EARLY SELECTION OF BLACK SPRUCE SEEDLINGS AND GLOBAL CHANGE - WHICH GENOTYPES SHOULD WE FAVOR

We investigated the effects of both soil fertility and predicted chang es in climate on the performance of different families of black spruce , Picea mariana (Mill.) B.S.P., during the first growing season. The r esults were used to examine whether reforestation programs should cons ider 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 condition s simulating present and mid-21 st century climatic conditions during the growing season. The realistic, simulated future climate included b oth elevated CO2 levels and seasonally appropriate increases in mean d aily temperature. To explore the dependence of climatic responses on s ite quality, seedlings were irrigated with solutions having either 5 o r 100 mg/L of nitrogen. The lower nitrogen level represents a poor sit e for black spruce growth and survival, but the higher level provides ample nitrogen. We also recorded seed size for each seedling to evalua te the degree to which maternal investments might buffer responses to future climate and fertility during the first year on the seedbed. See dling survival and growth increased both under the future climate regi me and with nitrogen fertilization. The two factors interacted synergi stically, with nitrogen enrichment significantly enhancing the positiv e effects of the future climate regime. Nitrogen-poor conditions, howe ver, did not preclude a positive seedling response to the future clima te. Our results indicate that seedling survival and height growth are highly dependent upon initial seed mass: larger seeds produced more vi gorous 1 st-yr seedlings. The families differed in seed mass, seed ger mination, and seedling survival and growth, but their relative perform ances did not vary significantly among the treatments. These results s uggest that black spruce families selected for rapid growth under pres ent conditions will also do well in the future, at least in terms of e arly establishment and performance on sites regenerated by seeding.