Carbon isotope ratio and the extent of daily CAM use by Bromeliaceae


Author for correspondence: S. Pierce Tel: +44 114222 4702 Fax: +44 114222 0002 E-mail:


  • • Use of carbon isotope ratio (δ 13 C) to resolve photosynthetic pathways (C 3 , C 4 or CAM) has limitations imposed by the use of intermediate photosynthetic modes by certain plant taxa.
  • • Diel gas-exchange patterns, leaf δ 13 C values and nocturnal tissue acidification were determined for 50 Bromeliaceae.
  • • δ 13 C values for well watered plants reflected the proportion of daily CO 2 uptake occurring at night. Thirteen per cent of species with δ 13 C values typical of C 3 plants (i.e. from −22.6 to −31.5‰) showed nocturnal acidification and either a small proportion (< 10%) of daily CO 2 uptake occurring nocturnally or internal CO 2 recycling during part of the night. None altered CAM expression in response to short-term drought, but the contribution of CAM to daily carbon gain became proportionally more important as C 3 CO 2 uptake failed.
  • • Surveys of plant communities using solely the carbon isotope technique underestimate the number of CAM-equipped plants.