Interaction Between Root Exudates of the Poisonous Plant Stellera chamaejasme L. and Arbuscular Mycorrhizal Fungi on the Growth of Leymus chinensis (Trin.) Tzvel

Dynamic response of allelopathic potency of Taxus cuspidata Sieb. et Zucc. mediated by allelochemicals in Ficus carica Linn. root exudates

In a mixed forest, certain plants can release allelochemicals that exert allelopathic effects on neighboring plants, thereby facilitating interspecific coexistence of two species. Previous studies have demonstrated that allelochemicals released from Ficus carica Linn. roots in mixed forest of F. carica and Taxus cuspidata Sieb. et Zucc. has phase characteristics over time, which can improve the soil physicochemical properties, enzyme activity and microbial diversity, thus promoting the growth of T. cuspidata. Based on the irrigation of exogenous allelochemicals, changes in soil fertility (soil physical and chemical properties, soil enzyme activity and soil microelement content) were observed in response to variations in allelochemicals during five phases of irrigation: initial disturbance phase (0-2 d), physiological compensation phase (2-8 d), screening phase (8-16 d), restore phase (16-32 d) and maturity phase (32-64 d), which was consistent with the response of soil microorganisms. The allelopathic response of growth physiological indexes of T. cuspidata, however, exhibited a slight lag behind the soil fertility, with distinct phase characteristics becoming evident on the 4th day following irrigation of allelochemicals. The findings demonstrated that the allelochemicals released by the root of F. carica induced a synergistic effect on soil fertility and microorganisms, thereby facilitating the growth of T. cuspidata. This study provides a comprehensive elucidation of the phased dynamic response-based allelopathic mechanism employed by F. carica to enhance the growth of T. cuspidata, thus establishing a theoretical basis for optimizing forest cultivation through allelopathic pathways.

Toxic nonpreferred species accelerate the natural restoration of plant productivity and diversity in degraded grasslands

Long-term overgrazing may lead to the degradation of grasslands which are often characterized by an increase in nonpreferred species, especially toxic plants. However, the impact of these toxic nonpreferred species on the restoration processes of degraded grasslands is not well understood, particularly their interactions with soil properties and other plant functional groups. To address this knowledge gap, we conducted an in situ grazing exclusion experiment in a temperate degraded grassland of Inner Mongolia, China. The objective of this study was to investigate how toxic nonpreferred plants influence the recovery of plant diversity and productivity in degraded grasslands and whether these effects can be explained by changes in soil properties. Our findings revealed that Stellera chamaejasme, a toxic nonpreferred species widely distributed in North China, directly altered plant community composition and improved species diversity in degraded grasslands dominated by Asteraceae plants. The presence of S. chamaejasme could inhibit Asteraceae abundance and increase soil copper content in this study area, because Asteraceae plants have a high copper accumulation capacity. Within the communities with S. chamaejasme, the alleviation of soil copper limitation to plants may subsequently enhance the abundance and aboveground productivity of Poaceae and Forbs. Our study demonstrated that the strong direct and indirect interactions of toxic nonpreferred species with other ecosystem components promoted competitive release in terms of biomass accumulation and species diversity. The change of soil limiting microelements content caused by toxic species exerts an important mediation function during the recovery process of degraded grasslands. Thus, these toxic nonpreferred species can act primarily as accelerators for the restoration of community structure and ecosystem function in degraded grasslands.

The effects of microplastics on crop variation depend on polymer types and their interactions with soil nutrient availability and weed competition

Microplastics pollution of agricultural soil is a global environmental concern because of its potential risk to food security and human health. Although many studies have tested the direct effects of microplastics on growth of Eruca sativa Mill., little is known about whether these effects are regulated by fertilization and weed competition in field management practices. Here, we performed a greenhouse experiment growing E. sativa as target species in a three-factorial design with two levels of fertilization (low versus. high), two levels of weed competition treatments (weed competition versus no weed competition) and five levels of microplastic treatments (no microplastics, Polybutylene adipate-co-terephthalate [PBAT], Polybutylene succinate [PBS], Polycaprolactone [PCL] or Polypropylene [PP]). Compared to the soil without microplastics, PBS and PCL reduced aboveground biomass and leaf number of the E. sativa. PBS also resulted in increased root allocation and thicker roots in E. sativa. In addition, fertilization significantly mitigated the negative effects of PBS and PCL on aboveground biomass of E. sativa, but weed competition significantly promoted these effects. Although fertilization alleviated the negative effect of PBS on aboveground biomass, such alleviation became weaker under weed competition than when E. sativa grew alone. The results indicate that the effects of specific polymer types on E. sativa growth could be regulated by fertilization, weed management, and even their interactions. Therefore, reasonable on-farm management practices may help in mitigating the negative effects of microplastics pollution on E. sativa growth in agricultural fields.

The inhibitory potential of green manure return on the germination and seedling growth of Eleusine indica L

Trifolium repens L. (white clover) and Lolium perenne L. (ryegrass) are green manures widely used in conservation tillage systems worldwide. Eleusine indica L. (goosegrass) is a globally recognized noxious weed. Herein, we investigated the effects of aqueous extracts, decomposed liquids, and different straw-to-soil ratios on the germination and growth of goosegrass. The results showed that high concentrations (≥ 30%) of aqueous extracts or decomposed liquids of both green manures significantly inhibited germination-related parameters of goosegrass. The strongest inhibitory effect was observed for the 7-day decomposition treatment, and white clover's inhibitory effect was greater than ryegrass's. A pot experiment showed that non-photochemical quenching, catalase, and peroxidase activity levels of goosegrass leaves were significantly increased. At the same time, the net photosynthetic rate significantly decreased. Seedling growth was inhibited when the straw-to-soil ratio was greater than 3:100. The ryegrass treatments inhibited goosegrass seedlings more than the white clover treatments. This study demonstrated the inhibitory potential of white clover and ryegrass straw return on seed germination and seedling growth of goosegrass. The study has also helped to identify weed-resistant substances in these green manures so that their weed-control properties can be used more effectively and herbicide usage can be reduced.

Establishing the Relationship Between Flavonoid Content, Mycorrhization, and Soil Nutritional Content in Different Species of the Genus Passiflora in Colombia

The genus Passiflora comprises more than 500 species distributed in tropical and semitropical regions. With a great diversity of species, it is estimated that one-third is found in Colombian territory. Besides the food importance, Passiflora species are important sources of biologically active compounds, such as flavonoids. The most important symbiosis between soil fungi and vascular plants related to plant nutrition and tolerance to stress conditions is mycorrhizae. Passiflora species form arbuscular mycorrhizae, with several species of Glomeromycota. This association has been reported to alter the production of secondary metabolites. Thus, the objective of this study was to determine the relation between flavonoid content, mycorrhization, and soil nutritional content of Passiflora alata, Passiflora quadrangularis, Passiflora maliformis, and Passiflora ligularis in Colombian crops. The extracts were prepared and analyzed using UPLC/PDA-MS, and total flavonoids were quantified with the method of AlCl3. Soil characteristics, including nutritional content and percentage of colonization by arbuscular mycorrhizal fungi, were also determined. All variables were analyzed using Spearman's correlation and principal component analysis. Chromatographic analysis of the extracts allowed us to visualize the different flavonoid compositions of each extract, identifying several C-glycosylflavonoids. In this paper, we report for the first time the presence of luteolin-8-C-rhamnosyl-4'-O-glucoside, apigenin-6-C-arabinosyl-7-O-glucoside, and orientin for P. maliformis. Statistical analysis showed a negative correlation between available phosphorus (ρ = -0.90, p = <0.05) and magnesium (Mg) saturation (ρ = -0.70, p = <0.05) on flavonoid content, whereas the calcium magnesium (Ca/Mg) ratio was positively correlated (ρ = 0.70, p = <0.01). There was a nonsignificant correlation between mycorrhization and flavonoid content (ρ = -0.70, p = >0.1). These results contribute to understanding the relationship between flavonoid-mycorrhization-soil nutritional content on Passiflora spp.

Interactive effects between the invasive weed Stellera chamaejasme and grass: can arbuscular mycorrhizal fungi and fungal pathogens coregulate interspecific relationships?

The interaction between poisonous weeds and neighboring plants is complex. Poisonous weeds frequently have a competitive advantage in the interaction between poisonous weeds and neighboring plants. Arbuscular mycorrhizal fungi (AMF) and plant pathogenic fungi (PPF) are closely related to the interspecific relationships of plants. However, the role of AMF and PPF between poisonous weeds and neighboring grasses remains unclear. Here, we designed a pot experiment to determine the interspecific relationship between Leymus chinensis and Stellera chamaejasme and the regulation of AMF and PPF. The results showed that interactive effects between L. chinensis and S. chamaejasme significantly inhibited the aboveground growth of both but promoted the underground growth of L. chinensis. As the proportions of S. chamaejasme increased, the total nitrogen content and pH in the rhizosphere soil of L. chinensis were reduced, the soil pH of S. chamaejasme was reduced, and the relative abundance of AMF in the rhizosphere soil of L. chinensis significantly increased and that of S. chamaejasme decreased considerably. The relative abundances of PPF in the rhizosphere soil of both in the mono-cultures were significantly higher than those in the mixed cultures. Structural equation modeling indicated that soil abiotic (pH and N availability) and biotic (AMF and PPF) factors are major drivers explaining the interactive effects between L. chinensis and S. chamaejasme. We provided new evidence for the interspecific interactions between poisonous weeds and neighboring grasses and revealed the regulatory role of AMF and PPF in the interactive effects of both plants. This study will provide a scientific basis for the prevention and control of poisonous weeds and the vegetation restoration of degraded grasslands in the future.

Yuexiandajisu diterpenoids from Euphorbia ebracteolata Hayata (Langdu roots): An overview

The roots of the plant Euphorbia ebracteolata Hayata (Yue Xian Da Ji) are commonly used in traditional Chinese medicine to treat multiple diseases such as chronic liver diseases, oedema, pulmonary diseases and cancer. It is the main ingredient of the TCM called Langdu which can be prepared also from roots of E. fischeriana Steud. and occasionally from Stellera chamaejasme species. Numerous bioactive natural products have been isolated from E. ebracteolata including a large diversity of diterpenoids with anti-inflammatory and anticancer properties. One little series of compounds has been named yuexiandajisu (A, B, C, D, D₁, E, F) which comprises two casbane-, one isopimarane-, two abietane-, and two rosane-type diterpenes including a dimeric molecule. The origin, structural diversity and properties of these little-known natural products is discussed here. Several of these compounds have been identified in the roots of other Euphorbia species, notably the potent phytotoxic agent yuexiandajisu C. The abietane diterpenes yuexiandajisu D-E exhibit marked anticancer properties but their mechanism of action remains unresolved. The dimeric compound, renamed yuexiandajisu D₁, also exhibit anti-proliferative properties against cancer cell lines, unlike the rosane diterpene yuexiandajisu F. The structural or functional analogy with other diterpenoids is discussed.

Piriformospora indica alter root-associated microbiome structure to enhance Artemisia annua L. tolerance to arsenic

Microorganisms in the rhizosphere are crucial allies for plant stress tolerance. Recent research suggests that by interacting with the rhizosphere microbiome, microorganisms can aid in the revegetation of soils contaminated with heavy metal(loid)s (HMs). However, it is unknown that how Piriformospora indica influences the rhizosphere microbiome to mitigate arsenic-toxicity in arsenic-enriched environments. Artemisia annua plants were grown in the presence or absence of P. indica and spiked with low (50) and high (150 µmol/L) concentrations of arsenic (As). After inoculation with P. indica, fresh weight increased by 37.7% and 10% in control and high concentration treated plants, respectively. Transmission electron microscopy showed that cellular organelles were severely damaged by As and even disappeared under high concentration. Furthermore, As was mostly accumulated by 5.9 and 18.1 mg/kg dry weight in the roots of inoculated plants treated with low and high concentrations of As, respectively. Additionally, 16 S and ITS rRNA gene sequencing were applied to analyze the rhizosphere microbial community structure of A. annua under different treatments. A significant difference was observed in microbial community structure under different treatments as revealed by non-metric multidimensional scaling ordination. The bacterial and fungal richness and diversity in the rhizosphere of inoculated plants were actively balanced and regulated by P. indica co-cultivation. Lysobacter and Steroidobacter were found to be the As-resistant bacterial genera. We conclude that P. indica inoculation could alter rhizosphere microecology, thereby mitigating As-toxicity without harming the environment.

Enhanced foliar 15 N enrichment with increasing nitrogen addition rates: Role of plant species and nitrogen compounds

Determining the abundance of N isotope (δ¹⁵ N) in natural environments is a simple but powerful method for providing integrated information on the N cycling dynamics and status in an ecosystem under exogenous N inputs. However, whether the input of different N compounds could differently impact plant growth and their ¹⁵ N signatures remains unclear. Here, the response of ¹⁵ N signatures and growth of three dominant plants (Leymus chinensis, Carex duriuscula, and Thermopsis lanceolata) to the addition of three N compounds (NH₄ HCO₃ , urea, and NH₄ NO₃ ) at multiple N addition rates were assessed in a meadow steppe in Inner Mongolia. The three plants showed different initial foliar δ¹⁵ N values because of differences in their N acquisition strategies. Particularly, T. lanceolata (N₂ -fixing species) showed significantly lower ¹⁵ N signatures than L. chinensis (associated with arbuscular mycorrhizal fungi [AMF]) and C. duriuscula (associated with AMF). Moreover, the foliar δ¹⁵ N of all three species increased with increasing N addition rates, with a sharp increase above an N addition rate of ~10 g N m^-2  year^-1 . Foliar δ¹⁵ N values were significantly higher when NH₄ HCO₃ and urea were added than when NH₄ NO₃ was added, suggesting that adding weakly acidifying N compounds could result in a more open N cycle. Overall, our results imply that assessing the N transformation processes in the context of increasing global N deposition necessitates the consideration of N deposition rates, forms of the deposited N compounds, and N utilization strategies of the co-existing plant species in the ecosystem.

Arbuscular Mycorrhizal Fungi Reduce Cadmium Leaching from Sand Columns by Reducing Availability and Enhancing Uptake by Maize Roots

To explore the effect of arbuscular mycorrhizal fungi (AMF) on the environmental migration of cadmium (Cd), a sand column-maize system containing 20 mg·L−1 Cd solution was used to investigate the AMF effect on maize growth, Cd uptake by maize, Cd adsorption by sand and Cd leaching loss. The results showed that AMF significantly increased the content of EE-GRSP and T-GRSP by 34.9% and 37.2%, respectively; the secretion of malonic acid, oxalic acid and succinic acid increased by 154.2%, 54.0% and 11.0%, respectively; the secretion of acetic acid and citric acid increased by 95.5% and 59.9%, respectively; and the length, surface area, volume, tip number and cross number of maize roots decreased by 10%, 15%, 17%, 20% and 36.4%, respectively. AMF significantly increased Cd adsorption by sand by 6.2%, Cd uptake by maize by 68.1%, and Cd leaching loss by 84.6%. In the sand column-maize system, 92.3% of the total Cd was adsorbed by sand, 5.9% was taken up by maize and 1.8% was lost due to leaching. Moreover, Cd adsorption by sand was significantly positively correlated with the GRSP content and oxalic acid secretion, and Cd uptake by roots was significantly negatively correlated with Cd leaching loss. Overall, AMF reduced the loss of Cd in the leaching solution by promoting the release of oxalic acid and GRSP, increasing the adsorption of Cd in the sand and fixing the Cd in the plant to the roots.

Effects of inoculation of Lactiplantibacillus plantarum and Lentilactobacillus buchneri on fermentation quality, aerobic stability, and microbial community dynamics of wilted Leymus chinensis silage

Leymus chinensis is an important crop that can be fed to ruminants. The purpose of this study was to investigate the roles of Lactiplantibacillus plantarum and Lentilactobacillus buchneri in fermentation quality, aerobic stability, and dynamics of wilted L. chinensis silage microorganisms. Wilted L. chinensis silages were ensiled with/without L. plantarum and L. buchneri. After 14 and 56 days of ensiling, the silos were opened and subjected to a 7-day aerobic deterioration test. This study looked at the composition of fermentation products as well as the microbial communities in silage. Silage inoculated with L. plantarum and L. buchneri had an increased lactic acid content as well as lactic acid bacterial (LAB) quantity, but a decrease in pH and levels of butyric acid, 2,3-butanediol, and ethanol was observed during ensiling. Non-treated and L. plantarum-treated silages deteriorated in the 7-day spoilage test after opening day-14 silos, whereas L. buchneri-inoculated silage showed no signs of deterioration. Lactobacillus abundance increased in the 7-day spoilage test after opening day-56 silos, while undesirable microorganisms such as Acetobacter, Bacillus, and molds, namely, Aspergillus and Penicillium were inhibited within L. plantarum- and L. buchneri-inoculated silages. The composition of fermentation products was related to the bacterial community, particularly Lactobacillus, Enterococcus, and Acetobacter. To summarize, L. plantarum- and L. buchneri-inoculated silage enhanced fermentation quality during ensiling and inhibited aerobic spoilage in a 7-day spoilage test of 56 days ensiling within wilted L. chinensis silage.

Aqueous Extracts of Three Herbs Allelopathically Inhibit Lettuce Germination but Promote Seedling Growth at Low Concentrations

Allelopathy is an important process in plant communities. The effects of allelopathy on seed germination and seedling development have been extensively investigated. However, the influences of extract soaking time and concentration on the foregoing parameters are poorly understood. Here, we conducted a seed germination assay to determine the allelopathic effects of the donor herbs Achnatherum splendens (Trin.) Nevski, Artemisia frigida Willd., and Stellera chamaejasme L., from a degraded grassland ecosystem in northern China, on lettuce (Lactuca sativa L.) seed germination and early seedling growth. Extract soaking times (12 h or 24 h) did not exhibit significantly different effects on lettuce seed germination or seedling development. However, all aqueous herb extracts inhibited lettuce seed germination and root length (RI < 0) and promoted lettuce shoot length, stem length, leaf length, and leaf width (RI > 0) at both low (0.005 g mL⁻¹) and high (0.05 g mL⁻¹) concentrations. Moreover, A. splendens extracts increased seedling biomass (RI > 0) and synthetical allelopathic effect (SE > 0) at both concentrations. In contrast, both A. frigida and S. chamaejasme extracts had hormesis effects, which stimulate at low concentrations (RI > 0) but inhibit at high concentrations (RI < 0) on seedling biomass and synthetical allelopathic effect (SE). The results suggest that allelopathic potential may be an important mechanism driving the dominance of A. frigida and S. chamaejasme in degraded grasslands. Reseeding allelopathy-promoting species such as A. splendens may be beneficial to grassland restoration. The present study also demonstrated that seedling biomass, root and shoot length, and seed germination rate are the optimal bioindicators in allelopathy assays and could be more representative when they are combined with the results of multivariate analyses.

Remediation of soils co-contaminated with cadmium and dichlorodiphenyltrichloroethanes by king grass associated with Piriformospora indica: Insights into the regulation of root excretion and reshaping of rhizosphere microbial community structure

Cadmium (Cd) and dichlorodiphenyltrichloroethane (DDT) are frequently detected in agricultural soils, which poses a threat to public health. This study investigated the effects of inoculation of king grass with Piriformospora indica on the remediation of soils co-contaminated with Cd and DDTs. After treatment for 90 days, the dry shoot and root biomass of king grass inoculated with P. indica markedly increased by 13.0-15.8% and 24.1-46.4%, respectively, compared with those of uninoculated plants. Inoculation with P. indica also increased the uptake of Cd and DDTs by shoots and roots of king grass. The removal efficiency of Cd and DDTs from soils reached 4.88-17.4% and 48.4-51.0%, respectively, in the presence of king grass inoculated with P. indica. Under three Cd-DDTs contamination conditions, root secretion of organic acids, alcohol, and polyamines was distinctively stimulated by P. indica inoculation of king grass compared with planting king grass alone. After phytoremediation, changes in soil bacterial and fungal community composition occurred at different contamination levels. Overall, the results showed that king grass associated with P. indica can be adopted for phytoextraction of Cd and DDTs from moderately contaminated soils by regulating root excretion and reshaping rhizosphere microbial community structure.

Endophytic bacterial community of Stellera chamaejasme L. and its role in improving host plants' competitiveness in grasslands

Stellera chamaejasme has become a problematic weed in northern and south-western grasslands of China. To evaluate a possible role of endophytes in its strong competitive capacity, the endophytic bacterial community of S. chamaejasme was investigated by culture-dependent and independent methods, and the growth-promoting traits of some culturable isolates as well as the benefit of endophyte ST3CS3 (Brevundimonas sp.) on host plants growth were studied. The results showed that 823 OTUs were generated with a 97% similarity level in the culture-independent study. They were classified into 29 phyla, 61 classes, 147 orders, 237 families and 440 genera. Among them, Pseudomonas and Ralstonia were the most dominant genera in belowground parts (G) (64.25%) and aboveground parts (S) (26.54%) respectively. The diversity and species richness of endophytes in S were significantly higher than that of G (P < 0.001, t-test). Contrary to this, the number of culturable bacteria in S was a little lower than that of G (P > 0.05, t-test). Totally, 176 isolates belonging to 30 morphotypes were obtained in the culture-dependent study. Among them, Acinetobacter was the most dominant genus in G (51.30%), then followed by Pseudomonas (6.09%) and Brevundimonas (6.09%), while Lysinibacillus (21.31%) was the most dominant genus in S, followed by Pseudomonas (11.48%). Growth-promoting trait tests indicated that 93.65% of the tested isolates (63) exhibited nitrogen-fixing, IAA-synthesizing, phosphorus or potassium solubilizing capacity, in which 77.97% belonged to Proteobacteria, a phylum found to contain more active isolates. Pot experiments demonstrated that endophyte ST3CS3 can significantly improve host plants growth and increase its nitrogen and chlorophyll content (P < 0.01, t-test). Therefore, we suggest that strong competitiveness of S. chamaejasme may in part be due to possession of high ratios of plant growth-promoting proteobacterial endophytes such as Pseudomonas, Acinetobacter and Brevundimonas.

Increasing flavonoid concentrations in root exudates enhance associations between arbuscular mycorrhizal fungi and an invasive plant

Many invasive plants have enhanced mutualistic arbuscular mycorrhizal (AM) fungal associations, however, mechanisms underlying differences in AM fungal associations between introduced and native populations of invasive plants have not been explored. Here we test the hypothesis that variation in root exudate chemicals in invasive populations affects AM fungal colonization and then impacts plant performance. We examined flavonoids (quercetin and quercitrin) in root exudates of native and introduced populations of the invasive plant Triadica sebifera and tested their effects on AM fungi and plant performance. We found that plants from introduced populations had higher concentrations of quercetin in root exudates, greater AM fungal colonization and higher biomass. Applying root exudates more strongly increased AM fungal colonization of target plants and AM fungal spore germination when exudate donors were from introduced populations. The role of root exudate chemicals was further confirmed by decreased AM fungal colonization when activated charcoal was added into soil. Moreover, addition of quercetin into soil increased AM fungal colonization, indicating quercetin might be a key chemical signal stimulating AM fungal associations. Together these results suggest genetic differences in root exudate flavonoids play an important role in enhancing AM fungal associations and invasive plants' performance, thus considering root exudate chemicals is critical to unveiling mechanisms governing shifting plant-soil microbe interactions during plant invasions.