The recovery of leaf water potential following burning of two droughted tropical pasture species

Abstract

Following burning (day 0) of a water-stressed sward of green panic and siratro, measurements were made both on unburned plants and on regrowth of burned plants of leaf water potential (°s) and stomatal conductance (gs) at 1.00 p.m. and of leaf extension. In the unburned plants °s, remained low (-23 to -45 bar for green panic, and -14 to -18 bar for siratro), the stomata were closed and no growth occurred. In the burned plants of both species, however, °s on day 12 was -9 to -11 bars, the stomata were open and growth occurred, presumably because the complete defoliation allowed the plants to make use of a limited store of soil water at higher water potential. In green panic °s fell rapidly, and growth stopped after day 19, but °s and g, in siratro were still high on day 28. Burning of droughted native pastures is a common management practice in the semi-arid tropics of Australia. The data may explain how the pastures are able to make the new growth that frequently occurs.