Effects of elevated atmospheric CO2 concentration on the nutrient uptake characteristics of Japanese larch (Larix kaempferi)

We evaluated the response of Japanese larch (Larix kaempferi Sieb. & Zucc.) to elevated atmospheric CO2 concentration ([CO2]) (689 +/- 75 ppm in 2002 and 697 +/- 90 ppm in 2003) over 2 years in a field experiment with open-top charnbers. Root activity was assessed as nitrogen, phosphorus and potassium uptake rates estimated from Successive measurements of absorbed amounts. Dry matter production of whole plants was unaffected by elevated [CO2] in the first year of treatment, but increased significantly in response to elevated [CO2] in the second year. In contrast, elevated [CO2] increased the root to shoot ratio and fine root dry mass in the first year, but not in the second year. Elevated [CO2] had no effect on tissue N, P and K concentrations. Uptake rates of N, P and K correlated with whole-plant relative growth rates, but were unaffected by growth [CO2], as was ectomycorrhizal colonization, a factor assumed to be important for nutrient uptake in trees. We conclude that improved growth of Larix kaempferi in response to elevated [CO2] is accompanied by increased root biomass, but not by increased root activity.