We investigated the effects of nitrogen availability and present versus future atmospheric environments (i.e., climate) on the seedling performance of 16 open-pollinated maternal families of Piceamariana (Mill.) B.S.P. over two simulated growing seasons. Diurnal and seasonal patterns of temperature, relative humidity, photoperiod, and light intensity were simulated. The simulated future climate included both elevated CO2 and seasonally appropriate increases in mean monthly temperatures. Compared with the present, the future climate increased seedling survival, total and root dry mass, rate of winter bud development, net photosynthetic rate, and water and nitrogen use efficiencies; decreased needle nitrogen content; and altered biomass allocation patterns. Greater nitrogen availability greatly improved seedling performance and changed biomass allocation patterns. Climate and nitrogen level interacted synergistically to promote seedling growth (branch number and root dry mass), survival, and bud development. The future climate increased seedling survival, rate of bud development, and nitrogen use efficiency much more in the low than in the high nitrogen regime. Seedling performance 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 fertilization suggest that families selected for rapid growth under present conditions may not do well in the future, at least in terms of early establishment. Forest managers and tree breeders should take this possibility into consideration in their tree improvement and reforestation programs.
Response of biomass allocation patterns to thinning in Pinus halepensis differs under dry and semiarid Mediterranean climates
