The dynamics of C and N in terrestrial ecosystems are not completely understood and the use of stable isotopes may be useful to gain further insight in the pathways of CO2emissions and leaching of dissolved organic carbon (DOC) and nitrogen (DON) during decomposition of litter. Objectives were (i) to study the decomposition dynamics ofCalamagrostis epigeios, a common grass species in forests, using13C-depleted and15N-enriched plants and (ii) to quantify the effect wood ash addition on the decomposition and leaching of DOC and DON. Decomposition was studied for 128 days under aerobic conditions at 8°C and moisture close to field capacity in a spodic dystric Cambisol with mor-moder layer. Variants included control plots and additions of (i)Calamagrostislitter and (ii)Calamagrostislitter plus 4 kg ash m−2.1.Decomposition ofCalamagrostisresulted in a CO2production of 76.2 g CO2–C m−2(10% of added C) after 128 days and cumulative DOC production was 14.0 g C m−2out of which 0.9g C m−2wasCalamagrostis-derived (0.1% of added C). The specific CO2formation and specific DOC production fromCalamagrostiswere 6 times higher (CO2) and 4 times smaller (DOC) than those from the organic layer. The amount ofCalamagrostis-derived total N (NH4+, NO3−, DON) leached was 0.7g N m−2(4.8% of added N). Cumulative DON production was 0.8g N m−2which was slightly higher than for the control. During soil passage, much of the DOC and DON was removed due to sorption or decomposition. DOC and DON releases from the mineral soil (17cm depth) were 6.3g C m−2and 0.5g N m−2.Addition of ash resulted in a complete fixing of CO2for 40 days due to carbonatisation. Afterwards, the CO2production rates were similar to the variant without ash addition. Production of DOC (98.6g C m−2) and DON (2.5g N m−2) was marked, mainly owing to humus decay. However, Calamagrostis-derived DOC and Culamagrostis-derived total N were only 3.9g C m−2(0.5 YO of added C) and 0.5g N m−2(3.4% of added N). The specific DOC production rate from the organic layer was 6 times higher than that from Cularnagrostis. The results suggest that with increasing humification from fresh plant residues to more decomposed material (OFand OHlayers) the production ratio of DOC/CO2-C increases. Addition of alkaline substances to the forest floor can lead to a manifold increase in DOC production.