Fungal-based soil food webs, not local plant nor abiotic properties, are most affected by rhizome-derived secondary metabolites of Japanese knotweed (Reynoutria japonica)

<p>Riparian zones, important hotspots for nitrogen retention, are at risk of losing ecosystem functioning by species invasion and chemical contaminants. Invasive <em>Fallopia japonica</em> is suspected of using polyphenolic compounds as a “novel weapon” to decrease nitrification which may be amplified by copper pollution. Inhibited nitrification results in lower nitrate availability for competing plants and is presumed to be part of <em>Fallopia japonica</em>´s competitive strategy. Polyphenols are known to enter the soil with leaf litter, but may also be exuded by roots. Yet, the entry pathway and the specific compounds hampering nitrification are not fully determined. Within the group of secondary metabolites produced by <em>Fallopia japonica</em>, emodin and resveratrol are frequently described, although their role in the invasion strategy via modification of nitrification has never been tested. As plants are likely to increase exudation and the production of polyphenols under stress, synergistic inhibition of nitrification may be expected under contaminant pollution. Hence, the following hypotheses were tested: (I) Resveratrol and emodin inhibit nitrification. (II) Under copper stress, <em>Fallopia japonica</em> increases the content of emodin and resveratrol. Therefore, both stressors act synergistically on nitrification inhibition. (III) As we assume polyphenols to enter the soil via root exudation, nitrification is more strongly inhibited in the rhizosphere compared to the non-rooted soil.</p><p>We ran a mesocosm experiment with <em>Fallopia japonica</em> and copper additions (0, 90, 270, 810 mg Cu kg<sup>-1</sup> soil) over two growing seasons. In September of the second year, we analyzed total polyphenol, resveratrol, and emodin concentration in roots, fresh leaves, and senescent leaves using LC-HRMS. Potential nitrification was measured in the rhizosphere and the non-rooted soil. All samples were analyzed in fivefold repetition across all copper concentrations. We further tested how the nitrification in soil responds to additions of resveratrol and emodin<em>.</em></p><p>Resveratrol inhibited nitrification while for emodin no significant effect was found. Under copper stress, concentrations of resveratrol in roots and emodin in senescent leaves were elevated, while total polyphenolic content was not influenced. Copper contamination had a strong concentration-dependent inhibitive effect on potential nitrification. Independent of the copper concentration, <em>Fallopia japonica</em> decreased the potential nitrification slightly more than the highest copper concentration (by 75 % compared to control). Despite the increase of resveratrol in roots, the stressors had neither a synergistic nor additive effect, because of the overwhelming influence of <em>Fallopia japonica </em>alone. In contrast to hypothesis (III), nitrification inhibition was lower in the rhizosphere compared to the non-rooted soil, suggesting that nitrification was not primarily controlled by active root exudation but possibly more by aboveground leachates or litter decomposition. We link this to <em>Fallopia japonica</em>´s competition strategy hampering nitrification more in the soil that provides nitrate for competing plants.</p><p>Our data reveals that polyphenols produced by <em>Fallopia japonica</em> may act as a “novel weapon” to benefit the own nutrition and to outcompete other plants. By inhibiting nitrification outside the own rhizosphere, the nitrogen availability for the riparian plant community could be substantially reduced having potentially negative effects on the biodiversity of riparian ecosystems and their ecosystem functioning.</p>

ABSTRACTThe invasive shrub Japanese knotweed (Fallopia japonica) is spreading through riparian forests in Central Pennsylvania. There is concern that detritus from this species may impact adjacent aquatic ecosystems, as allocthonous material forms the basis for aquatic food webs and may impact benthic community structure. This study compares key ecosystem processes within Japanese knotweed leaf litter to leaf litter of a native riparian species, American sycamore (Platanus occidentalis). We assess benthic macroinvertebrate communities and decomposition rates within experimental Japanese knotweed and American sycamore leaf packs at three sites within the Susquehanna River. Japanese knotweed detritus hosted a similar macroinvertebrate community to American sycamore and their assemblages had similar representation of functional feeding groups. The similarity between the invertebrate communities occupying American sycamore and Japanese knotweed detritus indicates that macroinvertebrates are able to utilize non-native litter for habitat and potentially as an energy source. American sycamore decomposed at a faster rate than Japanese knotweed, lending support to the Novel Weapons Hypothesis, which suggests that non-native species like Japanese knotweed may inhibit microbial colonization and subsequent litter breakdown. Our results suggest that invasion of Japanese knotweed along riparian corridors of large river systems may not have severe ecological consequences on local ecosystem processes.

Fallopia japonica is native to Japan, Taiwan and Korea. It is now widely naturalized in Europe and North America, and is regarded as one of the worst invasive alien species. For Japanese people, F. japonica has been one of the most familiar and useful wild plants for centuries. It is rare to regard the plant as a harmful weed in Japan. Fallopia japonica has many ethnobotanical uses as an edible and medicinal plant. Therefore it was recorded in many historical documents, by different names. A dictionary of local plant names recorded 689 words for F. japonica, and it was the plant with the most names among all plants listed. As a case study of F. japonica, we conducted surveys on its habitats and growth from the foot to the alpine belt of Mt. Fuji, the highest mountain in Japan. Fallopia japonica was found widely in man-made and natural habitats but was restricted to open, sunny sites. The plant was smaller in the habitats where the vegetation is cut repeatedly. Japanese phytosociological studies regarded F. japonica as the character species of an Artemisietea principis and as a constituent species of diverse herbaceous, shrub and open woodland communities. In Japan, vegetation is controlled by cutting or mowing near habitations and other infrastructure. In meadows, tall grasses dominate the vegetation. In mountainous areas, trees are dominant and open areas are limited. It is difficult for F. japonica to overgrow a wide area and to form a large stand. In addition, the plant has been regarded as useful plant. These matters seem to make F. japonica a common and familiar plant, not a pest, for Japanese people.

Summary Soil nematode communities are one of the most used bioindicators for assessing soil health and soil conditions. However, they are dependent on the presence of plants, some of which, known as ‘invasive’, affect local biodiversity when established. This study aimed to compare the communities of soil nematodes in riverbanks non-invaded and invaded by Fallopia japonica at three sites characterised by different environmental conditions. Our findings indicated that the ecosystem had a larger impact on the nematode communities than did the environmental variability at the study sites. Soil properties, such as pH, moisture content and organic-carbon content, differed significantly amongst the sites, but the nematode communities remained similar. Organic-carbon content was lower, and soil pH was higher, in the ecosystem with invasive F. japonica. Total nematode abundance, the abundances of fungivores, herbivores, omnivores and predators, and the maturity indices were significantly lower with invasive F. japonica. Fungivorous nematodes are essential for breaking down organic matter and releasing nutrients. Herbivorous nematodes respond to changes in the vegetation, and omnivorous and predatory nematodes contribute to the overall biodiversity and ecological balance in the soil ecosystem, so their lower abundance suggests a disturbance in the soil food web. The lower maturity indices suggested a disturbance or degradation of the soil ecosystem, which could have secondary negative effects on plant growth, nutrient availability and ecosystem resilience. These findings indicate that invasion both decreased the abundance of important soil organisms and disrupted the cycling of nutrients, potentially leading to long-term negative consequences for the invaded ecosystems. Understanding and managing the effects of invasive plants such as F. japonica are crucial for preserving soil health and promoting sustainable ecosystem functioning.

Allelopathic plants release secondary compounds into the soil that then suppress the growth of nearby plants. Allelopathy has been shown for the invasive Japanese knotweed (Fallopia japonica) and Bohemian knotweed (F. × bohemica). The aggressive and dominant invaders represent a serious threat to the local plant communities outside their native range. Here, we analysed the phenols in the knotweed rhizomes using nuclear magnetic resonance. We also evaluated the allelopathic potential of methanol extracts of F. japonica and F. × bohemica rhizomes and compared these with the effects of the individual knotweed phenols resveratrol, epicatechin and emodin, and their mixture. Rhizomes of both knotweeds contained similar amounts of epicatechin and emodin, with 24% higher resveratrol in F. × bohemica. Only the F. × bohemica methanol extract inhibited radish (Raphanus sativus) seed germination. After 3 days of treatments with 10% (w/v) extracts of both knotweeds, radish seedlings showed up to 70% shorter roots. In contrast, root growth of seedlings treated with the individual phenols resveratrol, epicatechin and emodin, and their mixture, was inhibited by up to 30%, similar to the 1% knotweed extracts. Biochemical parameters of oxidative stress also increased in the roots of treated seedlings, with high levels of malondialdehyde in particular indicating lipid peroxidation. Total antioxidative capacity was also increased in seedlings exposed to 0.6 mg/mL resveratrol and emodin. This study shows higher allelopathic potential of the knotweed methanol extracts compared to the individual phenols and their mixture.

Reynoutria japonica, a perennial herb of the Polygonaceae family, is a traditional Chinese medicinal plant known for its diverse pharmacological activities and broad applications in medicine, agriculture, and related fields. This review explores the functions and regulatory mechanisms of its secondary metabolites by summarizing their types, bioactivities, and biosynthetic regulation. Additionally, it examines how factors such as plant age, medicinal organ, soil composition, and cultivation conditions influence the secondary metabolite profile. These insights support the clinical application and industrial development of R. japonica.

Nematode communities indicate the negative impact of Reynoutria japonica invasion on soil fauna in ruderal habitats of tatra national park in Slovakia

In this study we investigated the communities of soil nematodes in the forest habitats invaded and uninvaded by Fallopia japonica (Houtt.) Ronse Decr., in Tatra National Park, Slovakia. We found that invasion by F. japonica altered nematode communities and their structures. Total nematode abundance, species number and nematode biomass were significantly lower in invaded than uninvaded plots, but species diversity remained unaffected throughout the study. The overall abundance of all nematode trophic groups well represented the negative impact of F. japonica invasion on soil food webs, supported by low values of all maturity indices, a structural index and the Jaccard index of faunal similarity. A weighted faunal analysis similarly characterized the food webs of invaded plots as poorly developed or highly disturbed, with bacterial decomposition and a low C/N ratio. Our findings thus suggest that dense plots of knotweed simplify the structural complexity of the soil environment by reducing the richness of plant species, which may have contributed to the negative changes in the structures of the nematode communities.

Plant species have been introduced increasingly into non-native ranges, where many have become exotic weeds with adverse impacts on native ecosystems, as well as on farming and other livelihoods. In biological control, the classical or inoculative approach is the one most commonly used for the management of invasive alien weeds and is based on the use of co-evolved natural enemies from the native range to control the invasive weed. Typically, the inundative or mycoherbicide approach targets problematic weeds using local plant pathogens that, in the case of introduced species, have 'jumped' onto the exotic host. The leaf-spot fungus, Mycosphaerella polygoni-cuspidati, co-evolved with its host, Reynoutria (Fallopia) japonica (Japanese knotweed), in Japan and has a unique history of being investigated both as a classical biological control agent and a mycoherbicide against this highly invasive weed in the United Kingdom and North America. Here, we highlight our research on M. polygoni-cuspidati as part of a biological control programme for Japanese knotweed and review the potential of mycoherbicides using exotic pathogens for the management of invasive alien weeds. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

The Asian knotweed species complex gathers some of the world’s most successful plant invaders including the Japanese knotweed (Reynoutria japonica), the giant knotweed (R. sachalinensis) and the hybrid of these two species, the Bohemian knotweed (R. × bohemica). Hybrid species often present higher competitive abilities compared to their parent species. While several studies have focused on the effects of knotweed invasion on plant communities, few have simultaneously considered (i) effects of the three taxa on native plant communities and (ii) effects on litter and soil faunal components. In this study, we compared the differential effects of three Asian knotweeds on vegetation and soil macroinvertebrates communities across seven sites on a regional scale in North Western France. All three knotweed species displayed similar negative effects on local plant species richness, while promoting the taxonomic richness of litter-dwelling macroinvertebrates. Belowground macroinvertebrate taxonomic richness appeared strongly reduced by the presence of the hybrid R. × bohemica, significantly more so than those of sites colonized by R. japonica or R. sachalinensis. These changes of belowground communities were correlated to associated changes of composition and richness within plant communities. This study provides new insight into the consequences of ecosystem invasion by these species, especially revealing the even further strength of impacts of the hybrid Bohemian knotweed on local vegetation and belowground macroinvertebrates than those of other Asian knotweeds, which points to the need for monitoring the spatial spread of R. × bohemica and describing further its effects on ecosystem properties.

Traditional medicinal plants are a large source of natural anticancer compounds that might serve as leads for the development of novel drugs. In recent years, the scientific community in the Western world has recognized the potential of natural products, used in Traditional Chinese Medicine (TCM). Since ancient times Japanese knotweed (Fallopia japonica), has been utilized in many TCM herbal preparations as anti-cancer agent. F. japonica (FJ) is known to produce a series of bioactive secondary metabolites, including anthraquinones, stilbens, tannins, lignans, anthocyanins, phenethyl alcohols, sterols, and essential oils. Resveratrol (a stilben) and emodin (an anthraquinone) are the major active ingredients of FJ. The anticancer activity of both compounds has various molecular modes of action and mechanisms through their ability to modulate the proliferation, apoptosis, cell cycle, growth factors, protein kinase C (PKC), NF-kappa B (NF-κB), and mitogen-activated protein kinase (MAPK) signaling cascades. This review presents an overview of the secondary metabolites of F. japonica and anticancer activities of the extract and main active principles, resveratrol and emodin. The possible molecular targets and potential chemopreventive effects are discussed.

Invasion by Fallopia japonica alters soil food webs through secondary metabolites

Adenosine deaminase (ADA) is an important enzyme in purine metabolism and is known as a potential therapeutic target for the treatment of lymphoproliferative disorders and cancer. Traditional Chinese Herbal Medicine (TCHM) is widely used alone or in combination with chemotherapy to treat cancer, due to its ability to deliver a broad variety of bioactive secondary metabolites as promising sources of novel organic natural agents. In the present study, 29 varieties of medicinal plants were screened for the presence of ADA inhibitors. Extracts from Reynoutria japonica, Glycyrrhiza uralensis, Lithospermum erythrorhizon, Magnolia officinalis, Gardenia jasminoides, Stephania tetrandra, Commiphora myrrha, Raphanus sativus and Corydalis yanhusuo demonstrated strong ADA inhibition with rates greater than 50%. However, Reynoutria japonica possessed the highest ADA inhibitory activity at 95.26% and so was used in our study for isolating the ADA inhibitor to be further studied. Eight compounds were obtained and their structures were identified. The compound H1 had strong ADA inhibitory activity and was deduced to be emodin by 1H and 13C-NMR spectroscopic analysis with an IC50 of 0.629 mM. The molecular docking data showed that emodin could bind tightly to the active site of ADA. Our results demonstrated that emodin displayed a new biological activity which is ADA inhibitory activity with high cytotoxic activity against K562 leukemia cells. The bioactivity of cordycepin was significantly increased when used in combination with emodin. Emodin may represent a good candidate anti-cancer therapy and adenosine protective agent.

Reynoutria japonica Houtt. (Japanese knotweed) is an invasive plant belonging to the Polygonaceae family. However, being native to East Asia, it has been used in natural medicine for ages because of its broad range of biological activity. Although R. japonica is known as a rich source of phenolic compounds, plant biomass collected from the field may be contaminated with toxic elements like heavy metals, and the level of metabolite accumulation depends on environmental conditions. Therefore, the aim of this study was to derive Japanese knotweed tissue cultures and investigate biomass production and phenolic compound synthesis in in vitro conditions. Plants were cultivated in a traditional agar-solidified medium, in a liquid medium with rotary shaking (agitated culture), and in a temporary immersion bioreactors Plantform™, as well as in soil (ex vitro conditions). Analyses of the growth index and dry weight accumulation were performed on the collected material. In the extracts obtained from examined plants, qualitative and quantitative analysis of phenolic derivatives using DAD-HPLC was conducted to determine the sum of phenolic compounds, as well as the quantity of selected phenolic acids, catechins, and other flavonoids. Results have shown that agitated cultures and temporary immersion bioreactors increased biomass accumulation compared to solid medium cultures. Tissue cultures of R. japonica had increased synthesis of phenolic compounds compared to plants from ex vitro conditions. Shoots and roots from agitated cultures were 2.8- and 3.3-fold richer in catechins, respectively, compared to plants cultivated in soil. Based on the obtained results it can be concluded that agitated and bioreactor cultures are the best source of Japanese knotweed biomass rich in valuable secondary metabolites.

As part of a research program whose aim is to determine the diversity of streptomycetes in order to discover new bioactive secondary metabolites, rhizosphere soils of three indigenous plants were analyzed. A total of 55 actinomycetes were isolated using three different medium from the samples. The rhizospheric soil of the plant Aethionema dumanii gave the highest number of actinomycetes, i.e., 42% versus 27% and 31% for the soils from Salvia aytachii and Achillea ketenoglui, respectively. The AIA is the most favorable medium for the isolation of the actinomycetes from different rhizospheric soils. 16S rDNA sequence analysis revealed that while some isolates belong to different cluster groups such as Streptomyces lydicus, S. rochei, S. microflavus, S. griseoflavus, S. albidoflavus and S. violaceusniger, the majority of the sequences did not considerable clustered with the member of different Streptomyces groups. The in vitro antimicrobial activities of the crude organic and aqueous extracts of isolates were screened using a disc diffusion assay against a panel of bacteria and C. albicans. A total of 22 isolates showed antimicrobial activity. The antibacterial action of the extracts is more pronounced on Gram-positive than on Gram-negative bacteria in most cases. About 18% of the actinomycetes showed also antifungal activity. Study of the influence of two different culture media on production of bioactive molecules showed that the higher antimicrobial activity was obtained in M2 when compared to TSB. The results from this study provide evidence that the streptomycetes in the rhizosphere soils could be promising sources for antimicrobial bioactive agents.