Ectomycorrhizal fungi with hydrophobic mycelia and rhizomorphs dominate in young pine trees surviving experimental drought stress

Mycorrhizal fungi can help plants to cope with drought, but research on the fungal communities that are more resistant to drought or alleviate drought stress of trees is still scarce. In this study, we investigated effects of drought on soil fungal communities and explored potential fungal traits related to drought resistance under greenhouse conditions. We manipulated water availability in pine seedlings belonging to three Spanish Pinus pinaster populations from geographical areas subjected to contrasting summer drought. A set of plant ecophysiological traits were quantified and soil fungi was quantified and profiled using ergosterol and Pacific Biosciences sequencing. Abundance of ectomycorrhizal (ECM) fungi in plants subjected to drought was lower than in well-watered plants. Most ECM taxa in plants surviving drought had long exploration types and were taxa typically forming rhizomorphs and hydrophobic mycelia. By contrast, ECM taxa in well-watered plants had wider range of distinct exploration types. No differences in fungal communities were found among P. pinaster populations. No associations between ECM fungi and plant ecophysiological traits were found, but significant interactions between drought treatments and belowground plant biomass were found for the relative abundances of ECM fungi, particularly ECM with long exploration types. Plants subjected to drought may benefit by associating to ECM taxa previously shown to transport water efficiently.