© 1991 Heron Publishing—Victoria, Canada
Net photosynthesis and leaf conductance of loblolly pine seedlings in 2 and 21% oxygen as influenced by irradiance, temperature
and provenance
Lisa J. Samuelson (1, 2) and Robert O. Teskey (1)
1. School of Forest Resources, University of Georgia, Athens, GA 30602, USA / 2. Department of Forestry, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, USA / Received March 21, 1990
Summary
Carbon dioxide assimilation and transpiration by secondary needles of two-year-old loblolly pines (Pinus taeda L.) were measured at 2 and 21% (ambient) oxygen. Measurements were made with a Georgia provenance at irradiances (photosynthetic
photon flux density) of 150, 300, 700 and 1200 μmol m–2 s–1 and a constant temperature of 25 °C, and at temperatures of 15, 25 and 35 °C and a constant irradiance of 1200 μmol m–2 s–1. Measurements were made with provenances from North Carolina, Florida, Arkansas, and Georgia at 25 °C and an irradiance of
1200 μmol m–2 s–1. There was no significant interaction between the effects of irradiance and oxygen on either net photosynthesis or leaf conductance.
Taking all irradiances together, photosynthesis was 16% less and leaf conductance 28% less in 2% oxygen than in 21% oxygen.
There was a significant interaction between the effects of temperature and oxygen concentration on both net assimilation and
leaf conductance. Net photosynthesis at 21% oxygen relative to that at 2% was significantly reduced at 25 and 35 °C, but not
at 15 °C, whereas leaf conductance at 21% oxygen relative to that at 2% was significantly increased at 15 and 25 °C, but not
at 35 °C. In the provenance study, net photosynthesis was 11% higher and leaf conductance 36% lower in 2% oxygen than in 21%
oxygen. There was no significant interaction between the effects of provenance and oxygen on either net photosynthesis or
leaf conductance.
