Belowground effects of enhanced tropospheric ozone and drought in a beech/spruce forest (Fagus sylvatica L./Picea abies [L.] Karst)

The effects of experimentally elevated O-3 on soil respiration rates, standing fine-root biomass, fine-root production and delta C-13 signature of newly produced fine roots were investigated in an adult European beech/Norway spruce forest in Germany during two subsequent years with contrasting rainfall patterns. During humid 2002, soil respiration rate was enhanced under elevated O-3 under beech and spruce, and was related to O-3-stimulated fine-root production only in beech. During dry 2003, the stimulating effect of O-3 on soil respiration rate vanished under spruce, which was correlated with decreased fine-root production in spruce under drought, irrespective of the O-3 regime. delta C-13 signature of newly formed fine-roots was consistent with the differing g, of beech and spruce, and indicated stomatal limitation by O-3 in beech and by drought in spruce. Our study showed that drought can override the stimulating O-3 effects on fine-root dynamics and soil respiration in mature beech and spruce forests. (C) 2009 Elsevier Ltd. All rights reserved.