# Carbon and Nitrogen Pools and Fluxes in Adjacent Mature Norway Spruce and European Beech Forests
## 1 Introduction  
Temperate forests are one of the most important features within the European landscape. They play an important ecological role--providing ecosystem services (e.g., ensuring vital water resources, maintaining biodiversity, scavenging air pollutants)--as well as a social role, with forests being perceived as a \"real\" natural heritage. Forests are also relevant economic resources (timber production, tourism). Broadleaf forests of lowlands and mixed confer-broadleaf forests of mid-altitude sites have always been influenced by human activities and therefore have been altered considerably [1; 2; 3]. The historical retreat of temperate forests, their considerable fragmentation, changes in woody species composition and soil degradation that resulted from over exploitation caused declines in ecosystem stability and biodiversity of temperate forests [4]. Especially in Central Europe, original forest stands dominated by _Fagus sylvatica_, _Abies alba_ and _Picea abies_ have been almost completely converted to even-aged Norway spruce monocultures. These changes significantly slow down soil formation [5] and alter understory vegetation composition [6]. The influence of tree species composition on the functioning of temperate forests has received increasing attention in recent years due to efforts to alter the even aged spruce monoculture management by introducing broadleaf tree species. Furthermore, spatial distributions of tree species areexpected to change as a result of ongoing climate change [7]. In natural forests, expansion of European beech has been well documented in different parts of Europe [8; 9; 10], and expansion of Norway spruce towards higher altitude was detected in tree-line ecotones in Central Europe [11]. Both natural and human-induced changes in tree species distribution have major impacts on forests functioning. [PERSON] and others [12] summarized the effects of evergreen gymnosperms (EG) and deciduous angiosperms (DA) on forest ecosystems, pointing out that EG species generally induce drier soil conditions. However, biomass and litter production were rather similar among tree species groups, and field evidence of higher accumulation of soil carbon stocks under DA species was lacking. Similarly, [PERSON] and others [13] have shown similar carbon (C) and nitrogen (N) soil stocks in spruce and beech stands, while higher forest floor C and N contents were measured in spruce compared to beech stands with the opposite trend in the mineral soil. A significant fraction of the forest ecosystem C pool is stored in the soil [14]. Carbon allocation from photosynthesis to belowground net primary productivity (NPP) and aboveground NPP might determine the longterm fate of assimilated C as a large proportion of recalcitrant soil C originates from root decomposition [15] and decaying mycorrhizal tissues [16]. Furthermore, beech has deeper roots compared to spruce [17], suggesting different vertical allocation of belowground NPP in the soil profile. Soil respiration (\(F_{8}\)) represents one of the major fluxes of C to the atmosphere [18] and equals about 55% of C fixed during photosynthesis [19]. It is important to identify environmental factors that control \(F_{8}\) and their effects on CO\({}_{2}\) emission rates when potential impacts of environmental change, including community shifts and alteration of moisture/temperature regimes, are studied. Along with soil temperature, moisture, physical and chemical properties, soil respiration varies with vegetation types. Nonetheless, vegetation type seems to be less important in controlling soil respiration rates compared to abiotic factors [20]. Among temperate forest ecosystems, the effect of different tree species on soil respiration rates has often been found to be minimal [21; 22; 23; 24]. Ecosystem productivity depends on various environmental factors, of which nutrient limitation plays an important role due to the stoichiometric constraints of elements in plant tissues [25].