Divergent belowground strategies of savanna grasses under varying fire regimes

· Frequent fires fueled by savanna grasses play a key role in maintaining tree-grass coexistence but also alter the biogeochemical cycling of phosphorus, potentially increasing soil available phosphorus post-fire. However, it remains unclear how savanna plants, especially dominant and highly diverse grasses, respond to fire-driven nutrient changes and whether they shift their belowground strategies. · We used a long-term fire experiment in Kruger National Park, South Africa to investigate how fire regimes shape soil phosphorus availability, and how savanna grasses subsequently adjust their root functional traits within the root economics space framework. · We found that soil available phosphorus decreased with less frequent fires (from annual to unburned treatments). Root trait variation unexpectedly decoupled from these nutrient shifts but was influenced by fire frequency. Community-weighted root traits in annually burned savannas aligned with “slow” strategies while traits in unburned savannas shifted toward “fast” and “do-it-yourself” strategies. · Root traits in savanna grasses responded to fire disturbance, but not due to fire-induced shifts in soil available phosphorus. While the underlying mechanisms warrant further study, this highlights fire as a dominant ecological filter and future trait-based frameworks should account for the direct effects of fire on traits to successfully model savanna dynamics.