Seasonal variation in crassulacean acid metabolism in Dudleya blochmanae (Crassulaceae)

Plants of Dudleya blochmanae were studied over a growing season (December-June) in their native habitat on the central California coast. During the season soil water potential fluctuated widely, becoming unmeasurably negative (< -5.0 MPa) by early May. In contrast, leaf water potential did not fluctuate greatly with the most negative value of -- 0.56 MPa occurring in June. The leaves exhibited nocturnal accumulation of titratable acidity at all sampling periods, with the greatest magnitudes of accumulation occurring late in the growing season. The fruits also exhibited nocturnal accumulation of titratable acidity. The biomass δ13C values of all organs were most negative in December and least negative in June. The findings confirmed earlier suggestions that there may be biologically important differences in carbon isotope content among the various organs of a single plant of D. blochmanae. The water potential of the photosynthetic organs was highly correlated (r2= 0.84) with the biomas δ13C value. A greenhouse study demonstrated that the fruits exhibit an apical dominance with regard to maintenance of plant water potential during drought.