Adaptive Trait Variation in Seedlings of Rare Endemic Mexican Spruce Provenances under Nursery Conditions

The distributions of the three Mexican spruces are fragmented, possibly leading to phenological, morphological and genetic differentiation, which is partly caused by local adaptation. In this study, we estimated for the first time the intra- and inter-specific phenotypic variation in 5641 seedlings from provenances of the three Mexican spruces. We examined (i) provenance-related differences in the seedling survival rate, diameter (D), height (H) and seed weight (SW) as quantitative traits, (ii) the association between the survival rate, D, H and SW and climatic and soil variables in the Picea provenances and (iii) (narrow-sense) heritability (within-provenance) based on D and H under the same nursery conditions, assuming that the response can be considered as a proxy for quantitative genetic differentiation between provenances. All Mexican spruce species differed significantly in H, and all eight provenances studied were significantly different in D and H, except for two neighboring provenances of P. mexicana. Very strong, significant correlations (up to R-2 = 0.96) were found between H, the survival rate and SW with respect to environmental factors of provenance/seed origin. Additionally, the heritability index explained a high percentage of the provenance-related variance. The use of germplasm for restoration in different sites and with different populations requires collecting seeds from numerous trees from as many provenances as possible, but should be carried out with caution owing to the apparently strong local adaptation in provenances of the Mexican spruces.