Phytotoxic Effect of Invasive Heracleum mantegazzianum Essential Oil on Dicot and Monocot Species.

Spreading of the plant species in new areas is supported by the hypothesis in which chemicals produced by alien species are allopathic to native plants. A novel weapon hypothesis was tested by using essential oil of dangerous alien species Heracleum mantegazzianum in laboratory conditions. Aboveground plant material was collected in south-east part of Slovakia, dried and hydrodistilled for essential oil isolation. Dominant compounds as octyl acetate (62.6%), hexyl 2-metylbutyrate (10.7%), hexyl isobutyrate (7.5%) and hexyl butyrate (6.5%) were identified by GC-MS. Potential phytotoxic activity was tested on three dicot plant species garden cress (Lepidium sativum L.), radish (Raphanus sativus L.) and lettuce (Lactuca sativa L.) and on one monocot plant species wheat Triticum aestivum L. Germination of the seeds of model plant species after influencing by different doses of essential oil of H. mantegazzianum as well as the roots length was evaluated. Lepidium sativum L. and Raphanus sativus L. were generally not sensitive to applied doses of essential oil although a little stimulation effect at some concentrations prevailed over inhibition effect. Similarly, in monocot species Triticum aestivum L., stimulation was visible in both root length and root number at two or one highest doses, respectively.

Intraspecific variability in allelopathy of Heracleum mantegazzianum is linked to the metabolic profile of root exudates.

BACKGROUND AND AIMS: Allelopathy may drive invasions of some exotic plants, although empirical evidence for this theory remains largely inconclusive. This could be related to the large intraspecific variability of chemically mediated plant-plant interactions, which is poorly studied. This study addressed intraspecific variability in allelopathy of Heracleum mantegazzianum (giant hogweed), an invasive species with a considerable negative impact on native communities and ecosystems. METHODS: Bioassays were carried out to test the alleopathic effects of H. mantegazzianum root exudates on germination of Arabidopsis thaliana and Plantago lanceolata. Populations of H. mantegazzianum from the Czech Republic were sampled and variation in the phytotoxic effects of the exudates was partitioned between areas, populations within areas, and maternal lines. The composition of the root exudates was determined by metabolic profiling using ultra-high-performance liquid chromatography with time-of-flight mass spectrometry, and the relationships between the metabolic profiles and the effects observed in the bioassays were tested using orthogonal partial least-squares analysis. KEY RESULTS: Variance partitioning indicated that the highest variance in phytotoxic effects was within populations. The inhibition of germination observed in the bioassay for the co-occurring native species P. lanceolata could be predicted by the metabolic profiles of the root exudates of particular maternal lines. Fifteen compounds associated with this inhibition were tentatively identified. CONCLUSIONS: The results present strong evidence that intraspecific variability needs to be considered in research on allelopathy, and suggest that metabolic profiling provides an efficient tool for studying chemically mediated plant-plant interactions whenever unknown metabolites are involved.

The impact of an invasive plant changes over time.

Many exotic plant invaders pose a serious threat to native communities, but little is known about the dynamics of their impacts over time. In this study, we explored the impact of an invasive plant Heracleum mantegazzianum (giant hogweed) at 24 grassland sites invaded for different periods of time (from 11 to 48 years). Native species' richness and productivity were initially reduced by hogweed invasion but tended to recover after ~30 years of hogweed residence at the sites. Hogweed cover declined over the whole period assessed. A complementary common garden experiment suggested that the dynamics observed in the field were due to a negative plant-soil feedback; hogweed survival and biomass, and its competitive ability were lower when growing in soil inocula collected from earlier-invaded grasslands. Our results provide evidence that the initial dominance of an invasive plant species and its negative impact can later be reversed by stabilising processes.

Biological activity and safety profile of the essential oil from fruits of Heracleum mantegazzianum Sommier & Levier (Apiaceae).

A composition of essential oils obtained from Heracleum mantegazzianum (Apiaceae) was examined using a GC-MS method. n-Octyl acetate (19.92%), n-hexyl-2-methylbutanoate (10.84%), n-octanol (10.13%), n-octyl butanoate (8.88%), n-octyl-2-methylbutanoate (8.01%), n-hexyl acetate (7.11%), n-octyl isobutanoate (5.5%) and n-hexyl isobutanoate (5.43%) were the main compounds. The high-performance counter-current chromatography was applied for purification of aliphatic alcohols and esters. A mixture of n-hexane, acetonitrile and tetr-butyl methyl ether (1:1:0.1, v/v) allowed to obtain n-octanol, n-octyl acetate, n-hexyl-2- methylbutanoate, n-octyl isobutanoate and n-octyl-2-methylbutanoate, with the purity range of 94-99%, in one single 74 min run. The antimicrobial activity was also determined against plant and foodborne pathogens. While n-octanol shares responsibility for the antibacterial activity of the essential oil, n-octyl acetate determines its antifungal action. The cytotoxic activity assessed on two normal kidney fibroblast cell lines: Vero (animal) and HEK-293 (human embryonic), and two human cancer cell lines: FaDu (squamous cell carcinoma of the pharynx) and SCC25 (squamous cell carcinoma of the tongue), showed a moderate cytotoxicity with CC50 values ranging from 262.3 to 567.8 µg/mL. Results indicate that normal cell lines were more sensitive to the tested essential oil than cancer cell lines. The antioxidant activity of oil and pure compounds was not significant.

Timing Is Important: Unmanned Aircraft vs. Satellite Imagery in Plant Invasion Monitoring.

The rapid spread of invasive plants makes their management increasingly difficult. Remote sensing offers a means of fast and efficient monitoring, but still the optimal methodologies remain to be defined. The seasonal dynamics and spectral characteristics of the target invasive species are important factors, since, at certain time of the vegetation season (e.g., at flowering or senescing), plants are often more distinct (or more visible beneath the canopy). Our aim was to establish fast, repeatable and a cost-efficient, computer-assisted method applicable over larger areas, to reduce the costs of extensive field campaigns. To achieve this goal, we examined how the timing of monitoring affects the detection of noxious plant invaders in Central Europe, using two model herbaceous species with markedly different phenological, structural, and spectral characteristics. They are giant hogweed (Heracleum mantegazzianum), a species with very distinct flowering phase, and the less distinct knotweeds (Fallopia japonica, F. sachalinensis, and their hybrid F. × bohemica). The variety of data generated, such as imagery from purposely-designed, unmanned aircraft vehicle (UAV), and VHR satellite, and aerial color orthophotos enabled us to assess the effects of spectral, spatial, and temporal resolution (i.e., the target species' phenological state) for successful recognition. The demands for both spatial and spectral resolution depended largely on the target plant species. In the case that a species was sampled at the most distinct phenological phase, high accuracy was achieved even with lower spectral resolution of our low-cost UAV. This demonstrates that proper timing can to some extent compensate for the lower spectral resolution. The results of our study could serve as a basis for identifying priorities for management, targeted at localities with the greatest risk of invasive species' spread and, once eradicated, to monitor over time any return. The best mapping strategy should reflect morphological and structural features of the target plant and choose appropriate spatial, spectral, and temporal resolution. The UAV enables flexible data acquisition for required time periods at low cost and is, therefore, well-suited for targeted monitoring; while satellite imagery provides the best solution for larger areas. Nonetheless, users must be aware of their limits.