Experimental drought results in a decline of ectomycorrhizae of Quercus pubescens Willd.

Experimental drought decreased the vitality of ectomycorrhiza and reduced the number of unique morphotypes.

Quercus pubescens (Willd.) is an ectomycorrhizal (ECM) tree species that is capable of withstanding occasional drought events, but the response of its ectomycorrhiza to drought is not well known. An experiment with two rain exclusion plots and two natural precipitation regime plots was established in a secondary sub-Mediterranean oak forest. ECM roots were sampled before the experiment and after 11 months of rain exclusion. ECM root tips were divided into vital and non-vital and quantified. Morphoanatomical characterization and molecular identification were performed for vital ectomycorrhizae to obtain diversity indices and perform community analyses. Soil water content (SWC) in rain exclusion plots was reduced by approx. 6 vol.% relative to natural precipitation regime and was devoid of major peaks in SWC after rain events. After 11 months, ECM vitality and species richness were significantly reduced on rain exclusion plots compared to the natural precipitation regime while ECM community was reduced to a small subset of the most frequent morphotypes, with strongly decreased number of the unique morphotypes. The reduction of unique morphotypes as a result of rain exclusion may compromise the functional diversity of ectomycorrhiza in their role of nutrient uptake, while the reduction of ECM vitality may decrease the absorptive surface for water and nutrients.