Biotic and abiotic controls on carbon storage in aggregates in calcareous alpine and prealpine grassland soils

Alpine and prealpine grasslands provide various ecosystem services and are hotspots for the storage of soil organic C (SOC) in Central Europe. Yet, information about aggregate-related SOC storage and its controlling factors in alpine and prealpine grassland soils is limited. In this study, the SOC distribution according to the aggregate size classes large macroaggregates (> 2000 mu m), small macroaggregates (250-2000 mu m), microaggregates (63-250 mu m), and silt-/clay-sized particles (< 63 mu m) was studied in grassland soils along an elevation gradient in the Northern Limestone Alps of Germany. This was accompanied by an analysis of earthworm abundance and biomass according to different ecological niches. The SOC and N stocks increased with elevation and were associated with relatively high proportions of water-stable macroaggregates due to high contents of exchangeable Ca2+ and Mg2+. At lower elevations, earthworms appeared to act as catalyzers for a higher microaggregate formation. Thus, SOC stabilization by aggregate formation in the studied soils is a result of a joined interaction of organic matter and Ca2+ as binding agents for soil aggregates (higher elevations), and the earthworms that act as promoters of aggregate formation through the secretion of biogenic carbonates (low elevation). Our study highlights the importance of aggregate-related factors as potential indices to evaluate the SOC storage potential in other mountainous grassland soils.

Automated summary

The study reveals that the storage of soil organic carbon (SOC) in alpine and prealpine grasslands is related to soil aggregation, with factors such as elevation and soil composition influencing the distribution and fixation of organic carbon. Earthworms play different roles in different elevation zones, contributing to the formation of soil aggregates in grassland soils.