Leaf flammability and fuel load increase under elevated CO₂ levels in a model grassland

Fire is a common process that shapes the structure of grasslands globally. Rising atmospheric CO2 concentration may have a profound influence on grassland fire regimes. In this study, we asked (1) does CO2 and soil P availability alter leaf flammability (ignitibility and fire sustainability); (2) are leaf tissue chemistry traits drivers of leaf flammability, and are they modified by CO2 and soil P availability?; (3) does CO2 and soil P availability alter fuel load accumulation in grasslands; and (4) does CO2 and soil P availability alter the resprouting ability of grassland species? We found that leaf flammability increased under elevated CO2 levels owing to decreased leaf moisture content and foliar N, whereas fuel load accumulation increased owing to decreased foliar N (slower decomposition rates) and increased aboveground biomass production. These plant responses to elevated CO2 levels were not modified by soil P availability. The increase in leaf flammability and fuel load accumulation under elevated CO2 levels may alter grassland fire regimes by facilitating fire ignition as well as shorter fire intervals. However, the increased root biomass of grasses under elevated CO2 levels may enhance their resprouting capacity relative to woody plants, resulting in a shift in the vegetation structure of grasslands.