Partitioning of carbon and nitrogen during decomposition of ¹³C ¹⁵N-labeled beech and ash leaf litter

The aim of this study was to determine the influence of leaf-litter type (i.e., European beech—Fagus sylvatica L. and European ash—Fraxinus excelsior L.) and leaf-litter mixture on the partitioning of leaf-litter C and N between the O horizon, the topsoil, the soil microbial biomass, and the CO2 emission during decomposition. In a mature beech stand of Hainich National Park, Thuringia, Germany, undisturbed soil cores (diameter 24 cm) were transferred to plastic cylinders and the original leaf litter was either replaced by 13C15N-labeled beech or ash leaf litter, or leaf-litter-mixture treatments in which only one of the two leaf-litter types was labeled. Leaf-litterderived CO2-C flux was measured every second week over a period of one year. Partitioning of leaf-litter C and N to the soil and microbial biomass was measured 5 and 10 months after the start of the experiment. Ash leaf litter decomposed faster than beech leaf litter. The decomposition rate was negatively related to initial leaf-litter lignin and positively to initial Ca concentrations. The mixture of both leaf-litter types led to enhanced decomposition of ash leaf litter. However, it did not affect beech leaf-litter decomposition. After 5 and 10 months of in situ incubation, recoveries of leaf-litter-derived C and N in the O horizon (7%–20% and 9%–35%, respectively) were higher than in the mineral soil (1%–5% and 3%–8%, respectively) showing no leaf-littertype or leaf-litter-mixture effect. Partitioning of leaf-litter-derived C and N to microbial biomass in the upper mineral soil (< 1% of total leaf-litter C and 2%–3% of total leaf-litter N) did not differ between beech and ash. The results show that short-term partitioning of leaf-litter C and N to the soil after 10 months was similar for ash and beech leaf litter under standardized field conditions, even though mineralization was faster for ash leaf litter than for beech leaf litter