Global meta-analysis of endophytic inoculation effects on seed germination, seedling growth, and nutrient uptake of trees

Abstract

Endophyte inoculation is emerging as a promising strategy to enhance tree growth, offering new possibilities for forest restoration in the face of climate change. While numerous studies report positive effects, a comprehensive quantitative synthesis remains lacking. This meta-analysis integrates findings from 71 studies, encompassing 1364 effect sizes, to evaluate the impact of endophyte inoculation on tree growth parameters across diverse experimental conditions, plant groups, and inoculum types. The results reveal significant positive effects on key growth variables, including root growth, shoot growth, height, dry weight, and nutrient uptake, with microbial consortia exerting the strongest influence. However, substantial heterogeneity in effect sizes was observed, shaped by differences in study design, environmental conditions, and host plant taxonomy. Angiosperms exhibited more pronounced growth responses than gymnosperms, while controlled environments, such as greenhouse conditions, yielded more consistent outcomes compared to field settings.

Variability in effect sizes, assessed through log response ratio (lnRR) and log coefficient of variation ratio (lnCVR) models, underscored the importance of both fixed and random effects in explaining observed trends. Notably, microbial consortia and bacterial inocula not only enhanced tree growth but also contributed to more stable and predictable outcomes, whereas fungal inocula exhibited greater variability in their effects. These findings highlight the potential of endophytes to promote tree growth and enhance stress resilience while emphasizing the need for standardized methodologies and ecological context considerations in future research. This work provides a comprehensive understanding of endophyte-mediated growth promotion and offers valuable insights for optimizing their application in forestry and ecosystem restoration.