Soil respiration and rates of soil carbon turnover differ among six common European tree species

The knowledge of tree species effects on soil organic carbon (C) turnover based on rigorous experimental designs is limited for common European deciduous tree species. We assessed soil respiration, and rates of C turnover in six tree species in a more than 30-year-old common garden experiment replicated at six sites in Denmark. The studied tree species were the broadleaves beech (Fagus sylvatica L), pedunculate oak (Quercus robur L.), lime (Tilia cordata L), sycamore maple (Acer pseudoplatanus L) and ash (Fraxinus excelsior L) and the conifer Norway spruce (Picea abies (L) Karst.). Rates of C turnover were estimated by (i) the ratio of estimated soil heterotrophic respiration (Rh) to C stock in forest floor and top mineral soil, (ii) the ratio of litterfall C to forest floor C, (iii) foliar mass loss in litterbags, and (iv) mineral soil C turnover assessed by laboratory incubation. Soil respiration differed significantly among several species and increased in the order beech < lime < spruce = oak = maple < ash. Soil respiration was temperature limited with no significant species difference in Q(10). Norway spruce soils were significantly driest, and soil respiration was also limited by soil moisture. Carbon turnover rates based on the ratio between Rh and C stock were significantly higher in ash than in all other species except maple, and maple also had higher C turnover than spruce. A similar influence of tree species on C turnover was indicated by the litterfall C to forest floor C ratio and by foliar mass loss; rates of C turnover increased in the order spruce < beech < oak < ash = lime = maple with significant differences between several of the species. Mineral soil C turnover during laboratory incubation was highest for ash, maple and oak, and significantly lower for spruce. The indices of soil C turnover were largely consistent and some were significantly correlated. Differences in C turnover were for the most part attributable to variation in litter quality and microclimatic conditions. Litterfall foliar N, Ca and Mg concentrations and to some extent lignin concentration correlated best with C turnover indices that integrated the forest floor. The results suggests that specific traits of Norway spruce and these five common broadleaf forest species should be taken into account in the modelling of soil C stock dynamics over decades. (C) 2011 Elsevier B.V. All rights reserved.