Does arbuscular mycorrhiza favor invasion of some Asteraceae tribes?

Invasive species, including more than three dozen Asteraceae, such as Solidago canadensis, Leucanthemum vulgare, Senecio inaequidens etc, pose serious threat to ecosystem health. Arbuscular mycorrhizal symbiosis is a key factor for distribution of invasive species of some Asteraceae tribes, including Astereae, Anthemideae, Senecioneae, Gnaphalieae, Cardueae, and Cichorieae. The formation of invasion-friendly plant communities has occurred through increasing nutrient and water availability, hormonal regulation, production of bioactive compounds, and mycorrhiza-induced resistance of host plants. Native species are displaced through the influence on soil microbiota, mycorrhizal and nutrient status of neighboring plants, and several other parameters. Allelopathic influences and symbiotic interactions with bacteria and other fungi can inhibit these processes. Understanding the mycorrhizal status of invasive weeds, in our opinion, is a necessary condition for their successful control.

Senecio inaequidens (South African ragwort).

S. inaequidens is a herbaceous perennial considered native to South Africa. It has spread rapidly in North and Central Europe following its accidental introduction from South Africa in wool exports. In the absence of rigorous phytosanitary controls, it is very likely to spread further along roads and railways. As its present realized niche differs to a large extent from its equilibrium niche (Vacchiano et al., 2013), it has to be expected that the species will spread into grasslands and pastures in the near future. S. inaequidens is a prolific achene producer, has vigorous growth and is toxic. Its economic impacts are currently minimal, and so far, no environmental impacts have been observed; however, due to its toxicity, its potential to spread into arable land should be considered a serious threat for cattle and human health. This species should in no case be considered for cultivation, even though its usefulness for health care (for example) has been demonstrated.

"Is there anybody else out there?" – First Insights from a Suspect Screening for Phytotoxins in Surface Water

To protect themselves, plants can produce toxic secondary metabolites (phytotoxins) that appear with widely varying structures and negative effects. These phytotoxins often show similar properties as known aquatic micropollutants in terms of mobility, persistence, toxicity, and possibly also ecotoxicity. However, their occurrence in surface waters remains largely unknown, which is also due to unknown ability of available screening approaches to detect them. Therefore, we performed a target and suspect screening based on a persistence-mobility prioritization for phytotoxins in small Swiss creeks using high resolution mass spectrometry. In total, three of 26 targets were detected, three of 78 suspects tentatively identified, and six suspects fully confirmed by reference standards. To the best of our knowledge, it is the first time that three different plant secondary metabolite classes are detected in the same surface water sample. Estrogenic isoflavones were detected at 73% of the sites with formononetin as main toxin, which is in agreement with previous studies. Furthermore, pyrrolizidine alkaloids and the indole alkaloid gramine were detected. Especially pyrrolizidine alkaloids might be critical due to their production by various plants including the invasive Senecio inaequidens, and their known importance in food and feed safety. Based on these first screening results, different phytotoxin classes should be assessed for their ecotoxicological effects and considered in future water monitoring.

New floristic records from Central Europe 6 (reports 81-98)

The presented sixth part of the series includes 18 new chorological records of vascular plants, five from Poland and thirteen from Slovakia. In Poland, the first spontaneous occurrence of Clinopodium nepeta subsp. nepeta outside cultivation is reported from Kraków. Also new localities of Euphorbia maculata, Panicum capillare, Plantago coronopus and Symphyotrichum ciliatum from southern Poland were found. In Slovakia, new records of alien Cardamine occulta, Lindernia dubia, Nigella damascena, Pistia stratiotes (with map of known records), Sagittaria latifolia, Senecio inaequidens, Silybum marianum and Vinca major were done as well as autochthonous Cotoneaster melanocarpus, Herniaria hirsuta, Verbascum speciosum and Xeranthemum annuum.

The exotic species Senecio inaequidens pays the price for arriving late in temperate European grassland communities

The exotic South African ragwort (Senecio inaequidens DC.) rapidly spread across Central Europe after its introduction, but we still do not know to what extent its timing of arrival in a plant community (i.e. before or after natives) and the composition of the native community being invaded affect (1) its capacity to invade a European grassland, (2) the performance of the native species, and (3) the direction and strength of priority effects. In a greenhouse experiment, we manipulated the timing of arrival of the exotic species (Senecio) and the composition of the native community to test the influence of these factors on the productivity and N content of exotic and native species. We also investigated if the plant species origin (native or exotic) and the native community composition affected the benefit of arriving early and the cost of arriving late in the community. The establishment success of Senecio strongly depended on its timing of arrival in a grassland community. Senecio benefited more from arriving early than did the natives. The presence of legumes in the community did not favour invasion by Senecio. When natives arrived later than Senecio, however, priority effects were weaker when legumes were part of the native community. Our results showed that inhibitory priority effects created by natives can lower the risk of invasion by Senecio. An early arrival of this species at a site with low native species abundance is a scenario that could favour invasion.

The exotic species Senecio inaequidens pays the price for arriving late in temperate European grasslands

The South African ragwort (Senecio inaequidens DC.) is one of the fastest exotic plant invaders in Central Europe but, despite its large distribution area, it is still not commonly found in European grasslands. In order to better understand the mechanisms behind invasion resistance of grassland communities to S. inaequidens, we determined (1) to what extent the timing of arrival of S. inaequidens in the community affected its invasiveness as well as the performance of the native species, and (2) how the direction and strength of priority effects were affected by the composition of the native community being invaded, particularly with regard to the presence of N2-fixing species (legumes). In a greenhouse experiment, we manipulated the timing of arrival of the exotic species in the community and the composition of the native background community to test the influence of these factors on the productivity and N content of exotic and native species. Using a set of interaction indices, we also investigated if the plant species origin (native or exotic) and the native community composition affected the benefit of arriving early and the cost of arriving late (i.e., priority effects) in the community. We showed that both exotic and native species created inhibitory priority effects for late-arriving species. The establishment success of S. inaequidens strongly depended on its timing of arrival in a grassland community. On average, S. inaequidens benefited more from arriving early than the natives. We did not find any evidence to support that the presence of legumes in the background community would favour invasion by S. inaequidens. When natives arrived later than S. inaequidens, however, priority effects were weaker when legumes were present in the native community. Synthesis: we showed that priority effects created by natives can lower the risk of invasion by S. inaequidens and are an important mechanism to explain why this exotic species is not commonly found in European grasslands yet. Our results suggest that an early arrival of this species at a site with low native species abundance (e.g., following a disturbance) is a scenario that could favour invasion by S. inaequidens.

Alien invasive plants in Belgian limestone quarries

Description of the subject. Vegetation of high conservation value can establish in quarries, during or after exploitation. Alien plants could hamper this process and cause additional rehabilitation costs. However, the situation of plant invasion in quarries is largely unknown. Objectives. We aimed to assess alien plant invasion in active and abandoned quarries, and to identify the most invaded quarry sectors. Method. We surveyed 6,692 plots in 31 quarries in Belgium and recorded occurrence, density and cover of the 65 listed alien invasive plants in Belgium. Results. Fourteen species were recorded and 25 quarries contained at least one species. The two most occurring species, Buddleja davidii Franch. and Senecio inaequidens DC., were more widespread in quarries in activity. All sectors of the quarries were affected by alien plant invasion. Conclusions. Alien plant invasion in limestone quarries is highly variable, but significant. Considering the ecological potential of quarry sites, this issue should be better tackled.