Soil Microbe Interaction and Extracellular Enzyme Activity Mediated by Encephalartos villosus in KwaZulu-Natal Scarp Forest Ecosystems

Cycads are ancient gymnosperms that play a crucial role in the soil health of scarp forests through their symbiotic associations with nutrient-cycling bacteria. However, the abundance of cycads in scarp forests has been decreasing at an alarming rate, highlighting the importance of determining the role of these species in nutrient cycling, microbial dynamics, and soil health. This study examined soil nutrient and microbial dynamics associated with Encephalartos villosus across four scarp forest sites in KwaZulu-Natal, South Africa. Soil samples were collected from the rhizosphere and non-rhizosphere zones (3-5 m away from the canopy) of mature plants. Results show that collection point did not influence soil nutrient and properties statistically; however, site-level variation was evident, with Hlathikhulu showing higher pH and nutrient concentrations, while Vernon Crookes exhibited lower pH and nutrient availability. Rhizosphere soils supported a greater diversity of nutrient-cycling bacteria, particularly taxa from the genera Bacillus, Burkholderia, Enterobacter, Luteibacter, and Pseudomonas with N-fixing, P-solubilizing, and N-cycling functions. Non-metric multidimensional scaling (NMDS) revealed that site differences, mainly driven by Mg, Ca, K, Zn, pH, and total cations, were stronger predictors of soil nutrient and microbial community variation than collection point alone. Enzyme assays showed that glucosaminidase and acid phosphatase were associated with community differences. These findings indicate that E. villosus enhances soil nutrient enrichment and microbial functional diversity in scarp forests, although the strength of these effects depends on local site conditions. Conservation of E. villosus is therefore critical, not only for species survival but also for sustaining soil fertility and ecosystem functioning in nutrient-limited scarp forest habitats.