Root System Development of Juvenile Ponderosa Pine as Influenced by Soil Type and Nutritional Augmentation

A comparison of the capacities of granitic and andesitic soils, with and without nutritional augmentation, to promote above- and below-ground development of ponderosa pine (Pinus ponderosa Dougl. ex Laws.) seedlings was conducted. Shoot dimensions and dry weight along with root system length and weight within both the coarse and fine fractions were all significantly enhanced in granitic soils compared to an andesitic one, and seedlings grown in the former had far more short roots and ectomycorrhizae as well. For both shoots and roots, the magnitude of these growth enhancements was somewhat more pronounced in a less weathered granitic soil than in a more weathered one such that at the conclusion of the study, total shoot biomass of seedlings grown in the andesitic soil averaged 38% of that produced in the less weathered granitic one and 47% of that in the more heavily weathered granitic soil, while such comparisons regarding that of the roots revealed values of 28% and 34%, respectively. Fertilization at the onset of the study with either N or P or N+P had little capacity to compensate for the growth deficiencies in either above- or below-ground seedling tissues attributable to the andesitic soil, and its influences in the granitic soils were muted and largely ephemeral. Shoot growth was well correlated with root system length and weight and at least moderately so with short root and mycorrhizal counts, although such counts were commensurate with stronger regression models primarily when limited to the fine rather the coarse root size fraction.