Poster: Ecophysiology

Abs # 44: Diel acid fluctuations and the water relations of cam plants

Presenter:	Bayless, Kellis M, kellis@ku.edu
Authors	Bayless, Kellis M (A)   Martin, Craig E (A)
Affiliations:	(A): University of Kansas, Department of Ecology & Evolutionary Biology

Leaf or stem tissues from 11 phylogenetically diverse CAM species were analyzed at the beginning and end of the day to determine diel fluctuations in malic acid, total acidity, and osmotic potential. When well-watered, four of the six terrestrials, as well as two of the five epiphytes, accumulated more total acid than could be accounted for by malic acid. Changes in malic acid accounted for one-third and one-half of the changes in osmotic potential in terrestrial and epiphytic species, respectively. When droughted, all species accumulated more acid at night than could be accounted for by malic acid. This discrepancy between the nocturnal malic acid accumulation and the total acid accumulated by the plant was significantly greater under drought stress than under well-watered conditions in the terrestrials, but was similar between the epiphytes under the two conditions. In contrast, the ratio of total acid to malic acid accumulation at night in both terrestrials and epiphytes significantly increased under droughted conditions relative to well-watered conditions. Only 20% of the variability in osmotic potential could be accounted for by changes in malic acid in the terrestrial species under drought stress conditions. In the epiphyte species under drought stress, diel changes in osmotic potential were not correlated with malic acid accumulations. Given the diversity of species examined, this study underscores the considerable degree of nocturnal accumulations of acids other than malic acid in plants performing CAM photosynthesis, as well as the weak correlation between diel changes in malic acid concentration and changes in tissue water relations.