Silvera Katia, Santiago Louis S, Winter Klaus
Smithsonian Tropical Research Institute, P.O. Box 2072, Balboa, Ancón, Republic of Panama.
Department of Integrative Biology and Center for Stable Isotope Biogeochemistry, 3060 Valley Life Science Building, University of California, Berkeley, CA 94720, USA.
Funct Plant Biol. 2005 Jul;32(5):397-407. doi: 10.1071/FP04179.
Crassulacean acid metabolism (CAM) is one of three metabolic pathways found in vascular plants for the assimilation of carbon dioxide. In this study, we investigate the occurrence of CAM photosynthesis in 200 native orchid species from Panama and 14 non-native species by carbon isotopic composition (δC) and compare these values with nocturnal acid accumulation measured by titration in 173 species. Foliar δC showed a bimodal distribution with the majority of species exhibiting values of approximately -28‰ (typically associated with the C pathway), or -15‰ (strong CAM). Although thick leaves were related to δC values in the CAM range, some thin-leaved orchids were capable of CAM photosynthesis, as demonstrated by acid titration. We also found species with C isotopic values and significant acid accumulation at night. Of 128 species with δC more negative than -22‰, 42 species showed nocturnal acid accumulation per unit fresh mass characteristic of weakly expressed CAM. These data suggest that among CAM orchids, there may be preferential selection for species to exhibit strong CAM or weak CAM, rather than intermediate metabolism.
景天酸代谢（CAM）是维管植物中发现的用于二氧化碳同化的三种代谢途径之一。在本研究中，我们通过碳同位素组成（δC）研究了巴拿马200种本土兰花物种和14种非本土物种中CAM光合作用的发生情况，并将这些值与173种通过滴定法测量的夜间酸积累值进行比较。叶片δC呈现双峰分布，大多数物种的δC值约为-28‰（通常与C途径相关）或-15‰（强CAM）。尽管厚叶与CAM范围内的δC值相关，但一些薄叶兰花也能够进行CAM光合作用，酸滴定结果证明了这一点。我们还发现了具有C同位素值且夜间有显著酸积累的物种。在128种δC比-22‰更负的物种中，有42种表现出每单位鲜质量夜间酸积累的特征，这是弱表达CAM的表现。这些数据表明，在CAM兰花中，物种可能更倾向于表现为强CAM或弱CAM，而不是中间代谢。
