From Moss to Mineral: Soil Organic Carbon Fractionation under Bryophytes in Temperate Forests

The persistence of soil organic carbon (SOC) in forest ecosystems depicts not only the quantity of organic matter (OM) inputs but also how carbon (C) is distributed among functionally distinct soil pools with different roles. In forest ecosystems, mosses significantly influence SOC dynamics not merely by increasing surface C stocks, but by altering its partitioning into more persistent, mineral associated fractions. However, the influence of mosses on C stability in occluded and mineral-associated SOM fractions based on contrasting temperate forest types has rarely been quantified.

To address this knowledge gap, our study aims to characterize and quantify soil particulate organic matter (POM) fractions to assess C sequestration potential under moss cover and forest types. A total of 42 soil samples were collected from coniferous mixed (Baden-Württemberg) and pine forests (Brandenburg) from the top soil layer (0-2 cm) with and without mosses. Physical density fractionation was done to quantify SOC distribution among free POM (FPOM), occluded POM (OPOM), and mineral-associated POM (MAPOM) which represent soil pools with varying turnover times.

The moss cover across coniferous mixed forest significantly increased the C concentration in MAPOM by up to 75% which indicate a long- term C stabilization via stable MAPOM. But the scenario was different for pine forest, where mosses significantly increased the C:N ratio of labile fractions which denote different decomposition dynamics. The results also indicate that the long-term SOC sequestration was highest in the moss-covered coniferous forests which stored about six- fold more C in MAPOM than pine forests. Further results will be presented at EGU 2026.