Invasive plants often succeed in novel environments due to their capacity to tolerate multiple stressors through physiological plasticity. In coastal habitats, particularly on cliffs, invasive Carpobrotus taxa frequently face multiple environmental stressors, including drought, salinity, nutrient limitation, along with limited rooting space, and aboveground stress from herbivores. Here, we examined whether root confinement modulates plant responses to herbivory by Aphis fabae and mechanical leaf puncture (simulated herbivory used to isolate the effects of mechanical tissue damage). Plants were grown in pots providing two levels of root confinement (low and high) and subsequently exposed to three herbivory treatments: no damage, aphid herbivory, and mechanical puncture. We measured biometric and physiological responses, including chlorophyll fluorescence, pigment composition, and antioxidant enzyme activities, to assess plant growth, photosynthetic performance, and oxidative stress. Regardless of herbivory treatment, high root confinement reduced shoot growth and altered biomass allocation, confirming root confinement as a major constraint on plant performance. However, herbivory effects were expressed primarily through physiological rather than morphological responses and were generally stronger following mechanical puncture than aphid herbivory, particularly under high root confinement. Plants maintained growth despite damage through photoprotective and antioxidant adjustments, indicating effective physiological tolerance rather than growth impairment. Thus, root confinement determined plant growth and shaped the physiological context in which responses to herbivory emerged. The ability of Carpobrotus spp. to maintain growth, under the imposed herbivory treatments, while adjusting photoprotective and antioxidant processes may help it cope with multiple environmental constraints, contributing to its invasive success across heterogeneous coastal habitats.
Herbaceous leguminous plants are increasingly invading grasslands worldwide, yet their effects on soil extracellular enzyme activities (EEAs) and microbial resource limitations remain inadequately understood. To address this gap, we integrated a global meta-analysis with a field experiment to assess the general effects of legume invasion on soil enzymatic properties and their underlying drivers. Meta-analysis across 18 grassland sites showed that increasing invasion intensity consistently enhanced soil carbon (C)-, nitrogen (N)-, and phosphorus (P)-acquiring enzyme activities (CEEA, NEEA, and PEEA), respectively. In contrast, our field experiment over 0–50 cm soil profile showed that the positive effect of Trifolium repens invasion on CEEA was stronger in the deeper soil layer, while NEEA and PEEA were significantly decreased by invasion across all depths. Specific enzyme activities generally increased with depth, while microbial C and P limitations decreased. Structural equation modeling indicated that Trifolium repens invasion indirectly promoted EEAs by enhancing soil element availability, and that invasion-induced shifts in soil and plant stoichiometry alleviated microbial P and C limitations, respectively. Although soil moisture declined with depth, weakening its positive influence on EEAs, intensified invasion counteracted this decline by improving moisture retention. Collectively, these findings highlight that the ecological outcomes of legume invasion are context-dependent, shaped by both environmental conditions and invasion characteristics. We emphasize the need for region-specific management strategies to mitigate the expanding impacts of herbaceous legume invasions in global grasslands.
Alien plants may remain under cultivation for decades before their first documented occurrence in the wild. Quantifying this interval is difficult because contemporary alien floras emphasize taxa already recorded outside cultivation, whereas taxa remaining in cultivation are rarely retained. We examined 678 alien vascular plant taxa in Saccardo’s national chronology of the Italian flora, which documents introductions from the Roman period to 1909. Historical records were linked to contemporary status and analysed using an interval-censored time-to-event framework that retained reported event years, uncertain intervals and taxa with no documented event. The estimated median time from first documented introduction to first documented occurrence in the wild was 130 years, and 40
The emerald ash borer (Agrilus planipennis) is an invasive insect in the United States that preferentially feeds on ash (Fraxinus spp.) trees, causing widespread ash decline. Resulting canopy gaps may facilitate understory invasion by non-native plants, such as Amur honeysuckle (Lonicera maackii). We investigated whether ash decline and invasive shrub management, which opens the shrub layer, interact to influence understory plant communities. We hypothesized that (1) ash tree decline facilitates L. maackii shrub layer growth, which suppresses understory plants, (2) invasive shrub treatment creates recruitment windows for understory plants, and (3) ash decline and invasive plant treatments interact to increase opportunities for co-occurring non-native species. We conducted our study at Homer Lake Forest Preserve, Champaign County, Illinois, where we sampled subplots in ash and non-ash understories across untreated regions (no invasive plant management) and treated regions (L. maackii and Eleagnus umbellata treated one year prior). We constructed competing linear models to test for interactions between ash status and treatment status and constructed piecewise structural equation models to test the effects of ash status, treatment, and canopy cover on understory cover and diversity. We found that treatment and ash status significantly interacted to influence canopy cover. Structural equation models revealed few short-term direct effects of ash or treatment status on understory plants. However, decreasing L. maackii shrub layer cover was associated with increases in native diversity and abundance. Our results suggest that additional monitoring and management may be warranted in areas experiencing ash decline and/or invasive shrub treatment to increase native plant recovery.
The spotted wing drosophila (Drosophila suzukii), a major invasive pest of soft fruits native to Asia, has recently expanded across South America. Reconstructing its invasion history is critical for understanding the demographic and evolutionary processes shaping biological invasions. Here, we infer the origin, invasion pathways and demographic dynamics of D. suzukii in South America, with a particular focus on Chile. We used mitochondrial COI sequences and an updated global microsatellite dataset (25 loci, 27 populations) to reconstruct invasion routes and estimate demographic parameters by applying Approximate Bayesian Computation (ABC) and ABC-Random-Forest frameworks. Mitochondrial data support a sequential colonisation through the Americas and reveal a strong reduction of genetic diversity in Chile. Microsatellite-based analyses provide higher resolution and uncover weak differentiation among eastern and central US populations but marked divergence among western US populations, consistent with multiple introductions. In South America, strong genetic continuity links Brazil, Argentina, and Chile, with Chilean populations forming a tight cluster derived from Argentina. Our analyses also support a single introduction into Chile followed by rapid, stepwise latitudinal expansion. Demographic inference indicates recurrent bottlenecks of variable intensity and heterogeneous admixture during the invasion of the Americas, highlighting the role of serial founder events and secondary spread in shaping genetic structure. Post-inference goodness-of-fit analyses indicate that the inferred scenario cannot be rejected given the observed data. Overall, our results refine the reconstruction of invasion routes at a continental scale and illustrate how large, standardized genotype datasets analysed with ABC-RF advance inference on large-scale invasion histories and support pest management.
