The influence of tissue phosphate on plant flammability: A kinetic study

The concentration of phosphate (P) in leaves is an important indicator of the ecological strategy of a plant species. P is also a fire retardant, which if effective at the low concentrations typical of plant tissue may influence wildfire behaviour, but the size of such effects is unknown. We studied two mechanisms of P fire retardance, gas-phase and solid-phase, using samples of pure cellulose with controlled quantities of added P. The gas-phase mechanism was not detectable at P concentrations found in plants. However, significant solid-phase effects led to increased charring and reduced supply of flammable tars to the flame. Activation energies were not significantly altered, but pre-exponential constants for charring and tar production were significantly increased and decreased, respectively. These data provide a basis for mechanistically modelling the influence of ecological variation in P on the behaviour of wildfires around individual plants and across vegetation boundaries.