RESPONSES OF BLACK SPRUCE SEEDLINGS TO SIMULATED PRESENT VERSUS FUTURE SEEDBED ENVIRONMENTS

We investigated the effects of nitrogen availability and present versu s future atmospheric environments (i.e., climate) on the seedling perf ormance of 16 open-pollinated maternal families of Picea mariana (Mill .) B.S.P. over two simulated growing seasons. Diurnal and seasonal pat terns of temperature, relative humidity, photoperiod, and light intens ity were simulated. The simulated future climate included both elevate d CO2 and seasonally appropriate increases in mean monthly temperature s. Compared with the present, the future climate increased seedling su rvival, total and root dry mass, rate of winter bud development, net p hotosynthetic rate, and water and nitrogen use efficiencies; decreased needle nitrogen content; and altered biomass allocation patterns. Gre ater nitrogen availability greatly improved seedling performance and c hanged biomass allocation patterns. Climate and nitrogen level interac ted synergistically to promote seedling growth (branch number and root dry mass), survival, and bud development. The future climate increase d seedling survival, rate of bud development, and nitrogen use efficie ncy much more in the low than in the high nitrogen regime. Seedling pe rformance in the second season was dependent on initial seed mass, but less than in the 1st year. Some of the differences among the families and in their interactions with the climate and (or) nitrogen fertiliz ation suggest that families selected for rapid growth under present co nditions may not do well in the future, at least in terms of early est ablishment. Forest managers and tree breeders should take this possibi lity into consideration in their tree improvement and reforestation pr ograms.