Dear Colleagues,

The ecological problems caused by invasive plants have become increasingly prominent, and the level of environmental risk caused by invasive plants will continue to increase with the rising frequency and intensity of anthropological activities. More importantly, biological invasion as a result of invasive plants has become a major cause of biodiversity loss in recent years. Therefore, further work is urgently needed to elucidate the key mechanisms underlying the successful invasion of invasive plants, assess the ecological risks of invasive plants, and identify the ecological management of invasive plants, as well as early warning signs and means of prevention.

This Special Issue will provide an in-depth analysis and comprehensive overview of the key mechanisms underlying the successful invasion of invasive plants, and offer an assessment of the ecological risk of invasive plants, the ecological management of invasive plants, and early warning signs and prevention.

Original research articles and reviews are welcome. Research areas may include (but are not limited to) the following:

(I) The key mechanisms underlying the successful invasion of invasive plants;
(II) Ecological risks of invasive plants;
(III) Ecological management of invasive plants;
(IV) Early warning and prevention of invasive plants.

Prof. Dr. Congyan Wang
Prof. Dr. Hongli Li
Guest Editors

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• invasion ecology
• biological invasion
• plant invasion
• invasive plants
• invasion mechanism
• invasion management
• early warning and prevention

Title: Trace metal exclusion mechanisms enhance invasion of Mediterranean ultramafic habitats by Ailanthus altissima (Simaroubaceae)
Authors: Lazzaro L.; Bettarini I.; Colzi I.; Coppi A.; Gonnelli C.; Mugnai M.; Selvi F.
Affiliation: Università degli Studi di Firenze, Florence, Italy
Abstract: Biological invasions are one of the major drivers of biodiversity loss worldwide. Globally, invasions by alien plants are rapidly increasing in extent and severity, leading to large-scale degradation of ecosystems. Ailanthus altissima is one of the most invasive alien trees in Europe, being able to spread mainly in urban habitats and along transportation corridors, but also in natural habitats. Based on our field observations in Italy, this species can also invade outcrops of ultramafic (serpentine) soil, which was never reported before. This work thus aimed to evaluate the ability of A. altissima to invade such peculiar and valuable habitats, focusing on its capacity to cope with the high concentrations of trace elements in the soil through tolerance or accumulation/exclusion mechanisms. For comparison, we used a native tree species with a similar pioneer attitude, also growing on both ultramafic and non-ultramafic soils (Fraxinus ornus, Oleaceae). Accordingly, we sampled five individuals of A. altissima and of F. ornus from eight populations, four from ultramafic soil and five from non-ultramafic soil as control. At each site soil samples were also collected. The concentration of trace elements (Ni, Cr, Co, Ca and Mg) was then measured in plant and soil samples, allowing to determine the bioaccumulation and translocation factors in both species. Results indicate that concentrations of trace elements in A. altissima tissues are comparable to those in F. ornus, and significantly lower than in the soil. This resulted in low bioaccumulation factors and suggested trace metal exclusion mechanisms in both species. Also, Ni concentration in roots were higher than in the leaves, resulting in low translocation factors. These data suggest that A. altissima is unable to accumulate trace metals in its tissues but is likely to possess exclusion mechanisms that enhance its invasive ability of Mediterranean ultramafic habitats.

Title: Experimental investigation of the allelopathic potentialities of three Mediterranean plant species to reduce the seed germination and seedling growth parameters of the two invasive species Acacia dealbata and Ailanthus altissima
Authors: Mathieu Santonja; Anne Bousquet-Melou
Affiliation: Aix Marseille University, Avignon University, CNRS, IRD, IMBE, 13397 Marseille, France
Abstract: Economically, invasive species generate costs, notably through depreciation of agricultural yields, restoration of invaded environments and management of invasive species in the field. Acacia dealbata and Ailanthus altissima are invasive plant species that cause significant damage to the railway network in the Mediterranean area and their management is very costly. But, allelopathic properties of Mediterranean plant species could be used as nature-based solutions to slow the spread of such invasive plant species along railway borders. In this context, a mesocosm experiment was set-up in order i) to test if there is an effect 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 determine if these allelopathic interactions depend on leaf aqueous extract concentration; and finally iii) to evaluate if these allelopathic interactions are altered by soil amendment. Cistus albidus, C. ladanifer and C. coggygria leaf aqueous extracts showed negative effects on both seed germination and seedling growth of A. dealbata and A. altissima. These allelopathic effects varied according to the dose extract, the use of compost and the target invasive species considered . A delay of seed germination could lead to a decrease of individual recruitment while a decrease in seedling growth may alter the competitiveness for resource access, preventing thus the establishment of then two invasive plant species.

Title: Fitness and Hard seededness of F2 and F3 descendants of hybridization between Herbicide-resistant Transgenic Soybean and Wild Soybean
Authors: Rong Liang; Sheng Qiang; Xiaoling Song
Affiliation: Weed Research Laboratory, College of Life Sciences, Nanjing Agricultural University, Nanjing 210095, China
Abstract: The commercial cultivation of herbicide-resistant (HR) transgenic soybeans [Glycine max (L.) Merr.] raises great concern that transgenes may introgress into wild soybeans (Glycine soja Sieb. et Zucc.) via pollen-mediated gene flow, which could increase ecological risks of transgenic weed populations and threaten the genetic diversity of wild soybean. To assess the fitness of hybrids derived from transgenic HR soybean and wild soybean, the F2 and F3 descendants of crosses of the HR soybean line T14R1251-70 and two wild soybean lines (LNTL, JLBC) were planted along with their parental lines in wasteland or farmland soil, and with or without weed competition. The fitness of F2 and F3 lines was significantly increased compared to the wild soybean lines under all test conditions, and they also showed a greater competitive ability against weeds. Seeds produced by F2 and F3 lines were superficially similar to wild soybeans in having a hard seed coat; however, closer morphological examination revealed that the hard-seededness was lower due to the seed coat structure, specifically the presence of thicker hourglass cells in seed coat layers and lower Ca content in palisade cells. Hybrid descendants containing the cp4-epsps HR allele were able to complete their life cycle and produce a large number of seeds in the test conditions, which suggests that they would be able to survive in the soil for beyond a single growing season, germinate and grow under suitable conditions. Our findings indicate that the hybrid descendants of HR soybean and wild soybean pose potential ecological risks in regions of soybean cultivation where wild soybean also occurs. Keywords: Wild soybean (Glycine soja); transgenic soybean; hybrids; fitness; hard seededness