Vegetation Cover Effects on Soil Organic Carbon Stocks in Arid Steppe Soils of Zmalet El Emir Abdelkader (Tiaret, Algeria)

Abstract

Steppe soils in the arid Algerian High Plateaus constitute a fragile and understudied edaphic resource whose organic carbon dynamics remain poorly documented at the local scale. This study assessed the physicochemical properties and organic carbon (OC) stock of topsoil (0-30 cm) in the commune of Zmalet El Emir Abdelkader (Tiaret province, Algeria) under three dominant steppe formations: Artemisia herba alba, Stipa tenacissima, and Peganum harmala. Fifteen composite samples (five per plant cover) were collected using a stratified random design and analysed for particle-size distribution, bulk density, pH (water and KCl), electrical conductivity, total and active calcium carbonate, and organic carbon/matter (Walkley–Black method). The soils were predominantly sandy-loam to loamy-sand in texture, loosely structured (bulk density 1.0-1.3 g cm⁻³), strongly calcareous, alkaline (pH 8.2-9.4), and virtually non-saline; none of these properties differed significantly among vegetation covers (one-way ANOVA, p > 0.1). Organic carbon stocks over 0–30 cm averaged only 18.96 ± 11.01 t C ha⁻¹ under Stipa tenacissima and 24.05 ± 10.67 t C ha⁻¹ under Peganum harmala, both at or below the ~20–25 t C ha⁻¹ reference range typically reported for Mediterranean arid soils, while Artemisia herba alba held a significantly higher stock of 46.36 ± 6.39 t C ha⁻¹ (one-way ANOVA, F(2,12) = 11.55, p = 0.0016; confirmed by Kruskal-Wallis, p = 0.0068; Tukey HSD, p < 0.01 vs. both other covers). Total CaCO₃, organic matter and organic carbon concentrations followed the same significant pattern, whereas S. tenacissima and P. harmala were not statistically distinguishable from one another for any parameter. These results identify vegetation cover - and Artemisia herba alba in particular - as the principal driver of surface organic carbon storage in these arid steppe soils, with direct implications for rangeland carbon management and restoration priorities.