Am J Bot. 1998 Jan;85(1):56.
Five plant communities in Western Australia, as well as selected desert and Rocky Mountain species of the western USA, were surveyed to evaluate associations among leaf structure, orientational properties, and the sunlight exposure and precipitation characteristic of each community. Selected leaf structural features have been associated previously with photosynthetic function and included shape, thickness, the ratio of thickness to width, stomatal distribution, leaf surface coloration, and the number and distribution of palisade cell layers. Decreases in annual precipitation (<4 to over 15 cm/yr) and increases in total daily sunlight (4.2 to 29.2 mol photons/m1) corresponded strongly to an increase in the percentage of species in a given community with more inclined (more inclined than +/- 45 degrees from horizontal) or thicker leaf mesophyll (>0.4 mm) leaves. Also, the percentage of species with a leaf thickness to width ratio >0.1, which were amphistomatous, or which had palisade cell layers beneath both leaf surfaces, increased from >20% in the highest rainfall and lowest sunlight community to >80% in the community with least rainfall but greatest sunlight exposure. Over 70% of the species in the most mesic, shaded community had lighter abaxial than adaxial leaf surfaces (leaf bicoloration). All of the above structural features were positively associated with a more inclined leaf orientation (r1 = 0.79), except for leaf bicoloration, which was negatively associated (r1 = 0.75). The ratio of adaxial to abaxial light was more strongly associated with leaf bicoloration (r1 = 0.83) and the presence of multiple adaxial and isobilateral palisade cell layers(r1 = 0.80) than with total incident sunlight on just the adaxial leaf surface (r1 = 0.69 and 0.73, respectively). These results provide field evidence that leaf orientation and structure may have evolved in concert to produce a photosynthetic symmetry in leaf structure in response to the amount of sunlight and other limiting factors of the community. This structural symmetry may serve fundamentally to regulate the distribution of both light and CO2 levels inside the leaf and, thus, increase photosynthetic CO2 uptake per unit leaf biomass.
对澳大利亚西部的五个植物群落以及美国西部选定的沙漠和落矶山物种进行了调查，以评估叶片结构、定向特性以及每个群落的阳光照射和降水特征之间的关系。先前已经将某些叶片结构特征与光合作用功能相关联，包括形状、厚度、厚度与宽度之比、气孔分布、叶片表面颜色以及栅栏细胞层的数量和分布。年降水量（<4 至超过 15 厘米/年）的减少和总日光照量（4.2 至 29.2 毫摩尔光子/m1）的增加与特定群落中叶片更倾斜（与水平方向的倾斜度大于 45 度）或叶片中叶质更厚（>0.4 毫米）的物种百分比呈强相关性。此外，具有叶片厚度与宽度比>0.1、具有两面气孔或两面都具有栅栏细胞层的物种的百分比从年降水量最高和光照最少的群落中的>20%增加到光照最多但降水最少的群落中的>80%。在最湿润、遮荫的群落中，超过 70%的物种的下表皮比上表皮（叶片双色性）更浅。除了叶片双色性，所有上述结构特征都与叶片更倾斜的定向（r1 = 0.79）呈正相关，叶片双色性与叶片更倾斜的定向呈负相关（r1 = 0.75）。与上表皮的光相比，上表皮和下表皮之间的光比值与叶片双色性（r1 = 0.83）和多个上表皮和等面栅栏细胞层的存在（r1 = 0.80）的相关性更强，而与上表皮上仅入射阳光的相关性较弱（r1 = 0.69 和 0.73）。这些结果提供了实地证据，表明叶片定向和结构可能已经协同进化，以响应群落中阳光和其他限制因素的数量，在叶片结构中产生光合作用的对称性。这种结构对称性可能从根本上有助于调节叶片内部的光和 CO2 水平的分布，从而增加单位叶片生物质的光合作用 CO2 摄取量。
