception and photosynthesis were studied in the second year of growth in an irrigated plantation near Rhinelander, Wisconsin, USA (lat. 45 degrees N). Leaves on the current terminal (CT) and on proleptic branches were measured between 0900 and 1500 h on five clear days from June to September 1980. Leaf orientation-based differences between these cultivars were evident as the second growing season progressed and the crowns of the trees in the plantation grew together. Leaves of Eugenei are erectophile or tilted from the horizontal. In this cultivar light penetrated throughout the crown; many leaves on the lowest branches were illuminated as fully as those on the upper CT and had higher photosynthetic rates than equivalent leaves in Tristis. However, by early September many of the lower branches on Eugenei trees had abscised. In the planophile Tristis, adaxial photon flux densities (PPFD) of leaves on the lower portion of the CT and on branches were only a fraction of those measured on the upper CT. This pattern became more extreme as the season progressed. Few of the lower branches of Tristis abscised during the growing season. Photosynthesis rates, especially on a whole-leaf basis, were closely related to incident PPFDs in both cultivars. The ecological significance of these results are discussed, as well as the hypothesized effect of leaf inclination on crop productivity.
在美国威斯康星州莱茵兰德附近（北纬45度）的一个灌溉种植园中，对杨树品种尤金尼（欧美杨）和特里斯特斯（香脂杨×北美香脂杨）叶片展示方式的差异对光截获和光合作用的影响进行了研究，研究对象为生长第二年的树木。1980年6月至9月期间，在五个晴天的09:00至15:00之间，对当年生顶梢（CT）和长枝上的叶片进行了测量。随着第二个生长季节的推进以及种植园中树木树冠的相互生长，这些品种之间基于叶片方向的差异变得明显。尤金尼的叶片为直立叶，即从水平方向倾斜。在这个品种中，光线贯穿整个树冠；最低枝条上的许多叶片与上部CT上的叶片一样受到充分光照，并且其光合速率高于特里斯特斯中同等位置的叶片。然而，到9月初，尤金尼树的许多下部枝条已经脱落。在平展叶的特里斯特斯中，CT下部和枝条上叶片的近轴光子通量密度（PPFD）仅为上部CT上测量值的一小部分。随着季节的推进，这种模式变得更加极端。特里斯特斯的下部枝条在生长季节很少脱落。两个品种的光合速率，尤其是基于整叶的光合速率，都与入射PPFD密切相关。文中讨论了这些结果的生态学意义，以及叶片倾斜对作物生产力的假设影响。
