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IntroductionComposting is one of the effective environmental protection and sustainable measures for improving soil quality and increasing crop yield. However, due to the special physical and chemical properties of saline-sodic soil and the complex rhizosphere microecological environment, the potential mechanism of regulating plant growth after applying compost in saline-sodic soil remains elusive.MethodsHere, we investigated the effects of different compost addition rates (0, 5, 15, 25%) on plant growth traits, soil chemical properties, and rhizosphere bacterial community structure.ResultsThe results showed that compost promoted the accumulation of plant biomass and root growth, increased soil nutrients, and enhanced the diversity and complexity of the rhizosphere bacterial communities. Moreover, the enriched core bacterial ASVs (Amplicon Sequence Variants) in compost treatment could be reshaped, mainly including dominant genera, such as Pseudomonas, Devosia, Novosphingobium, Flavobacterium, and Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium. The functions of these ASVs were energy resources and nitrogen cycle functions, suggesting the roles of these ASVs in improving plant root nutrient resource acquisition for alfalfa growth. The contents of available potassium, available phosphorus, total nitrogen, and organic carbon of the soil surrounding the roots, the root length, root surface area, root volume, and root tips affected the abundance of the core bacterial ASVs, and the soil chemical properties contributed more to the effect of plant biomass.DiscussionOverall, our study strengthens the understanding of the potentially important taxa structure and function of plant rhizosphere bacteria communities, and provides an important reference for developing agricultural microbiome engineering techniques to improve root nutrient uptake and increase plant productivity in saline-sodic soils.

Panax notoginseng and Panax quinquefolium are important economic plants that utilize dried roots for medicinal and food dual purposes; there is still insufficient research of their stems and leaves, which also contain triterpenoid saponins. The extraction process was developed with a total saponin content of 12.30 ± 0.34% and 12.19 ± 0.64% for P. notoginseng leaves (PNL) and P. quinquefolium leaves (PQL) extracts, respectively. PNL and PQL saponin extracts showed good antioxidant, antihypertensive, hypoglycemic, and anti-inflammatory properties in vitro and RAW264.7 cells. A total of 699 metabolites were identified in PNL and PQL saponin extracts, with the majority being triterpenoid saponins, flavonoids and amino acids. Fourteen ginsenosides, 18 flavonoids or alkaloids, and 16 amino acids were enriched in both saponin extracts. Overall, the utilization of saponins from medicinal plants PNL and PQL has been developed to facilitate systematic research in the functional food and natural product industries.

Soil salinization is considered a major global environmental problem due to its adverse effects on agricultural sustainability and production. Compost is an environmentally friendly and sustainable measure used for reclaiming saline–sodic soil. However, the responses of the physiological characteristics of alfalfa and the structure and function of rhizosphere fungal communities after compost application in saline–sodic soil remain elusive. Here, a pot experiment was conducted to explore the effect of different compost application rates on soil properties, plant physiological traits, and rhizosphere fungal community characteristics. The results showed that compost significantly increased soil nutrients and corresponding soil enzyme activities, enhanced leaf photosynthesis traits, and ion homeostasis compared with the control treatment. We further found that the rhizosphere fungal communities were dominated by Sodiomyces at the genus level, and the relative abundance of pathogenic fungi, such as Botryotrichum, Plectosphaerella, Pseudogymnoascus, and Fusarium, declined after compost application. Moreover, the α-diversity indexes of the fungal community under compost application rates of 15% and 25% significantly decreased in comparison to the control treatment. The soil SOC, pH, TP, and TN were the main environmental factors affecting fungal community composition. The leaf photosynthetic traits and metal ion contents showed significantly positive correlations with Sodiomyces and Aspergillus. The fungal trophic mode was dominated by Pathotroph–Saprotroph–Symbiotroph and Saprotroph. Overall, our findings provide an important basis for the future application of microbial-based strategies to improve plant tolerance to saline-alkali stress.

Soil alkalization severely limits plant growth and development, however, the mechanisms of alkaline response in plants remain largely unknown. In this study, we performed physiological and transcriptomic analyses using two alfalfa cultivars (Medicago sativa L.) with different sensitivities to alkaline conditions. The chlorophyll content and shoot fresh mass drastically declined in the alkaline-sensitive cultivar Algonquin (AG) following alkaline treatment (0–25 mM Na2CO3 solution), while the alkaline-tolerant cultivar Gongnong NO.1 (GN) maintained relatively stable growth and chlorophyll content. Compared with AG, GN had higher contents of Ca2+ and Mg2+; the ratios of Ca2+ and Mg2+ to Na+, proline and soluble sugar, as well as higher enzyme activities of peroxidase (POD) and catalase (CAT) under the alkaline conditions. Furthermore, transcriptomic analysis identified three categories of alkaline-responsive differentially expressed genes (DEGs) between the two cultivars: 48 genes commonly induced in both the cultivars (CAR), 574 genes from the tolerant cultivar (TAR), and 493 genes from the sensitive cultivar (SAR). Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses showed that CAR genes were mostly involved in phenylpropanoid biosynthesis, lipid metabolism, and DNA replication and repair; TAR genes were significantly enriched in metabolic pathways, such as biosynthesis of amino acids and secondary metabolites including flavonoids, and the MAPK signaling pathway; SAR genes were specifically enriched in vitamin B6 metabolism. Taken together, the results identified candidate pathways associated with genetic variation in response to alkaline stress, providing novel insights into the mechanisms underlying alkaline tolerance in alfalfa.

Soil alkalization triggers ion toxicity and osmotic and alkaline (high pH) stresses in plants, damaging their growth and productivity. Therefore, we investigated whether priming with abscisic acid (ABA) increases the tolerance of alfalfa seedlings to alkaline stress, and then examined the underlying molecular mechanisms. Alfalfa seedlings were pretreated with ABA (10 μM) for 16 h and then subjected to alkaline stress using a 15 mM Na2CO3 solution (pH 10.87). Compared with the control, ABA pretreatment significantly alleviated leaf damage and improved the fresh weight, water content, and survival rate of alfalfa seedlings under alkaline conditions. Abscisic acid pretreatment reduced accumulation of reactive oxygen species (ROS), increased activities of the antioxidant enzymes superoxide dismutase (SOD) and peroxidase (POD), maintained higher ratios of K+/Na+, Ca2+/Na+, and Mg2+/Na+, and increased accumulation of proline. In addition, ABA upregulated the expression of genes involved in proline biosynthesis (P5CS) and the sequestration of Na+ in vacuoles (NHX1 and AVP) under alkaline conditions. Abscisic acid priming increased tolerance to alkaline stress by maintaining homeostasis of ROS and metal ions and upregulating osmoprotection and the expression of stress tolerance-related genes.

Alkaline stress as a result of higher pH usually triggers more severe physiological damage to plants than that of saline stress with a neutral pH. In the present study, we demonstrated that silicon (Si) priming of alfalfa (Medicago sativa L.) seedlings increased their tolerance to high alkaline stress situations. Gongnong No. 1 seedlings were subjected to alkaline stress simulated by 25 mM Na2CO3 (pH 11.2). Alkaline stress greatly decreased the biomass and caused severe lodging or wilting of alfalfa seedlings. In contrast, the application of Si to alfalfa seedlings 36 h prior to the alkaline treatment significantly alleviated the damage symptoms and greatly increased the biomass and chlorophyll content. Because of being concomitant with increasing photosynthesis and water use efficiency, decreasing membrane injury and malondialdehyde content, and increasing peroxidase and catalase ascorbate activities in alfalfa leaves, thereby alleviating the triggered oxidative damage by alkaline stress to the plant. Furthermore, Si priming significantly decreased the accumulation of protein and proline content in alfalfa, thus reducing photosynthetic feedback repression. Si priming significantly accumulated more Na in the roots, but led to a decrease of Na accumulation and an increase of K accumulation in the leaves under alkaline stress. Meanwhile, Si priming decreased the accumulation of metal ions such as Mg, Fe, Mn, and Zn in the roots of alfalfa seedlings under alkaline stress. Collectively, these results suggested that Si is involved in the metabolic or physiological changes and has a potent priming effect on the alkaline tolerance of alfalfa seedlings. The present study indicated that Si priming is a new approach to improve the alkaline tolerance in alfalfa and provides increasing information for further exploration of the alkaline stress response at the molecular level in alfalfa.

Alkaline stress (high pH) severely damages root cells, and consequently, inhibits rice (Oryza sativa L.) seedling growth. In this study, we demonstrate the accumulation of reactive oxygen species (ROS) in root cells under alkaline stress. Seedlings of two rice cultivars with different alkaline tolerances, ‘Dongdao-4’ (moderately alkaline-tolerant) and ‘Jiudao-51’ (alkaline-sensitive), were subjected to alkaline stress simulated by 15 mM sodium carbonate (Na2CO3). Alkaline stress greatly reduced seedling survival rate, shoot and root growth, and root vigor. Moreover, severe root cell damage was observed under alkaline stress, as shown by increased membrane injury, malondialdehyde accumulation, and Evan’s Blue staining. The expression of the cell death-related genes OsKOD1, OsHsr203j, OsCP1, and OsNAC4 was consistently upregulated, while that of a cell death-suppressor gene, OsBI1, was downregulated. Analysis of the ROS contents revealed that alkaline stress induced a marked accumulation of superoxide anions (O2•-) and hydrogen peroxide (H2O2) in rice roots. The application of procyanidins (a potent antioxidant) to rice seedlings 24 h prior to alkaline treatment significantly alleviated alkalinity-induced root damage and promoted seedling growth inhibition, which were concomitant with reduced ROS accumulation. These results suggest that root cell damage, and consequently growth inhibition, of rice seedlings under alkaline stress is closely associated with ROS accumulation. The antioxidant activity of superoxide dismutase, catalase, peroxidase, and ascorbate peroxidase increased under alkaline stress in the roots, probably in response to the cellular damage induced by oxidative stress. However, this response mechanism may be overwhelmed by the excess ROS accumulation observed under stress, resulting in oxidative damage to root cells. Our findings provide physiological insights into the molecular mechanisms of alkalinity-induced damage to root cells, and will contribute to the improvement of alkaline stress tolerance in rice plants.

In response to pathogen attack, plants prioritize defense reactions generally at the expense of plant growth. In this work, we report that changes in phytohormone signaling pathways are associated with the stunted plant growth caused by blast disease in rice seedlings. Infection of rice seedlings with blast fungus Magnaporthe oryzae (race 007.0) at the four-leaf stage (three true leaves) resulted in considerable inhibition of the growth of the upper uninfected distal leaves; the length of leaf blade and leaf sheath of the sixth and seventh leaf was reduced by 27 and 82%, and 88 and 72%, respectively, compared to that in the uninoculated plant control. Interestingly, cutting off the blast-infected fourth leaf blade within 2 days post inoculation (dpi) significantly rescued the inhibition of leaf growth, implying that an inhibitory substance(s) and/or signal was generated in the blast-infected leaves (fourth leaf) and transmitted to the upper distal leaves (sixth and seventh) during the 2-dpi period that induced growth inhibition. Expression analysis of marker genes for phytohormone pathways revealed acute activation of the jasmonate (JA) and abscisic acid (ABA) signaling pathways, and repression of auxin, gibberellic acid (GA) and salicylic acid (SA) signaling pathways, in the sixth leaf. The genes related to cell wall expansion were also significantly downregulated. In the blast-infected fourth leaf, JA pathway was activated within 2 dpi, followed by activation of ABA pathway 3 dpi. Further, leaf inhibition caused by blast infection was partially rescued in the rice mutant line coleoptile photomorphogenesis 2 (cpm2), which is defective in the gene encoding allene oxide cyclase (OsAOC). These results indicate that the JA signaling pathway is at least partly involved in the growth inhibition processes. Collectively, our data suggest that, upon pathogen attack, rice seedlings prioritize defense reactions against the infecting pathogen by temporarily ceasing plant growth through the systemic control of phytohormone pathways.

Current indices of saline-alkaline (SA) tolerance are mainly based on the traditional growth and physiological indices for salinity tolerance and likely affect the accuracy of alfalfa tolerance predictions. We determined whether the inclusion of soil alkalinity-affected indices, particularly Ca2+, Mg2+, and their ratios to Na+ in plants, based on the traditional method could improve the prediction accuracy of SA tolerance in alfalfa, determine important indices for SA tolerance, and identify suitable alfalfa cultivars in alkaline salt-affected soils. Fifty alfalfa cultivars were evaluated for their SA tolerance under SA and non-SA field conditions. The SA-tolerance coefficient (SATC) for each investigated index of the alfalfa shoot was calculated as the ratio of SA to non-SA field conditions, and the contribution of SATC under different growth and physiological indices to SA tolerance was quantified based on the inclusion/exclusion of special alkalinity-affected indices. The traditional method, excluding the special alkalinity-affected indices, explained nearly all of the variation in alfalfa SA tolerance, and the most important predictor was the SATC of stem length. The new method, which included these special alkalinity-affected indices, had similar explanatory power but instead identified the SATC of shoot Ca2+/Na+ ratio, followed by that of stem length, as key markers for the field evaluation of SA tolerance. Ca2+, Mg2+, and their ratios to Na+ hold promise for enhancing the robustness of SA-tolerance predictions in alfalfa. These results encourage further investigation into the involvement of Ca2+ in such predictions in other plant species and soil types under more alkaline salt-affected conditions.

Soil salinization is the main factor that threatens the growth and development of plants and limits the increase of yield. It is of great significance to study the key soil environmental factors affecting plant root traits to reveal the adaptation strategies of plants to saline-alkaline-stressed soil environments. In this study, the root biomass, root morphological parameters and root mineral nutrient content of two alfalfa cultivars with different sensitivities to alkaline stress were analyzed with black soil as the control group and the mixed saline-alkaline soil with a ratio of 7:3 between black soil and saline-alkaline soil as the saline-alkaline treatment group. At the same time, the correlation analysis of soil salinity indexes, soil nutrient indexes and the activities of key enzymes involved in soil carbon, nitrogen and phosphorus cycles was carried out. The results showed that compared with the control group, the pH, EC, and urease (URE) of the soil surrounding the roots of two alfalfa cultivars were significantly increased, while soil total nitrogen (TN), total phosphorus (TP), organic carbon (SOC), and α-glucosidase activity (AGC) were significantly decreased under saline-alkaline stress. There was no significant difference in root biomass and root morphological parameters of saline-alkaline tolerant cultivar GN under saline-alkaline stress. The number of root tips (RT), root surface area (RS) and root volume (RV) of AG were reduced by 61.16%, 44.54%, and 45.31%, respectively, compared with control group. The ratios of K+/Na+, Ca2+/Na+ and Mg2+/Na+ of GN were significantly higher than those of AG (p < 0.05). The root fresh weight (RFW) and dry weight (RDW), root length (RL), RV and RT of alfalfa were positively regulated by soil SOC and TN, but negatively regulated by soil pH, EC, and URE (p < 0.01). Root Ca2+/Na+ ratio was significantly positively correlated with soil TN, TP and SOC (p < 0.01). The absorption of Mg and Ca ions in roots is significantly negatively regulated by soil β-glucosidase activity (BGC) and acid phosphatase activity (APC) (p < 0.05). This study improved knowledge of the relationship between root traits and soil environmental factors and offered a theoretical framework for elucidating how plant roots adapt to saline-alkaline stressed soil environments. [ABSTRACT FROM AUTHOR]

Salinization and alkalization are worldwide problems of soil. To compare the effects of saline-alkaline stress on seedling growth between rice mutant and its wild type, we selected NaCl, Na2CO3 and NaHCO3 to simulate saline-alkaline stress, respectively, and selected two rice materials, ML04 is rice mutant and G19 is its wild type. Under saline-alkaline stress, the rice biomass sharply decreased, and the shoot fresh weight of ML04 was higher than that of G19. The saline-alkaline stress promoted the rice taking up Na+ but inhibited absorbing K+ in shoots. The Na+ and K+ contents under the alkaline stress were much more than those of under saline stress, and the Na+ content of ML04 was higher than that of G19 under alkaline stress treatments. The saline-alkaline stress reduced the root numbers (RN), total root length (TRL), root surface area (RSA), root volume (RV) and shoot length, but increased the Na+/K+ ratio and the root diameter (RD). And all these root indices of ML04 were higher than G19 under alkaline stress treatments. The high pH of alkaline salt stress might be an important reason for the severe damage to rice root system, which further limited the rice aboveground parts growth. In conclusion, the saline-alkaline stress inhibited the rice seedling growth, and most of the indices showed that the rice mutant (ML04) was much more tolerant to alkaline stress than its wild type (G19). [ABSTRACT FROM AUTHOR]

Proline accumulation is a common physiological response of plants to various environmental stresses. However, the physiological importance of proline accumulation in stress tolerance remains controversial. Here, we examined whether proline accumulation in rice (Oryza sativa L.) seedlings is correlated with tolerance to saline-alkaline stress factors, namely, salt, alkaline and osmotic stresses, by using 25 japonica cultivars. The tolerance of seedlings to each stress treatment varied significantly among the cultivars as evaluated by membership degree (MD) of fuzzy set theory on the basis of changes in shoot length (SL), total root length (TRL), total root surface area (RSA), average root diameter (RD), total root volume (RV), and root numbers (RN), after 6 d of stress treatment. The proline levels in all thejaponica cultivars increased significantly in response to the investigated stresses. However, partial correlation analysis showed no significant correlations between the basal or elevated proline levels and tolerance to any of the investigated stress factors. These findings suggest that proline accumulation levels do not serve as reliable parameters for assessing saline-alkaline stress tolerance in rice. On the other hand, several root growth indices of rice seedlings, namely TRL, RSA, RD, RV, and RN, showed good correlations with the investigated stress tolerance, and therefore, represent a useful set of growth parameters for assessing saline-alkaline stress tolerance in rice. [ABSTRACT FROM AUTHOR]

Saline-alkaline (SA) stress is a complex effect of three main factors: ion toxicity from high salinity, alkalinity, and high osmotic pressure. In this study, we dissected response of rice (Oryza sativa L.) to above-mentioned SA stress factors simulated by using NaCl, Na2CO3, and PEG6000, respectively. Seed germination was most strongly affected by osmotic stress, followed by alkaline and salt stresses. Meanwhile, the seedling growth was most reduced under alkaline stress. The alkaline treatment significantly reduced total biomass, total root length (TRL), root surface area (RSA), root numbers (RN), and root volume (RV), while it increased root diameter (RD) and Na+/K+ ratio. Further, it caused severe damages to the root system as shown by a remarkable increase in degree of cell injury and expression of the cell death-related gene OsNAC4. On the other hand, salt stress reduced the total biomass, RSA and RV, and increased the Na+/K+ ratio, while to less extent than those under alkaline stress. These results suggest that the deleterious effect of alkaline stress on rice seedlings is due mainly to high alkalinity that induces cell injury in the root system. In contrast, the response to osmotic stress exhibited the typical adaptive responses to dehydration: reduced relative water content (RWC), RD, RV, and shoot biomass; whereas increased TRL, RSA, RN, and root biomass. In addition, we show that proline was accumulated most abundantly in response to alkaline treatment, and which was corroborated by the transcriptional induction of OsP5CS1 and OsP5CS2, the genes encoding proline carboxylate synthase. [ABSTRACT FROM AUTHOR]

In order to explore the impact of different anthropogenic disturbances on the ecological environment of natural rivers, the bacterial community in the channel sediments of the Jialing River was taken as the research object, and the high-throughput sequencing technique was used to analyze the community composition and functional changes of bacteria in the channel sediments of rivers with engineering disturbance, tributary disturbance, sand mining disturbance, reclamation disturbance, and undisturbed section. The results showed that there were significant differences in the physical and chemical properties of channel sediments and bacterial community diversity in different disturbance sections of the Jialing River ( P <0.05). The undisturbed section had the highest bacterial community diversity, whereas the sand mining disturbance and undisturbed section had the highest bacterial community uniformity, and tributary disturbance and reclamation disturbance both resulted in a decrease in bacterial community diversity and uniformity. The effect of engineering disturbance on bacterial community composition was significantly different from that of the other four disturbance sections. The dominant bacterial phyla were Proteobacteria, Actinobacteriota, Acidobacteriota, and Chloroflexi, and the dominant bacterial classes were γ -Proteobacteria, α -Proteobacteria, and Vicinamibacteria. Sand mining disturbance led to the increase in Actinobacteria, and engineering disturbance promoted the increase in Acidobacteria. Moisture content, total organic carbon, total nitrogen, and total phosphorus were the main environmental factors affecting the changes in sediment microbial communities. The bacterial communities mainly involved four categories of primary metabolic functions, including metabolism, genetic information processing, environmental information processing, and cellular processes, and 18 categories of secondary metabolic functions, such as global and overview maps, carbohydrate metabolism, amino acid metabolism, cofactor and vitamin metabolism, and energy metabolism. Human interference led to significant changes in energy metabolism, cofactor and vitamin metabolism, nucleotide metabolism, replication and repair, and translation ( P <0.05). In conclusion, anthropogenic disturbance led to the mutation of bacterial community diversity and function, which destroyed the stability of the microbial community structure in Jialing River sediments.

We present a rare case of invasive liver abscess syndrome due to Klebsiella pneumoniae (K. pneumoniae) with metastatic meningitis and septic shock. A previously healthy, 55-year-old female patient developed fever, liver abscess, septic shock, purulent meningitis and metastatic hydrocephalus. Upon admission, the clinical manifestations, laboratory and imaging examinations were compatible with a diagnosis of K. pneumoniae primary liver abscess. Her distal metastasis infection involved meningitis and hydrocephalus, which could flare abruptly and be life threatening. Even with early adequate drainage and antibiotic therapy, the patient's condition deteriorated and she ultimately died. To the best of our knowledge, this is the first case of K. pneumoniae invasive liver abscess syndrome with septic meningitis reported in mainland China. Our findings reflect the need for a better understanding of the epidemiology, risk factors, complications, comorbid medical conditions and treatment of this disease.

Aim: To investigate colorectal uptake of solid lipid nanoparticles (SLNs) in mice receiving different doses of 1,2-dimethylhydrazine (DMH) using magnetic resonance (MR) and laser-scanning confocal fluorescence microscope (LSCFM) imaging., Methods: Eight mice were sacrificed in a pilot study to establish the experimental protocol and to visualize colorectal uptake of SLNs in normal mice. Gadopentetate dimeglumine and fluorescein isothiocyanate (FITC)-loaded SLN (Gd-FITC-SLN) enemas were performed on mice receiving DMH for 10 wk (group 1, n = 9) or 16 wk (group 2, n = 7) and FITC-SLN enema was performed on 4 DMH-treated mice (group 3). Pre- and post-enema MR examinations were made to visualize the air-inflated distal colorectum. Histological and LSCFM examinations were performed to verify colorectal malignancy and to track the distribution of SLNs., Results: Homogeneous enhancement and dense fluorescence (FITC) deposition in colorectal wall were observed in normal mice and 1 DMH-treated mouse (group 1) on fluid attenuated inversion recovery (FLAIR) and LSCFM images, respectively. Heterogeneous mural enhancement was found in 6 mice (4 in group 1; 2 in group 2). No visible mural enhancement was observed in the other mice. LSCFM imaging revealed linear fluorescence deposition along the colorectal mucosa in all groups. Nine intraluminal masses and one prolapsed mass were detected by MR imaging with different enhancement modes and pathologies. Interstitial FITC deposition was identified where obvious enhancement was observed in FLAIR images. Bladder imaging agent accumulations were observed in 11 of 16 DMH-treated mice of groups 1 and 2., Conclusion: There are significant differences in colorectal uptake and distribution of SLNs between normal and DMH-treated mice, which may provide a new mechanism of contrast for MR colonography.