Plant–microbe interactions are increasingly recognised as drivers of plant invasion and adaptation, in part through their capacity to modulate phenotypic plasticity. Yet, while soil biota and plant–soil feedbacks are well studied in open or disturbed systems, their role in naturally resistant habitats—such as closed-canopy forest interiors—remains unclear. In such environments, microbial mediation of phenotypic plasticity could play a key role in overcoming strong abiotic constraints on establishment. We tested the hypothesis that the endomicrobiome promotes plant invasion by enhancing adaptive phenotypic plasticity, thereby increasing survival across heterogeneous environments. We addressed this hypothesis using the invasive plant Taraxacum officinale across the forest mosaic (core, edge, matrix) of the endangered Maulino Coastal Forest in central Chile, combining field and greenhouse experiments. We characterised the natural environmental gradient, revealing severe light limitation in forest cores, and transplanted plants with an intact endomicrobiome (E+) and a reduced endomicrobiome (E−) into core, edge, and matrix microsites to assess survival. We further quantified phenotypic plasticity to environmental heterogeneity (growing plants under simulated core and matrix conditions) for functional traits (height, specific leaf area, and BBX24 gene expression, a shade-induced cell elongation regulator) and performance traits (net CO₂ assimilation rate, biomass, and number of flowers). In the field experiment, E+ plants sustained higher survival in shaded forest cores, whereas E- plants declined sharply, showing strong dependence on high-light conditions. E+ plants showed greater plasticity in functional traits while maintaining stable performance across environments in the greenhouse experiment. Higher functional-trait plasticity was positively associated with field survival. Our results indicate that the endomicrobiome can amplify functional-trait plasticity and thereby improve establishment in habitats long considered invasion-resistant, a microbiome-mediated “jack-and-master” strategy. We advocate integrating plant–microbiome interactions into invasion ecology frameworks, particularly where microbial mediation may erode forest biotic resistance.

Phenotypic plasticity can increase under changing environments but may decrease as those become predictable. We propose a conceptual framework integrating the heterogeneity and range--centre hypotheses, generating predictions for plasticity magnitude, its spatio-temporal evolution, and fitness consequences. A five-year resurrection experiment was conducted on the invasive plant Taraxacum officinale using seeds collected in 2015--2019 across five populations, spanning a 1750 km latitudinal precipitation gradient in central Chile. We measured morphological and physiological plant traits under moist and drought conditions and quantified overall plasticity. Multivariate trait responses were structured by drought, latitude and year. Across populations, overall plasticity declined through time, consistent with genetic assimilation. Furthermore, the plasticity--fitness relationship shifted from positive in early cohorts to negative by 2019 as drought became more predictable. Our findings demonstrate that plasticity can evolve through genetic assimilation, providing a framework for predicting plasticity and its implications for plant adaptation under climate change.

While the evidence supports a role for the soil microbiome to modulate the environmental tolerance of various plant species, its role in the invasion success remains seldom assessed. Here we show results from two complementary experiments aimed at understanding the role of the soil microbiome on the performance of T. officinale (dandelion) plants. Since the relative importance of soil microbiome on plant fitness can differ between native versus introduced origins, we conducted a full cross-transplant experiment to compare the plant performance from different origins (native/introduced) in their original or exotic soils, along with manipulated soil microbiome. In addition, since the relevance of soil microbiome for plant fitness can depend on the level of environmental stress, we compared the plant performance under different soil microbiome treatments in an introduced latitudinal gradient. We found positive effects of soil microbiome on performance traits for T. officinale plants from most of the evaluated populations, being particularly relevant for plants in the introduced range and under stressful conditions.