Floristic condition drives differential response to cultural burns in grassy woodlands for ectomycorrhizal and arbuscular mycorrhizal fungi

Abstract

Societal Impact Statement Cultural burns are a critical Indigenous land management practice with diverse cultural and biodiversity benefits, now being reintroduced by Indigenous communities to Australian grassy woodlands after long post‐colonization suppression. How these burns influence soil fungi, critical partners in plant nutrition, remains poorly understood. On Wiradjuri Country, we show that vegetation condition before a burn shapes how fungi respond. Woodlands rich in native plants kept the slow‐growing fungi of mature eucalypt roots; degraded sites favored fast‐colonizing fungi and the partners of exotic grasses. Assessing condition beforehand may show where burning will sustain existing fungi, and where further management could improve outcomes. Summary Low‐intensity “cool burns” are increasingly used for ecological management, drawing on Indigenous cultural burning, yet their belowground effects remain poorly understood. We examined how Indigenous‐led cultural burns influence mycorrhizal fungi across a floristic condition gradient in southeastern Australian box‐gum grassy woodlands. Using DNA metabarcoding and hyphal in‐growth bags, we assessed ectomycorrhizal (EcM) and arbuscular mycorrhizal (AM) communities, alongside hyphal biomass and chemistry 6 months post‐burn across eight paired burnt–unburnt sites. Floristic condition was quantified before burning to test whether vegetation legacies shaped fungal responses. Cultural burns acted as a selective filter on fungal communities that varied with floristic condition, but measured functions did not respond, except for fungal carbon content; hyphal biomass was instead linked to soil ammonium. High floristic condition buffered fire‐driven EcM declines, supporting the persistence of competitive taxa post‐fire. Conversely, AM fungi (primarily Glomus ) proliferated with burning but were suppressed in high floristic condition sites, putatively via EcM exclusion. These findings indicate that mycorrhizal fungal responses to low‐intensity cultural burns varied with floristic condition. Assessing vegetation condition before cultural burning could indicate fungal responses, identifying where existing fungi are maintained and where additional management may be needed to improve outcomes at lower floristic condition sites.