Experimental investigation of fire ecology in the C₃ and C₄ subspecies of Alloteropsis semialata

1. C₄ grasses possess characteristics that potentially advantage growth in fire-prone environments, including high photosynthetic productivity, efficient light and nutrient use and significant allocation to below-ground reserves and reproduction. Such characteristics allow fast regeneration after fire, and may be the consequence of photosynthetic physiology, phylogenetic ancestry or may have been acquired as adaptations to frequently burnt environments. 2. The aim of this study was to examine the role of photosynthetic pathway by comparing fire ecology in the closely related C₃ and C₄ subspecies of Alloteropsis semialata. Its focus was on above-ground characteristics that would contribute to a fire fuel load, and the re-growth responses of plants subsequent to a controlled experimental burn during the natural winter fire season. 3. Prior to the burn, but after frost, above-ground biomass was entirely dead in the C₄ plants, and was more flammable than that of the C₃ plants. C₃ plants maintained 33% of their canopy alive despite frosts and hence lost a significant proportion of living tissue in the experimental burn. 4. Subsequent to the burn, C₃ plants did not entirely recover their above-ground biomass, but canopy area returned to its pre-burn level through the production of leaves with greater specific leaf area. There was little evidence of the remobilization of below-ground reserves, which were less than half the size of C₄ reserves. Re-growth of C₄ plants was strongly supported by the reallocation of below-ground biomass and was similar for burnt and control plants, although fire had a weak stimulatory effect on re-growth. 5. Synthesis. Differences in the responses of the A. semialata subspecies indicated that the C₄ subspecies is better adapted to fire. Not only did it produce a flammable fuel load, but it was not detrimentally affected by the fire and recovered more rapidly than the C₃ subspecies, without the requirement for altered growth allometry. Such characteristics may be the direct consequence of photosynthetic pathway or an indirect effect of adaptation in the C₃ and C₄ subspecies to environments with differing fire regimes.