Fire and herbivory are important natural disturbances in grassy biomes. Both drivers are likely to influence belowgroundmicrobial
communities but no studies have unravelled the long-term impact of both fire and herbivory
on bacterial and fungal communities. We hypothesized that soil bacterial communities change through
disturbance-induced shifts in soil properties (e.g. pH, nutrients) while soil fungal communities change through
vegetation modification (biomass and species composition). To test these ideas, we characterised soil physicochemical
properties (pH, acidity, C, N, P and exchangeable cations content, texture, bulk density, moisture),
plant species richness and biomass,microbial biomass and bacterial and fungal community composition and diversity
(using 16S and ITS rRNA amplicon sequencing, respectively) in six long-term (18 to 70 years) ecological research sites in South African savanna and grassland ecosystems.We found that fire and herbivory regimes profoundly
modified soil physico-chemical properties, plant species richness and standing biomass. In all sites, an
increase in woody biomass (ranging from 12 to 50%) was observed when natural disturbances were excluded.
The intensity and direction of changes in soil properties were highly dependent on the topo-pedo-climatic context.
Overall, fire and herbivory shaped bacterial and fungal communities through distinct driving forces: edaphic
properties (including Mg, pH, Ca) for bacteria, and vegetation (herbaceous biomass and woody cover) for fungi.
Fire and herbivory explained on average 7.5 and 9.8% of the fungal community variability, respectively, compared
to 6.0 and 5.6% for bacteria. The relatively small changes inmicrobial communities due to natural disturbance is in
stark contrast to dramatic vegetation and edaphic changes and suggests that soilmicrobial communities, having
evolved with disturbance, are resistant to change. This represents both a buffer to short-term anthropogenicinduced
changes and a restoration challenge in the face of long-term changes.The National Research Foundation, South Africa and the Patterson Foundation via Conservation International, South Africa.http://www.elsevier.com/locate/scitotenvam2022BiochemistryGeneticsMicrobiology and Plant Patholog
