Functional Redundancy Buffers Soil Fungal Turnover Against Vegetation Change in an African Savanna

Abstract

ABSTRACT Savannas, co‐dominated by trees and grasses, are experiencing increasing tree cover driven by fire suppression and, in some regions, afforestation for carbon sequestration. Understanding how such vegetation shifts affect soil fungal communities, key regulators of carbon and nutrient cycling, is critical for managing savanna ecosystem functions. Yet, the effects of increasing tree cover on fungal diversity, composition, and functional groups, particularly in tropical savannas, remain poorly understood. We leveraged savanna–forest boundaries in Hluhluwe‐iMfolozi Park, South Africa, as a natural space‐for‐time framework to examine fungal community changes during the savanna‐to‐forest transition. Soil samples were collected along six transects, and DNA was extracted for sequencing the ITS1 region. Our results show that alpha diversity of soil fungi did not differ significantly between savanna and forest soils, with comparable amplicon sequence variant richness, Shannon diversity, and Simpson evenness. However, savannas and forests were composed of substantially different fungal taxa and harbored distinct indicator genera, driven largely by high turnover, indicating that forest soils supported a largely new set of fungal taxa rather than a subset of savanna taxa. Despite this turnover, the relative abundance of major fungal guilds (mycorrhizal, pathogenic, saprotrophic) remained similar; only litter saprotrophs were significantly more abundant in forest soils than in savannas. These findings suggest that while fungal communities reorganize during vegetation change, broad functional redundancy maintains ecosystem processes across the savanna‐to‐forest transition.