© 1992 Heron Publishing—Victoria, Canada
Abscisic acid accumulation in leaves of two contrasting hybrid poplar clones affected by nitrogen fertilization plus cyclic
flooding and soil drying
Zhijun Liu (1) and Donald I. Dickmann (1, 2)
1. Department of Forestry, Michigan State University, East Lansing, MI 48824-1222, USA / 2. Author to whom correspondence should be sent / Received November 18, 1991
Summary
Cuttings of hybrid Populus clones Tristis and Eugenei growing in pots in a greenhouse were treated with nitrogen fertilizer at two rates and subjected
to repeated soil flooding or drying. Periodically, gas exchange measurements and radioimmunoassays, to determine abscisic
acid (ABA) concentrations, were made on recently mature leaves.
In both clones, photosynthesis and stomatal conductance were depressed five days after flooding, but leaf ABA concentrations
remained relatively constant. In contrast, an initial, 9-day period of soil drying resulted in substantial ABA accumulation
in leaves, which closely correlated with declines in photosynthesis and conductance. A second soil drying cycle of up to 9
days was less effective in modifying gas exchange and leaf ABA concentrations. High-N supply stimulated leaf ABA production
as the soil dried. On the resumption of watering, gas exchange in Tristis recovered fully and rapidly and leaf ABA concentrations
quickly returned to control values, whereas gas exchange in Eugenei recovered slowly and leaf ABA concentrations remained
high for longer.
Gas exchange in Eugenei was unaffected by soil drying until leaf ABA concentrations exceeded 100 ng gdw–1, whereas Tristis showed a reduction in stomatal conductance and photosynthesis at leaf ABA concentrations of only 10 ng gdw–1. A rise in internal CO2 concentrations was associated with increased leaf ABA concentrations in Tristis, but not in Eugenei. Clonal differences in
the relationship between gas exchange and leaf ABA concentration suggest contrasting physiological strategies for survival
under prolonged drying conditions.
