Seed transfer across geographic regions in different climates leads to reduced tree growth and genetic admixture in Quercus mongolica var. crispula

Seed transfer may affect not only the performance of trees growing from transferred seeds but also the reproduction of the trees and the performance of their progeny. We investigated Quercus mongolica var. crispula trees transplanted from multiple provenances and their seedlings naturally regenerated in northeastern and southwestern test sites in Japan. The test sites and provenances were grouped into seven regions based on their geographic and climatic profiles. We defined the local population as trees from provenances in a region of either test site and the foreign population as trees from provenances in the other regions. Tree size was larger in the local population than in the foreign population in both test sites. We estimated foreign population ancestry from the allele frequencies in the local and foreign populations in each test site using microsatellite genotypes. We discriminated the local and foreign populations using foreign population ancestry although genetic differentiation between these populations were relatively low (0.022 <= F-ST <= 0.034). Different frequency distributions of foreign population ancestry between transplanted trees and regenerated seedlings indicated crossing between the local and foreign populations. Tree size decreased as foreign population ancestry increased in both test sites. Seedling mass increased in the northeastern test site but decreased in the southwestern test site as foreign population ancestry increased, indicating larger mass of seedlings with genetic properties of southwestern provenances. The findings suggest that seed transfer between regions results in reduced performance of trees growing from transferred seeds and admixed progeny of trees from local and foreign regions.