Summary• The Bromeliaceae encompass predominantly rosette, terrestrial or epiphytic species, including C3 and crassulacean acid metabolism (CAM) photosynthetic types within its three subfamilies. Here, leaf diurnal changes and longitudinal gradients of soluble sugars, organic acids and starch, were quantified to estimate the rates of carbohydrate translocation from mature leaves of C3 and CAM species.• Leaves of Ananas comosus , Aechmea fendleri , Bromelia humilis , Guzmania mucronata , Tillandsia fendleri , Tillandsia flexuosa and Tillandsia utriculata , were sampled at the base, middle, and upper sections during the day. We measured osmolality in sap from frozen subsamples, sugars and organic acids in hot-water extracts from microwave-dried subsamples, and starch hydrolysed with α -amylase or 1.1% HCl.• CAM activity was expressed by malate accumulation, citrate was present, but fluctuations were not significant. Nocturnal reductions in sucrose in bromelioid CAM species accounted for most of the acidification requirements. Tillandsioid CAM species used starch for acid synthesis. Both CAM and C3 bromeliads exported significant amounts of hexose during the night, particularly from the leaf base.• Leaf bases of CAM species showed lowest acid accumulation but similar or more positive δ 13 C-values to the active CAM sections. Exported carbohydrates probably derive from carbon fixed during the night period.

The genus Ananas has its centre of origin in northern South America. In this area, several varieties of Ananas comosus are widely cultivated, and a number of wild species are found growing under variable conditions of light intensity, soil fertility and water availability. Here we report detailed daily courses of titratable acidity, and malate, citrate and free‐sugars content of several cultivated varieties of A. comosus and of A. ananassoides, a closely related species growing on granitic rock‐outcrops in southern Venezuela. Day‐night oscillations of both malate and citrate were detected in plants growing under full sun, but malate was by far the most important organic anion associated with CAM performance in ail populations sampled. Fructose was the dominant compound in the neutral fraction, but only sucrose showed a consistent inverse relation with the cycle of titratable acidity. The diel oscillations of free sugars measured were not always enough to account for the amount of organic anions accumulated during the night. Plants cultivated under shady conditions always showed a lower night‐time increase in titratable acidity and organic acids, and also smaller oscillations in the amount of free sugars than sun exposed plants. In all populations growing under full sun, osmolality increased during the night, but it was not always possible to explain these changes on the basis of variations in molar concentrations of organic acids and sugars. Besides, no diel variations in the cations K+, Ca2+ and Mg2+ were detected. K+ was always the dominant cation (K/Ca ratios ∼ 19), while Mg2+ was always higher than Ca2+ (Mg/Ca ∼ 2).