Depth-dependent effects of aggregate-associated organic, inorganic carbon, and stoichiometry on soil structural stability following farmland abandonment

Abstract

Vegetation restoration through farmland abandonment is an effective strategy for enhancing soil quality and aggregate stability in fragile ecosystems. However, the long-term effects of abandonment on soil aggregate stability, particularly associated with soil inorganic carbon (SIC) and ecological stoichiometry across different soil depths, remain unclear in semi-arid regions. We investigated the effects of farmland abandonment on soil aggregate stability and associated carbon and nutrient dynamics across soil depths of 0–50 cm using a chronosequence approach spanning five abandonment stages (0, 6, 15, 25, and 45 years). Initially, SIC in aggregates decreased by 12–37 % after 6 years but subsequently increased as abandonment progressed. Both soil organic carbon (SOC) and total nitrogen in the 0–20 cm depth increased by 39–143 % and 32–180 %, respectively. The C:P and N:P ratios within aggregates increased with abandonment time but decreased with soil depth, while the C:N ratio remained stable. Soil aggregate stability significantly improved after abandonment, with mean weight diameter in the topsoil (0–30 cm) increasing by up to 118 % after 45 years. In the topsoil, aggregate-associated N:P and C:P ratios had the largest positive effect on stability, followed by aggregate-associated SOC, whereas aggregate-associated SIC negatively affected stability. In contrast, in the subsoil (30–50 cm), aggregate-associated SIC positively influenced stability, while aggregate-associated nutrients, particularly total phosphorus, had a negative effect. These findings highlight the depth-dependent and contrasting roles of aggregate-associated organic and inorganic carbon forms in soil restoration processes, providing valuable insights into ecosystem restoration strategies in semi-arid regions.