Beyond its native range: widespread mycorrhizal colonization in seedlings of the early invader Juniperus communis along a precipitation gradient in Patagonia

Abstract

Biological invasions are a major contemporary driver of biodiversity loss and economic impacts, and their outcomes often depend on invader reproduction processes. Across environmental gradients, variation in abiotic and biotic conditions (including plant–soil interactions), can strongly influence seedling establishment, a key bottleneck for invaders’ spread. Mycorrhizal fungi may further modulate this process depending on environmental context and symbiont availability. In Andean Patagonia (Argentina), the coniferJuniperus communis has been identified as an incipient invader along a precipitation gradient spanning forest, shrubland, and steppe habitats. However, its mycorrhizal associations and their relationship with environmental conditions remain poorly understood. Here, we characterized the mycorrhizal status (presence, type, and abundance) of naturally established J. communis seedlings along a precipitation gradient in Patagonia, and evaluated its relationships with environmental factors and seedling growth. Seedling abundance was higher in wetter forest habitats than in shrubland and steppe sites. While ectomycorrhizal associations were absent, arbuscular mycorrhizal colonization was consistently high and similar among habitats (72.6% ± 2.3 and present in 98% of seedlings) and showed no relationship with seedling growth. Only 1.6% of seedlings lacked mycorrhizae. These results indicate that, although environmental conditions structure seedling distribution along the gradient, they did not affect the degree of mycorrhizal colonization. However, potential context effects on AM fungal community composition cannot be ruled out. Accordingly, early seedling growth was not constrained by mycorrhizal colonization. Overall, these findings highlight the vulnerability of Patagonian forests to J. communis invasion and the importance of early management to limit its spread.