Senna italica as an Ecosystem Engineer: Enhancing Soil Fertility and Function in Nutrient-Poor Sandy Soils

Abstract

Arid and semi-arid soils are typically characterised by low fertility, limited nutrient availability, and weak structural stability, posing major challenges for sustainable land management. Native plant species that naturally improve soil quality may provide environmentally sustainable solutions for restoring degraded sandy ecosystems. This study evaluated the influence of Senna italica, a native leguminous shrub, on the physicochemical properties and fertility of nutrient-poor sandy soils in Jeddah, Saudi Arabia. Soil samples were collected beneath naturally established S. italica plants and from adjacent non-vegetated areas for comparison. Soil texture, pH, electrical conductivity (EC), and available nitrogen (N), phosphorus (P), and potassium (K) were determined, and root samples were stained and examined for arbuscular mycorrhizal fungal (AMF) colonisation. Although both soils were classified as sandy, soils beneath S. italica contained a greater proportion of fine particles (4.20% vs. 2.12% silt + clay). Rhizosphere soils exhibited significantly lower pH and significantly greater concentrations of available N, P, and K than adjacent non-vegetated soils, whereas EC did not differ significantly. Microscopic observations confirmed extensive AMF colonisation of S. italica roots, including hyphae and vesicles. These findings suggest that S. italica enhances soil fertility through integrated plant–soil–microbe interactions involving biological nitrogen fixation, rhizosphere-mediated nutrient mobilisation, and mycorrhizal associations. The study identifies S. italica as a potential ecosystem engineer with promising applications in ecological restoration, soil rehabilitation, and sustainable management of degraded sandy soils in arid and semi-arid regions.