Pine seedlings select a consistent ectomycorrhizal community regardless of water availability and inoculum origin

The effect of water stress on mutualistic interactions can play a key role in forest response to drought. We tested the effects of water availability on the mutualism between Aleppo pine seedlings and ectomycorrhizal fungi (EMF) originating from soil spore banks of pine forests along a steep climatic gradient. The composition of the EMF communities in the soil varied along the climatic gradient, whereas the communities on pine seedlings' roots which were inoculated with these soil spore banks remained largely consistent. Water stress reduced seedling growth, which was influenced by EMF presence and not by inoculum origin. These results suggest that even under water shortage, pine seedlings maintain similar partnerships despite variable EMF availability. This raises important questions regarding the role of EMF richness at different stages of tree growth and at different ecological scales and improves our understanding of forest regeneration dynamics under extreme climatic conditions.