Can allelopathic potentialities of Mediterranean plant species reduce the spread of invasive plant species, Acacia dealbata and Ailanthus altissima?

Beyond ecological and health impacts, invasive alien plant species can generate indirect and direct costs, notably through reduced agricultural yields, restoration, and management of the invaded environment. Acacia dealbata and Ailanthus altissima are invasive plant species that cause particularly significant damage to the railway network in the Mediterranean area. The allelopathic properties of Mediterranean plant species could be used as nature-based solutions to slow down the spread of such invasive plant species along railway borders. In this context, a mesocosm experiment was set-up: (i) to test the potential allelopathic effects of Cistus ladanifer, Cistus albidus, and Cotinus coggygria leaf aqueous extracts on seed germination and seedling growth of A. dealbata and A. altissima; (ii) to evaluate whether these effects depend on the extract dose; and finally, (iii) to estimate whether these effects are modified by soil amendment. Leaf aqueous extracts of the three native plant species showed negative effects on both seed germination and seedling growth of the two invasive species. Our results show that the presence of allelochemicals induces a delay in seed germination (e.g., A. dealbata germination lasted up to 269% longer in the presence of high-dose leaf aqueous extracts of C. coggygria), which can lead to a decrease in individual recruitment. They also highlight a decrease in seedling growth (e.g., high-dose C. coggygria leaf aqueous extracts induced a 26% decrease in A. dealbata radicle growth), which can alter the competitiveness of invasive species for resource access. Our results also highlight that compost addition limits the inhibitory effect of native Mediterranean plants on the germination of invasive alien plants, suggesting that soil organic matter content can counteract allelopathic effects on invasive alien plants. Thus, our findings revealed that the allelopathic potential of certain Mediterranean plant species could be a useful tool to manage invasive plant species.

Heavy ionic pollution disrupts assemblages of algae, macroinvertebrates and riparian vegetation.

Urban streams display consistent ecological symptoms that commonly express degraded biological, physical, and chemical conditions: the urban stream syndrome (USS). Changes linked to the USS result in consistent declines in the abundance and richness of algae, invertebrates, and riparian vegetation. In this paper, we assessed the impacts of extreme ionic pollution from an industrial effluent in an urban stream. We studied the community composition of benthic algae and benthic invertebrates and the indicator traits of riparian vegetation. The dominant pool of benthic algae, benthic invertebrates and riparian species were considered as euryece. However, ionic pollution impacted these three biotic compartments' communities, disrupting these tolerant species assemblages. Indeed, after the effluent, we observed the higher occurrence of conductivity-tolerant benthic taxa, like Nitzschia palea or Potamopyrgus antipodarum and plant species reflecting nitrogen and salt contents in soils. Providing insights into organisms' responses and resistance to heavy ionic pollution, this study sheds light on how industrial environmental perturbations could alter the ecology of freshwater aquatic biodiversity and riparian vegetation.

Yellow-legged gull populations (Larus michahellis) link the history of landfills to soil eutrophication and time-related vegetation changes on small Mediterranean islands.

Seabird colonies have a strong influence on both the physical and chemical soil parameters and plant communities of the islands where they settle to nest. Scientists have studied the effects of the demographic explosion of seabird populations, but few have explored the long-term effects when the colonies were in decline. The aim of this study was to investigate diachronic changes over a 24 year period of soil parameters, floristic composition and plant functionnal types (Raunkiaer growth forms and Grime life strategies) up to the decrease of the number of nesting yellow-legged gulls (Larus michahellis Naumann, 1840) on Mediterranean islands. We used 78 permanent plots to survey the vegetation and the soil parameters on 9 islands and one mainland area within the Calanques National Park (south east of France), for three periods (i.e., 1997, 2008, 2021). Since 1997, the increase of nesting gulls has caused a nitrogen and pH increase and organic carbon and C/N ratio decrease, although the values were still higher than mainland plots without nesting gulls. This has led to changes in plant species composition e.g., higher values of N favouring the development of ruderal plant species, still present in high frequency in 2021. Furthermore, plant species highly tolerant to disturbances (i.e., R Grime strategy) in harsh environments were still favoured even after the decline of gull abundance. However, both the frequency of the chamaephytes and the vegetation cover has increased with the decline of gull colony. In 2021, measures of trace elements' concentrations and calculation of pollution load index (Cu, Pb and Zn) reveals relatively low multi-contamination levels on the mainland and the archipelagos. On naturally oligotrophic and semi-arid Mediterranean islands, gull colonies induce a persistent alteration in soil characteristics that still influences plant communities (composition and functional types), 11 years after the decline in bird abundance.

Landscape and Local Drivers Affecting Flying Insects along Fennel Crops (Foeniculum vulgare, Apiaceae) and Implications for Its Yield.

Agricultural landscapes are increasingly characterized by intensification and habitat losses. Landscape composition and configuration are known to mediate insect abundance and richness. In the context of global insect decline, and despite 75% of crops being dependent on insects, there is still a gap of knowledge about the link between pollinators and aromatic crops. Fennel (Foeniculum vulgare) is an aromatic plant cultivated in the South of France for its essential oil, which is of great economic interest. Using pan-traps, we investigated the influence of the surrounding habitats at landscape scale (semi-natural habitat proportion and vicinity, landscape configuration) and local scale agricultural practices (insecticides and patch size) on fennel-flower-visitor abundance and richness, and their subsequent impact on fennel essential oil yield. We found that fennel may to be a generalist plant species. We did not find any effect of intense local management practices on insect abundance and richness. Landscape configuration and proximity to semi-natural habitat were the main drivers of flying insect family richness. This richness positively influenced fennel essential oil yield. Maintaining a complex configuration of patches at the landscape scale is important to sustain insect diversity and crop yield.

Pollinator Specific Richness and Their Interactions With Local Plant Species: 10 Years of Sampling in Mediterranean Habitats.

In the context of global pollinator decline, little is known about the protection status and ecology of many species. This lack of knowledge is particularly important for Mediterranean protected areas that harbor diverse pollinator communities and are subject to considerable anthropogenic pressures. Calanques National Park (85 km2), which is located near Marseille (France), is dominated by Mediterranean low-vegetation habitats, such as phrygana and scrublands. These habitats offer favorable conditions for pollinator species due to the important amount of floral resources. Within a 10-yr period, we recorded bee (Hymenoptera: Apoidea: Anthophila), hover fly (Diptera: Syrphidae), and bee fly (Diptera: Bombyliidae) species and their interactions with the local flora through 10 field campaigns. We caught 250 pollinator species, including 192 bees, 38 hover flies, and 20 bee flies, for a total of 2,770 specimens. We recorded seven threatened bees (six near threatened and one endangered). Among the bee species, 47.9% were below-ground nesting species, and 54.7% were generalist species. Analysis of the pollination network showed that generalist and specialist pollinators do not share the same floral resources. The Cistaceae plant family (Malvales: Cistaceae) acted as a central node in the plant-pollinator network, interacting with 52 different pollinator species, which shows the importance of large open flowers that could be easily visited by both short and long-tongued pollinators in Mediterranean habitats. The occurrence of pollinator species and their ecological traits should strongly contribute to reinforcing the available information to provide or ameliorate the conservation statuses determined by IUCN Red List.

How can a rare protected plant cope with the metal and metalloid soil pollution resulting from past industrial activities? Phytometabolites, antioxidant activities and root symbiosis involved in the metal tolerance of Astragalus tragacantha.

Astragalus tragacantha is a protected plant species in France that grows even in the trace metal and metalloid (TMM) polluted soils of the Calanques National Park (PNCal). Soils are mainly contaminated by lead, copper, zinc and arsenic. An ex situ experiment was conducted, firstly to determine the molecular responses and root traits involved in the TMM tolerance of this plant species by growing individuals in a soil from the surroundings of one of the brownfields of the PNCal, known as l'Escalette, where this plant species grows spontaneously. Secondly, in order to determine the plasticity of these responses, seeds were collected from three different populations, at l'Escalette (polluted site), one from the Frioul archipelago (non-polluted, insular site) and one from La Seyne (non-polluted, littoral site). The results of this study confirmed the capacity of A. tragacantha to germinate and grow in TMM contaminated soils. Only moderate significant variations in chlorophyll and flavonol indices, proline content and antioxidant activities were detected between polluted and control soil conditions for all populations. The main driver for A. tragacantha TMM tolerance seemed to be its ability to be associated with root symbionts i.e. arbuscular mycorrhizal fungi and dark septate endophytes, corresponding to a nutrient-uptake strategy trait. This work provides support for the challenge of A. tragacantha conservation along the littoral of the PNCal, because increasing the number of A. tragacantha individuals would both increase vegetation cover of the polluted soils to reduce the pollution transfer and reinforce the populations of this species.

Geographical isolation caused the diversification of the Mediterranean thorny cushion-like Astragalus L. sect. Tragacantha DC. (Fabaceae).

Understanding the origin and evolution of Mediterranean vascular flora within the long-term context of climate change requires a continuous study of historical biogeography supported by molecular phylogenetic approaches. Here we provide new insights into the fascinating but often overlooked diversification of Mediterranean xerophytic plants. Growing in some of the most stressing Mediterranean environments, i.e. coastal and mountainous opened habitats, the circum-Mediterranean Astragalus L. sect. Tragacantha DC. (Fabaceae) gathers several thorny cushion-like taxa. These have been the subjects of recent taxonomical studies, but they have not yet been investigated within a comprehensive molecular framework. Bayesian phylogenetics applied to rDNA ITS sequences reveal that the diversification of A. sect. Tragacantha has roots dating back to the Pliocene, and the same data also indicate an eastern-western split giving rise to the five main lineages that exist today. In addition, AFLP fingerprinting supports an old east-west pattern of vicariance that completely rules out the possibility of a recent eastern origin for western taxa. The observed network of genetic relationships implies that contrary to what is widely claimed in the taxonomic literature, it is range fragmentation, as opposed to a coastal-to-mountain ecological shift, that is likely the main driver of diversification.

Eradications as scientific experiments: progress in simultaneous eradications of two major invasive taxa from a Mediterranean island.

BACKGROUND: Black rats, Rattus rattus, and mat-forming iceplants, Carpobrotus aff. acinaciformis and Carpobrotus edulis, are pervasive pests on Mediterranean islands. Their cumulative impacts on native biotas alter the functioning of island ecosystems and threaten biodiversity. A report is given here of the first attempt to eradicate both taxa from a protected nature reserve in south-eastern France (Bagaud Island). In order to minimise unwanted hazardous outcomes and produce scientific knowledge, the operations were embedded in a four-step strategy including initial site assessment, planning, restoration and monitoring. RESULTS: Trapping, which resulted in the removal of 1923 rats in 21 045 trap-nights, made it possible to eliminate a substantial proportion of the resident rat population and to reduce the amount of rodenticide delivered in the second stage of the operation. Forty tons of Carpobrotus spp. were manually uprooted from a total area of 18 000 m(2) ; yet careful monitoring over a decade is still required to prevent germinations from the seed bank. CONCLUSION: Two years after the beginning of the interventions, both eradication operations are still ongoing. Biosecurity measures have been implemented to reduce reinvasion risks of both taxa. With the long-term monitoring of various native plants and animals, Bagaud Island will become a reference study site for scientific purposes.

Unexpected morphological and karyological changes in invasive Carpobrotus (Aizoaceae) in Provence (S-E France) compared to native South African species.

Hybridization processes can lead to evolutionary changes, particularly in co-introduced congeneric plant species, such as Carpobrotus spp. which are recognized as invasive in Mediterranean climate regions. Morphological and karyological comparisons have therefore been made between native Carpobrotus edulis and C. acinaciformis in South Africa and their invasive counterparts in Provence (C. edulis and C. aff. acinaciformis). Morphological data exhibited the most significant differences in invasive C. aff. acinaciformis that forms a new phenotypic variant. Unexpected chromosomal restructuring has been highlighted for both taxa in Provence, with in particular a clear decrease in asymmetry, an increase in the intraspecific variability, and an interspecific convergence of karyotypes. These changes suggest a drift that has facilitated various crosses, and has been amplified through hybridization/introgression. Furthermore, several morphological and karyological transgressive characters have been found in the two invasive taxa. These results stress the important role and the rapidity of karyological changes in invasive processes.

Germination traits explain soil seed persistence across species: the case of Mediterranean annual plants in cereal fields.

BACKGROUND AND AIMS: Seed persistence in the soil under field conditions is an important issue for the maintenance of local plant populations and the restoration of plant communities, increasingly so in the light of rapidly changing land use and climate change. Whereas processes important for dispersal in space are well known, knowledge of processes governing dispersal in time is still limited. Data for morphological seed traits such as size have given contradictory results for prediction of soil seed persistence or cover only a few species. There have been few experimental studies on the role of germination traits in determining soil seed persistence, while none has studied their predictive value consistently across species. Delayed germination, as well as light requirements for germination, have been suggested to contribute to the formation of persistent seed banks. Moreover, diurnally fluctuating temperatures can influence the timing of germination and are therefore linked to seed bank persistence. METHODS: The role of germination speed measured by T(50) (days to germination of 50 % of all germinated seeds), light requirement and reaction to diurnally fluctuating temperatures in determining seed persistence in the soil was evaluated using an experimental comparative data set of 25 annual cereal weed species. KEY RESULTS: It is shown that light requirements and slow germination are important features to maintain seeds ungerminated just after entering the soil, and hence influence survival of seeds in the soil. However, the detection of low diurnally fluctuating temperatures enhances soil seed bank persistence by limiting germination. Our data further suggest that the effect of diurnally fluctuating temperatures, as measured on seeds after dispersal and dry storage, is increasingly important to prevent fatal germination after longer burial periods. CONCLUSIONS: These results underline the functional role of delayed germination and light for survival of seeds in the soil and hence their importance for shaping the first part of the seed decay curve. Our analyses highlight the detection of diurnally fluctuating temperatures as a third mechanism to achieve higher soil seed persistence after burial which interacts strongly with season. We therefore advocate focusing future research on mechanisms that favour soil seed persistence after longer burial times and moving from studies of morphological features to exploration of germination traits such as reaction to diurnally fluctuating temperatures.

Genetic signs of connectivity in Primula vulgaris (Primulaceae) in a hedgerow network landscape.

The effects of landscape configuration on the genetic connectivity of the heterostylous species Primula vulgaris Huds. (Primulaceae) were studied using AFLP markers. Isolation by distance pattern was shown by spatial autocorrelation analysis; moreover, hedgerow network distances were found to contribute less than Euclidian distances to spatial genetic structure. Pollen flow is probably the main factor shaping the spatial genetic structure rather than seed dispersal, which is limited in this myrmecochorous species. Detailed analysis on the genetic similarity between neighborhoods and differentiation rates showed that density of hedgerow networks impede gene flow. We therefore concluded that a high degree of habitat contiguity does not necessarily promote genetic connectivity.

The seed bank longevity index revisited: limited reliability evident from a burial experiment and database analyses.

BACKGROUND AND AIMS: Seed survival in the soil contributes to population persistence and community diversity, creating a need for reliable measures of soil seed bank persistence. Several methods estimate soil seed bank persistence, most of which count seedlings emerging from soil samples. Seasonality, depth distribution and presence (or absence) in vegetation are then used to classify a species' soil seed bank into persistent or transient, often synthesized into a longevity index. This study aims to determine if counts of seedlings from soil samples yield reliable seed bank persistence estimates and if this is correlated to seed production. METHODS: Seeds of 38 annual weeds taken from arable fields were buried in the field and their viability tested by germination and tetrazolium tests at 6 month intervals for 2.5 years. This direct measure of soil seed survival was compared with indirect estimates from the literature, which use seedling emergence from soil samples to determine seed bank persistence. Published databases were used to explore the generality of the influence of reproductive capacity on seed bank persistence estimates from seedling emergence data. KEY RESULTS: There was no relationship between a species' soil seed survival in the burial experiment and its seed bank persistence estimate from published data using seedling emergence from soil samples. The analysis of complementary data from published databases revealed that while seed bank persistence estimates based on seedling emergence from soil samples are generally correlated with seed production, estimates of seed banks from burial experiments are not. CONCLUSIONS: The results can be explained in terms of the seed size-seed number trade-off, which suggests that the higher number of smaller seeds is compensated after germination. Soil seed bank persistence estimates correlated to seed production are therefore not useful for studies on population persistence or community diversity. Confusion of soil seed survival and seed production can be avoided by separate use of soil seed abundance and experimental soil seed survival.