Seminar: De Shorn Bramble

The largest share of total soil organic matter is associated with soil minerals, making the formation of mineral-associated organic matter (MAOM) a key factor in the global carbon (C) cycle. The type of mineral as well as factors that shape the quantity and quality of C inputs, such as land use and management intensity, are known to control the amount of MAOM formation and its stability. However, the relative importance of these drivers across a large spatial scale is still unknown, largely because their individual roles in MAOM formation and stabilization is often obscured by the high diversity of minerals in soils and legacy effects of land use and management history. To overcome this challenge, we exposed containers with pristine minerals of either the iron oxyhydroxide, goethite, or the clay mineral, illite, for five years in topsoils of 150 forest and 150 grassland sites in three regions across Germany. We quantified MAOM formation at all 300 sites and assessed its stability at a subset of sites (32 forests and 36 grasslands). Irrespective of land use and management intensity, both formation and stability of MAOM was higher for goethite than illite. More MAOM formed under coniferous forest than deciduous forests and grasslands. Mineral-associated organic matter stability was also higher for forests than grasslands, but did not differ between forest types. Overall, we demonstrate that differences in mineral composition can strongly affect the accumulation and stability of MAOM in soils and potentially obscure land use effects.