Changes in precipitation patterns alter aggregate stability-related cations and micronutrients in a desert grassland

Altered rainfall caused by climate change affects soil cations and aggregate stability and thus affecting the soil productivity of ecosystems. However, little is known regarding the changes of soil nutrients and aggregate stability with rainfall change in desert grassland. To investigate the effect of rainfall on the soil nutrients and aggregate stability, cations of Ca²⁺, Mg²⁺, K⁺, Na⁺ and Al³⁺ and micronutrients of Fe²⁺, Mn²⁺, Cu²⁺ and Zn²⁺ in bulk soil and three soil aggregate sizes classes (microaggregate, < 0.25 mm; small macroaggregate, 0.25–2 mm; large macroaggregate, > 2 mm) from rainfall manipulation (i.e., ambient rainfall amount as a control, ± 20% and ± 40% of ambient rainfall) were examined in a desert grassland of the western Loess Plateau. The Na⁺ content under extreme drought (− 40%) was significantly increased in all aggregate size classes and bulk soil and further increased effective cation exchange capacity (ECEC) in the microaggregate. Fe²⁺ in microaggregate under + 20% treatment was significantly increased compared to ± 40% and CK (ambient rainfall). Although the significant differences in Mg²⁺, Ca²⁺, Mn²⁺, Cu²⁺ and Zn²⁺ in aggregates and bulk soil were not found among rainfall treatments, more micronutrients tended to accumulate in the small macroaggregate. Extreme drought reduced soil aggregate stability resulting from the increased soil fractal dimension (D) due to the accumulation of Na⁺. The contribution of large macroaggregate to cations and micronutrients in bulk soil, soil mean weight diameter (MWD) and geometric mean diameter (GMD) significantly increased with increased rainfall. In contrast, D, erodibility (K) as well as the contribution of microaggregate to nutrients in bulk soil increased with the decreased rainfall. This work highlights the importance of cations for aggregate stabilization under altered rainfall regimes in a desert grassland. Moreover, the response of micronutrients to rainfall alteration needs to be investigated in the aspect of aggregate and bulk soil.