Crassulacean acid metabolism (CAM) was observed in three species of tropical
ferns, the epiphytes Microsorium punctatum and
Polypodium crassifolium and the lithophyte
Platycerium veitchii.
Polypodium crassifolium and
P. veitchii exhibited characteristics of weak CAM.
Although no net nocturnal CO2 uptake was observed, the
presence of CAM was inferred from nocturnal increases in titratable acidity of
4.7 and 4.1 µequiv (g fr wt)–1 respectively,
a reduction in the rates of net CO2 evolution during the
first half of the dark period, and the presence of a CAM-like decrease in net
CO2 uptake during the early light period. In
M. punctatum net CO2 uptake during
the first half of the dark period was accompanied by an increase in titratable
acidity of 39.2 µequiv (g fr wt)–1 and a
pronounced reduction in net CO2 uptake during the early
light period. When water was withheld from
P. crassifolium and M. punctatum,
net CO2 uptake during the light was reduced markedly but
there was no change in the extent or patterns of CO2
exhange in the dark. As a consequence, the proportion of carbon gained due to
CO2 fixation in the dark increased from 2.8 and
10% to 63.5 and 49.3%, respectively (100% being net
CO2 uptake during the light plus the estimated
CO2 uptake during the dark). After 9 days without added
water, dark CO2 uptake was responsible for the
maintenance of a net 24 h carbon gain in
P. crassifolium.
Platycerium veitchii,
P. crassifolium and M. punctatum
exhibited carbon isotope ratios of between –25.9 and –22.6‰
indicating that carbon isotope ratios may not, by themselves, be sufficient
for the identification of weak CAM. We suggest that CAM may be more prevalent
in tropical epiphytic and lithophytic ferns than currently envisaged.
Sensitive detection of testosterone and testosterone prohormone administrations based on urinary concentrations and carbon isotope ratios of androsterone and etiocholanolone
