Endogenous IAA affected fluoranthene accumulation by regulating H+-ATPase and SOD activity in ryegrass

This study explores the role of endogenous indole-3-acetic acid (IAA) in modulating plant responses to pollution stress and its effect on pollutant accumulation, with a focus on fluoranthene (Flu) in ryegrass. To elucidate the mechanism, we employed an IAA promoter (α-aminobutyric acid [α-AB]) and an IAA inhibitor (naphthylphthalamic acid [NPA]) to regulate IAA levels and analyze Flu uptake characteristics. The experimental setup included a Flu treatment group (ryegrass with Flu addition) and a control group (ryegrass without Flu). Our findings demonstrate that Flu treatment enhanced IAA content and plant growth in ryegrass compared to the control. The Flu+AB treatment further enhanced these effects, while the Flu+NPA treatment exhibited a contrasting trend. Moreover, Flu+AB treatment led to increased Flu accumulation, in contrast to the inhibitory effect observed with Flu+NPA treatment. Flu treatment also enhanced the activities of key antioxidant enzymes (SOD, POD, CAT) and increased soluble sugar and protein levels, indicative of enzymatic and nonenzymatic defense responses, respectively. The Flu+AB treatment amplified these responses, whereas the Flu+NPA treatment attenuated them. Significantly, Flu treatment raised H+-ATPase activity compared to the control, an effect further elevated by Flu+AB treatment and diminished by Flu+NPA treatment. A random forest analysis suggested that Flu accumulation dependency varied under different treatments: it relied more on H+-ATPase activity under Flu+AB treatment and more on SOD activity under Flu+NPA treatment. Additionally, Flu+AB treatment boosted the transpiration rate in ryegrass, thereby increasing the Flu translocation factor, a trend reversed by Flu+NPA treatment. This research highlights crucial factors influencing Flu accumulation in ryegrass, offering potential new avenues for controlling the gathering of contaminants within plant systems.

Insights into soil bacterial and physicochemical properties of annual ryegrass-maize rotation (ARMR) system in southern China

The popularized application of annual ryegrass-maize rotation (ARMR) in southern China has been proposed to fully utilize the farmlands and to increase forage yield and quality. Herein, one growth cycle of ARMR was conducted and soil bacteria were analyzed by 16S rRNA sequencing for control (CK), after the preceding crop (monoculture, or mixed sowing of annual ryegrass and oat) and the successive crop (maize). Our results indicated that the α-diversity of soil bacteria was changed in the ARMR system, which was related to the activity of urease and available phosphatase. The mixed sowing of annual ryegrass and oat in preceding crop could improve the yield and quality, while it was accompanied by unbalanced soil community. With the increased sowing proportion of oat to annual ryegrass, the soil pH increased while the soil available phosphatase decreased. The ARMR system was found to benefit the soil microenvironment by increasing the beneficial soil bacteria and enzyme activity or decreasing the harmful soil bacteria. Considering the soil bacteria α-diversity index and physicochemical properties comprehensively, the recommended sowing regime is the mixed sowing of M2 (22.5 kg·hm-2 annual ryegrass with 75 kg·hm-2 oat).

Growth-promoting effects of Bradyrhizobium soybean symbionts in black oats, white oats, and ryegrass

Although inoculating soybean with rhizobia for biological nitrogen fixation is a common practice in agriculture, rhizobia are also known to associate with grasses. In this study, we evaluate the potential utility of the rhizobial strains SEMIA 587 and 5019 (Bradyrhizobium elkanii), 5079 (Bradyrhizobium japonicum), and 5080 (Bradyrhizobium diazoefficiens), recommended for Brazilian soybean inoculation, in colonizing black oat plants and promoting growth in black and white oats, and ryegrass. Inoculation of white oats with SEMIA 587 increase the seed germination (SG) by 32.09%, whereas the SG of black oats inoculated with SEMIA 587 and 5019 increased by 40.38% and 37.85%, respectively. Similarly, inoculation of ryegrass with all strains increased SG values between 24.63 and 27.59%. In addition, white oats with SEMIA 587 and 5080 had root areas significantly superior to those in other treatments, whereas inoculation with SEMIA 5079 and 5080 resulted in the highest volume of roots. Likewise, SEMIA 5079 and 5080 significantly increased the length, volume, and area of black oats roots, whereas SEMIA 587 increased the volume, area, and dry mass of roots and shoot. Inoculation in ryegrass with SEMIA 587 significantly increased the root volume. Moreover, most strains transformed with gfp and gus were observed to colonize the roots of black oats. Collectively, the findings of this study indicate that rhizobial strains recommended for inoculation of soybean can also be used to promote the growth of the three assessed grass species, and are able to colonize the roots of black oats.

Reciprocal allopolyploid grasses (Festuca × Lolium) display stable patterns of genome dominance

Allopolyploidization entailing the merger of two distinct genomes in a single hybrid organism, is an important process in plant evolution and a valuable tool in breeding programs. Newly established hybrids often experience massive genomic perturbations, including karyotype reshuffling and gene expression modifications. These phenomena may be asymmetric with respect to the two progenitors, with one of the parental genomes being "dominant." Such "genome dominance" can manifest in several ways, including biased homoeolog gene expression and expression level dominance. Here we employed a k-mer-based approach to study gene expression in reciprocal Festuca pratensis Huds. × Lolium multiflorum Lam. allopolyploid grasses. Our study revealed significantly more genes where expression mimicked that of the Lolium parent compared with the Festuca parent. This genome dominance was heritable to successive generation and its direction was only slightly modified by environmental conditions and plant age. Our results suggest that Lolium genome dominance was at least partially caused by its more efficient trans-acting gene expression regulatory factors. Unraveling the mechanisms responsible for propagation of parent-specific traits in hybrid crops contributes to our understanding of allopolyploid genome evolution and opens a way to targeted breeding strategies.

Biostimulating effect of l-tryptophan on the yield and chemical and microbiological quality of perennial ryegrass (Lolium perenne) herbage and silage for ruminant

BACKGROUND

This study aimed to evaluate the effect of l-tryptophan (l-TRP) used in the cultivation of Lolium perenne on the yield, and chemical and microbiological quality of its herbage and silage. l-Tryptophan was applied in doses of 5, 0.5, 0.05 kg ha^-1 . The experiment was conducted with a control group (C) and a comparative control group (C+) with higher nitrogen fertilization.

RESULTS

The dose of 5 kg ha^-1 had a significant effect on herbage yield, which increased by 15% compared to group C and approximated the value achieved in group C+. The treatment with l-TRP caused a significant increase in water-soluble carbohydrate (WSC) content only in Tr5 (165 g kg^-1 DM), which was reflected in a more beneficial course of fermentation, lower pH (4.59), and a higher sum of fermentation acids, including lactic acid (94.7 g kg^-1 DM). Ryegrass treatment with a high l-TRP dose effectively reduced the loads of Clostridium spp. and fungi, and increased the count of Bacillus spp. The l-TRP significantly reduced N-NH₃ content in Tr05 (98.6 g kg^-1 TN) compared with C+ (123 g kg^-1 TN) and butyric acid content in Tr05 (from 1.35 g kg^-1 DM in the C to 0.38 g kg^-1 DM).

CONCLUSION

The most effective dose turned out to be a dose of 5 kg ha^-1 , which allowed a higher yield and a better fermentation course to be achieved. This work presents the feasibility of using l-TRP to optimize nutrient consumption by Lolium perenne and ultimately to affect the quality of its silage as a feedstuff. © 2020 Society of Chemical Industry.

Biodegradation of bio-sourced and synthetic organic electronic materials towards green organic electronics

Ubiquitous use of electronic devices has led to an unprecedented increase in related waste as well as the worldwide depletion of reserves of key chemical elements required in their manufacturing. The use of biodegradable and abundant organic (carbon-based) electronic materials can contribute to alleviate the environmental impact of the electronic industry. The pigment eumelanin is a bio-sourced candidate for environmentally benign (green) organic electronics. The biodegradation of eumelanin extracted from cuttlefish ink is studied both at 25 °C (mesophilic conditions) and 58 °C (thermophilic conditions) following ASTM D5338 and comparatively evaluated with the biodegradation of two synthetic organic electronic materials, namely copper (II) phthalocyanine (Cu-Pc) and polyphenylene sulfide (PPS). Eumelanin biodegradation reaches 4.1% (25 °C) in 97 days and 37% (58 °C) in 98 days, and residual material is found to be without phytotoxic effects. The two synthetic materials, Cu-Pc and PPS, do not biodegrade; Cu-Pc brings about the inhibition of microbial respiration in the compost. PPS appears to be potentially phytotoxic. Finally, some considerations regarding the biodegradation test as well as the disambiguation of "biodegradability" and "bioresorbability" are highlighted.

Cadmium stress suppresses the tillering of perennial ryegrass and is associated with the transcriptional regulation of genes controlling axillary bud outgrowth

Perennial ryegrass (Lolium perenne L.), a grass species with superior tillering capacity, plays a potential role in the phytoremediation of cadmium (Cd)-contaminated soils. Tiller production is inhibited in response to serious Cd stress. However, the regulatory mechanism of Cd stress-induced inhibition of tiller development is not well documented. To address this issue, we investigated the phenotype, the expression levels of genes involved in axillary bud initiation and bud outgrowth, and endogenous hormone biosynthesis and signaling pathways in seedlings of perennial ryegrass under Cd stress. The results showed that the number of tillers and axillary buds in the Cd-treated seedlings decreased by 67% and 21%, respectively. The suppression of tiller production in the Cd-treated seedlings was more closely associated with the inhibition of axillary bud outgrowth than with bud initiation. Cd stress upregulated the expression level of genes related to axillary bud dormancy and downregulated bud activity genes. Additionally, genes involved in strigolactone biosynthesis and signaling, auxin transport and signaling, and cytokinin degradation were upregulated in Cd-treated seedlings, and cytokinin biosynthesis gene expression were decreased by Cd stress. The content of zeatin in the Cd-treated pants was significantly reduced by 69~85% compared to the control plants. The content of indole-3-acetic acid (IAA) remains constant under Cd stress. Overall, Cd stress induced axillary bud dormancy and subsequently inhibited axillary bud outgrowth. The decrease of zeatin content and upregulation of genes involved in strigolactone signaling and bud dormancy might be responsible for the inhibition of axillary bud outgrowth.

Synergistic effect of organo-mineral amendments and plant growth-promoting rhizobacteria (PGPR) on the establishment of vegetation cover and amelioration of mine tailings

Mine tailings pose a huge hazard for environmental and human health, and the establishment of vegetation cover is crucial to reduce pollutant dispersion for the surroundings. However, their hostile physicochemical conditions hamper plant growth, compromising phytoremediation strategies. This study aims to investigate the role of organo-mineral amendments and plant growth-promoting rhizobacteria (PGPR) on the improvement of mine tailings properties and Lolium perenne L. (ryegrass) growth. Plants were grown in mine tailings mixed with an agricultural soil (1:1), 10% compost, and supplied with two different inorganic amendments - rock phosphate (6%) or lime (3%), and inoculated with the rhizobacterial strains Advenellakashmirensis BKM20 (B1) and Mesorhizobium tamadayense BKM04 (B2). The application of organo-mineral amendments ameliorated tailings characteristics, which fostered plant growth and further enhanced soil fertility and microbial activity. These findings were consistent with the increase of total organic carbon levels, with the higher numbers of heterotrophic and phosphate solubilizing bacteria, and higher dehydrogenase and urease activities, found in these substrates after plant establishment. Plant growth was further boosted by PGPR inoculation, most noticeable by co-inoculation of both strains. Moreover, inoculated plants showed increased activities for several antioxidant enzymes (catalase, peroxidase, polyphenoloxidase, and glutathione reductase) which indicate a reinforced antioxidant system. The application of agricultural soil, compost and lime associated with the inoculation of a mixture of PGPR proved to enhance the establishment of vegetation cover, thus promoting the stabilization of Kettara mine tailings. Nonetheless, further studies are needed in order to confirm its effectiveness under field conditions.

Individual and combined application of Cu-tolerant Bacillus spp. enhance the Cu phytoextraction efficiency of perennial ryegrass

Forage grasses have recently received a remarkable amount of attention as promising candidates for decontaminating metal-polluted soils, but this strategy is time-consuming and inefficient. The present study aimed to address the beneficial effects of screened plant growth-promoting rhizobacteria (PGPR) strains Bacillus sp. EhS5 and EhS7 on perennial ryegrass and tall fescue. Single or combined inoculation considerably increased the biomass yield and Cu content of inoculated ryegrass compared with uninoculated plants, thereby enhancing the extraction efficiency at different Cu contamination levels. Bioaugmentation did not show a positive impact on the improvement of fescue's phytoextraction efficiency. Principal component analysis (PCA) and Pearson correlation coefficient results identified root development and photosynthesis as the key variables influencing ryegrass biomass. Antioxidant activities and Cu bioavailability are the key variables influencing Cu accumulation. The inoculated ryegrass showed improved photosynthetic status as the photosystem II system efficiency parameters increased and energy dissipation in the form of heat (DI_o/RC) decreased with the help of PGPR. The root length, diameter, surface area, and forks of inoculated ryegrass increased remarkably. The levels of scavengers of reactive oxygen species were enhanced in these plants. Moreover, PGPR significantly increased soil Cu bioavailability by secreting siderophores and organic acid and by increasing soil organic carbon content. Dual inoculation showed better results than individual inoculation in improving ryegrass growth and Cu translocation under high Cu contamination level according to PCA. This study systematically explored the effects and mechanisms of the Bacillus-ryegrass combined remediation and provided a novel method for cleaning Cu-contaminated sites.

Cadmium accumulation in oilseed rape is promoted by intercropping with faba bean and ryegrass

The mechanisms of intercropping increasing plant biomass, cadmium accumulation, and organic acids secreted in rhizosphere soil are still unclear. Oilseed rape and intercrops were grown in boxes separated either with no barrier between the compartments or by a nylon mesh barrier (37 μm) to license partial root interaction, or a solid barrier to stop any root interactions. Two intercropping systems (oilseed rape-faba bean and oilseed rape-ryegrass) were carried out in soil with Cd content of 5 mg/kg. The intermingling of roots between oilseed rape and faba bean enhanced the biomass of oilseed rape. However, the biomass was negatively affected implying the higher nutrient apportionment to the ryegrass than oilseed rape. Oilseed rape intercropping with both faba bean and ryegrass played a positive role in the shoot Cd concentration of oilseed rape. The intermingling of roots played a positive role in the citric and malic acids when intercropping with faba bean. A remarkable increase in water-soluble Cd and DTPA-Cd content was observed during oilseed rape-faba bean complete root interaction treatment, up to 175.00% and 46.65%, respectively, which compare with the monoculture treatment. In both systems, the translocation factor values were higher for oilseed rape (O-F system) than for the other test plants and were always >1. Thus the Cd removal potential of oilseed rape can be further improved in the future by optimizing agronomic practices and intercropping with faba bean.

Impact of TiO2 and ZnO Nanoparticles on Soil Bacteria and the Enantioselective Transformation of Racemic-Metalaxyl in Agricultural Soil with Lolium perenne: A Wild Greenhouse Cultivation

The effects of TiO₂ and ZnO nanoparticles on soil bacteria and enantioselective transformation of racemic-metalaxyl (rac-metalaxyl) in agricultural soil with or without Lolium perenne were investigated in an outdoor greenhouse. After a 70-day exposure to 2‰ ZnO, microbial biomass carbon decreased by 66% and bacterial community composition significantly changed. Meanwhile, ZnO decreased chlorophyll cumulation in L. perenne by 34%. ZnO also inhibited the enantioselective transformation of metalaxyl enantiomers and changed the enantiomer fraction of metalaxyl. TiO₂ showed similar effects but to a lesser extent. L. perenne promoted the transformation of rac-metalaxyl and ingested TiO₂ and ZnO. L. perenne changed the bacterial co-occurrence networks and biomarkers in native soil and soil exposed to TiO₂ and ZnO. L. perenne reduced the inhibition effects of TiO₂ and ZnO on the transformation of rac-metalaxyl. The decrease in the relative abundance of soil keystone taxa such as Acidobacteria and Gemmatimonas might respond to the corresponding slow transformation of rac-metalaxyl in soils exposed to TiO₂ and ZnO, regardless of L. perenne. Our results demonstrated the existence of mutual interactions among the impact of engineered nanoparticles on different components (microbes, plants, and coexisting pollutants) in the terrestrial ecosystem.

Milk production and estimated enteric methane emission from cows grazing ryegrass pastures in small-scale dairy systems in Mexico

The work assessed the productive response and estimated enteric methane (CH₄) emissions of dairy cows grazing in small-scale dairy systems. Treatments were grazing annual pasture (AP) mainly of annual ryegrass and perennial pasture (PP) mainly of perennial ryegrass, complemented daily with 3.72 kg DM/cow of commercial concentrate. Eight Holstein cows were used in a double cross-over design with three 14-day-each experimental periods for animal variables and CH₄ emissions. Pasture variables were analysed with a split-plot design. AP showed higher sward height (P < 0.05) with no differences (P > 0.05) in net herbage accumulation or in herbage chemical composition. Cows on AP yielded 24.6% more milk (P < 0.001) than grazing PP, but there were no differences in milk fat and protein content. There were differences (P ≤ 0.05) among periods for milk yields, but no differences among periods for milk fat and protein. Milk urea nitrogen was significantly higher (P < 0.001) in PP than in AP with no differences among periods. There was higher (P < 0.001) DMI for AP than PP with a significant decline (P < 0.05) as periods progressed. There was a trend (P = 0.08) for higher daily CH₄/cow in AP, but significantly lower emissions (7.2%) in AP/kg DMI, and 20.1% lower emission intensity of g CH₄/kg milk. The proportion of gross energy lost as CH₄ for AP was lower (P < 0.01). Higher milk yields in AP resulted in a 26% higher margin over feed costs than for PP. Results show that grazing annual pastures with moderate concentrate supplementation results in higher milk yields, higher incomes, and reduces the intensity of CH₄ emissions.

Use of Zinc Carbonate Spiking to Obtain Phytotoxicity Thresholds Comparable to Those in Field-Collected Soils

Several studies have reported the presence of smithsonite (ZnCO₃ ) in soils polluted by zinc mining. The present study aimed to determine upper critical threshold values of Zn phytotoxicity in a substrate spiked with ZnCO₃ and to compare them with those obtained in field-collected soils. We studied Zn toxicity to perennial ryegrass (Lolium perenne L.) grown in pots with unpolluted peat treated with increasing concentrations of ZnCO₃ that produced nominal total Zn concentrations of 0, 0.7, 1.3, 2.0, 2.6, and 3.3%. To keep constant near-neutral pH value in all the treatments, we used decreasing concentrations of dolomitic lime. In the treatment with total soil Zn of 3.3% (pH 6.8), the foliar Zn concentration of L. perenne was 1914 ± 211 mg kg^-1 , falling into the range of 2400 ± 300 mg kg^-1 reported for Lolium species grown under similar laboratory conditions in a polluted soil (total soil Zn 5.4%, pH 7.3) collected near a Zn smelter. The value of 92 ± 98 mg kg^-1 was obtained for the median effective concentration (EC50) values of 0.01 M KNO₃ -extractable Zn using the responses of shoot dry biomass, shoot length, and total pigments. This value falls within the range of 95 ± 46 mg kg^-1 reported in other studies for the EC50 values of salt-extractable Zn using field-collected soils. The application of ZnCO₃ for spiking was able to mimic foliar Zn concentrations of Lolium species observed in field-collected soils. The effective concentrations of soil Zn obtained in the present study are comparable to those obtained in field-collected soils. Future research should determine effective concentrations of metals using soils spiked with metal-containing compounds that mimic a real source of contamination. Environ Toxicol Chem 2020;39:1790-1796. © 2020 SETAC.

Growth and carbohydrate dynamic of perennial ryegrass seedlings during PEG-simulated drought and subsequent recovery

Due to the increasing occurrence of drought events, drought recovery has become equally important as drought resistance for long-term growth and survival of plants. However, information regarding the mechanism that controls growth recovery of herbaceous perennials is not available. In this study, perennial ryegrass (Lolium perenne) was rewatered after eight-day exposure to three drought intensities simulated by polyethylene glycol-6000. The growth, nonstructural carbohydrates (NSC, i.e. sucrose, glucose, fructose and starch), shoot δ¹³C, and activities of enzymes for sucrose conversion were monitored for 24 days after rewatering, allowing investigation of the dynamic of NSCs and its relation with growth in the recovery phase. In response to drought, growth and NSC content decreased mainly in shoot rather than root, and the total dry matter was negatively correlated to shoot δ¹³C. After rewatering, the growth of drought-treated groups still lagged behind that of control (CK) group for more than 16 days, but it was no longer correlated to shoot δ¹³C, suggesting that the limited growth is caused by non-stomatal factors related to photosynthesis. On day 24 after rewatering, the final growth of drought-treated groups caught up or even exceeded that of CK group, and was accompanied by higher dry weight root to shoot ratio (R/S) and root NSC content, which may facilitate water and nutrient acquisition and emergency of new tillers, respectively. During drought and subsequent recovery, the variation of R/S and root NSC content mainly attributed to root acid invertase rather than leaf sucrose phosphate synthase activity.

Miscanthus x giganteus culture on soils highly contaminated by metals: Modelling leaf decomposition impact on metal mobility and bioavailability in the soil-plant system

Miscanthus x giganteus is suggested as a good candidate for phytostabilization of metal-polluted soils. Its late harvest in winter generates large amounts of leaf litter on the soil surface. However, little is known about the mobility and the bioavailability of metals following leaf decomposition and the consequences on the succeeding culture. Ex situ artificial aging for 1, 3, and 6 months was conducted with miscanthus leaf fragments incorporated into three agricultural soils displaying a gradient concentration in Cd (0.6, 3.1 and 7.9 mg kg^-1), Pb (32.0, 194.6 and 468.6 mg kg^-1), and Zn (48.4, 276.3 and 490.2 mg kg^-1) to simulate the leaf litter input over 20 years of miscanthus culture. We investigated the impacts on physicochemical and biological soil parameters, CaCl₂-extractable metal, and their subsequent ryegrass shoot concentrations, and hence on ryegrass health. The results showed that the amended soils possessed higher pH along with greater available phosphorous and soil organic carbon values. The respiratory activity and microbial biomass carbon in the amended soils increased mainly after 1 month of aging, and decreased afterwards. Despite the higher Pb- and Zn-CaCl₂ extractability in the amended soils, the phytoavailability slightly increased only in the most contaminated soils. Moreover, leaf incorporation did not affect the ryegrass biomass, photosynthetic pigment contents, nor the antioxidative enzyme activities. Conclusively, leaf incorporation induced slight variations in soil physicochemical and biological parameters, as well as metal extractability, but not to an extent that might cause a considerable threat to the subsequent culture. Nevertheless, these results are preliminary data that require confirmation by long-term in-situ experimentations as they reflect the modelization of long-term impact of leaf decomposition on soil-plant system.

Chlorophyll Metabolism and Gene Expression in Response to Submergence Stress and Subsequent Recovery in Perennial Ryegrass Accessions Differing in Growth Habits

Submergence-induced leaf senescence may alter chlorophyll metabolism. The objective of this study was to characterize chlorophyll biosynthesis and degradation in contrasting perennial ryegrass (Lolium perenne) in response to submergence stress and recovery. The light-green and fast-growing accession PI238938 and the darker-green and slow-growing cultivar BrightStar SLT were exposed to 0, 6 h, 1-, 3-, and 7-d of submergence stress and 1- and 5- d of de-submergence, respectively. Plant growth of PI238938 were more severely inhibited by submergence stress and recovery. Both accessions showed increased leaf malondialdehyde under stress and recovery, but reduced chlorophyll (Chl) concentrations were observed at 3- and 7-d of stress and at recovery. The reduction in Chl was more severe in BrightStar SLT at 7 d of stress. The concentration of 5-aminolevulenic acid was unaffected by stress but increased at 1d of recovery. Activities of 5-aminolevulinic acid dehydratase (ALAD) involved in Chl biosynthesis remained unchanged under stress and recovery, while the activities of Chl degrading enzymes chlorophyllase (CHL) and pheophytinase (PPH) increased at 3 d or 7 d of stress, and returned to the control level after recovery in both accessions. The downregulation of Chl-biosynthetic genes CHLI, POR, and CHLP and the upregulation of Chl-degrading genes CLH, PPH, and SGR were observed in both accessions under most of the stress periods. BrightStar SLT exhibited much lower expressions of the Chl-biosynthetic genes PBGD, CHS, and CHID under stress, while PI238938 had remarkably higher expressions of genes involved in Chl breakdown including CLH, PPH, PAO, RCCR, and SGR, and the expressions of these genes remained at a higher level at 1 d of recovery. The results indicated that submergence-induced leaf senescence and declines in Chl were associated with downregulation of more Chl-biosynthetic genes in slow-growing genotype and upregulation of more Chl-degrading genes in fast-growing genotype of perennial ryegrass.

Exogenous phosphorus treatment facilitates chelation-mediated cadmium detoxification in perennial ryegrass (Lolium perenne L.)

Cadmium (Cd) is an on-going environmental pollutant associated with hindered plant growth. In response, plants possess various strategies to alleviate Cd stress, including reactive oxygen species (ROS) scavenging and chelation-mediated Cd detoxification. The present study examined the Cd defense mechanism of perennial ryegrass (Lolium perenne L.), taking into account the effect of exogenous phosphorus (P) input. It was found that despite triggering antioxidant enzyme activity, Cd stress heightened lipid peroxidation levels. Exogenous P input partially mitigated the lipid peroxidation impact and decreased the levels of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) antioxidant enzymes, revealing reduced ROS-scavenging activity. Importantly, notable relationships were determined between the amount of Cd uptake in the root and the amount of non-protein thiols (R² = 0.914), glutathione (R² = 0.805) and phytochelatins (R² = 0.904) in proportion to the amount of exogenous P applied. The levels of amino acids proline and cysteine were also enhanced by exogenous P input showing their influence in alleviating Cd stress. Overall, it is reported that Cd detoxification in ryegrass plants can be stimulated by exogenous P input, which facilitates chelation-mediated Cd detoxification processes.

Towards sustainable maize production in the U.S. upper Midwest with interseeded cover crops

The incorporation of cover crops into the maize (Zea mays L.)-soybean [Glycine max (L.) Merr.] rotation in the U.S. upper Midwest may improve sustainability. Long, cold winters in the region make identifying successful cover crop species and management practices a challenge. Two experiments were conducted in Minnesota, USA from fall 2016 through spring 2019 to examine the effect of cover crops interseeded at four- to six-leaf collar (early-interseeded) and dent to physiological maturity (late-interseeded) on biomass and grain yield of maize. Annual ryegrass (Lolium multiflorum L.) and cereal rye (Secale cereale L.) were evaluated as monocultures and in mixtures with crimson clover (Trifolium incarnatum L.) and forage radish (Raphanus sativus L.). Differences in canopy cover and biomass of late-interseeded cover crops were observed at the southernmost location in 2018. Additional accumulated growing-degree days in fall 2018 did not translate into increased cover crop canopy coverage of late-interseeded cover crops. Differences in cover crop canopy cover and biomass of early-interseeded cover crops were observed by fall frost at all locations in 2017 and at the northernmost location in 2018. Cover crop canopy cover and biomass at termination before planting maize, soil moisture at maize planting as well as maize aboveground biomass and yield were not affected by spring cereal rye regrowth of cover crops late-interseeded the previous year. Similarly, early-interseeded cover crops did not affect maize aboveground biomass or yield. We attribute these results to limited cover crop growth. This highlights the potential of a variety of cover crop strategies interseeded into maize in the U.S. upper Midwest; however, efforts to fine-tuning cover crop management and weather conditions are needed to benefit from such practice.

EDTA-enhanced phytoremediation of heavy metals from sludge soil by Italian ryegrass (Lolium perenne L.)

Landscaping of sludge is a kind of recycling disposal, but the potential heavy metal risks limit its application. In this paper, the sludge soil was remediated by ryegrass, and the effect of ethylene diamine tetraacetic acid (EDTA) was studied through pot experiments. Italian ryegrass was planted in the sludge soil treated with six gradients concentrations of 0, 1, 2, 3, 4, 5 mmol kg^-1 of EDTA, and the planting conditions were kept the same. After 45 days of planting, compared with the control group (without EDTA treated), the application of 1-5 mmol kg^-1 EDTA decreased ryegrass biomass by 2-43%, reduced soil pH value by 0.21-0.34 unit, and reduced 4.1-9.7% capacity of exchange cation, but increased 1.4-8.6% soil organic matter. After growing ryegrass, the contents of heavy metals decreased by 10% for Cu, 15% for Zn, 6% for Ni, 14% for Cd and 44% for Pb; and after spraying EDTA decreased again by 33% for Cu, 31% for Zn, 56% for Ni, 24% for Cd, and 68% for Pb. In ryegrass, the uptake heavy metals were enhanced, and bio-concentration factor of Cu, Zn, Ni, Cd, and Pb of EDTA treated groups were 1.9, 1.6, 4.1, 2.7, and 4.8 times of the control group, respectively. However, EDTA only significantly increased transfer factor values of Cu and Zn, and made bio-extraction factor value of Cu greater than 1. The remediation factor values were used to comprehensive assess accumulation capacity of heavy metals by ryegrass under EDTA treating, and they ordered in Zn > Cu > Ni > Cd > Pb, and the best dose was 2 mmol kg^-1 EDTA. Prediction models for bio-concentration factor were established by using stepwise multiple linear regression, explaining 94.9-99.3% of the corresponding elements with soil organic matter, EDTA dosage, and/or pH value (p < 0.005). This paper provided effective heavy metals remediation data for municipal sludge landscape and the prediction models.

Mixture toxicity and uptake of 1-butyl-3-methylimidazolium bromide and cadmium co-contaminants in water by perennial ryegrass (Lolium perenne L.)

Ionic liquids, a kind of emerging and persistent organic contaminants, always coexist with heavy metals in aquatic and terrestrial environments. However, the feasibility of phytoremediation to remove ionic liquids and heavy metals co-contaminants is still unclear. Thus, in this study, the hydroponic experiment was conducted to investigate the combined effect of 1-butyl-3-methylimidazolium bromide ([C₄mim]⁺Br^-) and cadmium (Cd²⁺) on growth and physiological indictors of perennial ryegrass, together with their uptake and translocation by plants. Results show that the exposure of ryegrass to [C₄mim]⁺ and Cd²⁺ mixture significantly inhibited the biomass growth and affected the photosynthetic pigments contents in leaves. The increases of lipid peroxidation and catalase, peroxidase activity were also observed under the co-exposure experiments. The mixture toxicity of [C₄mim]⁺ and Cd²⁺ to ryegrass growth showed an additive effect predicted by concentration addition and independent action. [C₄mim]⁺ uptake and acropetal translocation by ryegrass were significantly inhibited with dosing Cd²⁺. In contrast, [C₄mim]⁺ had no obvious effect on Cd²⁺ uptake by ryegrass, while enhanced Cd²⁺ translocation from roots to shoots occurred with increasing [C₄mim]⁺ dosages. These results indicate that the co-contamination of ionic liquids and heavy metals would affect their fates during phytoremediation.

Application of co-composted biochar significantly improved plant-growth relevant physical/chemical properties of a metal contaminated soil

A woody-biochar was added to waste biomass during a composting process. The resulting compost-char was amended to a metal contaminated soil and two plant species, L. perenne and E. sativa, were grown in a pot experiment to determine 1) plant survival and stress factors, 2) uptake of metals to plants and, 3) chemical characteristics of sampled soils and pore waters. Compost supplemented with biochar after the composting process were also tested, as well as a commercially available compost, for comparison. Co-composting with biochar hastened the composting process, resulting in a composite material of reduced odour, increased maturity, circum-neutral pH and increased moisture retention than compost (increase by 3% of easily removable water content). When amended to the soil, CaCl₂ extractable and pore water metals s were reduced by all compost treatments with little influence of biochar addition at any tested dose. Plant growth success was promoted furthest by the addition of co-composted biochar to the test soil, especially in the case of E. sativa. For both tested plant species significant reductions in plant metal concentrations (e.g. 8-times for Zn) were achieved, against the control soil, by compost, regardless of biochar addition. The results of this study demonstrate that the addition of biochar into the composting process can hasten the stability of the resulting compost-char, with more favourable characteristics as a soil amendment/improver than compost alone. This appears achievable whilst also maintaining the provision of available nutrients to soils and the reduction of metal mobility, and improved conditions for plant establishment.

Phytotoxic neo-clerodane diterpenoids from the aerial parts of Scutellaria barbata

Bioactivity guided the isolation of extracts from the aerial parts Scutellaria barbata D. Don to discover neo-clerodane diterpenoids with potent phytotoxic activity. Of the 34 isolates, 13 neo-clerodane diterpenoids were described for the first time. The structures of these undescribed compounds were elucidated by extensive analysis of NMR spectroscopic data, and the absolute configurations of scutebarbolides A and L and scutebata W were determined by X-ray diffraction. The phytotoxic activity of all compounds against the growth of the roots and shoots of L. perenne and L. sativa seedlings were first reported, and some compounds showed considerable inhibitory effects, especially scutebarbolide K, whose inhibition rates were higher than those of the positive control at concentrations ranging from 25 to 200 μg/mL. When L. perenne and L. sativa seedlings were treated at a concentration of 200 μg/mL, scutebarbolide K caused wilting symptoms on and finally death of these two tested plant seedlings. In addition, the structure-activity relationships of these neo-clerodane diterpenoids were also discussed.

Iron fertilization to enhance tolerance mechanisms to copper toxicity of ryegrass plants used as cover crop in vineyards

Ryegrass (Lolium perenne L.) is a plant species that can express mechanisms of tolerance to copper (Cu) toxicity. Therefore, the agronomical approach of intercropping system with ryegrass may represent a promising tool to limit the onset of Cu toxicity symptoms in the other intercropped plants species, particularly when an inadequate nutrient availability like iron (Fe) shortage is also concurrently present. This study aimed at assessing the mechanisms involved in the mitigation of Cu phytotoxicity and the stress effects on plant growth, root morphology and nutrition of ryegrass fertilized with two different Fe sources. To this purpose, seedlings of ryegrass were hydroponically grown for 14 days in controlled conditions with 4 different levels of Cu (0.2, 5.0, 25 and 50 μM) and with either 100 μM Fe-EDDHA or Fe-EDTA. Results show that high levels of Cu availability enhanced the root content of organic anions as well as the root exudation. Different Fe fertilizations at the condition of 50 μM Cu induced changes in root phenolic compounds, citrate and fumarate contents and the exudation pattern of phenolic compounds. Differences in plant growth were not observed between the two Fe sources, although Cu concentration in plant tissue fed with Fe-EDTA was lower in the condition of 50 μM Cu. The enhanced root exudation of Cu-complexing organic compounds (including phenolics) in ryegrass plants when exposed to excessive Cu availability could be at the basis of the ameliorated edaphic rhizosphere conditions (lower Cu availability). For this reason, from the agronomical point of view ryegrass plants used in intercropping systems with crops like vine plants could represent a promising strategy to control Cu toxicity in vineyard soils. Further studies under the field conditions must be taken to support present findings.

Full-Length Transcriptome Assembly of Italian Ryegrass Root Integrated with RNA-Seq to Identify Genes in Response to Plant Cadmium Stress

Cadmium (Cd) is a toxic heavy metal element. It is relatively easily absorbed by plants and enters the food chain, resulting in human exposure to Cd. Italian ryegrass (Lolium multiflorum Lam.), an important forage cultivated widely in temperate regions worldwide, has the potential to be used in phytoremediation. However, genes regulating Cd translocation and accumulation in this species are not fully understood. Here, we optimized PacBio ISO-seq and integrated it with RNA-seq to construct a de novo full-length transcriptomic database for an un-sequenced autotetraploid species. With the database, we identified 2367 differentially expressed genes (DEGs) and profiled the molecular regulatory pathways of Italian ryegrass with Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis in response to Cd stress. Overexpression of a DEG LmAUX1 in Arabidopsis thaliana significantly enhanced plant Cd concentration. We also unveiled the complexity of alternative splicing (AS) with a genome-free strategy. We reconstructed full-length UniTransModels using the reference transcriptome, and 29.76% of full-length models had more than one isoform. Taken together, the results enhanced our understanding of the genetic diversity and complexity of Italian ryegrass under Cd stress and provided valuable genetic resources for its gene identification and molecular breeding.

Evaluation of the Rhizosphere Contribution to the Environmental Fate of the Herbicide Prometryn

Plant protection products (PPPs) undergo rigorous regulatory assessment to ensure that they do not pose unacceptable risks to the environment. Elucidation of their fate and behavior in soil is an integral part of this environmental risk assessment. The active substance degradation in soil of PPPs is first assessed in laboratory studies (typically following Organisation for Economic Co-operation and Development [OECD] test guideline 307). Conditions in guideline laboratory studies are far removed from those occurring under agricultural use, and the contribution of crop roots has currently not been assessed. We integrated viable plant root systems, representative of 3 different crop types, into the OECD test guideline 307 design to assess their impact on the dissipation of the herbicide prometryn. Significantly faster decline of parent residue and higher formation of nonextractable residues were observed in all 3 planted systems. This led to a reduction in the time required for 50% of the compound to dissipate (DT50) of approximately one-half in the presence of rye grass and hot pepper and of approximately one-third in the presence of red clover. These findings imply that plants and their associated root networks can have a significant influence on PPP dissipation. Based on these data, greater environmental realism could be added to the standardized laboratory study design by the inclusion of plant root systems into higher tier studies, which, in turn, could serve to improve the environmental risk assessment process. Environ Toxicol Chem 2020;39:450-457. © 2019 SETAC.

Species-dependent effect of cover cropping on trace elements and nutrients in vineyard soil and Vitis

BACKGROUND

The research focused on the evaluation of the impact of cover cropping on trace metals (Fe, Mn, Cu, Zn, Pb, Co and Cd) and nutrients in vineyard soils and Vitis vinifera L. For this purpose, two types of cover crops (Lolium perenne L. and Medicago sativa L.) and their mixture were planted between vine rows of Muscat white in the vineyard in South Crimea. Trace elements, nutrients and other parameters were analyzed in the soil layers, leaves and grapevines of control and cover cropped plots.

RESULTS

The effect of cover cropping was dependent on applied plant species. Ryegrass (L. perenne L.) seems to compete with V. vinifera L. for nutrients - these were lower in the soil and vines of the treated plot. In parallel, lead (Pb) bioconcentration in grapevines was reduced. In contrast, under lucerne (M. sativa L.), nitrogen in the soil and vines, and trace metal bioconcentration (Fe, Pb and Co) were higher.

CONCLUSIONS

Our results indicate that cover cropping can influence the chemical composition of soil and vines. This should be considered when selecting cover crops. © 2019 Society of Chemical Industry.

Effects of tetracycline on growth, oxidative stress response, and metabolite pattern of ryegrass

Tetracycline is an antibiotic that frequently contaminates the environment. In this study, the growth and metabolites of ryegrass seedlings treated with tetracycline (0, 1, 10 or 100 mg/L) for 5 days were investigated. The results showed that the growth of ryegrass and the concentrations of carotenoid and chlorophyll decreased as the tetracycline concentration increased. Tetracycline increased the production of reactive oxygen species (ROS) and cell permeability and triggered mitochondrial membrane potential loss in the roots of ryegrass. The metabolic profiles of ryegrass differed between the control and tetracycline-treated groups. The contents of glucose, shikimic acid, aconitic acid, serine, lactose, phenylalanine, mannitol, galactose, gluconic acid, asparagine, and glucopyranose were positively correlated with root length and had high variable importance projection values. These compounds may have crucial functions in root extension. Tetracycline also affected aminoacyl-tRNA biosynthesis, nitrogen metabolism, and alanine, aspartate and glutamate metabolism in the roots. Tetracycline may affect root extension by regulating the synthesis/degradation of these metabolites or the activity of their biosynthetic pathways. These results provide an insight into the stress response of ryegrass to tetracycline.

Syntheses and Phytotoxicity of All Stereoisomers of 6-(2-Hydroxy-6-phenylhex-1-yl)-5,6-dihydro-2H-pyran-2-one and Determination of the Effect of the α,β-Unsaturated Carbonyl Structure and Hydroxy Group Bonding to Chiral Carbon

All four stereoisomers of naturally occurring 6-(2-hydroxy-6-phenylhex-1-yl)-5,6-dihydro-2H-pyran-2-one (1) were synthesized by employing yeast-reduction products with high optical purity [from 95% enantiomeric excess (ee) to more than 99% ee], and then their phytotoxicities against lettuce and Italian ryegrass were evaluated. In the Italian ryegrass seedlings test, (6S,2'R)-1 showed the most potent and stereospecific activity against the shoots (IC50 = 260 μM) and roots (IC50 = 43.2 μM), with a significant difference from other stereoisomers. The highest seed germination inhibitory activity against Italian ryegrass seed was also observed in (6S,2'R)-1, showing a 53% germination ratio from the control at 1000 μM. This advantageous (6S,2'R) stereochemistry was employed in the syntheses of α,β-dihydro, 2'-dehydroxy, and 2'-methoxy derivatives 13-15. By the test using these derivatives, the importance of the α,β-unsaturated double bond and hydroxy group bonding to a chiral center on the 6-alkyl chain of 5,6-dihydro-α-pyrone for phytotoxicity was determined. In the test against lettuce, the 6S configuration and (6S,2'S) configuration were necessary for growth inhibition (IC50 = ca. 60 μM) and germination inhibition (63% germination ratio at 1000 μM), respectively.

Cigarette butts have adverse effects on initial growth of perennial ryegrass (gramineae: Lolium perenne L.) and white clover (leguminosae: Trifolium repens L.)

Cigarette filters (butts) are currently the most abundant form of anthropogenic litter on the planet, yet we know very little about their environmental impacts on terrestrial ecosystems, including plant germination and primary production. When discarded, filters contain a myriad of chemicals resulting from smoking tobacco and some still contain unsmoked remnants. A greenhouse experiment was used to assess the impacts of discarded filters of regular or menthol cigarette, either from unsmoked, smoked, or smoked cigarettes with remnant tobacco, on the growth and development of Lolium perenne (perennial ryegrass) and Trifolium repens (white clover). After 21 days, shoot length and germination success were significantly reduced by exposure to any type of cigarette filter for the grass and clover. Although total grass biomass was not measurably affected, the root biomass and root:shoot ratio were less in the clover when exposed to filters from smoked regular cigarettes and those with remnant tobacco. Cigarette filters caused an increase in chlorophyll-a in clover shoots and an increase in chlorophyll-b in grass shoots. Accordingly, whilst the chlorophyll a:b ratio was increased in the clover exposed to cigarette filters, it was decreased in grass. This study indicates the potential for littered cigarette filters to reduce growth and alter short-term primary productivity of terrestrial plants.

Effects of crop straw and its derived biochar on the mobility and bioavailability in Cd and Zn in two smelter-contaminated alkaline soils

In this study, comparative investigations on the effects of crop straw and its derived biochars on soil Cd and Zn mobility and availability were conducted. Crop straws (i.e. maize straw, rapeseed straw, and wheat straw) and their derived biochars were incubated with two contaminated alkaline soils (FX and TG soils) at 2.5% (w/w). The changes of soil properties like pH, EC, organic matter content, and dissolved organic matter content were investigated along with metal mobility, speciation distribution, and accumulation in ryegrass (Lolium multiflorum Lam.). Results indicated biochar, especially those were high in pH, enhanced soil pH (>0.2 units, p < 0.05), whereas a continuous reduction of soil pH was observed among treatments with crop straws. Both soil EC and the organic matter content increased with the application of both crop straws and biochars. In term of metals, Cd and Zn mobility were reduced with 6-14%/1-5% and 6-27%/7-15% reduction in the DTPA extractable Cd and Zn contents in TG and FX soil treatments, respectively. Moreover, distinct changes of metals in different fractions were also observed (acid soluble and reducible fraction → oxidizable fraction in straw treatments; acid soluble fraction → reducible soluble fraction in biochar amendments). Furthermore, the biological analysis revealed that the growth of ryegrass was promoted, but the accumulation of metals in ryegrass shoots was reduced, especially in MS₇₀₀ treatment. Apart from the amendments, metal immobilization efficiencies were negatively correlated with the contamination status. Despite that, a higher rate of biochar application (>10%) could dramatically reduce the amount of available metal in soil extracts, except for Zn in FX soil treatments. This present work demonstrated that biochars, especially those produced at a higher temperature, are superior to crop straws to immobilize metals in soils. However, the remediation efficiencies were strongly restricted by soil pH and contamination status.

Metrics of biomass, live-weight gain and nitrogen loss of ryegrass sheep pasture in the 21st century

This study argues that several metrics are necessary to build up a picture of yield gain and nitrogen losses for ryegrass sheep pastures. Metrics of resource use efficiency, nitrous oxide emission factor, leached and emitted nitrogen per unit product are used to encompass yield gain and losses relating to nitrogen. These metrics are calculated from field system simulations using the DAYCENT model, validated from field sensor measurements and observations relating to crop yield, fertilizer applied, ammonium in soil and nitrate in soil and water, nitrous oxide and soil moisture. Three ryegrass pastures with traditional management for sheep grazing and silage are studied. As expected, the metrics between long-term ryegrass swards in this study are not very dissimilar. Slight differences between simulations of different field systems likely result from varying soil bulk density, as revealed by a sensitivity analysis applied to DAYCENT. The field with the highest resource use efficiency was also the field with the lowest leached inorganic nitrogen per unit product, and vice versa. Field system simulation using climate projections indicates an increase in nitrogen loss to water and air, with a corresponding increase in biomass. If we simulate both nitrogen loss by leaching and by gaseous emission, we obtain a fuller picture. Under climate projections, the field with the lowest determined nitrous oxide emissions factor, had a relatively high leached nitrogen per product amongst the three fields. When management differences were investigated, the amount of nitrous oxide per unit biomass was found to be significantly higher for an annual management of grazing only, than a silage harvest plus grazing, likely relating to the increased period of livestock on pasture. This work emphasizes how several metrics validated by auto-sampled data provide a measure of nitrogen loss, efficiency and best management practise.

A sustainable approach to manage metal-contaminated soils: a preliminary greenhouse study for the possible production of metal-enriched ryegrass biomass for biosourced catalysts

Two kitchen garden soils (A and B) sampled in contaminated areas were amended using phosphates in sustainable quantities in order to reduce the environmental availability of potentially toxic inorganic elements (PTEs) and to favour the availability of alkali, alkali earth and micronutrients. The environmental availability of PTEs was evaluated using a potential plant for revegetation of contaminated soils (ryegrass) and a mixture of low molecular weight organic acids. Despite the highest contamination level of B, the concentration of metals was highest in the ryegrass shoots grown on A for the two harvests. These results correlated well with those obtained using low molecular weight organic acids for Cd, Zn and Cu, whereas this mixture failed to represent the transfer of nutrients due to the presence of biological and physiological mechanisms. The statistical differences between the biomass of ryegrass obtained at the first and the second harvests were attributed to the decrease of available potassium, implicated in the growth and development of plants. Phosphates increased the ratios Zn/Cd, Zn/Pb and Zn/Cu up to 176 ± 48, 38 ± 6 and 80 ± 12, respectively, and made possible the reduction of the concentration of Cd and Pb in the shoots of ryegrass by 22% and 25%, respectively. The concentration of Zn in the shoots of ryegrass from the first and the second harvests grown on soil A were in the range 1050-2000 mg kg^-1, making this plant a potential biomass to (i) produce biosourced catalysts for organic chemistry applications in a circular economy concept and (ii) limit human exposure to commercial Lewis acids. A preliminary application was identified.

Comparison of the feasibility of different washing solutions for combined soil washing and phytoremediation for the detoxification of cadmium (Cd) and zinc (Zn) in contaminated soil

Soil heavy metal contamination is a serious environmental problem needed to be addressed due to the toxicities of metals to both humans and living organisms. In this study, the remediation efficiencies of washing-coupled phytoremediation on Cd and Zn contaminated soils were evaluated with multiple washing reagents (i.e., hydrochloric acid (HCl), ethylene diamine tetraacetic acid (EDTA), nitrilotriacetic acid (NTA), several biodegradable natural low molecular mass organic acids (LMMOAs)) and ryegrass (Lolium perenne L.). Results indicated that soil washing with different reagents (at 100 mM) effectively removed metals from contaminated soils with the rates ranged from 4.73% to 81.0% and from 12.3% to 43.5% for Cd and Zn, respectively. Metal varieties and the properties washing reagents affected the detoxification performance. As for Cd, the removal rates decreased from over 80% to less than 10% in the order of EDTA > HCl > NTA > LMMOAs. By comparison, HCl and LMMOAs had higher removal efficiencies for Zn than other chelating reagents. The leaching of metals in the acid-extractable fraction was the main contribution to the overall metal removed. Additionally, soil nutrient contents, Ca specifically, were significantly decreased after washing, and the germination and growth of ryegrass were partly inhibited. Despite that, soil biota and enzyme activities responded differently among different treatments. This research also showed LMMOAs, especially citric acid (CA), were more suitable than HCl, EDTA, and NTA as reagents for the combined soil washing and phytoremediation, regarding their comparable metal removal efficiencies and less disturbing on soil fertilities and plant growth.

Current and residual phosphorous availability from compost in a ryegrass pot test

Compost can provide nitrogen (N) and especially phosphorous (P) available for plant growth, thus representing a potential alternative to chemical P-fertilizers a non-renewable resource. However, little is known about their residual capacity to provide plant-available P. In this study four compost: a green waste compost (GWC), one from anaerobically-digested bio-waste (DC), one from sewage sludge (SSC), and one from bio-waste (BWC), were compared (10 and 20 Mg VS ha^-1) in a ryegrass pot test (112 days), for their N- and P-relative mineral fertilizer equivalence (MFE; %) vs. a chemical fertilizer (NPK). After the test period, the exploited treatments were tested for their MFE during an additional ryegrass growth cycle (112 days) in an N-rich environment (N+). After 112 days, the pot test showed that DC and SSC produced dry biomass in the same range as did NPK, attaining the best N-MFE (80-100%) and P-MFE (100-125%), whereas GWC and BWC performed poorly (60-80 and 80-90%; N-MFE and P-MFE). At the end of the first growth cycle, DC and SSC still showed relevant Olsen-P (20-30 mg kg^-1). This was reflected in the best ryegrass P-MFE in DC and SSC at the end of the second growth cycle (N+), after 224 days (100-110%), whereas BWC and GWC poorly performed (90-95%). DC and SSC may therefore represent valuable sources of N available for plant nutrition in the short term, and also represent medium-term valuable P sources, alternative to rock phosphate P fertilizers. This promising approach need further field-scale investigation to confirm the medium-long term capacity of composts to be alternative to rock phosphate P fertilizers.

Phytotoxic and nematicide evaluation of Croton ehrenbergii (Euphorbiaceae)

BACKGROUND

Within its natural habitat, Croton ehrenbergii exhibits an innate defense mechanism that is not seen in other plants; it grows unharmed amidst predators and nature, while other species perish. In light of its capacity for defense, C. ehrenbergii was evaluated to better understand the scope of its phytotoxic and nematicide properties. To assess this, fractions obtained by bipartition of a hydro-alcoholic extract, and l-quebrachitol, the main constituent of C. ehrenbergii, were evaluated on Lactuca sativa (dicotyledon) and Lolium perenne (monocotyledon) seeds. Additionally, bipartition fractions and l-quebrachitol were evaluated on a population of Meloidogyne incognita for their nematicide activity.

RESULTS

From this phytochemical research, l-quebrachitol (1), phenylalanine (2), trans-4-hydroxy-N-methylproline (3) and the flavonoids: kaempferol (4), tiliroside (5), nicotiflorine (6) and rutin (7) were identified by spectroscopic analysis. Both methanol and hexane fractions from aerial parts of the plant inhibited the germination and elongation of roots and stems in L. sativa, but not in Lolium perenne, showing that these fractions mostly inhibit the dicotyledon species used in this research. l-Quebrachitol showed slightly higher seed germination inhibition for Lolium perenne in comparison with L. sativa. Three of the fractions evaluated showed nematicide activity against Meloidogyne incognita larvae (J2) at the 48 h benchmark, compared with carbofuran. l-Quebrachitol shows higher mortality after 48 h exposure at a lower concentration than carbofuran.

CONCLUSION

A variety of compounds were isolated from this research, some were common within the Croton genus (4-7), whereas others were not (1-3). This is the first phytochemical, phytotoxic and nematicide report on C. ehrenbergii. Methanol and hexane fractions from the aerial parts of C. ehrenbergii and l-quebrachitol could be used as alternative natural herbicides, predominantly against dicotyledon weed seeds. All fractions had a good mortality percentage against J2 Meloidogyne incognita larvae. © 2019 Society of Chemical Industry.

Immobilization Mechanism of Nano-Hydroxyapatite on Lead in the Ryegrass Rhizosphere Soil Under Root Confinement

The immobilization effect and mechanism of nano-hydroxyapatite(NHAP) on Pb in the ryegrass rhizosphere soil were studied by root-bag experiment. The speciation analysis results revealed that the residual Pb concentrations in the rhizosphere soil significantly increased after NHAP application. The acid-soluble and reducible Pb concentrations significantly decreased, indicating that NHAP had obviously immobilized Pb. Meanwhile, NHAP significantly promoted the secretion of tartaric acid from ryegrass roots, resulting the rhizosphere soil pH had been below that of the control group. This helped to relieve the stress of Pb on ryegrass, also promoted the dissolution of NHAP, resulting the formation of stable precipitation with more Pb ions. NHAP increased the rhizosphere soil pH by 0.03 to 0.17, which promoted the conversion of Pb to non-utilizable bioavailability. The total Pb mass balance indicated only a very small proportion Pb transferred to the shoots through ryegrass roots. The formation of pyromorphite by Pband NHAP in soil was accordingly to interpret the dominant mechanism for Pb immobilization.

Phytoremediation of Three Herbaceous Plants to Remove Metals from Urban Runoff

Phytoremediation experiments were carried out to assess the ability of different herbaceous buffer strips to absorb metals. Results revealed the Medicago sativa buffer strip had the best removal capacity for copper, lead, and cadmium in the runoff and seepage flow. Copper and lead content in M. sativa were significantly higher than in Lolium perenne and Poa pratensis (p < 0.05). Cadmium content in P. pratensis was significantly higher than in L. perenne and M. sativa(p < 0.05). Total accumulation of copper and lead in M. sativa buffer strips was 13.45 mg kg^-1 and 1.01 mg kg^-1, respectively. Total cadmium accumulation was approximately 0.50 mg kg^-1 in both M. sativa and P. pratensis. Overall, results indicated that using M. sativa in the buffer strips was optimal for the remediation of copper, lead, and cadmium in sewage water.

Benefits of phytoremediation amended with DC electric field. Application to soils contaminated with heavy metals

The objective of this study was to determine the influence of the DC electric current in the physicochemical properties of soil. The electric current may induce changes in pH and electric conductivity that will be reflected in the distribution of the electric potential in the soil specimen. This information will be used for the development of a phytoremediation technology amended with electric current. The results showed that low or moderate voltage gradients (0.67 V/cm) induced small changes in physicochemical properties of soil that do not compromise plant survival. The selected voltage gradient was used in electro-phytoremediation tests in soil contaminated with heavy metals (Cd, Co, Cr, Cu, Pb and Zn). Two plants species adapted to the soil and climate conditions were selected (Brassica rapa L. subsp. rapa and Lolium perenne L.). The electric field enhanced the plant growing, mainly in L. perenne, and increased the phytoremediation of the 6 metals. Mixed cultures of the two plant species showed interesting results for large scale applications.

Differential gene expression and gene ontologies associated with increasing water-stress in leaf and root transcriptomes of perennial ryegrass (Lolium perenne)

Perennial ryegrass (Lolium perenne) is a forage and amenity grass species widely cultivated in temperate regions worldwide. As such, perennial ryegrass populations are exposed to a range of environmental conditions and stresses on a seasonal basis and from year to year. One source of potential stress is limitation on water availability. The ability of these perennial grasses to be able to withstand and recover after periods of water limitation or drought can be a key component of grassland performance. Thus, we were interested in looking at changes in patterns of gene expression associated with increasing water stress. Clones of a single genotype of perennial ryegrass were grown under non-flowering growth room conditions in vermiculite supplemented with nutrient solution. Leaf and root tissue was sampled at 4 times in quadruplicate relating to estimated water contents of 35%, 15%, 5% and 1%. RNA was extracted and RNAseq used to generate transcriptome profiles at each sampling point. Transcriptomes were assembled using the published reference genome sequence and differential gene expression analysed using 3 different programmes, DESeq2, edgeR and limma (with the voom transformation), individually and in combination, deriving Early, Middle and Late stage comparisons. Identified differentially expressed genes were then associated with enriched GO terms using BLAST2GO. For the leaf, up-regulated differentially expressed genes were strongly associated with GO terms only during the Early stage and the majority of GO terms were associated with only down-regulated genes at the Middle or Late stages. For the roots, few differentially expressed genes were identified at either Early or Middle stages. Only one replicate at 1% estimated water content produced high quality data for the root, however, this indicated a high level of differential expression. Again the majority of enriched GO terms were associated with down-regulated genes. The performance of the different analysis programmes and the annotations associated with identified differentially expressed genes is discussed.

Exploring the Use of Species Sensitivity Distributions to Define Protective Limits for the Use of Organic Wastes as Soil Amendments

The use of organic wastes as soil amendments can be an important measure to improve soil quality and reduce waste accumulation and landfilling. However, the potential contaminant loads of such wastes, can be a source of environmental concern. Consequently, legislation has been developed to regulate the use of these wastes in agricultural soils. However, the regulations only consider chemical parameters, which are insufficient to establish the level of environmental risk. A possible solution is the use of species sensitivity distributions (SSDs), employing ecotoxicological data from test batteries that could be incorporated into legislation. In the present study, 2 different hazardous concentrations affecting 5 and 50% of the soil community (HC5 and HC50, respectively) were determined using ecotoxicological data (effect concentrations, 10 and 50% [EC10 and EC50, respectively]) for 5 different wastes. The results demonstrate that, as expected, current legislative thresholds do not translate to environmental risk/protection and that SSDs may be an important tool allowing the simple inclusion and interpretation of ecotoxicological data from test batteries in legislation. On the other hand, SSDs must be used with caution because there are still doubts about their actual value in risk prediction and about which estimates provide adequate protection. For instance, the use of HC50EC10 values is not recommended; these values overlap with the more conservative HC5EC50 data, highlighting the fact that the use of lower effect concentrations may not always provide the most protective approach. Also, hazardous concentrations need to be calibrated at the field or semifield level, to verify environmental protection in different soils/environments and the adequacy of standard test organisms. Environ Toxicol Chem 2019;38:1569-1576. © 2019 SETAC.

Structural and metabolic alterations in root systems under limited water conditions in forage grasses of Lolium-Festuca complex

Drought resistance is a crucial attribute of plants and to properly decipher its mechanisms, a valuable plant model is required. Lolium multiflorum is a forage grass characterized by a low level of abiotic stress resistance, whereas Festuca arundinacea is recognized as a species with drought resistance, including both stress avoidance and tolerance strategies. These two species can be crossed with each other. Two closely related L. multiflorum/F. arundinacea introgression forms with distinct levels of field drought resistance were involved, thus enabling the dissection of this complex trait into its crucial components. The processes occurring in roots were shown to be the most significant for the expression of drought resistance. Thus, the analysis was focused on the root architecture and the accumulation of selected hormones, primary metabolites and glycerolipids in roots. The introgression form, with a higher resistance to field water deficit was characterized by a deeper soil penetration by its roots, and it had a higher accumulation level of primary metabolites, including well recognized osmoprotectants, such as proline, sucrose or maltose, and an increase in phosphatidylcholine to phosphatidylethanolamine ratio compared to the low resistant form. A comprehensive model of root performance under water deficit conditions is presented here for the first time for the grass species of the Lolium-Festuca complex.

Differentiation between physical and chemical effects of oil presence in freshly spiked soil during rhizoremediation trial

Petroleum contamination and its remediation via plant-based solutions have got increasing attention by environmental scientists and engineers. In the current study, the physiological and growth responses of two diesel-tolerant plant species (tolerance limit: 1500-2000 mg/kg), Italian ryegrass (Lolium multiflorum) and Birdsfoot trefoil (Lotus corniculatus), have been investigated in vegetable oil- and diesel oil-amended soils. A long-term (147-day) greenhouse pot experiment was conducted to differentiate the main focus of the study: physical and chemical effects of oil (vegetable and diesel) in freshly spiked soils via evaluating the plant performance and hydrocarbon degradation. Moreover, plant performance was evaluated in terms of seed germination, plant shoot biomass, physiological parameters, and root biomass. Addition of both diesel oil and vegetable oil in freshly spiked soils showed deleterious effects on seedling emergence, root/shoot biomass, and chlorophyll content of grass and legume plants. Italian ryegrass showed more sensitivity in terms of germination rate to both vegetable and diesel oil as compared to non-contaminated soils while Birdsfoot trefoil reduced the germination rate only in diesel oil-impacted soils. The results of the current study suggest that both physical and chemical effects of oil pose negative effects of plant growth and root development. This observation may explain the phenomenon of reduced plant growth in aged/weathered contaminated soils during rhizoremediation experiments.

The evaluation of resistance to Co 2+ of lawn plant at seedling stage and its concentration property at adult stage

In order to evaluate the resistance of lawn plant to Co²⁺ at germination stage and discuss its concentration property at adult stage, four kinds of lawn plant which have some growth advantages in Co²⁺ polluted environment were selected as experimental materials in this research. They are tall fescue, timothy grass, inflorescences, and annual ryegrass. The results show that the evaluation of resistance to Co²⁺ of tall fescue's seed is the highest; the evaluation of resistance to Co²⁺ of annual ryegrass seed is the lowest. The low consistence Co²⁺ could improve the seed germination. With Co²⁺ concentration increase, the accumulation coefficient of four plants increased at first and decreased later; the accumulation coefficient of underground portion is higher than the accumulation coefficient of aboveground; with Co²⁺ concentration increase, the transfer coefficient of four plants have a remarkable decline. In these plants, the accumulation coefficient of tall fescue and annual ryegrass is bigger than other two plants. As the concentration of Co²⁺ treatment increased to 100 mg/kg, the aboveground enrichment of Co²⁺ in F. elata reached 75 mg/kg, followed by L. multiflorum (68.9 mg/kg), P. pratense (48.8 mg/kg), and D. glomerata (27.2 mg/kg).The highest underground enrichment of Co²⁺ in F. elata reached 836.46 mg/kg, in contrast to the lowest underground enrichment in D. glomerata, 264.67 mg/kg. It shows that fescue and annual ryegrass have a better enrichment property to Co²⁺ and have a better prospect for the treatment of cobalt-contaminated soil. This research could provide some scientific basis and main technical approach for the soil contaminated by Co²⁺.

The potential of ryegrass (Lolium perenne L.) to clean up multi-contaminated soils from labile and phytoavailable potentially toxic elements to contribute into a circular economy

Aided phytoremediation was studied for 48 weeks with the aim of reducing extractable and phytoavailable toxic elements and producing potential marketable biomass. In this sense, biomass of ryegrass was produced under greenhouse on two contaminated garden soils that have been amended with two successive additions of phosphates. After the first addition of phosphates, seeds of ryegrass were sown and shoots were harvested twice. A second seedling was performed after carefully mixing the roots from the first production (used as compost), soils and phosphates. Forty-eight weeks after starting the experiments, the concentrations of Cd, Pb, Zn, Cu, Fe, and Mn extracted using the rhizosphere-based method were generally lower than those measured before the addition of phosphates and cultivation (except for Pb and Fe in the most contaminated soil). The concentrations of metals in the shoots of ryegrass from the second production were lower than those from the first (except for Al). The best results were obtained with phosphates and were the most relevant in the lowest contaminated soil, demonstrating that the available metal concentrations have to be taken into account in the management of contaminated soils. In view of the concentration of metals defined as carcinogens, mutagens, and reprotoxics (e.g., Cd, Pb) and those capable to be transformed into Lewis acids (e.g., Zn, Fe), the utilization of ryegrass in the revegetation of contaminated soils and in risk management may be a new production of marketable biomass. The development of phytomanagement in combination with this type of biomass coincided with the view that contaminated soils can still represent a valuable resource that should be used sustainably.

Use of identifiability analysis in designing phenotyping experiments for modelling forage production and quality

Agricultural systems models are complex and tend to be over-parameterized with respect to observational datasets. Practical identifiability analysis based on local sensitivity analysis has proved effective in investigating identifiable parameter sets in environmental models, but has not been applied to agricultural systems models. Here, we demonstrate that identifiability analysis improves experimental design to ensure independent parameter estimation for yield and quality outputs of a complex grassland model. The Pasture Simulation model (PaSim) was used to demonstrate the effectiveness of practical identifiability analysis in designing experiments and measurement protocols within phenotyping experiments with perennial ryegrass. Virtual experiments were designed combining three factors: frequency of measurements, duration of the experiment. and location of trials. Our results demonstrate that (i) PaSim provides sufficient detail in terms of simulating biomass yield and quality of perennial ryegrass for use in breeding, (ii) typical breeding trials are insufficient to parameterize all influential parameters, (iii) the frequency of measurements is more important than the number of growing seasons to improve the identifiability of PaSim parameters, and (iv) identifiability analysis provides a sound approach for optimizing the design of multi-location trials. Practical identifiability analysis can play an important role in ensuring proper exploitation of phenotypic data and cost-effective multi-location experimental designs. Considering the growing importance of simulation models, this study supports the design of experiments and measurement protocols in the phenotyping networks that have recently been organized.

Mixed-surfactant-enhanced phytoremediation of PAHs in soil: Bioavailability of PAHs and responses of microbial community structure

The present study was conducted to explore the mechanisms of surfactant-enhanced phytoremediation of soils contaminated with polycyclic aromatic hydrocarbons (PAHs), focusing on the bioavailability of PAHs and microbial diversity. We investigated the remediation efficiencies of phenanthrene and pyrene after the addition of mixed surfactants (sodium dodecyl benzene sulfonate (SDBS) and Tween 80) of different ratios (1:1, 1:2, and 2:1) at the concentration of 100 mg/kg to soils cultured with ryegrass (Lolium multiflorum L.). The fractions of phenanthrene and pyrene were determined using a sequential extraction method, and the microbial diversity was evaluated using 16S rRNA gene high-throughput sequencing. The results showed that mixed surfactants could enhance the remediation efficiencies of PAHs, and mainly occurred in the initial 21 days. Mixed surfactants at the ratio of 1:1 (HM1) showed the best remediation efficiency in enhancing the dissipation of pyrene in 21 days. Mixed surfactants showed little effects on the removal of phenanthrene. In general, HM1 significantly decreased the bioavailable, bound and residual fractions of pyrene; additionally, higher abundances of PAH-degradation bacteria and degradation-related genes were observed. Pearson correlation analysis among PAH degraders, degradation-related genes and bioavailable fraction of PAHs was performed. Our results indicated that mixed surfactants could promote the transformation of pyrene from the bound and residual fractions to bioavailable fractions and enhance the abundances of PAH degradation bacteria and PAH degradation-related genes, thereby enhancing the degradation of pyrene.

Nitrate leaching losses during pasture renewal - Effects of treading, urine, forages and tillage

Pasture renewal is a key component of intensive temperate grassland farming. This practice is performed to improve pasture yields, but it may increase nitrate (NO₃^-) leaching losses, which can impact on water quality. Farmers face many choices when renewing pasture, however, there is limited information to guide decisions to reduce leaching losses. An experiment was established to study how different management practices and grazing affect biomass production and NO₃^- leaching during pasture renewal on a heavy soil. Long-term pasture was either re-sown into ryegrass (Lolium perenne) in autumn (GG) or into forage rape (Brassica napus) followed by ryegrass in spring (GCG). Rape was established following ploughing or direct-drilling. Grazing was simulated in winter, whereby split plots ±urine (600 kg N ha^-1) and ±treading were established. Nitrate concentrations at 1 m depth were measured with suction cups and drainage predicted using a crop model. Estimated NO₃^- leaching losses at 1 m depth ranged from 16 to 38 kg N ha^-1, with little difference between GCG and GG. However, the risk of future leaching was much greater below GCG plots. At the end of the study, soil NO₃^- between 0.6 and 1 m ranged from 28 to 130 kg N ha^-1 in GCG plots and 1-28 kg N ha^-1 in the GG plots. Timing of leaching differed between renewal systems, reflecting the differences in plant N uptake and fallow period. Overall, there was no difference in dry matter production between the two systems. Treading resulted in greater compaction, especially in tilled plots and reduced NO₃^- leaching by c. 40% - this can be attributed to increased denitrification. Our study demonstrates the complex nature of management and environmental factors and their interaction during pasture renewal. We show that management practices affect the risk and timing of N leaching. Practical implications for farmers are discussed.

Analysis of Epichloë festucae small secreted proteins in the interaction with Lolium perenne

Epichloë festucae is an endophyte of the agriculturally important perennial ryegrass. This species systemically colonises the aerial tissues of this host where its growth is tightly regulated thereby maintaining a mutualistic symbiotic interaction. Recent studies have suggested that small secreted proteins, termed effectors, play a vital role in the suppression of host defence responses. To date only a few effectors with important roles in mutualistic interactions have been described. Here we make use of the fully assembled E. festucae genome and EffectorP to generate a suite of 141 effector candidates. These were analysed with respect to their genome location and expression profiles in planta and in several symbiosis-defective mutants. We found an association between effector candidates and a class of transposable elements known as MITEs, but no correlation with other dynamic features of the E. festucae genome, such as transposable element-rich regions. Three effector candidates and a small GPI-anchored protein were chosen for functional analysis based on their high expression in planta compared to in culture and their differential regulation in symbiosis defective E. festucae mutants. All three candidate effector proteins were shown to possess a functional signal peptide and two could be detected in the extracellular medium by western blotting. Localization of the effector candidates in planta suggests that they are not translocated into the plant cell, but rather, are localized in the apoplastic space or are attached to the cell wall. Deletion and overexpression of the effector candidates, as well as the putative GPI-anchored protein, did not affect the plant growth phenotype or restrict growth of E. festucae mutants in planta. These results indicate that these proteins are either not required for the interaction at the observed life stages or that there is redundancy between effectors expressed by E. festucae.

An investigation of genotype-phenotype association in a festulolium forage grass population containing genome-spanning Festuca pratensis chromosome segments in a Lolium perenne background

Alien chromosome introgression is used for the transfer of beneficial traits in plant breeding. For temperate forage grasses, much of the work in this context has focused on species within the ryegrasses (Lolium spp.) and the closely related fescues (Festuca spp.) particularly with a view to combining high forage quality with reliability and enhanced environmental services. We have analysed a L. perenne (perennial ryegrass) population containing the majority of a F. pratensis (meadow fescue) genome as introgressed chromosome segments to identify a) marker-trait associations for nutrient use and abiotic stress response across the family, and b) to assess the effects of introgression of F. pratensis genomic regions on phenotype. Using container-based assays and a system of flowing solution culture, we looked at phenotype responses, including root growth, to nitrogen and phosphorus status in the growing medium and abiotic stresses within this festulolium family. A number of significant marker/trait associations were identified across the family for root biomass on chromosomes 2, 3 and 5 and for heading date on chromosome 2. Of particular interest was a region on chromosome 2 associated with increased root biomass in phosphorus-limited conditions derived from one of the L. perenne parents. A genotype containing F. pratensis chromosome 4 as a monosomic introgression showed increased tiller number, shoot and root growth and genotypes with F. pratensis chromosome segment introgressions at different ends of chromosome 4 exhibited differential phenotypes across a variety of test conditions. There was also a general negative correlation between the extent of the F. pratensis genome that had been introgressed and root-related trait performances. We conclude that 1) the identification of alleles affecting root growth has potential application in forage grass breeding and, 2) F. pratensis introgressions can enhance quantitative traits, however, introgression can also have more general negative effects.

Temporal changes in genetic diversity and forage yield of perennial ryegrass in monoculture and in combination with red clover in swards

Agricultural grasslands are often cultivated as mixtures of grasses and legumes, and an extensive body of literature is available regarding interspecific interactions, and how these relate to yield and agronomic performance. However, knowledge of the impact of intraspecific diversity on grassland functioning is scarce. We investigated these effects during a 4-year field trial established with perennial ryegrass (Lolium perenne) and red clover (Trifolium pratense). We simulated different levels of intraspecific functional diversity by sowing single cultivars or by combining cultivars with contrasting growth habits, in monospecific or bispecific settings (i.e. perennial ryegrass whether or not in combination with red clover). Replicate field plots were established for seven seed compositions. We determined yield parameters and monitored differences in genetic diversity in the ryegrass component among seed compositions, and temporal changes in the genetic composition and genetic diversity at the within plot level. The composition of cultivars of both species affected the yield and species abundance. In general, the presence of clover had a positive effect on the yield. The cultivar composition of the ryegrass component had a significant effect on the yield, both in monoculture, and in combination with clover. For the genetic analyses, we validated empirically that genotyping-by-sequencing of pooled samples (pool-GBS) is a suitable method for accurate measurement of population allele frequencies, and obtained a dataset of 22,324 SNPs with complete data. We present a method to investigate the temporal dynamics of cultivars in seed mixtures grown under field conditions, and show how cultivar abundances vary during subsequent years. We screened the SNP panel for outlier loci, putatively under selection during the cultivation period, but none were detected.