Pure stands of temperate forest tree species modify soil respiration and N turnover

Abstract. The effects of five different tree species common in the temperate zone, i.e. beech (Fagus sylvatica L.), pedunculate oak (Quercus robur L.), Norway spruce (Picea abies [L.] Karst), Japanese larch (Larix leptolepis [Sichold and Zucc.] Gordon) and mountain pine (Pinus mugo Turra), on soil respiration, gross N mineralization and gross nitrification rates were investigated. Soils were sampled in spring and summer 2002 at a forest trial in Western Jutland, Denmark, where pure stands of the five tree species of the same age were growing on the same soil. Soil respiration, gross rates of N mineralization and nitrification were significantly higher in the organic layers than in the A_h horizons for all tree species and both sampling dates. In summer (July), the highest rates of soil respiration, gross N mineralization and gross nitrification were found in the organic layer under spruce, followed by beech > larch > oak > pine. In spring (April), these rates were also higher under spruce compared to the other tree species, but were significantly lower than in summer. For the A_h horizons no clear seasonal trend was observed for any of the processes examined. A linear relationship between soil respiration and gross N mineralization (r²=0.77), gross N mineralization and gross nitrification rates (r²=0.72), and between soil respiration and gross nitrification (r²=0.81) was found. The results obtained underline the importance of considering the effect of forest type on soil C and N transformations.