Early Selection of Black Spruce Seedlings and Global Change: Which Genotypes Should We Favor?

We investigated the effects of both soil fertility and predicted changes in climate on the performance of different families of black spruce, Picea mariana (Mill.) B.S.P., during the first growing season. The results were used to examine whether reforestation programs should consider changing their preferred family lines in anticipation of altered performance given global climate change. We grew seedlings of 16 open—pollinated maternal families of black spruce under phytotron conditions simulating present and mid—21st century climatic conditions during the growing season. The realistic, simulated future climate included both elevated CO₂ levels and seasonally appropriate increases in mean daily temperature. To explore the dependence of climatic responses on site quality, seedlings were irrigated with solutions having either 5 or 100 mg/L of nitrogen. The lower nitrogen level represents a poor site for black spruce growth and survival, but the higher level provides ample nitrogen. We also recorded seed size for each seedling to evaluate the degree to which maternal investments might buffer responses to future climate and fertility during the first year on the seedbed. Seedling survival and growth increased both under the future climate regime and with nitrogen fertilization. The two factors interacted synergistically, with nitrogen enrichment significantly enhancing the positive effects of the future climate regime. Nitrogen—poor conditions, however, did not preclude a positive seedling response to the future climate. Our results indicate that seedling survival and height growth are highly dependent upon initial seed mass: larger seeds produced more vigorous 1st—yr seedlings. The families differed in seed mass, seed germination, and seedling survival and growth, but their relative performances did not vary significantly among the treatments. These results suggest that black spruce families selected for rapid growth under present conditions will also do well in the future, at least in terms of early establishment and performance on sites regenerated by seeding.