Phragmites australis root secreted phytotoxin undergoes photo-degradation to execute severe phytotoxicity

Common mycorrhizal network: the predominant socialist and capitalist responses of possible plant-plant and plant-microbe interactions for sustainable agriculture

Plants engage in a variety of interactions, including sharing nutrients through common mycorrhizal networks (CMNs), which are facilitated by arbuscular mycorrhizal fungi (AMF). These networks can promote the establishment, growth, and distribution of limited nutrients that are important for plant growth, which in turn benefits the entire network of plants. Interactions between plants and microbes in the rhizosphere are complex and can either be socialist or capitalist in nature, and the knowledge of these interactions is equally important for the progress of sustainable agricultural practice. In the socialist network, resources are distributed more evenly, providing benefits for all connected plants, such as symbiosis. For example, direct or indirect transfer of nutrients to plants, direct stimulation of growth through phytohormones, antagonism toward pathogenic microorganisms, and mitigation of stresses. For the capitalist network, AMF would be privately controlled for the profit of certain groups of plants, hence increasing competition between connected plants. Such plant interactions invading by microbes act as saprophytic and cause necrotrophy in the colonizing plants. In the first case, an excess of the nutritional resources may be donated to the receiver plants by direct transfer. In the second case, an unequal distribution of resources occurs, which certainly favor individual groups and increases competition between interactions. This largely depends on which of these responses is predominant ("socialist" or "capitalist") at the moment plants are connected. Therefore, some plant species might benefit from CMNs more than others, depending on the fungal species and plant species involved in the association. Nevertheless, benefits and disadvantages from the interactions between the connected plants are hard to distinguish in nature once most of the plants are colonized simultaneously by multiple fungal species, each with its own cost-benefits. Classifying plant-microbe interactions based on their habitat specificity, such as their presence on leaf surfaces (phyllospheric), within plant tissues (endophytic), on root surfaces (rhizospheric), or as surface-dwelling organisms (epiphytic), helps to highlight the dense and intricate connections between plants and microbes that occur both above and below ground. In these complex relationships, microbes often engage in mutualistic interactions where both parties derive mutual benefits, exemplifying the socialistic or capitalistic nature of these interactions. This review discusses the ubiquity, functioning, and management interventions of different types of plant-plant and plant-microbe interactions in CMNs, and how they promote plant growth and address environmental challenges for sustainable agriculture.

Altitudinal Variation of Metabolites, Mineral Elements and Antioxidant Activities of Rhodiola crenulata (Hook.f. & Thomson) H.Ohba

Rhodiolacrenulata (Hook.f. & Thomson) H.Ohba is an alpine medicinal plant that can survive in extreme high altitude environments. However, its changes to extreme high altitude are not yet clear. In this study, the response of Rhodiola crenulata to differences in altitude gradients was investigated through chemical, ICP-MS and metabolomic methods. A targeted study of Rhodiola crenulata growing at three vertical altitudes revealed that the contents of seven elements Ca, Sr, B, Mn, Ni, Cu, and Cd, the phenolic components, the ascorbic acid, the ascorbic acid/dehydroascorbate ratio, and the antioxidant capacity were positively correlated with altitude, while the opposite was true for total ascorbic acid content. Furthermore, 1165 metabolites were identified: flavonoids (200), gallic acids (30), phenylpropanoids (237), amino acids (100), free fatty acids and glycerides (56), nucleotides (60), as well as other metabolites (482). The differential metabolite and biomarker analyses suggested that, with an increasing altitude: (1) the shikimic acid-phenylalanine-phenylpropanoids-flavonoids pathway was enhanced, with phenylpropanoids upregulating biomarkers much more than flavonoids; phenylpropanes and phenylmethanes upregulated, and phenylethanes downregulated; the upregulation of quercetin was especially significant in flavonoids; upregulation of condensed tannins and downregulation of hydrolyzed tannins; upregulation of shikimic acids and amino acids including phenylalanine. (2) significant upregulation of free fatty acids and downregulation of glycerides; and (3) upregulation of adenosine phosphates. Our findings provide new insights on the responses of Rhodiola crenulata to extreme high altitude adversity.

Microbial Spectra, Physiological Response and Bioremediation Potential of Phragmites australis for Agricultural Production

Common reed (Phragmites australis) can invade and dominate in its natural habitat which is mainly wetlands. It can tolerate harsh environments as well as remediate polluted and environmental degraded sites such as mine dumps and other polluted wastelands. For this reason, this can be a very critical reed to reclaim wastelands for agricultural use to ensure sustainability. The present review manuscript examined the microbial spectra of P. australis as recorded in various recent studies, its physiological response when growing under stress as well as complementation between rhizosphere microbes and physiological responses which result in plant growth promotion in the process of phytoremediation. Microbes associated with P. australis include Proteobacteria, Bacteriodetes, and Firmicutes, Fusobacteria, Actinobacteria, and Planctomycetes families of bacteria among others. Some of these microbes and arbuscular mycorrhizal fungi have facilitated plant growth and phytoremediation by P. australis. This is worthwhile considering that there are vast areas of polluted and wasted land which require reclamation for agricultural use. Common reed with its associated rhizosphere microbes can be utilized in these land reclamation efforts. This present study suggests further work to identify microbes which when administered to P. australis can stimulate its growth in polluted environments and help in land reclamation efforts for agricultural use.

A Review and Secondary Analysis of Competition-Related Impacts of Nonindigenous Aquatic Plants in the Laurentian Great Lakes

The Laurentian Great Lakes of North America are home to thousands of native fishes, invertebrates, plants, and other species that not only provide recreational and economic value to the region but also hold an important ecological value. However, there are also 55 nonindigenous species of aquatic plants that may be competing with native species and affecting this value. Here, we use a key regional database-the Great Lakes Aquatic Nonindigenous Species Information System (GLANSIS)-to describe the introduction of nonindigenous aquatic plants in the Great Lakes region and to examine patterns relating to their capacity to compete with native plants species. Specifically, we used an existing catalog of environmental impact assessments to qualitatively evaluate the potential for each nonindigenous plant species to outcompete native plant species for available resources. Despite an invasion record spanning nearly two centuries (1837-2020), a great deal remains unknown about the impact of competition by these species. Nonetheless, our synthesis of existing documentation reveals that many of these nonindigenous species have notable impacts on the native plant communities of the region in general and on species of concern in particular. Furthermore, we provide a thorough summary of the diverse adaptations that may contribute to giving these nonindigenous plants a competitive advantage. Adaptations that have been previously found to aid successful invasions were common in 98% of the nonindigenous aquatic plant species in the database.

Evaluation of Two Major Rhodiola Species and the Systemic Changing Characteristics of Metabolites of Rhodiola crenulata in Different Altitudes by Chemical Methods Combined with UPLC-QqQ-MS-Based Metabolomics

Rhodiola species have a long history of use in traditional medicine in Asian and European countries and have been considered to possess resistance to the challenges presented by extreme altitudes. However, the influence of different Rhodiola species on quality is unclear, as well as the influence of altitude on phytochemicals. In this study, the phenolic components and antioxidant abilities of two major Rhodiola species are compared, namely Rhodiolacrenulata and Rhodiola rosea, and the metabolomes of Rhodiolacrenulata from two representative elevations of 2907 and 5116 m are analyzed using a UPLC-QqQ-MS-based metabolomics approach. The results show that the phenolic components and antioxidant activities of Rhodiolacrenulata are higher than those of Rhodiola rosea, and that these effects in the two species are positively correlated with elevation. Here, 408 metabolites are identified, of which 178 differential metabolites (128 upregulated versus 50 downregulated) and 19 biomarkers are determined in Rhodiola crenulata. Further analysis of these differential metabolites showed a significant upregulation of flavonoids, featuring glucosides, the enhancement of the phenylpropanoid pathway, and the downregulation of hydrolyzed tannins in Rhodiola crenulata as elevation increased. Besides, the amino acids of differential metabolites were all upregulated as the altitude increased. Our results contribute to further exploring the Rhodiola species and providing new insights into the Rhodiola crenulata phytochemical response to elevation.

Benthic archaeal community structure and carbon metabolic profiling of heterotrophic microbial communities in brackish sediments

Benthic Archaea play a crucial role in the biogeochemical cycles and food webs, however, their spatiotemporal distribution and environmental drivers are not well investigated in brackish sediments. The composition and abundances of benthic archaeal communities were examined from a coastal lagoon; Chilika (India) which is experiencing an intense pressure from anthropogenic and natural factors. High-throughput sequencing of 16S rRNA genes revealed that sediment (n = 96) archaeal communities were largely composed of Crenarchaeota (18.76%), Euryarchaeota (18.34%), Thaumarchaeota (13.45%), Woesearchaeota (10.05%), and Pacearchaeota (4.21%). Archaeal taxa affiliated to methanogens, sulfate-reducers, and ammonia-oxidizers were detected suggesting that carbon, sulfur, and nitrogen cycles might be prominent in benthic sediments. Salinity, total organic carbon, available nitrogen, available phosphorus, macrophyte (Phragmites karka) and inter-taxa relationships between community members and with bacterial communities played steering roles in structuring the archaeal communities. Marine sites with mesohaline-polyhaline regime were dominated by Nitrosopumilus and Thaumarchaeota. In contrast, riverine sites with oligohaline regime demonstrated a higher abundance of Thermoprotei. Macrophyte dominated zones were enriched in Methanomicrobia and Methanobacteria in their rhizosphere sediments, whereas, bulk (un-vegetated) sediments were dominated by Nitrosopumilus. Spatial patterns in archaeal communities demonstrated 'distance-decay' patterns which were correlated with changes in physicochemical factors over geographical distances. Heterotrophic microbial communities showed much higher metabolic diversity and activity in their carbon utilization profiles in rhizosphere sediments than the bulk sediments. This baseline information on benthic archaea and their environmental drivers would be useful to assess the impact of anthropogenic and natural pressures on these communities and associated biogeochemical cycles.

Nitrogen immobilization may reduce invasibility of nutrient enriched plant community invaded by Phragmites australis

Nutrient enrichment, particularly nitrogen, is an important determinant of plant community productivity, diversity and invasibility in a wetland ecosystem. It may contribute to increasing colonization and dominance of invasive species, such as Phragmites australis, especially during wetland restoration. Providing native species a competitive advantage over invasive species, manipulating soil nutrients (nitrogen) may be an effective strategy to control the invasive species and that management tool is essential to restore the degraded ecosystems. Therefore, we examined competition between Phragmites australis and Melaleuca ericifolia in a greenhouse setting with activated carbon (AC) treatments, followed by cutting of Phragmites shoots in nutrient-rich soils. Additionally, we evaluated the effect of AC on plant-free microcosms in the laboratory, to differentiate direct effects of AC on soil microbial functions from indirect effects. Overall, the objective was to test whether lowering nitrogen might be an effective approach for reducing Phragmites invasion in the wetland. The AC reduced Phragmites total biomass more significantly in repeated cut regime (57%) of Phragmites shoots compared to uncut regime (39%). Conversely, it increased Melaleuca total biomass by 41% and 68% in uncut and repeated cut regimes, respectively. Additionally, AC decreased more total nitrogen in above-ground biomass (41 to 55%) and non-structural carbohydrate in rhizome (21 to 65%) of Phragmites, and less total nitrogen reduction in above-ground biomass (25 to 24%) of Melaleuca in repeated cut compared to uncut regime. The significant negative correlation between Phragmites and Melaleuca total biomass was observed, and noticed that Phragmites acquired less biomass comparatively than Melaleuca in AC-untreated versus AC-treated pots across the cutting frequency. AC also caused significant changes to microbial community functions across Phragmites populations, namely nitrogen mineralization, nitrification, nitrogen microbial biomass and dehydrogenase activity (P ≤ 0.05) that may potentially explain changes in plant growth competition between Phragmites and Melaleuca. The overall effects on plant growth, however, may be partially microbially mediated, which was demonstrated through soil microbial functions. Results support the idea that reducing community vulnerability to invasion through nutrient (nitrogen) manipulations by AC with reducing biomass of invasive species may provide an effective strategy for invasive species management and ecosystem restoration.

Can nutrient enrichment influence the invasion of Phragmites australis?

Plant invasion and nutrient enrichment because of anthropogenic landscape modifications seriously threaten native plant community diversity in aquatic and wetland ecosystems. It is poorly understood, however, whether these two disturbances interact with the functional identity of recipient native plants to drive community change. We performed combined studies in the fields and greenhouse to examine whether nutrient enrichment may trigger the invasion of Phragmites australis in wetlands through competitive advantage over native Melaleuca ericifolia. Chemical characterizations of rhizosphere water were distinguished in two different nutrient enriched wetlands associated with and without Phragmites over the seasons. Significant changes in rhizosphere water were observed in invaded area compared to uninvaded area at both sites. High nitrogen (NO₃^-), phosphorous (PO₄^3-), dissolved organic carbon, phenolics contents, with low pH were found in invaded areas compared to uninvaded areas. Total biomass of Phragmites was positively regressed with rhizosphere water nitrogen (NO₃^-) and phosphorous (PO₄^3-) content. Nutrient addition significantly enhanced the growth and competitive ability of Phragmites over Melaleuca. In contrast, Melaleuca was significantly less competitive than Phragmites. There was a significantly positive correlation between the growth of Phragmites grown alone and its competitive ability. The findings in greenhouse studies coupled with characteristics of Phragmites and its' rhizosphere chemistry in the nutrient enriched fields suggest that nutrient enrichment may enhance Phragmites invasion through correspondingly increasing growth and maintaining inherent competitive advantages of Phragmites. Nutrient management could limit the vigorous growth of Phragmites in wetlands and thereby reduce invasion through competitive advantages over natives, which might have important management implications for wetland managers.

Allelopathy and resource competition: the effects of Phragmites australis invasion in plant communities

BACKGROUND

Phragmites australis, a ubiquitous wetland plant, has been considered one of the most invasive species in the world. Allelopathy appears to be one of the invasion mechanisms, however, the effects could be masked by resource competition among target plants. The difficulty of distinguishing allelopathy from resource competition among plants has hindered investigations of the role of phytotoxic allelochemicals in plant communities. This has been addressed via experiments conducted in both the greenhouse and laboratory by growing associated plants, Melaleuca ericifolia, Rumex conglomeratus, and model plant, Lactuca sativa at varying densities with the allelopathic plant, P. australis, its litter and leachate of P. australis litter. This study investigated the potential interacting influences of allelopathy and resource competition on plant growth-density relationships.

RESULTS

In greenhouse, the root exudates mediated effects showed the strongest growth inhibition of M. ericifolia at high density whereas litter mediated results revealed increased growth at medium density treatments compared to low and high density. Again, laboratory experiments related to seed germination and seedling growth of L. sativa and R. conglomeratus exhibited phytotoxicity decreased showing positive growth as plant density increased and vice versa. Overall, the differential effects were observed among experiments but maximum individual plant biomass and some other positive effects on plant traits such as root and shoot length, chlorophyll content occurred at an intermediate density. This was attributed to the sharing of the available phytotoxin among plants at high densities which is compatible to density-dependent phytotoxicity model.

CONCLUSIONS

The results demonstrated that plant-plant interference is the combined effect of allelopathy and resource competition with many other factors but this experimental design, target-neighbor mixed-culture in combination of plant grown at varying densities with varying level of phytotoxins, mono-culture, can successfully separate allelopathic effects from competition.

Responses of plant species diversity and soil physical-chemical-microbial properties to Phragmites australis invasion along a density gradient

The invasion of ecosystems by strongly colonising plants such as Phragmites australis is viewed as one of the greatest threats to plant diversity and soil properties. This study compared a range of diversity measures including soil properties and mycorrhizal potential under different degrees of Phragmites density among three populations in coastal wetland, Victoria, Australia. Species richness, evenness and Shanon-Wiener index had significantly higher values in low degree of Phragmites density in all populations. Higher densities had the lowest diversity, with Shannon-Wiener index = 0 and Simpson’s index = 1 indicating its mono-specificity. Significant alterations in soil properties associated with different degrees of Phragmites density were noticed. These had interactive effects (population × density) on water content, dehydrogenase activity, microbial biomass (C, N and P) but not on pH, electrical conductivity, phenolics, organic carbon, and spore density. Furthermore, the study elucidated decrease of competitive abilities of native plants, by interfering with formation of mycorrhizal associations and biomass. Overall, our results suggest that significant ecological alterations in vegetation and soil variables (including mycorrhizal potential) were strongly dependent on Phragmites density. Such changes may lead to an important role in process of Phragmites invasion through disruption of functional relationships amongst those variables.

Isothermal titration calorimetry uncovers substrate promiscuity of bicupin oxalate oxidase from Ceriporiopsis subvermispora

Isothermal titration calorimetry (ITC) may be used to determine the kinetic parameters of enzyme-catalyzed reactions when neither products nor reactants are spectrophotometrically visible and when the reaction products are unknown. We report here the use of the multiple injection method of ITC to characterize the catalytic properties of oxalate oxidase (OxOx) from Ceriporiopsis subvermispora (CsOxOx), a manganese dependent enzyme that catalyzes the oxygen-dependent oxidation of oxalate to carbon dioxide in a reaction coupled with the formation of hydrogen peroxide. CsOxOx is the first bicupin enzyme identified that catalyzes this reaction. The multiple injection ITC method of measuring OxOx activity involves continuous, real-time detection of the amount of heat generated (dQ) during catalysis, which is equal to the number of moles of product produced times the enthalpy of the reaction (ΔH_app). Steady-state kinetic constants using oxalate as the substrate determined by multiple injection ITC are comparable to those obtained by a continuous spectrophotometric assay in which H₂O₂ production is coupled to the horseradish peroxidase-catalyzed oxidation of 2,2′-azinobis-(3-ethylbenzthiazoline-6-sulfonic acid) and by membrane inlet mass spectrometry. Additionally, we used multiple injection ITC to identify mesoxalate as a substrate for the CsOxOx-catalyzed reaction, with a kinetic parameters comparable to that of oxalate, and to identify a number of small molecule carboxylic acid compounds that also serve as substrates for the enzyme.

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ITC is used to assay the catalytic activity of oxalate oxidase.

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ITC enzymatic assay is sensitive, direct, and continuous.

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Mesoxalate and other carboxylic acids are substrates for oxalate oxidase.

Invasive swallow-worts: an allelopathic role for -(-) antofine remains unclear

Pale swallow-wort (Vincetoxicum rossicum) and black swallow-wort (V. nigrum) are two invasive plant species in the northeastern United States and eastern Canada that have undergone rapidly expanding ranges over the past 30 years. Both species possess a highly bioactive phytotoxin -(-) antofine in root tissues that causes pronounced inhibition in laboratory bioassays of native plant species co-located in habitats where swallow-wort is found. To further evaluate the allelopathic potential of -(-) antofine, we: determined its concentration in young plant tissues; used in situ approaches to assess antofine stability, potential activity of degradation products, activity in sterile and nonsterile soil; and determined accumulation and concentration in hydroponic cultivation and field collected soil samples. Extracts of seeds and young seedlings were found to have approximately 2-3 times the level of -(-) antofine in comparison to root extracts of adult plants. Breakdown products of antofine accumulated rapidly with exposure to light, but more slowly in the dark, at ambient temperatures, and these products did not retain biological activity. Extraction efficiencies of control soil spiked with -(-) antofine were low but easily detectable by HPLC. Soil samples collected over two growing seasons at four different sites where either pale swallow-wort or black swallow-wort populations are present were negative for the presence of -(-) antofine. Dose response curves using sterile and nonsterile soil spiked with -(-) antofine demonstrated a requirement for at least 20-55 × greater -(-) antofine concentrations in soil to produce similar phytotoxic effects to those previously seen in agar bioassays with lettuce seedlings. Sterile soil had a calculated EC50 of 686 μM (250 μg/g) as compared to nonsterile soil treatments with a calculated EC50 of 1.88 mM (640 μg/g). When pale swallow-wort and black swallow-wort adult plants were grown in hydroponic cultivation, -(-) antofine was found in root exudates and in the growing medium in the nM range. The concentrations in exudate were much lower than that needed for biological activity (μM) although they might be an underestimate of what may accumulate over time in an undisturbed rhizosphere. Based on these various results, it remains uncertain as to whether -(-) antofine could play a significant allelopathic role for invasive swallow-worts.

Suppression of native Melaleuca ericifolia by the invasive Phragmites australis through allelopathic root exudates

PREMISE OF THE STUDY

Invasive plants are a great threat to the conservation of natural ecosystems and biodiversity. Allelopathy as a mechanism for invasion of plants such as Phragmites australis, one of the most aggressive invaders, has the potential to suppress neighboring plant species. Allelopathic interference, through root exudates of P. australis on native Melaleuca ericifolia, was investigated to find out the underlying invasion mechanisms.

METHODS

Germination and growth effects of P. australis on M. ericifolia were studied in the greenhouse using potting mix both with and without activated carbon, and a combination of single and repeated cuttings of P. australis as the management tool.

KEY RESULTS

P. AUSTRALIS had significant negative effects on germination and growth of M. ericifolia by inhibiting germination percentage, maximum root length and plant height, biomass, stem diameter, and number of growth points with little effect on leaf physiology. Activated carbon (AC) in turn moderately counteracted these effects. The cutting of P. australis shoots significantly reduced the suppressive effects on M. ericifolia compared to the addition of AC to soil. Furthermore, significant changes in soil such as pH, electrical conductivity, osmotic potential, phenolics, and dehydrogenase activity were identified among cutting treatments with little variation between AC treatments.

CONCLUSION

The results demonstrated that allelopathy through root exudates of P. australis had relatively low contribution in suppressing M. ericifolia in comparison to other competitive effects. Management tools combining repeated cutting of P. australis shoots with AC treatments may assist partly in the restoration of native ecosystems invaded by P. australis.

Evidence does not support a role for gallic acid in Phragmites australis invasion success

Gallic acid has been reported to be responsible for the invasive success of nonnative genotypes of Phragmites australis in North America. We have been unable to confirm previous reports of persistent high concentrations of gallic acid in the rhizosphere of invasive P. australis, and of high concentrations of gallic acid and gallotannins in P. australis rhizomes. The half-life of gallic acid in nonsterile P. australis soil was measured by aqueous extraction of soils and found to be less than 1 day at added concentrations up to 10,000 μg g(-1). Furthermore, extraction of P. australis soil collected in North Carolina showed no evidence of gallic acid, and extractions of both rhizomes and leaves of samples of four P. australis populations confirmed to be of invasive genotype show only trace amounts of gallic acid and/or gallotannins. The detection limits were less than 20 μg gallic acid g(-1) FW in the rhizome samples tested, which is approximately 0.015 % of the minimum amount of gallic acid expected based on previous reports. While the occurrence of high concentrations of gallic acid and gallotannins in some local populations of P. australis cannot be ruled out, our results indicate that exudation of gallic acid by P. australis cannot be a primary, general explanation for the invasive success of this species in North America.

Bactericidal action of photoirradiated gallic acid via reactive oxygen species formation

It is known that gallic acid shows antimicrobial activity. In the present study, photoirradiation induced reactive oxygen species formation was investigated for augmentation of the antimicrobial activity of gallic acid. Staphylococcus aureus suspended in 4 mmol/L gallic acid was exposed to blue light of a LED at 400 nm. This treatment killed the bacteria, and a >5-log reduction of the viable counts was observed within 15 min. By contrast, neither the LED treatment alone nor the treatment with gallic acid alone showed substantial bactericidal effect. When hydroxyl radical scavengers were added to the suspension, the bactericidal effect of photoirradiated gallic acid was attenuated. Furthermore, electron spin resonance analysis demonstrated that hydroxyl radicals were generated by the photoirradiation of gallic acid. Thus, the present study suggests that the photo-oxidation can enhance the antimicrobial activity of gallic acid via hydroxyl radical formation.