© 1997 Heron Publishing—Victoria, Canada
Carbon isotopic composition, gas exchange, and growth of three populations of ponderosa pine differing in drought tolerance
J. W. Zhang (1), Z. Feng (2, 3), B. M. Cregg (2, 4) and C. M. Schumann (2, 5)
1. Department of Forestry, Fisheries and Wildlife, University of Nebraska at Lincoln, East Campus, Lincoln, NE 68583-0822, USA / 2. USDA Forest Service, Rocky Mountain Research Station, National Agroforestry Center, East Campus-UNL, Lincoln, NE 68583-0822,
USA / 3. College of Forestry, Shandong Agricultural University, Tai'an, Shandong 271018, P.R. China / 4. Union Camp Corporation, 1720 Goza Road, Mayesville, SC 29104, USA / 5. USDA-ARS, Appalachian Soil and Water Conservation Laboratory, 1224 Airport Road, P.O. Box 400, Beaver, WV 25813, USA / Received July 17, 1996
Summary
Effects of water supply on gas exchange, carbon isotopic composition, and relative growth rate were compared among seedlings
from three populations of ponderosa pine (Pinus ponderosa Dougl. ex Laws.) grown in a controlled environment chamber. The three populations were chosen to represent high, moderate
and low drought tolerance. There was no indication that drought tolerance was related to high water-use efficiency. Populations
differed (P < 0.05) in relative growth rate (RGR), but did not differ (P > 0.10) in gas exchange variables or carbon isotope ratio (δ13C). Well-watered seedlings had significantly higher RGR, xylem pressure potential (Ψxpp), net photosynthesis (A), stomatal conductance to water vapor (g), and lower δ13C and instantaneous water-use efficiency than water-stressed seedlings. With decreasing Ψxpp, A decreased linearly, whereas g decreased exponentially. Seedlings of the highly drought-tolerant population were more sensitive to water availability than
seedlings from the other populations; they used water quickly when water was available, but closed their stomata in response
to water stress. We conclude that, in ponderosa pine, the drought avoidance mechanism is more important for survival and growth
in arid and semiarid environments than the efficient use of water.
Keywords:
carbon isotope ratio, net photosynthesis, Pinus ponderosa, relative growth rate, stomatal conductance, water-use efficiency,
xylem pressure potential.
