Centro Internacional de Agricultura Tropical, Apartado Aéreo, 6713, Cali, Colombia.
Photosynth Res. 1987 Jan;12(3):219-35. doi: 10.1007/BF00055122.
The gas exchange characteristics of cassava were compared with one C3 species, common bean, and two C4 species, maize and amaranthus. Cassava leaf photorespiration, about 12% of maximum net photosynthesis in normal air, and the CO2 release in CO2-free air under intense light were lower than the values typically reported for C3 species. The CO2 compensation point of whole leaves (25 cm(3) CO2m(-3)) was intermediate between C3 and C4 species values.Gas exchange was restricted to either the upper or lower surface of amphistomatous leaves by covering one side of the leaf with silicone grease. The CO2 compensation point of the upper leaf surface was less than 6 cm(3) CO2m(-3) and the CO2 release into CO2-free air in the light was essentially zero. On the lower leaf surface considerable CO2 release occurred in both the light and the dark.The hypothesis presented to explain these results is the existence of an efficient CO2 recycling mechanism in the palisade layer in the upper half of the leaf. In the light of recent data (presented in the second paper of this series) indicating that cassava produces C4 acids as primary products of photosynthesis, it is proposed that this hypothesis is consistent with the possible existence of the C4 photosynthetic pathway in the palisade layer of cassava leaves.The results and hypothesis are discussed in relation to the crop's adaptation to the environmental conditions where it is normally grown. The implications of variation in anatomical features such as stomatal distribution on both surfaces of the leaf are analyzed with a view to enhancing the potential productivity of cassava under stress conditions.
木薯的气体交换特性与一种 C3 植物（普通菜豆）和两种 C4 植物（玉米和苋菜）进行了比较。木薯叶片的光呼吸约为正常空气中最大净光合作用的 12%，在强光下无 CO2 空气中的 CO2 释放量低于通常报道的 C3 植物的值。整叶的 CO2 补偿点（25 cm3 CO2m-3）在 C3 和 C4 物种值之间。通过用硅脂覆盖叶片的一侧，将 Amphistomatous 叶片的气体交换限制在上表面或下表面。上表面的 CO2 补偿点小于 6 cm3 CO2m-3，在光下 CO2 释放到无 CO2 空气中基本上为零。在下表面，在光和暗下都发生了相当大的 CO2 释放。提出的解释这些结果的假设是在上半叶的栅栏层中存在有效的 CO2 再循环机制。鉴于本系列第二篇论文中提出的最近的数据表明木薯产生 C4 酸作为光合作用的主要产物，因此提出该假设与木薯叶片栅栏层中可能存在 C4 光合作用途径是一致的。讨论了这些结果和假设与作物对其正常生长环境条件的适应有关。分析了叶片两面的解剖特征（如气孔分布）的变化对增强木薯在胁迫条件下的潜在生产力的影响。
