Soil respiration in pure and mixed stands of European beech and Norway spruce following removal of organic horizons

Abstract

Soil respiration was measured in adjacent pure and mixed stands of European beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) Karst.) at Solling, Germany. Forest type had a significant effect on soil respiration, which was highest in the pure beech stand and lowest in the pure spruce stand. Both throughfall and soil temperature increased with the proportion of beech. Additionally, microbial respiration and biomass in the organic (O) horizons increased sequentially from the pure spruce to the pure beech stand, suggesting that abiotic and biotic factors enhanced the decomposition of litter under beech. Because the spruce litter decomposition rate was low, carbon (C) stocks of the O horizons increased with the proportion of spruce, from 1.6 to 5.1 kg C·m–2. The removal of the O horizons decreased soil respiration by 31%–45%, indicating a large contribution of the mineral soil and roots to total soil respiration. Turnover times of organic C in the O horizons ranged between 5.5 years in the pure beech stand and 20.6 years in the pure spruce stand. Our results suggest that tree species conversion may alter the turnover of soil organic matter, and thus the sequestration of organic C in the O horizons.