Contrasting soil fungal communities in Mediterranean pine forests subjected to different wildfire frequencies

Mediterranean forest ecosystems are characterized by various vascular plant groups with their associated mycorrhizae (e.g. pines and Cistaceae with ectomycorrhiza; ericaceous shrubs with ericoid mycorrhiza) and free living soil fungi with various ecological functions. Fire plays a major role in Mediterranean ecosystem dynamics and impacts both above- and below-ground community structure and functioning. However studies on below-ground fire ecology are few. The objectives of this study were to evaluate by using two different molecular methods the effects of different wildfire regimes on soil fungal community structure. We investigated the long-term effects of wildfire on soil fungal communities associated with maritime pine forests in central Portugal, by comparing the results of Denaturing Gradient Gel Electrophoresis (DGGE)-based profiling with those obtained with 454 pyrosequencing. Four forest stands with differing fire history and vegetation cover (mature forest, early successional stage of pine regeneration, and forest converted to shrubland) were sampled 6 years after the last fire event. Pyrosequencing-based approach indicated ca. ten-fold higher number of taxa than DGGE. However, fungal community fingerprinting data obtained for the different study stands with DGGE were congruent with those obtained with pyrosequencing. Both short and long fire return intervals favoured the abundance of early successional fungal species belonging to the Thelephoraceae and short wildfire return intervals induced a significant shift towards Ascomycota and Cortinariaceae. Wildfire occurrence reduced significantly the frequency of late stage successional species and species belonging to the Mucorales that mostly include soil ubiquitous saprotrophs. The significantly higher frequency of mycorrhizal fungal taxa (host specificity associated with ericaceous shrubs or Cistaceae) in the short fire return interval stands highlighted the relationship between post-fire vegetation composition and cover (vegetation successional stage), and fungal symbionts.