Effects of elevated CO2, water and nutrients on Picea sitchensis (Bong.) Carr. seedlings.

Sitka spruce (Picea sitchensis (Bong.) Carr.) seedlings were grown from seed for one year in naturally lit growth chambers with either ambient or ambient + 250 ppm concentrations of CO2. In the following year the plants were grown in the same CO2 treatments for the whole growing season at two concentrations of nutrients and were either well-watered or subjected to a long-term, gradually increasing drought. Elevated CO2 increased significantly growth in all treatments except the well-watered, unfertilized treatment. The relative increases in end-of-year biomass in the elevated CO2 treatment compared with the ambient treatment were: well-watered, fertilized + 52%, well-watered, unfertilized +19%, droughted, fertilized+ 44%, and droughted, unfertilized + 49%. Growth analysis revealed that treatment effects on both unit leaf rates and leaf area duration were important in determining the final masses of the plants. Plants growing in elevated CO2 had increased relative growth rates in the first half of the growing season but only slightly increased or even slightly decreased relative growth rates in the later part of the growing season in all water × nutrient treatments. Overall there was a significant CO2× water × nutrient interaction on end-of-year biomass. A combination of small nutrient concentration and adequate water supply led to the smallest growth response to elevated CO2