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Genetic variation for resource use efficiencies in lodgepole pine Smets, Pia

Abstract

This study investigates genetic variation for resource-use efficiencies in lodgepole pine (Pinus contorta Dougl. ssp. contorta and ssp. latifolia). Because of the species' frequent occurrence on marginal sites, these resource-use efficiencies are expected to play an important role in its adaptation and evolution. A deeper understanding of the patterns of adaptation is needed to enable a more fine-tuned management of the existing genetic variation in the breeding program. Since natural selection acts on phenotypes, both genotype and environment are considered jointly. Since the effects of genotypes, traits and environmental factors may not be separable, all of these elements are observed jointly in a controlled experiment. Under the null hypothesis, traits evolve independently to single environmental variables. Under the alternative hypothesis, there is an integrated physiological system that differs among genotypes, that reacts as a whole to multiple environmental variables and evolves as a whole in adaptation to those source variables. Water-use efficiency and nitrogen-use efficiency were measured on one-year old seedlings of lodgepole pine in the controlled environment of the greenhouse. These traits were observed over a range of environments, created by controlled levels of available water and nitrogen. A preliminary experiment was set up in 1996 with provenances of lodgepole pine, mainly to proofrun the nursery techniques, to confirm the existence of genetic variation for resource-use efficiencies, to determine sources of variation in the experiment, and to investigate separability of the effects in general. A second experiment was set up in 1997, using selected families incorporating a more continuous range of variation for source variables than is possible with a provenance structure. It had the added advantage that 10-year field site data are available for comparison. Genetic variation exists for mean trait expression as well as for plasticity for both water-use efficiency and nitrogen-use efficiency. Genetic variability within populations tends to be high despite pronounced differentiation of populations. Populations are somewhat adapted to their local environments, but not very precisely: the breeder is not limited to specific seed sources in order to ensure adaptation to marginal sites. Genetic correlations do not indicate conflicts between selection for growth and adaptation. Genotype-environment rank order change exists for several traits and no simple, consistent patterns for it emerge. Patterns of trait integration vary across environments. Especially nitrogen deficiency can drastically change trait relationships. Thus, multiple environmental factors and multiple traits act jointly to create a large number of environmental niches, resulting in more opportunities for the maintenance of genetic variation. The result of this complex process is that patterns of adaptation for single traits, if present, are not narrowly defined.

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