© 1995 Heron Publishing—Victoria, Canada
Stomatal and mesophyll limitations of photosynthesis in black spruce seedlings during multiple cycles of drought
J. D. Stewart (1, 2), A. Zine el Abidine (2) and P. Y. Bernier (1)
1. Forestry Canada, Quebec Region, C.P. 3800, Sainte-Foy, Quebec G1V 4C7, Canada / 2. Centre de Recherche en Biologie Forestière, Faculté de Foresterie et de Géomatique, Université Laval, Sainte-Foy, Québec G1K
7P4, Canada / Received June 7, 1993
Summary
Container-grown black spruce (Picea mariana (Mill.) B.S.P.) seedlings were planted in trays containing a sand and peat mixture, and placed in a climate-controlled greenhouse.
One group of seedlings was kept well-watered, and another group was subjected to three cycles of drought. Gas exchange analysis
showed that mesophyll photosynthetic function was largely unimpaired by drought. In contrast, stomatal conductance was sensitive
to drought, although it became less sensitive with each drought cycle. Both stomatal and mesophyll conductances increased
with time in control and drought-stressed seedlings, but mesophyll conductance increased with time more rapidly than did stomatal
conductance. Limitation of photosynthetic rate was dominated by the mesophyll. In control seedlings, relative stomatal limitation
increased from 6 to 16% by the end of the experiment. In drought-stressed seedlings, relative stomatal limitation of photosynthesis
reached 40% during the first drought, but decreased to near control values immediately after rewatering. Because the third,
most severe drought had only a minor effect on stomatal conductance, relative stomatal limitation of photosynthesis was similar
to that in control seedlings by the end of the experiment. Inhibition of ontogenetic change during drought stress may be responsible
for the apparent acclimation of mesophyll photosynthetic processes. We conclude that it would be more effective to select
for high photosynthetic capacity than for reduced stomatal sensitivity when breeding for increased drought resistance in black
spruce seedlings.
Keywords:
acclimation, container stock, drought resistance, mesophyll conductance, Picea mariana, stomatal limitation, stomatal sensitivity.
