© 2003 Heron Publishing—Victoria, Canada
Selfing results in inbreeding depression of growth but not of gas exchange of surviving adult black spruce trees
Kurt Johnsen (1, 2), John E. Major (3) and Chris A. Maier (1)
1. USDA Forest Service, Southern Research Station, 3041 Cornwallis Road, RTP, NC 27709, USA / 2. Author to whom correspondence should be addressed (kjohnsen@fs.fed.us) / 3. Natural Resources Canada, Canadian Forest Service, Atlantic Forestry Centre, Fredericton, NB E3B 5P7, Canada / Received January 31, 2003; accepted March 29, 2003; published online September 1, 2003
Summary
In most tree species, inbreeding greatly reduces seed production, seed viability, survival and growth. In a previous large-scale
quantitative analysis of a black spruce (Picea mariana (Mill.) B.S.P.) diallel experiment, selfing had large deleterious effects on growth but no impact on stable carbon isotope
discrimination (an indirect measure of the ratio of net photosynthesis (A) to stomatal conductance (gwv)). It was hypothesized that selfing has no effect on carbon (C) fixation at the leaf level but impairs subsequent utilization
of C. Alternatively, A and gwv may be impacted by selfing to the same extent. However, no gas exchange data were collected to test these hypotheses. We
have now obtained photosynthetic gas exchange data from three selfed families and three outcrossed families (all the result
of controlled pollination) from the same diallel experiment. Photosynthetic responses to intercellular CO2 concentration (A–Ci curves) were generated on four replicates per family, one block per day, over a 4-day period in July. There were no differences
between selfed and outcrossed families in maximum carboxylation rate, maximum electron transport, A or gwv (both estimated at 370 ppm CO2), or the ratio A/gwv. Because selfed trees had higher mortality than outcrossed trees during the experiment, we cannot exclude the possibility
that previously living selfed progeny had low A. Nevertheless, the data indicate that inbreeding can result in trees that have low productivity despite high A, supporting our hypothesis that gas exchange is similar between selfed and outcrossed progeny trees. We conclude that utilization
of fixed C is modified in the surviving selfed progeny.
Keywords:
carbon isotope discrimination, photosynthesis, Picea mariana, stomatal conductance.
