Saline-alkali stress reduces soil bacterial community diversity and soil enzyme activities

Investigating the Mechanism of Cadmium-Tolerant Bacterium Cellulosimicrobium and Ryegrass Combined Remediation of Cadmium-Contaminated Soil

Cadmium (Cd) pollution has been rapidly increasing due to the global rise in industries. Cd not only harms the ecological environment but also endangers human health through the food chain and drinking water. Therefore, the remediation of Cd-polluted soil is an imminent issue. In this work, ryegrass and a strain of Cd-tolerant bacterium were used to investigate the impact of inoculated bacteria on the physiology and biochemistry of ryegrass and the Cd enrichment of ryegrass in soil contaminated with different concentrations of Cd (4 and 20 mg/kg). The results showed that chlorophyll content increased by 24.7% and 41.0%, while peroxidase activity decreased by 56.7% and 3.9%. In addition, ascorbic acid content increased by 16.7% and 6.3%, whereas glutathione content decreased by 54.2% and 6.9%. The total Cd concentration in ryegrass increased by 21.5% and 10.3%, and the soil's residual Cd decreased by 86.0% and 44.1%. Thus, the inoculation of Cd-tolerant bacteria can improve the antioxidant stress ability of ryegrass in Cd-contaminated soil and change the soil's Cd form. As a result, the Cd enrichment in under-ground and above-ground parts of ryegrass, as well as the biomass of ryegrass, is increased, and the ability of ryegrass to remediate Cd-contaminated soil is significantly improved.

Assessing the biodiversity of rhizosphere and endophytic fungi in Knoxia valerianoides under continuous cropping conditions

BACKGROUND

Rhizosphere and endophytic fungi play important roles in plant health and crop productivity. However, their community dynamics during the continuous cropping of Knoxia valerianoides have rarely been reported. K. valerianoides is a perennial herb of the family Rubiaceae and has been used in herbal medicines for ages. Here, we used high-throughput sequencing technology Illumina MiSeq to study the structural and functional dynamics of the rhizosphere and endophytic fungi of K. valerianoides.

RESULTS

The findings indicate that continuous planting has led to an increase in the richness and diversity of rhizosphere fungi, while concomitantly resulting in a decrease in the richness and diversity of root fungi. The diversity of endophytic fungal communities in roots was lower than that of the rhizosphere fungi. Ascomycota and Basidiomycota were the dominant phyla detected during the continuous cropping of K. valerianoides. In addition, we found that root rot directly affected the structure and diversity of fungal communities in the rhizosphere and the roots of K. valerianoides. Consequently, both the rhizosphere and endophyte fungal communities of root rot-infected plants showed higher richness than the healthy plants. The relative abundance of Fusarium in two and three years old root rot-infected plants was significantly higher than the control, indicating that continuous planting negatively affected the health of K. valerianoides plants. Decision Curve Analysis showed that soil pH, organic matter (OM), available K, total K, soil sucrase (S_SC), soil catalase (S_CAT), and soil cellulase (S_CL) were significantly related (p < 0.05) to the fungal community dynamics.

CONCLUSIONS

The diversity of fungal species in the rhizosphere and root of K. valerianoides was reported for the first time. The fungal diversity of rhizosphere soil was higher than that of root endophytic fungi. The fungal diversity of root rot plants was higher than that of healthy plants. Soil pH, OM, available K, total K, S_CAT, S_SC, and S_CL were significantly related to the fungal diversity. The occurrence of root rot had an effect on the community structure and diversity of rhizosphere and root endophytic fungi.

Exploring Phosphate Solubilizing Bacterial Communities in Rhizospheres of Native and Exotic Forage Grasses in Alkaline-Sodic Soils of the Flooding Pampa

The flooding pampa is one of the most important cattle-raising regions in Argentina. In this region, natural pastures are dominated by low-productivity native grass species, which are the main feed for livestock. In this context, previous studies in the region with the subtropical exotic grass Panicum coloratum highlight it as a promising species to improve pasture productivity. Cultivable phosphate solubilizing bacteria (PSB) communities associated to native (Sporobolus indicus) and exotic (Panicum coloratum) forage grasses adapted to alkaline-sodic soils of the flooding pampa were analyzed. PSB represented 2-14% of cultivable rhizobacteria and Box-PCR fingerprinting revealed a high genetic diversity in both rhizospheres. Taxonomic identification by MALDI-TOF showed that PSB populations of P. coloratum and S. indicus rhizospheres are dominated by the phylum Proteobacteria (92,51% and 96,60% respectively) and to a lesser extent (< 10%), by the phyla Actinobacteria and Firmicutes. At the genus level, both PSB populations were dominated by Enterobacter and Pseudomonas. Siderophore production, nitrogen fixation, and indoleacetic acid production were detected in a variety of PSB genera of both plant species. A higher proportion of siderophore and IAA producers were associated to P. coloratum than S. indicus, probably reflecting a greater dependence of the exotic species on rhizospheric microorganisms to satisfy its nutritional requirements in the soils of the flooding pampa. This work provides a novel knowledge about functional groups of bacteria associated to plants given that there are no previous reports dedicated to the characterization of PSB rhizosphere communities of S indicus and P coloratum. Finally, it should be noted that the collection obtained in this study can be useful for the development of bioinputs that allow reducing the use of chemical fertilizers, providing sustainability to pasture production systems for livestock.

Ecological characteristics of sugar beet plant and rhizosphere soil in response to high boron stress: A study of the remediation potential

High boron (B) stress degrades the soil environment and reduces plant productivity. Sugar beet has a high B demand and potential for remediation of B-toxic soils. However, the mechanism regarding the response of sugar beet plants and rhizosphere soil microbiome to high B stress is not clear. In the potted soil experiment, we set different soil effective B environments (0.5, 5, 10, 30, 50, and 100 mg kg-1) to study the growth status of sugar beets under different B concentrations, as well as the characteristics of soil enzyme activity and microbial community changes. The results showed that sugar beet growth was optimal at 5 mg kg-1 of B. Exceeding this concentration the tolerance index decreased. The injury threshold EC20 was reached at an available B concentration of 35.8 mg kg-1. Under the treatment of 100 mg kg-1, the B accumulation of sugar beet reached 0.22 mg plant-1, and the tolerance index was still higher than 60%, which had not yet reached the lethal concentration of sugar beet. The abundance of Acidobacteriota, Chloroflexi and Patescibacteria increased, which was beneficial to the resistance of sugar beet to high B stress. In summary, under high B stress sugar beet had strong tolerance, enhanced capacity for B uptake and enrichment, and changes in soil microbial community structure. This study provides a theoretical basis for clarifying the mechanism of sugar beet resistance to high B stress and soil remediation.

Ginger polysaccharide alleviates the effects of acute exposure to carbonate in crucian carp (Carassius auratus) by regulating immunity, intestinal microbiota, and intestinal metabolism

Alkaline stress poses a significant challenge to the healthy growth of fish. Ginger polysaccharide (GP) is one of the main active substances in ginger and has pharmacological effects, such as anti-oxidation and immune regulation. However, the physiological regulatory mechanism of GP addition to diet on alkalinity stress in crucian carp remains unclear. This study aimed to investigate the potential protective effects of dietary GP on antioxidant capacity, gene expression levels, intestinal microbiome, and metabolomics of crucian carp exposed to carbonate (NaHCO3). The CK group (no GP supplementation) and COG group (NaHCO3 stress and no GP supplementation) were set up. The GPCS group (NaHCO3 stress and 0.4% GP supplementation) was stressed for seven days. Based on these data, GP significantly increased the activities of total antioxidant capacity (T-AOC), superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-PX), acid phosphatase (ACP), and alkaline phosphatase (AKP) in carp under alkalinity stress (p < 0.05) and decreased the activity of malon dialdehyde (MDA) (p < 0.05). GP restored the activity of GSH-PX, ACP, and AKP to CK levels. The expression levels of tumor necrosis factor β (TGF-β), tumor necrosis factor-alpha (TNF-α), interferon-gamma (IFN-γ), and interleukin 8 (IL-8) genes were decreased, and the expression levels of determination factor kappa-B (NF-κB) and interleukin 10 (IL-10) genes were increased (p < 0.05). Based on 16 S rRNA high-throughput sequencing, GP improved the changes in the intestinal microbial diversity and structural composition of crucian carp caused by NaHCO3 exposure. In particular, GP increased the relative abundance of Proteobacteria and Bacteroidetes and decreased the relative abundance of Actinobacteria. The metabolic response of GP to NaHCO3 exposed crucian carp guts was studied using LC/MS. Compared to the COG group, the GPCS group had 64 different metabolites and enriched 10 metabolic pathways, including lipid metabolism, nucleotide metabolism, and carbohydrate metabolism. The addition of GP to feed can promote galactose metabolism and provide an energy supply to crucian carp, thus alleviating the damage induced by alkalinity stress. In conclusion, GP can mitigate the effects of NaHCO3 alkalinity stress by regulating immune function, intestinal flora, and intestinal metabolism in crucian carp. These findings provide a novel idea for studying the mechanism of salt-alkali tolerance in crucian carp by adding GP to feed.

The potential and prospects of modified biochar for comprehensive management of salt-affected soils and plants: A critical review

Soil salinization has become a global problem that threatens farmland health and restricts crop production. Salt-affected soils seriously restrict the development of agricultural, mainly because of sodium ion (Na+) toxicity, nutrient deficiency, and structural changes in the soil. Biochar is a carbon (C)-based substance produced by heating typical biomass waste at high temperatures in anaerobic circumstances. It has high cation exchange capacity (CEC), adsorption capacity, and C content, which is often used as a soil amendment. Biochar generally reduces the concentration of Na+ in soil colloids through its strong adsorption, or uses the calcium (Ca) or magnesium (Mg) rich on its surface to exchange sodium ions (Ex-Na) from soil colloids through cation exchange to accelerate salt leaching during irrigation. Nowadays, biochar is widely used for acidic soils improvement due to its alkaline properties. Although the fact that biochar has gained increasing attention for its significant role in saline alkali soil remediation, there is currently a lack of systematic research on biochar improvers and their potential mechanisms for identifying physical, chemical, and biological indicators of soil eco-environment assessment and plant growth conditions affected by salt stress. This paper reviews the preparation, modification, and activation of biochar, the effects of biochar and its combination with beneficial salt-tolerant strains on salt-affected soils and plant growth. Finally, the limitations, benefits, and future needs of biochar-based soil health assessment technology in salt-affected soils and plant were discussed. This article elaborates on the future opportunities and challenges of biochar in the treatment of saline land, and a green method was provided for the integrate control to salt-affected soils.

Inoculation of cadmium-tolerant bacteria to regulate microbial activity and key bacterial population in cadmium-contaminated soils during bioremediation

The perennial ryegrass Lolium perenne can be used in conjunction with cadmium (Cd)-tolerant bacteria such as Cdq4-2 (Enterococcus spp.) for bioremediation of Cd-contaminated soil. In this study, a theoretical basis was provided to increase the efficiency of L. perenne remediation of Cd-contaminated soil using microorganisms to maintain the stability of the soil microbiome. The experimental design involved three treatment groups: CK (soil without Cd addition) as the control, 20 mg·kg-1 Cd-contaminated soil, and 20 mg·kg-1 Cd-contaminated soil + Cdq4-2, all planted with L. perenne. The soil was collected on day 60 to determine the soil microbial activity and bacterial community structure and to analyze the correlation between soil variables, the bacterial community, available Cd content in the soil, Cd accumulation, and L. perenne growth. The soil microbial activity and bacterial community diversity decreased under Cd stress, and the soil microbial community composition was changed; while inoculation with Cdq4-2 significantly increased soil basal respiration and the activities of urease, invertase, and fluorescein diacetate (FDA) hydrolase by 83.65%, 79.72%, 19.88%, and 96.15% respectively; and the stability of the community structure was also enhanced. The Actinobacteriota biomass, the amount of available Cd, and the above- and belowground Cd content of L. perenne were significantly negatively correlated with the total phosphorus, total potassium, and pH. The activity of urease, invertase, and FDA hydrolase were significantly positively correlated with the biomasses of Acidobacteriota and L. perenne and significantly negatively correlated with the Chloroflexi biomass. Further, the available soil Cd content and the above- and belowground Cd levels of L. perenne were significantly positively correlated with the Actinobacteriota biomass and significantly negatively correlated with the Gemmatimonadetes biomass. Overall, inoculating Cd-tolerant bacteria improved the microbial activity, diversity, and abundance, and changed the microbial community composition, facilitating the remediation of Cd-contaminated soil by L. perenne.

Evaluation of the evolutionary genetics and population structure of Culex pipiens pallens in Shandong province, China based on knockdown resistance (kdr) mutations and the mtDNA-COI gene

BACKGROUND

Mosquitoes are important vectors for a range of diseases, contributing to high rates of morbidity and mortality in the human population. Culex pipiens pallens is dominant species of Culex mosquito in northern China and a major vector for both West Nile virus and Bancroftian filariasis. Insecticide application were largely applied to control the mosquito-mediated spread of these diseases, contributing to increasing rates of resistance in the mosquito population. The voltage-gated sodium channel (Vgsc) gene is the target site of pyrethroids, and mutations in this gene cause knockdown resistance (kdr). While these kdr mutations are known to be critical to pyrethroid resistance, their evolutionary origins remain poorly understood. Clarifying the origins of these mutations is potential to guide further vector control and disease prevention efforts. Accordingly, the present study was designed to study the evolutionary genetics of kdr mutations and their association with the population structure of Cx. p. pallens in Shandong province, China.

METHODS

Adult Culex females were collected from Shandong province and subjected to morphological identification under a dissection microscope. Genomic DNA were extracted from the collected mosquitoes, the Vgsc gene were amplified via PCR and sequenced to assess kdr allele frequencies, intron polymorphisms, and kdr codon evolution. In addition, population genetic diversity and related population characteristics were assessed by amplifying and sequencing the mitochondrial cytochrome C oxidase I (COI) gene.

RESULTS

Totally, 263 Cx. p. pallens specimens were used for DNA barcoding and sequencing analyses to assess kdr allele frequencies in nine Culex populations. The kdr codon L1014 in the Vgsc gene identified two non-synonymous mutations (L1014F and L1014S) in the analyzed population. These mutations were present in the eastern hilly area and west plain region of Shandong Province. However, only L1014F mutation was detected in the southern mountainous area and Dongying city of Shandong Province, where the mutation frequency was low. Compared to other cities, population in Qingdao revealed significant genetic differentiation. Spatial kdr mutation patterns are likely attributable to some combination of prolonged insecticide-mediated selection coupled with the genetic isolation of these mosquito populations.

CONCLUSIONS

These data suggest that multiple kdr alleles associated with insecticide resistance are present within the Cx. p. pallens populations of Shandong Province, China. The geographical distributions of kdr mutations in this province are likely that the result of prolonged and extensive insecticide application in agricultural contexts together with frequent mosquito population migrations. In contrast, the low-frequency kdr mutation detected in central Shandong Province populations may originate from the limited selection pressure in this area and the relative genetic isolation. Overall, the study compares the genetic patterns revealed by a functional gene with a neutral marker and demonstrates the combined impact of demographic and selection factors on population structure.