Consequences of season of prescribed burning on two spring-flowering terrestrial orchids and their endophytic fungi

Abstract

Prescribed burning is mandated in seasonally dry regions of the world to reduce fuel load and fire risk. This study investigated the effects of prescribed burning at different seasons on two Australian terrestrial orchids (Glossodia major R.Br. and Thelymitra pauciflora R.Br.) and their orchid mycorrhizal fungi (OMF) to find the least damaging season for a burn. Burns were conducted mid-season in autumn, winter, spring and summer. Orchids were enumerated and measured and their OMF isolated during their flowering seasons. The OMF were grouped and identified using their internal transcribed spacer (ITS) regions and tested for sensitivity to smoke water. Orchid numbers decreased by up to 100% after autumn and winter burns but not spring and summer burns. Plant height, leaf and flower dimensions decreased between the two years. Fire reduced success in the isolation of OMF. The relative frequencies of ITS sequences of Serendipita Roberts from G. major (but not of Tulasnella asymmetrica Warcup and P.H.B. Talbot from Th. pauciflora) changed after burns. OMF from G. major were up to 100% inhibited by smoke water, twice the inhibition of the OMF from Th. pauciflora. Prescribed burning during active orchid growth damaged both the orchids and their OMF. The least damaging practical season for a prescribed burn was in late spring, soon after seed dispersal.