Large macroaggregates determine distribution of soil amidohydrolase activities at different landscape positions

Abstract Microbial activities have been shown to be regulated by soil aggregation. However, it is unknown how landscape-induced changes in the soil structure shape microbial activity in the soil ecosystems. This study aims to analyze the spatial distribution of amidohydrolase activities within the soil aggregates obtained from different landscape positions. Soil samples were collected from five landscape positions (summit, shoulder, backslope, footslope, and toeslope) at two pasture sites with contrasting climatic condition. Soil organic C (SOC) content, total N (TN), urease (URS), l -glutaminase (LGL), and l -asparaginase (LAS) activities were measured in five sizes of soil aggregates (4–2, 2–1, 1–0.5, 0.5–0.25 and 0.25–0.05 mm). The results showed that the landscape position significantly influenced the mass distribution of aggregates. This was observed, in particular, for larger macroaggregates (4–2 mm). By increasing the SOC and TN contents along both the landscapes studied, the macroaggregate mass fractions (4–2; 2–1; 1–0.5 mm) increased. The results also showed that the SOC and TN contents as well as amidohydrolase activities were heterogeneously distributed within soil aggregates. Macroaggregates (generally 4–2 mm) exhibited greater SOC and TN contents as well as amidohydrolase activities compared to microaggregate, though the 4–2 mm aggregates constituted a small component of most soils. Our findings also revealed that proportional distribution of amidohydrolase activities within the soil aggregates was influenced by the landscape position. With increasing soil aggregation along the landscapes, the amidohydrolase activities tended to increase into macroaggregate fractions. Moreover, SOC, TN and, the enzyme activities in larger macroaggregates are more sensitive to landscape-induced changes than other size of aggregates.