Low abundance of phytophagous nematodes under invasive exotic Pinus elliottii - enemy release and plant-soil feedbacks.

According to the enemy release hypothesis (ERH), the fitness of exotic plants and their capacity to become invasive in their area of introduction may partly be attributable to the loss of their natural enemies. Invasive species may also benefit from modifying soil attributes and thereby creating a positive soil-plant feedback. We assessed the relationship between time since the establishment of the invasive Pinus elliottii and enemy release in a montane pine-nematode-specific context within the Atlantic Forest domain, by comparing soil nematode communities/functional diversity along a virtual chronosequence of invasion. Our findings confirmed the premises of the ERH and suggest that invasion may be facilitated by a lesser nematode load on pine compared to that on native species. The impact of P. elliottii on nematode communities over time was mainly driven by changes in the trophic structure with a major depletion of phytophagous species and overall nematode richness. The findings suggest that P. elliottii after experiencing an initial reduction in natural enemy pressure in its exotic range, further changes the composition of soil organisms in its rhizosphere. This has implications for plant-soil feedbacks which, in turn, affect the dynamics of pine invasion in neotropical montane ecosystems.