Soil Systems

Desertification is a major environmental problem in drylands, resulting from the interaction between climatic and anthropogenic factors and involving processes such as vegetation loss and soil erosion. In northeastern Brazil, long-term land-use pressure has intensified the vulnerability of semi-arid landscapes, leading to severe degradation and reduced environmental resilience. Within this context, the Salitre River Basin (Bahia State) represents a particularly relevant area for investigating desertification, as it combines a history of intense human pressure and soil degradation with arid climatic conditions recently recognized through climatological assessments. This study investigates the micromorphological organization, hillslope dynamics, and environmental degradation of carbonate soils of the Salitre river basin, aiming to reconstruct pedogeomorphological evolution and identify indicators of desertification. A toposequence-based approach was applied using ten soil profiles distributed across sectors with contrasting erosion intensity. Soil horizons were characterized through field descriptions, physical and chemical analyses, and micromorphological observations of thin sections. Soils are predominantly eutrophic, carbonate-rich, shallow Calcisols, with very high CaCO₃ contents (500–900 g kg⁻¹), alkaline pH, and low total organic carbon. The spatial organization of profiles results from strong lithological and geomorphological controls, with well-developed horizons in stable sectors, whereas truncated and homogeneous profiles occur in areas affected by severe erosion. Micromorphological features, including planar and moldic voids, Fe–Mn nodules, calcite coatings, and needle calcite infillings, indicate active carbonate dissolution/redistribution processes under increasing seasonality and aridity (calcification). The coexistence of inherited dissolution and recent precipitation features suggests polyphasic pedogenesis linked to Holocene climatic oscillations. The preservation of well-developed needle-fiber calcite is consistent with prolonged water-deficit conditions, although its precise chronological significance remains unconstrained in the absence of direct dating. At landscape scale, these processes are associated with hillslope retreat and dense networks of linear erosion, defining a scenario of severe land degradation.

Erosion affects soil health, nutrient cycling, and ecosystem productivity. Although the physical manifestations of erosion are well known, further research is needed to understand how its biochemical consequences interact to limit soil functionality and plant productivity. We investigated this in erosion-threatened chernozem soils of the Czech Republic using a pot experiment and a synthetic soil quality index (SQI) with Festuca rubra under varying nitrogen fertilization rates (0–250 kg N ha⁻¹). Erosion significantly degraded soil biochemical quality, reducing soil organic carbon content from 1.40% to 0.78% (p < 0.001) and total nitrogen content from 0.15% to 0.13%. Microbial functions were severely disrupted, as evidenced by a 57% decrease in dehydrogenase activity (p < 0.001) and a 35% decrease in urease activity (p < 0.001). From a production perspective, erosion significantly reduced plant biomass (p = 0.004) across all treatment groups. While nitrogen fertilization significantly stimulated biomass production up to an intermediate rate of 50 kg N ha⁻¹ (p < 0.001), higher application rates led to a strict yield plateau. These results demonstrate that erosion-induced deterioration of the soil’s biochemical complex acts as a primary constraint on crop growth, which cannot be compensated for by increasing doses of mineral nitrogen fertilizer.

Soil metal contamination poses potential risks to ecosystem health, yet its vertical distribution and impacts on microbial communities in protected wildlife habitats remain poorly understood. This study investigated the vertical variation (0–80 cm) in seven metals or metalloids (Zn, Cr, Cu, Co, Ni, As, and Pb) and their correlations with soil bacterial communities in the Chinese Changxing Alligator Nature Reserve, Zhejiang Province, China. Soil samples were collected from two functional zones—the Reserved Breeding Zone (FY) and Reintroduction Zone (FG)—at four depth intervals. The results revealed distinct vertical stratification for both soil elements (metals and metalloids) and bacterial communities. Soil element concentrations exhibited depth-dependent variations, with surface layers showing higher accumulation of Zn, Ni, Cu, Cr and Pb, while As was enriched in deeper horizons. Bacterial alpha diversity declined with depth, and community composition shifted markedly: Pseudomonadota and Actinomycetota dominated surface soils, whereas Acidobacteriota and Chloroflexota increased in deeper layers. Network analysis revealed that microbial co-occurrence network complexity decreased with soil depth, indicating greater stability and environmental adaptability of surface soil microbial communities. Pearson correlation and Mantel analyses revealed significant depth-related variation in soil element concentrations (Zn, Co, Ni, Cu, Pb, Cr, and As), and these patterns were closely associated with shifts in soil bacterial community structure. This study provides systematic evidence of vertical differentiation in soil element–microbe interactions within reserve soil profiles, offering a scientific basis for habitat quality assessment, ecological risk warning, and Chinese alligator habitat conservation and management.