Do arbuscular mycorrhizal fungi exhibit phylogenetic conservatism in their response to drought?

Diversity of arbuscular mycorrhizal fungi (AMF) in soil is considered as one of the major factors contributing to the maintenance of plant biodiversity and to grassland ecosystem functioning. It is therefore of great interest to understand how AMF communities respond to disturbances expected with climate change, such as drought. Thus far, however, the impact of drought on AMF diversity in soil has been largely overlooked. By means of a tag-assisted MiSeq (Illumina) sequencing approach, we addressed changes in the composition of soil AMF communities in the field-based mesocosm experiment by de Vries et al. (this meeting), after imposing an experimental drought. Approx. 800,000 AMF 18S amplicons (ca. 420 bp-long) obtained from soil samples collected under different plant assemblages at four time-points (before, at the end, and two and eight weeks after ending the drought treatment) were analyzed. The AMF diversity covered by the primers used was (almost) saturated in most samples (per sample Good's coverage estimator ranging 0.873-1.000). 97% sequence identity OTUs were identified as Virtual Taxa (VTX) using a customized reference repository, derived from the MaarjAM database (http://maarjam.botany.ut.ee/). Most (80%) of the 60 VTX retrieved following subsampling at even sampling depth were unaffected by the treatment. However, sequence abundances of 12 VTX significantly increased or decreased at either the end and eight weeks after drought (METASTATS, 1000 permutations). At both time points, VTX exhibiting a significant increase in the treated samples belonged to the Glomeraceae or Claroideoglomaceae (Glomerales), whereas VTX exhibiting a decrease belonged to the Acaulosporaceae or Gigasporaceae (Diversisporales). This finding suggests a certain degree of phylogenetic conservatism in the response of AMF to drought disturbance.