Phytomelatonin and plant mineral nutrition.

Plant mineral nutrition is critical for agricultural productivity and for human nutrition; however, the availability of mineral elements is spatially and temporally heterogeneous in many ecosystems and agricultural landscapes. Nutrient imbalances trigger intricate signalling networks that modulate plant acclimation responses. One signalling agent of particular importance in such networks is phytomelatonin, a pleiotropic molecule with multiple functions. Evidence indicates that deficiencies or excesses of nutrients generally increase phytomelatonin levels in certain tissues, and it is increasingly thought to participate in the regulation of plant mineral nutrition. Alterations in endogenous phytomelatonin levels can protect plants from oxidative stress, influence root architecture, and influence nutrient uptake and efficiency of use through transcriptional and post-transcriptional regulation; such changes optimize mineral nutrient acquisition and ion homeostasis inside plant cells and thereby help to promote growth. This review summarizes current knowledge on the regulation of plant mineral nutrition by melatonin and highlights how endogenous phytomelatonin alters plant responses to specific mineral elements. In addition, we comprehensively discuss how melatonin influences uptake and transport under conditions of nutrient shortage.

Melatonin: A master regulator of plant development and stress responses.

Melatonin is a pleiotropic molecule with multiple functions in plants. Since the discovery of melatonin in plants, numerous studies have provided insight into the biosynthesis, catabolism, and physiological and biochemical functions of this important molecule. Here, we describe the biosynthesis of melatonin from tryptophan, as well as its various degradation pathways in plants. The identification of a putative melatonin receptor in plants has led to the hypothesis that melatonin is a hormone involved in regulating plant growth, aerial organ development, root morphology, and the floral transition. The universal antioxidant activity of melatonin and its role in preserving chlorophyll might explain its anti-senescence capacity in aging leaves. An impressive amount of research has focused on the role of melatonin in modulating postharvest fruit ripening by regulating the expression of ethylene-related genes. Recent evidence also indicated that melatonin functions in the plant's response to biotic stress, cooperating with other phytohormones and well-known molecules such as reactive oxygen species and nitric oxide. Finally, great progress has been made towards understanding how melatonin alleviates the effects of various abiotic stresses, including salt, drought, extreme temperature, and heavy metal stress. Given its diverse roles, we propose that melatonin is a master regulator in plants.

Melatonin ameliorates aluminum toxicity through enhancing aluminum exclusion and reestablishing redox homeostasis in roots of wheat.

Melatonin is a universal regulator modulating plant development and responses to abiotic stresses. The alteration and potential roles of melatonin in mediating aluminum (Al) tolerance were investigated in two wheat genotypes differing in Al resistance. Using the high-resolution mass spectrometry, we observed that melatonin contents in Xi Aimai-1 were 1.7-fold higher than that in Yangmai-5. Application of melatonin conferred Al resistance in both genotypes. Melatonin treatment scavenged reactive oxygen species (ROS) accumulation and alleviated Al-induced oxidative damage to lipids and proteins by stimulating antioxidant enzymes and augmenting antioxidants. Additionally, melatonin treatment decreased root tip-Al contents by 19.0% and 15.5% in Xi Aimai-1 and Yangmai-5, respectively. Malate efflux, however, was not altered by melatonin under Al stress. The amount of cell wall polysaccharide and pectin methylesterase activity was significantly increased by Al treatment; but suppressed by melatonin. Melatonin synthesis inhibitor, p-CPA, significantly increased the amount of the Al binding in cell walls of the tolerant genotype, whereas exogenous melatonin decreased cell wall Al content in the sensitive genotype. These results suggest that melatonin alleviated Al toxicity through augmenting antioxidants and inducing antioxidant enzymes to control ROS and enhancing exclusion of Al from root apex by altering cell wall polysaccharides in wheat.

Alteration of Phenolic Composition in Lettuce (Lactuca sativa L.) by Reducing Nitrogen Supply Enhances its Anti-Proliferative Effects on Colorectal Cancer Cells.

Consumption of vegetables rich in phenolic compounds has become a useful method to reduce the risk of developing several types of cancer. This study investigated the potential relationship between the alteration of phenolic compounds in lettuce induced by reduced nitrogen supply and its anti-proliferative effects on Caco-2 colorectal cancer cells. Our results showed that phenolic extracts from lettuce grown under low nitrogen conditions (LP) exhibited better anti-proliferative effects against Caco-2 cells, in part, by interfering with the cell cycle and inducing apoptosis, compared with those from lettuce supplied with adequate nitrogen. High performance liquid chromatography (HPLC) analysis and correlation analysis indicated that the better anticancer activity of LP may be not only related to the increased phenolic content, but also associated with the increased percentage contribution of quercetin to total phenolics. Taken together, alteration of phenolic composition by reduced nitrogen supply can be an effectively strategy for the development of healthy vegetables as anticancer products.

Reduced nitrogen supply enhances the cellular antioxidant potential of phenolic extracts through alteration of the phenolic composition in lettuce (Lactuca sativa L.).

BACKGROUND: Nitrogen availability is an important environmental factor that determines the production of phenolic compounds in vegetables, but the relationship between low nitrogen-induced alterations of phenolic compounds in vegetable crops and the cellular antioxidant activities of these compounds remains unclear. This study investigated the effect of reduced nitrogen supply (0.05 mmol L-1 nitrate) on phenolic metabolism in lettuce and the protective role of phenolic extracts against H2 O2 -induced oxidative stress in Caco-2 cells by determining cell damage, reactive oxygen species (ROS) content and antioxidant enzyme activities. RESULTS: Reduced nitrogen supply significantly improved the accumulation of phenolic compounds in lettuce, which was partially correlated with the upregulation of genes related to the phenolic synthesis pathway. Phenolic extracts from lettuce cultivated in low-nitrogen medium exhibited a better protective effect against H2 O2 -induced oxidative damage in Caco-2 cells than those from lettuce cultivated with adequate nitrogen. These extracts act by increasing the activities of antioxidant enzymes and, subsequently, by inhibiting ROS overproduction, which leads to a decrease in mitochondrial membrane and DNA damage. The results of HPLC and correlation analyses implied that the improvement in the protective capacity of lettuce extracts after low-nitrogen treatment may be related, not only to the increased content of phenolic compounds, but also to the increased percentage contribution of chlorogenic acid and quercetin derivatives to the total phenolic content. CONCLUSION: Reduction in nitrogen supply can be a powerful strategy to modify phenolic metabolism and composition in lettuce and, consequently, to improve their antioxidant capacity. © 2019 Society of Chemical Industry.

Auxin Acts Downstream of Ethylene and Nitric Oxide to Regulate Magnesium Deficiency-Induced Root Hair Development in Arabidopsis thaliana.

This study examines the association of auxin with ethylene and nitric oxide (NO) in regulating the magnesium (Mg) deficiency-induced root hair development in Arabidopsis thaliana. With Mg deficiency, both ethylene and NO promoted the elevation of root auxin levels in roots by inducing the expression of AUXIN-RESISTANT1 (AUX1), PIN-FORMED 1 (PIN1) and PIN2 transporters. In turn, auxin stimulated ethylene and NO production by activating the activities of 1-aminocyclopropane-1-carboxylate (ACC) oxidase (ACO), ACC synthase (ACS), nitrate reductase (NR) and NO synthase-like (NOS-L). These processes constituted an NO/ethylene-auxin feedback loop. Interestingly, however, the roles of ethylene and NO in regulating Mg deficiency-induced root hair development required the action of auxin, but not vice versa. In summary, these results suggest that Mg deficiency induces a positive interaction between the accumulation of auxin and ethylene/NO in roots, with auxin acting downstream of ethylene and NO signals to regulate Mg deficiency-induced root hair morphogenesis.

Decreasing methylation of pectin caused by nitric oxide leads to higher aluminium binding in cell walls and greater aluminium sensitivity of wheat roots.

Nitric oxide (NO) is an important bioactive molecule involved in cell wall metabolism, which has been recognized as a major target of aluminium (Al) toxicity. We have investigated the effects of Al-induced NO production on cell wall composition and the subsequent Al-binding capacity in roots of an Al-sensitive cultivar of wheat (Triticum aestivum L. cv. Yang-5). We found that Al exposure induced NO accumulation in the root tips. Eliminating NO production with an NO scavenger (cPTIO) significantly alleviated the Al-induced inhibition of root growth and thus reduced Al accumulation. Elimination of NO, however, did not significantly affect malate efflux or rhizosphere pH changes under Al exposure. Levels of cell wall polysaccharides (pectin, hemicelluloses 1, and hemicelluloses 2) and pectin methylesterase activity, as well as pectin demethylation in the root apex, significantly increased under Al treatment. Exogenous cPTIO application significantly decreased pectin methylesterase activity and increased the degree of methylation of pectin in the root cell wall, thus decreasing the Al-binding capacity of pectin. These results suggest that the Al-induced enhanced production of NO decreases cell wall pectin methylation, thus increasing the Al-binding capacity of pectin and negatively regulating Al tolerance in wheat.

Nitric oxide alleviates aluminum-induced oxidative damage through regulating the ascorbate-glutathione cycle in roots of wheat.

The possible association with nitric oxide (NO) and ascorbate-glutathione (AsA-GSH) cycle in regulating aluminum (Al) tolerance of wheat (Triticum aestivum L.) was investigated using two genotypes with different Al resistance. Exposure to Al inhibited root elongation, and triggered lipid peroxidation and oxidation of AsA to dehydroascorbate and GSH to glutathione disulfide in wheat roots. Exogenous NO significantly increased endogenous NO levels, and subsequently alleviated Al-induced inhibition of root elongation and oxidation of AsA and GSH to maintain the redox molecules in the reduced form in both wheat genotypes. Under Al stress, significantly increased activities and gene transcriptional levels of ascorbate peroxidase, glutathione reductase, and dehydroascorbate reductase, were observed in the root tips of the Al-tolerant genotype Jian-864. Nitric oxide application enhanced the activity and gene transcriptional level of these enzymes in both wheat genotypes. γ-Glutamylcysteine synthetase was not significantly affected by Al or NO, but NO treatments increased the activity of glutathione peroxidase and glutathione S-transferase to a greater extent than the Al-treated wheat seedlings. Proline was significantly decreased by Al, while it was not affected by NO. These results clearly suggest that NO protects wheat root against Al-induced oxidative stress, possibly through its regulation of the AsA-GSH cycle.

Nitrate reductase-mediated early nitric oxide burst alleviates oxidative damage induced by aluminum through enhancement of antioxidant defenses in roots of wheat (Triticum aestivum).

• Nitric oxide (NO) is an important signaling molecule involved in the physiological processes of plants. The role of NO release in the tolerance strategies of roots of wheat (Triticum aestivum) under aluminum (Al) stress was investigated using two genotypes with different Al resistances. • An early NO burst at 3 h was observed in the root tips of the Al-tolerant genotype Jian-864, whereas the Al-sensitive genotype Yang-5 showed no NO accumulation at 3 h but an extremely high NO concentration after 12 h. Stimulating NO production at 3 h in the root tips of Yang-5 with the NO donor relieved Al-induced root inhibition and callose production, as well as oxidative damage and ROS accumulation, while elimination of the early NO burst by NO scavenger aggravated root inhibition in Jian-864. • Synthesis of early NO in roots of Jian-864 was mediated through nitrate reductase (NR) but not through NO synthase. Elevated antioxidant enzyme activities were induced by Al stress in both wheat genotypes and significantly enhanced by NO donor, but suppressed by NO scavenger or NR inhibitor. • These results suggest that an NR-mediated early NO burst plays an important role in Al resistance of wheat through modulating enhanced antioxidant defense to adapt to Al stress.

Comparison of nitrification inhibitors for mitigating cadmium accumulation in pakchoi and their associated microbial mechanisms. / å‡æŽ§å°é’èœé•‰æ±¡æŸ“çš„é«˜æ•ˆç¡åŒ–æŠ‘åˆ¶å‰‚ç­›é€‰åŠå ¶å¾®ç”Ÿç‰©å­¦æœºåˆ¶ç ”ç©¶.

The use of nitrification inhibitors has been suggested as a strategy to decrease cadmium (Cd) accumulation in crops. However, the most efficient nitrification inhibitor for mitigating crop Cd accumulation remains to be elucidated, and whether and how changes in soil microbial structure are involved in this process also remains unclear. To address these questions, this study applied three commercial nitrification inhibitors, namely, dicyandiamide (DCD), 3,4-dimethylpyrazole phosphate (DMPP), and nitrapyrin (NP), to pakchoi. The results showed that both DCD and DMPP (but not NP) could efficiently decrease Cd concentrations in pakchoi in urea- and ammonium-fertilized soils. In addition, among the three tested nitrification inhibitors, DMPP was the most efficient in decreasing the Cd concentration in pakchoi. The nitrification inhibitors decreased pakchoi Cd concentrations by suppressing acidification-induced Cd availability and reshaping the soil microbial structure; the most effective nitrification inhibitor was DMPP. Ammonia oxidation generates the most protons during nitrification and is inhibited by nitrification inhibitors. Changes in environmental factors and predatory bacterial abundance caused by the nitrification inhibitors changed the soil microbial structure and increased the potential participants in plant Cd accumulation. In summary, our study identified DMPP as the most efficient nitrification inhibitor for mitigating crop Cd contamination and observed that the soil microbial structural changes caused by the nitrification inhibitors contributed to decreasing Cd concentration in pakchoi.

Nitric oxide enhances development of lateral roots in tomato (Solanum lycopersicum L.) under elevated carbon dioxide.

Elevated carbon dioxide (CO2) has been shown to enhance the growth and development of plants, especially of roots. Amongst them, lateral roots play an important role in nutrient uptake, and thus alleviate the nutrient limitation to plant growth under elevated CO2. This paper examined the mechanism underlying CO2 elevation-induced lateral root formation in tomato. The endogenous nitric oxide (NO) in roots was detected by the specific probe 4-amino-5-methylamino-2',7'-difluorofluorescein diacetate (DAF-FM DA). We suggest that CO2 elevation-induced NO accumulation was important for lateral root formation. Elevated CO2 significantly increased the activity of nitric oxide synthase in roots, but not nitrate reductase activity. Moreover, the pharmacological evidence showed that nitric oxide synthase rather than nitrate reductase was responsible for CO2 elevation-induced NO accumulation. Elevated CO2 enhanced the activity of nitric oxide synthase and promoted production of NO, which was involved in lateral root formation in tomato under elevated CO2.

Inhibition of BRUTUS Enhances Plant Tolerance to Zn Toxicity by Upregulating Pathways Related to Iron Nutrition.

The identification of the key genes regulating plant tolerance to Zn stress is important for enhancing the Zn phytoremediation of targeted plants. Here, we showed that the T-DNA insertion-induced inhibition of the BRUTUS (BTS) gene in the bts-1 mutant greatly improved Zn tolerance, as indicated by increased biomass production and reduced leaf chlorosis. The ProBTS::BTS-GFP complementation in the bts-1 mutant abolished the improvement of Zn tolerance. Unexpectedly, the bts-1 mutant had higher and comparable Zn concentrations in the roots and citrate effluxer shoots, respectively, compared to wild-type plants. As a result, the shoots and roots of bts-1 mutants had 53% and 193% more Zn accumulation than the wild-type plants, respectively. RNA-seq analyses revealed that the Fe nutrition-related genes were upregulated in bts-1 mutants, especially under Zn stress conditions. Therefore, the bts-1 mutants had a greater Fe concentration and a higher Fe/Zn ratio than the wild-type plants exposed to Zn toxicity. Further study showed that the differences in Zn tolerance between bts-1 and wild-type plants were minimized by eliminating Fe or supplementing excessive Fe in the growth medium. Taken together, the T-DNA insertion-induced inhibition of BTS improves plant Zn tolerance by optimizing Fe nutrition; thus, the knockdown of BTS may be a promising approach for improving Zn phytoremediation efficiency.

Enhanced nitrogen use efficiency, growth and yield of wheat through soil urea hydrolysis inhibition by Vachellia nilotica extract.

Soil urease inhibition slows down the urea hydrolysis and prolongs nitrogen (N) stay in soil, resulting in an increased N uptake by plants. Apart from several chemical urease inhibitors, the urease inhibition potential of plant extracts is rarely reported. In our previous study, the soil urease inhibition by Vachellia nilotica leaf extract was reported; however, its role in relation to growth and yield of wheat (Triticum aestivum) under pot and field conditions remains unknown. The acetonic extracts of 10, 20, and 50 g Vachellia nilotica leaves were given code names viz. Vn.Fl-10, Vn.Fl-20 and Vn.Fl-50, respectively, and coated on 100 g of urea individually. The enhancements of growth (total number of tillers, number of productive tillers, number of spikelets per spike, number of grains per spike, and 1000-grains weight) and yield (biological yield, straw yield, and grain yield) parameters of wheat by Vn.Fl-20 and Vn.Fl-50 coated urea treatments were compared with uncoated urea in a pot experiment. The experiment indicated that the Vachellia nilotica extract coatings were effective at improving N persistence in soil, as reflected by increased grain and straw N concentrations as well as uptakes. The reproduction of the aforementioned results, at the half and full recommended dose of urea under field conditions, reconfirmed the effectiveness of Vachellia nillotica coatings. Moreover, the Vn.Fl-20 and Vn.Fl-50 coated urea, at the half as well as full recommended dose under field conditions, proved equally effective in terms of higher biological, straw, and grain yield, and grain N uptake. The increments in the total number of tillers, number of productive tillers, 1000-grain weight, biological yield, straw yield, grain yield, grain N concentration, grain N-, and straw N uptake along with nitrogen use efficiency (NUE) components, i.e. nitrogen partial factor productivity (NPFP), nitrogen agronomic efficiency (NAE), partial nitrogen balance (PNB), and nitrogen recovery efficiency (NRE) of wheat highlighted the superiority of Vn.Fl-20 coating over the hydroquinone (Hq) coating on urea at the full recommended dose under field conditions. Given the findings of this study, Vachellia nilotica leaf extract coating (Vn.Fl-20) can be used as a natural urease inhibitor to reduce urea hydrolysis and enhance wheat productivity.

The ferroxidases are critical for Fe(II) oxidation in xylem to ensure a healthy Fe allocation in Arabidopsis thaliana.

The long-distance transport of iron (Fe) in the xylem is critical for maintaining systemic Fe homeostasis in plants. The loading form of Fe(II) into the xylem and the long-distance translocation form of Fe(III)-citrate have been identified, but how Fe(II) is oxidized to Fe(III) in the xylem remains unknown. Here, we showed that the cell wall-resided ferroxidases LPR1 and LPR2 (LPRs) were both specifically expressed in the vascular tissues of Arabidopsis thaliana, while disruption of both of them increased Fe(II) in the xylem sap and caused excessive Fe deposition in the xylem vessel wall under Fe-sufficient conditions. As a result, a large amount of Fe accumulated in both roots and shoots, hindering plant growth. Moreover, under low-Fe conditions, LPRs were preferentially induced in old leaves, but the loss of LPRs increased Fe deposition in the vasculature of older leaves and impeded Fe allocation to younger leaves. Therefore, disruption of both LPRs resulted in severer chlorosis in young leaves under Fe-deficient conditions. Taken together, the oxidation of Fe(II) to Fe(III) by LPRs in the cell wall of vasculature plays an important role in xylem Fe allocation, ensuring healthy Fe homeostasis for normal plant growth.

Auxin modulates the enhanced development of root hairs in Arabidopsis thaliana (L.) Heynh. under elevated CO(2).

Root hairs may play a critical role in nutrient acquisition of plants grown under elevated CO(2) . This study investigated how elevated CO(2) enhanced the development of root hairs in Arabidopsis thaliana (L.) Heynh. The plants under elevated CO(2) (800 µL L(-1)) had denser and longer root hairs, and more H-positioned cells in root epidermis than those under ambient CO(2) (350 µL L(-1)). The elevated CO(2) increased auxin production in roots. Under elevated CO(2) , application of either 1-naphthoxyacetic acid (1-NOA) or N-1-naphthylphthalamic acid (NPA) blocked the enhanced development of root hairs. The opposite was true when the plants under ambient CO(2) were treated with 1-naphthylacetic acid (NAA), an auxin analogue. Furthermore, the elevated CO(2) did not enhance the development of root hairs in auxin-response mutants, axr1-3, and auxin-transporter mutants, axr4-1, aux1-7 and pin1-1. Both elevated CO(2) and NAA application increased expressions of caprice, triptychon and rho-related protein from plants 2, and decreased expressions of werewolf, GLABRA2, GLABRA3 and the transparent testa glabra 1, genes related to root-hair development, while 1-NOA and NPA application had an opposite effect. Our study suggests that elevated CO(2) enhanced the development of root hairs in Arabidopsis via the well-characterized auxin signalling and transport that modulate the initiation of root hairs and the expression of its specific genes.

Cross-Talk between Hydrogen Peroxide and Nitric Oxide during Plant Development and Responses to Stress.

Nitric oxide (NO) and hydrogen peroxide (H2O2) are gradually becoming established as critical regulators in plants under physiological and stressful conditions. Strong spatiotemporal correlations in their production and distribution have been identified in various plant biological processes. In this context, NO and H2O2 act synergistically or antagonistically as signals or stress promoters depending on their respective concentrations, engaging in processes such as the hypersensitive response, stomatal movement, and abiotic stress responses. Moreover, proteins identified as potential targets of NO-based modifications include a number of enzymes related to H2O2 metabolism, reinforcing their cross-talk. In this review, several processes of well-characterized functional interplay between H2O2 and NO are discussed with respect to the most recent reported evidence on hypersensitive response-induced programmed cell death, stomatal movement, and plant responses to adverse conditions and, where known, the molecular mechanisms and factors underpinning their cross-talk.

Molecular functions of nitric oxide and its potential applications in horticultural crops.

Nitric oxide (NO) regulates plant growth, enhances nutrient uptake, and activates disease and stress tolerance mechanisms in most plants, making NO a potential tool for use in improving the yield and quality of horticultural crop species. Although the use of NO in horticulture is still in its infancy, research on NO in model plant species has provided an abundance of valuable information on horticultural crop species. Emerging evidence implies that the bioactivity of NO can occur through many potential mechanisms but occurs mainly through S-nitrosation, the covalent and reversible attachment of NO to cysteine thiol. In this context, NO signaling specifically affects crop development, immunity, and environmental interactions. Moreover, NO can act as a fumigant against a wide range of postharvest diseases and pests. However, for effective use of NO in horticulture, both understanding and exploring the biological significance and potential mechanisms of NO in horticultural crop species are critical. This review provides a picture of our current understanding of how NO is synthesized and transduced in plants, and particular attention is given to the significance of NO in breaking seed dormancy, balancing root growth and development, enhancing nutrient acquisition, mediating stress responses, and guaranteeing food safety for horticultural production.

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We investigated the effects of dicyandiamide (DCD) on the growth and Cd concentrations in pakchoi cultivated under different instant soluble N fertilizers [ammonium sulfate, ammonium sulfate and sodium nitrate (1:1, ammonium/nitrate), and urea] in Cd-contaminated soils. The results showed that the fresh weight of the edible parts of Cd-stressed pakchoi were increased by 583.3%, 41.5%, and 206.8% under ammonium, ammonium/nitrate, and urea treatments in the presence of DCD, respectively compared with control, and the tolerance index and photosynthetic rate significantly increased, whereas no significant changes were observed under nitrate supply. Under all N treatments with DCD, the MDA and H2O2 contents and the superoxide radical production rate in the leaves of pakchoi were decreased, with the highest reduction occurred in ammonium and urea treatments. Cd concentrations in the leaves of pakchoi fertilized with ammonium, ammonium/nitrate, and urea were lowered by 58.3%, 34.0%, and 44.5% and those in the petioles were lowered by 61.8%, 29.4%, and 55.6%, respectively. Cd concentration in the leaves and petioles of pakchoi in the nitrate treatment did not differ significantly from control. These changes could be attributable to the reduction in the acidification of rhizosphere soil in response to the combined application of N fertilizer and DCD. Accordingly, in Cd-contaminated soils with a low buffering capacity, the application of DCD combined with ammonium, ammonium/nitrate, or urea N fertili-zers could alleviate Cd-induced growth stress and inhibit photosynthesis in pakchoi plants and effectively minimize the Cd accumulation.

The chirality of imazethapyr herbicide selectively affects the bacterial community in soybean field soil.

The chiral herbicide imazethapyr (IM) is frequently used to control weeds in soybean fields in northeast China. However, the impact of IM enantiomers on microbial communities in soil is still unknown. Genetic markers (16S rRNA V3-V4 regions) were used to characterize and evaluate the variation of the bacterial communities potentially effected by IM enantiomers. Globally, the bacterial community structure based on the OTU profiles in (-)-R-IM-treated soils was significantly different from those in (+)-S-IM-treated soils, and the differences were enlarged with the treatment dose increasing. Interestingly, the Rhizobiaceae family and several other beneficial bacteria, including Bradyrhizobium, Methylobacterium, and Paenibacillus, were strongly enriched in (-)-R-IM treatment compared to (+)-S-IM treatment. In contrast, the pathogenic bacteria, including Erwinia, Pseudomonas, Burkholderia, Streptomyces, and Agrobacterium, were suppressed in the presence of (-)-R-IM compared to (+)-S-IM. Furthermore, we also observed that the bacterial community structure in (-)-R-IM-treated soils was more quickly restored to its original state compared with those in (+)-S-IM-treated soils. These findings unveil a new role of chiral herbicide in the development of soil microbial ecology and provide theoretical support for the application of low-persistence, high-efficiency, and eco-friendly optical rotatory (-)-R-IM.

Estimating nutrient uptake requirements for radish in China based on QUEFTS model.

Imbalanced fertilization has caused lower yield and nutrient use efficiency for radish (Raphanus sativus L.) production in China. Estimating nutrient requirements for radish is crucial in optimizing fertilization to resolve the problem. On-farm experiments in the radish-growing regions of China from 2000 to 2017 were collected to investigate the relationship between fleshy root yield and nutrient accumulation in radish plant using the Quantitative Evaluation of the Fertility of Tropical Soils (QUEFTS) model. The QUEFTS model predicted a linear increase in fleshy root yield if nutrients were taken up in balanced amounts until yield reached about 60%-70% of the potential yield. The balanced N, P, and K requirements in radish plant simulated by the QUEFTS model were 2.15, 0.45, and 2.58 kg to produce 1000 kg of fleshy root, and the corresponding internal efficiencies (IEs, kg fleshy root per kg nutrient in total plant dry matter) for N, P, and K were 465.1, 2222.2, and 387.1 kg kg-1. The simulated balanced N, P, and K removal by fleshy root to produce 1000 kg fleshy root were 1.34, 0.30, and 1.93 kg, respectively. Approximately 62%, 67%, and 75% of N, P, and K in radish plant were presented in the fleshy root and removed from the soil. Field validation experiments confirmed the consistency between the observed and simulated nutrient uptake values. The QUEFTS model was proven to be effective for estimating nutrient requirements of radish and will contribute to develop fertilizer recommendations for radish cultivated in China.