Zimmerman J K, Ehleringer J R
Department of Biology, University of Utah, 84112, Salt Lake City, UT, USA.
Oecologia. 1990 Jun;83(2):247-9. doi: 10.1007/BF00317759.
Carbon isotope composition ((13)C/(12)C) in leaves of the Panamanian epiphytic orchid Catasetum viridiflavum were measured on individuals growing in canopies over a water surface to distinguish the effects of a change in source CO(2) and humidity from those of intercellular CO(2) concentration in determining isotopic composition. Carbon isotope ratios were observed to vary by over 4 in response to changes in total daily photon flux (PFD, 400-700 nm). Changes in isotopic composition of source CO(2) or changes in humidity were not likely to have played a role in determining leaf isotopic composition. Observed changed in carbon isotope discrimination (Δ) of leaves experiencing different light levels ranged from 17 to 21. Because leaf nitrogen contents were similar among all orchids, we suggest that the carbon isotope discrimination data indicated that stomatal limitation to photosynthesis increased with increasing irradiance.
对生长在水面上方树冠层中的巴拿马附生兰花绿黄卡特兰叶片的碳同位素组成（(13)C/(12)C）进行了测量，以区分在确定同位素组成时，源二氧化碳和湿度变化的影响与细胞间二氧化碳浓度的影响。观察到碳同位素比率会因每日总光合有效辐射（PFD，400 - 700纳米）的变化而变化超过4。源二氧化碳同位素组成的变化或湿度的变化不太可能在决定叶片同位素组成中起作用。观察到处于不同光照水平的叶片的碳同位素分馏（Δ）变化范围为17至21。由于所有兰花的叶片氮含量相似，我们认为碳同位素分馏数据表明，光合作用的气孔限制随着光照强度的增加而增加。
