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The influence of fire regimes on soil microbial diversity in montane grasslands is a relatively unexplored area of interest. Understanding the belowground diversity is a crucial stepping-stone toward unravelling community dynamics, nutrient sequestration, and overall ecosystem stability. In this study, metabarcoding was used to unravel the impact of fire disturbance regimes on bacterial and arbuscular mycorrhizal fungal community structures in South African montane grasslands that have been subjected to an intermediate (up to five years) term experimental fire-return interval gradient. Bacterial communities in this study exhibited a shift in composition in soils subjected to annual and biennial fires compared to the controls, with carbon and nitrogen identified as significant potential chemical drivers of bacterial communities. Shifts in relative abundances of dominant fungal operational taxonomic units were noted, with Glomeromycota as the dominant arbuscular mycorrhiza observed across the fire-return gradient. A reduction in mycorrhizal root colonisation was also observed in frequently burnt autumnal grassland plots in this study. Furthermore, evidence of significant mutualistic interactions between bacteria and fungi that may act as drivers of the observed community structure were detected. Through this pilot study, we can show that fire regime strongly impacts bacterial and fungal communities in southern African montane grasslands, and that changes to their usually resilient structure are mediated by seasonal burn patterns, chemical drivers, and mutualistic interactions between these two groups. [ABSTRACT FROM AUTHOR]

The mesic montane grasslands of the uKhahlamba-Drakensberg, which produce cured flammable fuel, have evolved under and are sustained by recurrent fires. The Brotherton burning trial (12 replicated treatments) was established at Cathedral Peak (1 890 m asl) in 1980 to understand how burn season and frequency control the composition and diversity of the montane catchment grassland. Multivariate methods were used to examine the long-term (almost 40 years). compositional stability under different burning regimes. The species composition deviated steadily and markedly from the initial state (Bray–Curtis dissimilarity) by 43.4 ± 9.32% with quinquennial burning (alternating autumn/spring) and by 64.6 ± 2.24% with attempted fire exclusion (three unplanned burns). Composition was rapidly transformed (by 53.1 ± 4.6%) by biennial summer burning (discontinued in 1991). Dominance shifted from Themeda triandra to other grasses (Stiburus alopecuroides, Tristachya leucothrix, Harpochloa falx) with biennial summer and infrequent burning. In contrast, regular dormant season burning annually or biennially (in autumn, winter, or spring) maintained a stable grassland close to the original composition (mean deviation 23.08%). Burning homogenised the composition, overriding the initial extant small-scale spatial variation. Results support the current practice to burn biennially in the dormant season to maintain stable grassland in the Drakensberg catchments. [ABSTRACT FROM AUTHOR]