Local adaptation to serpentine soils in Pinus ponderosa
Local adaptation to serpentine soils is studied using both transplant experiments and molecular genetic techniques. In long-lived species, such as pines, it is unclear how soon after germination local adaptation becomes detectable. Here I present results of a 36-year reciprocal transplant experiment using Pinus ponderosa, along with allozyme analyses from the same trees. Using a repeated measures analysis of variance, there is evidence for adaptation to serpentine soils; however, significant differences between source soil types do not become apparent until 20 years after the start of the experiment. Analysis of allozyme data showed no evidence for differentiation between the serpentine and non-serpentine populations. Comparing the performance of families over the course of the experiment found that there was little correlation between performance after 1 or 4 years of growth in the field and performance after 36 years. This suggests that short-term transplant experiments may not provide definitive evidence for adaptation to serpentine soils. A literature survey of all transplant studies using pine species growing on and off of serpentine soils found that studies that lasted fewer than 2 years showed no evidence for adaptation. However, in the two experiments (this one included) that lasted more than 2 years, both showed evidence for adaptation to serpentine soils. More long-term experiments are required to validate these results.
KeywordsPinus ponderosa Local adaptation Serpentine soils Reciprocal transplant experiment Allozymes
Since 1967, this project has been conducted by a dedicated team of scientists, to whom I am indebted for their years of careful work. First and foremost among these is James L. Jenkinson, whose vision and planning made this experiment possible. Over the years, cones and data were collected by Carrol W. Busche, Edwin Jack Carpender, Johnny P. Cramer, David R. Johnson, and Roger A. Stutts. I thank each of them for their efforts. Paul Hodgskiss was responsible for collecting the allozyme data. I also thank R. Latta, D. R. Johnson, P. Hodgskiss and two anonymous reviewers for helpful comments on an earlier draft. This research has been supported over the years by the Institute of Forest Genetics, USDA-Forest Service.
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