### Carbon, nitrogen and phosphorus net mineralization in organic layers of temperate forests: Stoichiometry and relations to organic matter quality

*Christine Heuck*^{1}, Marie Spohn^{1}

^{1} Soil Biogeochemistry, University Bayreuth

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*in* Paving the way for research: Databases, instruments, networks

& Open Session
13.10.2016, 16:00-16:15, H36, NW III

Decomposition in the organic layer of forest ecosystems ends with mineralization of carbon (C), nitrogen (N) and phosphorus (P). The rates of mineralization processes influence C sequestration and soil fertility, but despite their importance for ecosystem functioning, C, N and P net mineralization rates are seldom evaluated in combination. Hence, we assessed the relationships between net mineralization rates and organic matter stoichiometry in an eight-week incubation experiment with Oi, Oe and Oa horizon material of six beech, one spruce and one pine site. We determined C, N and P net mineralization rates, organic C quality and C:N:P stoichiometry. Net N mineralization started at molar organic matter C:N ratios of 41 (Oi) or 28 (Oa) and N:P ratios of 40 (Oi) or 60 (Oa) and increased with decreasing C:N and N:P ratios. Net P mineralization started at C:P ratios of 1400 (Oi) and N:P ratios of 41 (Oi) and increased with decreasing C:P and N:P ratios. N and P net mineralization were strongly positively correlated with each other, whereas correlations of both net N and net P mineralization with C mineralization were weak. The average C:N:P stoichiometry of net mineralization was 620:4:1 (beech, Oi), 15350:5:1 (coniferous, Oi), 1520:8:1 (Oe) and 2160:36:1 (Oa). On average, ratios of C-to-N net mineralization were higher, and ratios of N-to-P net mineralization lower than organic matter C:N and N:P ratios. This difference contributes to the decrease of C:N ratios and increase of N:P ratios from the Oi to the Oa horizons. In conclusion, the C, N and P net mineralization rates were closely related to organic matter stoichiometry.

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Keywords: critical ratio, ecological stoichiometry, forest floor, nutrient cycling, respiration, threshold element ratio

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