High nutrient supply and interspecific belowground competition enhance the relative performance of Picea mariana (Mill). B.S.P seedlings over Picea glauca [Moench] Voss. under elevated CO2

Abstract

We tested how nutrient supply and interspecific belowground competition affect ecophysiological and morphological responses to elevated CO\n 2\n in black (\n Picea mariana\n (Mill). B.S.P) and white spruce (\n Picea glauca\n [Moench] Voss.). It is found that belowground competition and high nutrient greatly enhanced the relative performance of black spruce over white spruce at elevated CO\n 2\n .\n We have previously found that interspecific belowground competition reduce growth, whole seedling photosynthesis, and biomass allocation to leaf and that belowground competition and nutrient supply affect responses to elevated CO2 in the above two species, but we did not examine the physiological and morphological mechanisms of the responses. To examine the interactive effects of belowground competition, nutrient supply and elevated CO2 on root morphology, photosynthetic rate, and biochemical and photochemical capacity of photosynthesis in black spruce (Sb, Picea mariana [Mill.] B.S.P.) and white spruce (Sw, Picea glauca [Moench] Voss.). Seedlings were grown in individual containers (no belowground competition) or in a common container (belowground competition) under 380 vs. 720\xa0µmol\xa0mol−1 CO2 and high vs. low nutrient supply in the greenhouse for one growing season. Elevated CO2 stimulated photosynthesis and nutrient use efficiency to a much greater degree in black than white spruce when they were grown in the same container, particularly under high nutrient supply. The ability to produce a greater length of roots per unit volume of soil was associated with the response of black spruce. The synergistic effects of elevated CO2 and belowground competition on the physiology and root morphology of black spruce suggest that elevated CO2 will likely increase the relative competitiveness of black spruce over white spruce.