CO₂ enrichment increases nutrient leaching from model forest ecosystems in subtropical China

Abstract. The effect of high atmospheric CO₂ concentrations on the dynamics of mineral nutrient is not well documented, especially for subtropical China. We used model forest ecosystems in open-top chambers to study the effects of CO₂ enrichment alone and together with N addition on the dynamics of soil cations and anions. Two years of exposure to a 700 ppm CO₂ atmospheric concentration resulted in increased annual nutrient losses by leaching below 70 cm soil profile. Compared to the control, net Mg²⁺ losses increased by 385%, K⁺ by 223%, Ca²⁺ by 167% and NO₃⁻-N by 108%, respectively. Increased losses following exposure to elevated CO₂ were related to both faster weathering of minerals/organic matter decomposition and greater amounts of leaching water. Net annual nutrient losses in the high CO₂ concentration chambers reached 22.2 kg ha⁻¹ year⁻¹ for K⁺, 171.3 kg ha⁻¹ year⁻¹ for Ca²⁺, 8.2 kg ha⁻¹ year⁻¹ for Mg²⁺ and about 2 kg ha⁻¹ year⁻¹ for NO₃⁻-N. The N addition alone had no significant effect on the mineral nutrient leaching losses. However, addition of N together with the high CO₂ treatment significantly reduced mineral nutrient losses.We hypothesize that forests in subtropical China might suffer from nutrient limitation and reduction in plant biomass under elevated CO₂ concentration due to mineral leaching losses in the future.