Soil Physicochemical Gradients Shape Arbuscular Mycorrhizal Fungal Communities and Root Colonization of Non-Reported Host Plants in Tropical Ecosystems

Abstract

Soil physicochemical properties and rhizosphere conditions are key determinants of arbuscular mycorrhizal fungi (AMF) diversity, spore production, and symbiotic functioning. This study investigated AMF diversity, spore abundance, and root colonization across six contrasting land-use systems in Southern Nigeria, with particular emphasis on previously unreported host plant species. Pronounced variations in soil physicochemical properties occurred among sites. All soils were coarse-textured and sand-dominated, with pH values ranging from strongly to moderately acidic (3.54 – 5.19) and clear nutrient gradients across ecosystems. Dumpsite soils contained the highest levels of total nitrogen (0.67), organic carbon (1.18) and available phosphorus (107.27), followed by cropland and mangrove soils. Electrical conductivity varied widely, from 29 mmho cm⁻¹ in the derived savanna to 2,897 mmho cm⁻¹ in mangrove soils, reflecting land-use intensity and tidal influence. Six AMF taxa were identified using spore morphology. Acaulospora spp. dominated all ecosystems, followed by Rhizophagus and Glomus spp., whereas Gigaspora and Funneliformis spp. were sparsely distributed. Total spore abundance peaked in cropland (384 spores 100 g⁻¹ dry soil), mangrove (378), and dumpsite (368) soils, and was lowest in freshwater swamp soils (298). Root colonization was evaluated in 28 plant species across multiple families, revealing widespread AMF associations. Colonization levels were highest in dumpsite and lowland forest soils (28-30%), intermediate in derived savanna and mangrove ecosystems (24-27%), and lowest in freshwater swamp and cropland systems (10-24%). All values fell within ranges reported for tropical ecosystems (10 - 40%). Overall, this study provides a first integrated assessment of AMF patterns across land-use systems in Nigeria.