Ectomycorrhizal fungi inoculation of conifers increases growth, but not stress resistance: A meta-analysis

Symbiotic relationships with ectomycorrhizal fungi (EMF) are critical for the survival and growth of many woody plants, including conifers. Early tree growth is a key predictor of seedling survival and long-term establishment in disturbed environments. Effective regeneration of conifer plantations following disturbances such as insect attack, pathogens or abiotic disturbances such as drought, and metal pollution requires the identification of EMF species capable of colonizing and establishing symbiosis with target conifer hosts under given site conditions. Consequently, interactions between conifer hosts and EMF symbionts have been a focal point of research and forest management for decades. Experimental studies of conifer-EMF interactions carried out under diverse environmental conditions have yielded inconsistent outcomes, complicating the establishment of standardized management protocols. We did a systematic meta-analysis to quantify the extent to which specific EMF species promote growth and stress resistance of conifer hosts in the genera Pinus (pine) and Picea (spruce). A comprehensive literature search was conducted to identify experimental studies where pine and/or spruce species were inoculated with a single EMF strain and parameters reflecting tree growth and/or stress resistance were measured. Of the 1806 articles retrieved, 32 studies examining growth effects and 26 studies evaluating stress resistance met the inclusion criteria for quantitative analysis. The meta-analysis revealed that EMF inoculation significantly enhances conifer growth, whereas its impact on stress resistance was not statistically significant. These findings underscore the potential of EMF to support forest regeneration and restoration efforts through improved growth outcomes, while highlighting the need for further research to elucidate the mechanisms underlying stress resistance in conifer-EMF interactions. • EMF significantly enhance conifer growth under diverse experimental conditions. • EMF effects on conifer stress resistance were not statistically significant. • Field studies on EMF-conifer interactions remain scarce and needed.