AbstractWildAnanasspecies in northern South America occur in shady environments and appear to be relatively intolerant to droughts associated with growth under full sun exposure. This behaviour contrasts with the higher productivity of commercial varieties ofAnanas comosuswhen grown under full sun exposure. Such differentiation within the genus offers an opportunity to study the process of adaptation of apparently high light avoiding species into true sun plants. As a first approximation, the analysis of nitrogen content and carbon and hydrogen isotope ratios of bromeliads growing under natural conditions was undertaken to test the following hypotheses: 1. Leaf nitrogen content of plants grown under partial shade is higher than that of the same species in the same habitat growing under full sun exposure, due to the higher availability to nitrogen in the under‐canopy, but also to the lower proportion of structural carbohydrates in shade leaves; 2. δ13C values are usually more negative in CAM bromeliads growing under partial shade because of the lower contribution of CAM to total carbon gain, and the probable fixation of CO2originating from soil respiration; 3. δD values of CAM bromeliads are less negative than those of C3 bromeliads, but CAM bromeliads grown in shady habitats tend to have more negative δD values because of the lower relative accumulation of deuterium in leaf tissue water, and also because of their relatively lower CAM activity. The results show a clear differentiation between CAM and C3 bromeliads based on δ13C values, and in general δD values are less negative in CAM bromeliads. However, in several species overlapping δD values between C3 and CAM bromeliads were observed. The analysis of paired samples of the same species grown under contrasting light intensity usually conformed with the expectations. A number of deviations from the hypotheses were observed which appeared to be related to particular environmental conditions. The interpretation of δD values obtained from total organic matter is made difficult by the local variation of hydrogen/deuterium ratios in water available to t