Context-dependent benefits of ectomycorrhiza on Aleppo pine seedling performance under ecologically relevant settings

Droughts significantly impact forests, with long-term forest existence largely depending on seedling recruitment. However, seedling establishment under natural conditions is often limited by numerous interacting factors such as water availability, competition with herbaceous vegetation, and interaction with ectomycorrhizal fungi (EMF). We performed two greenhouse experiments to examine these factors and their interacting effects on the establishment of Aleppo pine seedlings. In both experiments, Geopora, a genus known to colonize seedlings in dry habitats, predominantly colonized the seedlings' roots, regardless of the EMF inoculum's origin. EMF inoculation enhanced seedling height, biomass, and branch number. However, under combined drought and competition, EMF had no growth impact. When facing competition or consistent water scarcity, EMF's positive effects decreased. Interestingly, during intermittent drought periods (resource pulses), EMF benefits persisted even in severe drought. This discrepancy in pine performance across treatments highlights the complexity of benefits provided to seedlings by EMF under ecologically relevant settings.