Responses of the Soil Microbial Community to Salinity Stress in Maize Fields

Biochar and saline soil: mitigation strategy by incapacitating the ecological threats to agricultural land

Soil salinity caused a widespread detrimental issue that hinders productivity in agriculture and ecological sustainability, while waste-derived soil amendments like biochar have drawn attention for their capacity to act as a mitigating agent, by enhancing the physical and chemical features of soil, and contributing to the recovery of agricultural waste resources. However, the information concerning biochar and salinity which affect the physicochemical characteristics of soils, crop physiology, and growth is limited. To investigate whether biochar mitigates the salinity stress on wheat crop seedlings, we grow them with salinity stress (120 mM), and biochar (20 tons ha-1), and its interactive effects. The soil properties of soil organic carbon (SOC), soil organic matter (SOM), dissolved organic carbon (DOC), and soil available phosphorus (SAP) decreased in the saline soil by 36.71%, 46.97%, 26.31%, and 15.00%, while biochar treatment increased SOC, DOC, and SAP contents by 7.42%, 31.57%, and 15.00%, respectively. On the other hand, dissolved organic nitrogen (DON) contents decreased in all the treatments compared to the control. The root growth traits, SPAD values, leaf nitrogen, photosynthetic parameters, antioxidant enzymes, and reactive oxygen species decreased in the saline treatment while increasing in the biochar and interactive treatment. Thus, these activities resulted in higher leaves and root biomass in the biochar treatment alone and interactive treatment of salinity and biochar. According to principal component analysis, redundancy analysis, and the mantel test, using biochar in conjunction with salinity treatment was found to be more effective than salinity treatment alone. The results of this study suggest that biochar can be used as a sustainable agricultural technique and a means of mitigation agent by lowering soil salinity while increasing the biomass of crops.

Effects of Fishery Utilization on the Physicochemical Index and Microbial Community Composition in Saline-Alkaline Water

Fishery utilization of idle saline-alkaline water resources offers various benefits including reducing surrounding soil salinity, improving the ecological environment, increasing arable land area, and providing economic advantages to the fishery industry. However, for decades, the characteristics and regulatory mechanisms of microbial communities that affect fishery utilization have not been clear, which restricts their application. In this study, high-throughput 16S rRNA amplicon sequencing was employed to analyze the bacterial community in these water resources. The sequencing yielded high-quality sequences (2,765,063), resulting in the identification of 18,761 bacterial operational taxonomic units (OTUs). Analysis revealed that the type of saline-alkaline water had a more significant influence on the bacterial community compared to seasonal variations within the aquaculture period. The Chao index for saline-alkaline ponds (ASW) was significantly lower (P < 0.05) than for still saline-alkaline water (SSW) and flowing saline-alkaline water (FSW), while the Shannon index for ASW was also significantly lower (P < 0.05) compared to FSW. When comparing ASW to nonaquaculture saline-alkaline water, a decrease in Proteobacteria to 26.87% was noted, particularly α-proteobacteria and γ-proteobacteria, accompanied by a rapid increase in Actinobacteria and Cyanobacteria to 28.60%. Networkx analysis further revealed that ASW significantly increased competition and amensalism from secondary saline-alkaline water microorganisms, resulting in a more solitary bacterial community composition as an adaptive strategy to cope with intense environmental pressures. Key bacterial species such as Pseudomonas, Hydrogenophaga, and Flavobacterium were found to be involved in hydrogen-cycling, nitrogen-cycling, and carbon-cycling, respectively, with all three exhibiting high abundance in FSW. Consequently, FSW demonstrates significant advantages in biogeochemical cycling, pollutant degradation, and the utilization of indigenous probiotic bacteria. Although the surface of abandoned secondary saline-alkaline land was covered with white salt particles, the fishery utilization of saline-alkaline water with low salinity levels (4.0-5.5), and the presence of nitrate and phosphate were identified as primary determinants of bacterial community composition. Nevertheless, a comparison of coastal high-salinity ponds indicated that salinity still selectively affects bacterial communities to some extent. Overall, our study provides valuable insights into the microbial regulation of nitrite during saline-alkaline water aquaculture, thereby aiding in the efficient utilization of secondary saline-alkaline water resources for fisheries.

Enhancing Maize Productivity and Soil Health under Salt Stress through Physiological Adaptation and Metabolic Regulation Using Indigenous Biostimulants

Salinity poses a persistent threat to agricultural land, continuously jeopardizing global food security. This study aimed to enhance sweet corn (SC) fitness under varying levels of salinity using indigenous biostimulants (BioS) and to assess their impacts on plant performance and soil quality. The experiment included control (0 mM NaCl), moderate stress (MS; 50 mM NaCl), and severe stress (SS; 100 mM NaCl) conditions. Indigenous biostimulants, including compost (C), Bacillus sp., Bacillus subtilis (R), and a consortium of arbuscular mycorrhizal fungi (A) were applied either individually or in combination. Growth traits, physiological and biochemical parameters in maize plants, and the physico-chemical properties of their associated soils were assessed. SS negatively affected plant growth and soil quality. The RC combination significantly improved plant growth under SS, increasing aerial (238%) and root (220%) dry weights compared to controls. This treatment reduced hydrogen peroxide by 54% and increased peroxidase activity by 46% compared to controls. The indigenous biostimulants, particularly C and R, enhanced soil structure and mineral composition (K and Mg). Soil organic carbon and available phosphorus increased notably in C-treated soils. Furthermore, RC (437%) and CAR (354%) treatments exhibited a significant increase in glomalin content under SS. Indigenous biostimulants offer a promising strategy to mitigate salinity-related threats to agricultural land. They improve plant fitness, fine-tune metabolism, and reduce oxidative stress. In addition, the biostimulants improved the soil structure and mineral composition, highlighting their potential for reconstitution and sustainability in salt-affected areas. This approach holds promise for addressing salinity-related threats to global food security.

Exploring the potential of halotolerant bacteria from coastal regions to mitigate salinity stress in wheat: physiological, molecular, and biochemical insights

Salinity stress, a significant global abiotic stress, is caused by various factors such as irrigation with saline water, fertilizer overuse, and drought conditions, resulting in reduced agricultural production and sustainability. In this study, we investigated the use of halotolerant bacteria from coastal regions characterized by high salinity as a solution to address the major environmental challenge of salinity stress. To identify effective microbial strains, we isolated and characterized 81 halophilic bacteria from various sources, such as plants, rhizosphere, algae, lichen, sea sediments, and sea water. We screened these bacterial strains for their plant growth-promoting activities, such as indole acetic acid (IAA), phosphate solubilization, and siderophore production. Similarly, the evaluation of bacterial isolates through bioassay revealed that approximately 22% of the endophytic isolates and 14% of rhizospheric isolates exhibited a favorable influence on seed germination and seedling growth. Among the tested isolates, GREB3, GRRB3, and SPSB2 displayed a significant improvement in all growth parameters compared to the control. As a result, these three isolates were utilized to evaluate their efficacy in alleviating the negative impacts of salt stress (150 mM, 300 mM, and seawater (SW)) on the growth of wheat plants. The result showed that shoot length significantly increased in plants inoculated with bacterial isolates up to 15% (GREB3), 16% (GRRB3), and 24% (SPSB2), respectively, compared to the control. The SPSB2 strain was particularly effective in promoting plant growth and alleviating salt stress. All the isolates exhibited a more promotory effect on root length than shoot length. Under salt stress conditions, the GRRB3 strain significantly impacted root length, leading to a boost of up to 6%, 5%, and 3.8% at 150 mM, 300 mM, and seawater stress levels, respectively. The bacterial isolates also positively impacted the plant's secondary metabolites and antioxidant enzymes. The study also identified the WDREB2 gene as highly upregulated under salt stress, whereas DREB6 was downregulated. These findings demonstrate the potential of beneficial microbes as a sustainable approach to mitigate salinity stress in agriculture.

Microbial life in 25-m-deep boreholes in ancient permafrost illuminated by metagenomics

This study describes the composition and potential metabolic adaptation of microbial communities in northeastern Siberia, a repository of the oldest permafrost in the Northern Hemisphere. Samples of contrasting depth (1.75 to 25.1 m below surface), age (from ~ 10 kyr to 1.1 Myr) and salinity (from low 0.1-0.2 ppt and brackish 0.3-1.3 ppt to saline 6.1 ppt) were collected from freshwater permafrost (FP) of borehole AL1_15 on the Alazeya River, and coastal brackish permafrost (BP) overlying marine permafrost (MP) of borehole CH1_17 on the East Siberian Sea coast. To avoid the limited view provided with culturing work, we used 16S rRNA gene sequencing to show that the biodiversity decreased dramatically with permafrost age. Nonmetric multidimensional scaling (NMDS) analysis placed the samples into three groups: FP and BP together (10-100 kyr old), MP (105-120 kyr old), and FP (> 900 kyr old). Younger FP/BP deposits were distinguished by the presence of Acidobacteriota, Bacteroidota, Chloroflexota_A, and Gemmatimonadota, older FP deposits had a higher proportion of Gammaproteobacteria, and older MP deposits had much more uncultured groups within Asgardarchaeota, Crenarchaeota, Chloroflexota, Patescibacteria, and unassigned archaea. The 60 recovered metagenome-assembled genomes and un-binned metagenomic assemblies suggested that despite the large taxonomic differences between samples, they all had a wide range of taxa capable of fermentation coupled to nitrate utilization, with the exception of sulfur reduction present only in old MP deposits.

Mitigating soil salinity stress with titanium gypsum and biochar composite materials: Improvement effects and mechanism

Titanium gypsum and biochar are considered effective amendments for mitigating soil salinity stress. However, the knowledge is inadequate regarding their efficiency and application as an improvement. In this study, TG-B composite was prepared by using industrial by-products titanium gypsum and biochar as raw materials and then modified by ball milling method, to characterize its microscopic characteristics and explore the improvement effect on saline-alkali soil and plant growth. Besides, we explored the mechanism of TG-B in improving saline-alkali soil and the dynamic balance of the solution reaction process. Our results showed that the CaSO₄·2H₂O particles in TG-B were finer, dispersed evenly, and contacted fully with soil gelatinous particles, which was more conducive to the improvement of saline-alkali soil. The results of TG-B with different ball milling ratios and different materials dosages indicated that the application rate of TG-B was 5%, and the optimum ratio of TG-B was TG: B (mass ratio) = 10:1, with the best soil improvement effect. The pot experiment proved that the indicators of indicating soil salinity such as pH, EC, SAR, and soluble Na⁺ decreased by 20.74%, 77.24%, 68.77%, and 44.70%, respectively, thus playing a good role in improving saline-alkali soil. In addition, pot experiments demonstrated that compared with the control group, the soil porosity and soil moisture content in the TG-B group increased by 15.95% and 38.71%, respectively, and further improve the structure and diversity of soil bacterial community when compared with titanium gypsum and biochar alone. Finally, the application of TG-B promoted the germination and growth of rice significantly through the synergistic effects of composite material components. These results all suggested that the application of TG-B was an effective strategy to improve soil salinity and promote plant growth. Therefore, it might provide new insights into the utilization of solid waste resources to improve saline-alkali lands.

Effects of multiwalled carbon nanotube and Bacillus atrophaeus application on crop root zone thermal characteristics of saline farmland

Presently, the effects of crop roots on crop root zone thermal characteristics are poorly understood, and new fertilizers are rarely considered from the perspective of changing crop root zone thermal characteristics. This study explored the effect of applying two new fertilizers, multiwalled carbon nanotubes (MWCNTs) and Bacillus atrophaeus (B. atrophaeus), on the crop root zone thermal characteristics of saline farmland soils through in situ measurements. The results showed that MWCNTs and B. atrophaeus could indirectly affect crop root zone thermal characteristics by changing the crop root growth. Combined application of MWCNTs and B. atrophaeus could promote both to induce positive effects, promote crop root growth, and significantly alleviate the adverse effects of soil salinization. The thermal conductivity and heat capacity of the shallow root zone were reduced due to the presence of crop roots, while the opposite was true in the deep root zone. For example, the thermal conductivity of the 0-5 cm rich root zone in the MWCNT treatment was 0.8174 W m^-1 ·K^-1, and the thermal conductivity of the poor root zone was 13.42% higher than that of the rich root zone. MWCNTs and B. atrophaeus can also change the spatial distribution of soil moisture, soil salt, and soil particle size characteristics by influencing the root-soil interactions and indirectly affecting crop root zone thermal characteristics. In addition, MWCNTs and B. atrophaeus could directly affect the root zone thermal characteristics by changing the soil properties. The higher the soil salt content was, the more obvious the effect of the MWCNTs and B. atrophaeus on the crop root zone thermal characteristics. The thermal conductivity and heat capacity of the crop root zone were positively correlated with the soil moisture content, soil salt content and soil particle specific surface area and negatively correlated with the soil particle size and the fresh and dry root weights. In summary, MWCNTs and B. atrophaeus significantly affected crop root zone thermal characteristics directly and indirectly and could adjust the temperature of the crop root zone.

Crop diversity promotes the recovery of fungal communities in saline-alkali areas of the Western Songnen Plain

Introduction

Phytoremediation is an effective strategy for saline land restoration. In the Western Songnen Plain, northeast China, soil fungal community recovery for saline phytoremediation has not been well documented among different cropping patterns. In this study, we tested how rotation, mixture, and monoculture cropping patterns impact fungal communities in saline-alkali soils to assess the variability between cropping patterns.

Methods

The fungal communities of the soils of the different cropping types were determined using Illumina Miseq sequencing.

Results

Mixture and rotation promoted an increase in operational taxonomic unit (OTU) richness, and OTU richness in the mixture system decreased with increasing soil depth. A principal coordinate analysis (PCoA) showed that cropping patterns and soil depths influenced the structure of fungal communities, which may be due to the impact of soil chemistry. This was reflected by soil total nitrogen (TN) and electrical conductivity (EC) being the key factors driving OTU richness, while soil available potassium (AK) and total phosphorus (TP) were significantly correlated with the relative abundance of fungal dominant genus. The relative abundance of Leptosphaerulina, Alternaria, Myrothecium, Gibberella, and Tetracladium varied significantly between cropping patterns, and Leptosphaerulina was significantly associated with soil chemistry. Soil depth caused significant differences in the relative abundance of Fusarium in rotation and mixture soils, with Fusarium more commonly active at 0-15 cm deep soil. Null-model analysis revealed that the fungal community assembly of the mixture soils in 0-15 cm deep soil was dominated by deterministic processes, unlike the other two cropping patterns. Furthermore, fungal symbiotic networks were more complex in rotation and mixture than in monoculture soils, reflected in more nodes, more module hubs, and connectors. The fungal networks in rotation and mixture soils were more stable than in monoculture soils, and mixture networks were obviously more connected than rotations. FUNGuild showed that the relative proportion of saprotroph in rotation and mixture was significantly higher than that in monocultures. The highest proportion of pathotroph and symbiotroph was exhibited in rotation and mixture soils, respectively.

Discussion

Overall, mixture is superior to crop rotation and monocultures in restoring fungal communities of the saline-alkali soils of the Western Songnen Plain, northeast China.

Effects of saline-alkali stress on bacterial and fungal community diversity in Leymus chinensis rhizosphere soil

The salinization of grassland in arid and semi-arid areas is a serious environmental issue in China. Halophytes show extreme salt tolerance and are grown in saline-alkaline environments. Their rhizosphere microorganisms contribute significantly to plant stress tolerance. To study bacterial and fungal community structure changes in Chinese ryegrass (Leymus chinensis) rhizosphere soil under salt and alkali stress, pot experiments were conducted with different salt and alkali stress intensities. High-throughput sequencing was conducted, and the microbial diversity, community structure, and driving factors were analyzed in rhizosphere soil. The salinization of grassland in arid and semi-arid areas is a serious environmental issue in China. Halophytes show extreme salt tolerance and grow in saline-alkaline environments. A total of 549 species of bacteria from 28 phyla and 250 species from 11 phyla of fungi were detected in the rhizosphere soil of Leymus chinensis with different saline-alkali gradients. Alpha diversity analysis along saline-alkali gradients showed that bacterial community richness and diversity were the highest in the moderate saline-alkali group (pH = 8.28, EC = 160.4 μS·cm^-1), while fungi had high richness and diversity in the control group (pH = 7.35, EC = 134.5 μS·cm^-1). The bacteriophyta Proteobacteria, Acidobacteria, Plantomycetes, and the eumycota Ascomycota, Basidiomycota, and Glomeromycota were found with relative abundances of more than 10%. Saline-alkali gradients had significant effects on the abundance of the bacterial and fungal groups in the rhizosphere. The distribution of bacterial colony structure was not significant at the species level (P > 0.05). However, there were significant differences in the distribution of fungal structure and considerable differences in the composition of fungal species among the moderate saline-alkali group, severe saline-alkali group, and control group (P < 0.05). Correlation analysis showed that the bacterial phylum Gemmatimonadetes had a highly significant positive correlation with pH and EC (P < 0. 01). Saline-alkali stress significantly inhibited the abundance of the bacteria Latescibacteria, Cyanobacteria, and Bacteroides, and the fungi Zoopagomycota, Mortierllomycota, and Cryptomycota (P < 0. 05). Compared with fungi, bacterial community composition was most closely correlated with soil salinization. This report provided new insights into the responses of relationships between rhizosphere soil microorganisms and salt and alkali tolerance of plants.

Irrigation water salinity structures the bacterial communities of date palm (Phoenix dactylifera)-associated bulk soil

The irrigation of date palms (Phoenix dactylifera) with saline groundwater is routinely practiced in the agroecosystems of arid environments because of freshwater scarcity. This leads to salts deposition in topsoil layers and increases soil salinization. However, how different irrigation sources affect soil microbiota is poorly understood. Bulk soil samples were collected from date farms receiving non-saline water and saline groundwater to examine bacterial communities using metabarcoding. Overall, bacterial diversity measures (Shannon diversity index, richness, and evenness) did not vary between irrigation sources. Bacterial communities were structured based on irrigation water sources and were significantly associated with their electrical conductivity. Of 5,155 operational taxonomic units (OTUs), 21.3% were unique to soil irrigated with saline groundwater, 31.5% received non-saline water irrigation, and 47.2% were shared. The Proteobacteria abundance was higher in soil under saline groundwater irrigation while Actinobacteriota abundance was lower. A compositional shift at the genera level was also evident; the abundance of Subgroup_10 and Mycobacterium was higher under saline groundwater irrigation. Mycobacterium was a key indicator of OTU under saline groundwater irrigation while Solirubrobacter was an indicator of non-saline water irrigation. Functional gene analyses showed enrichment of fatty acid, cell wall, and starch biosynthesis pathways in soil under saline groundwater irrigation. These findings provide insights into how "salinity filtering" influences bacterial communities, key taxa, and the potential metabolic function in soil under increasing irrigation water salinities, and have broad implications for arid agroecosystems.

Salinity of irrigation water selects distinct bacterial communities associated with date palm (Phoenix dactylifera L.) root

Saline water irrigation has been used in date palm (Phoenix dactylifera L.) agriculture as an alternative to non-saline water due to water scarcity in hyper-arid environments. However, the knowledge pertaining to saline water irrigation impact on the root-associated bacterial communities of arid agroecosystems is scarce. In this study, we investigated the effect of irrigation sources (non-saline freshwater vs saline groundwater) on date palm root-associated bacterial communities using 16S rDNA metabarcoding. The bacterial richness, Shannon diversity and evenness didn’t differ significantly between the irrigation sources. Soil electrical conductivity (EC) and irrigation water pH were negatively related to Shannon diversity and evenness respectively, while soil organic matter displayed a positive correlation with Shannon diversity. 40.5% of total Operational Taxonomic Units were unique to non-saline freshwater irrigation, while 26% were unique to saline groundwater irrigation. The multivariate analyses displayed strong structuring of bacterial communities according to irrigation sources, and both soil EC and irrigation water pH were the major factors affecting bacterial communities. The genera Bacillus, Micromonospora and Mycobacterium were dominated while saline water irrigation whereas contrasting pattern was observed for Rhizobium, Streptomyces and Acidibacter. Taken together, we suggest that date-palm roots select specific bacterial taxa under saline groundwater irrigation, which possibly help in alleviating salinity stress and promote growth of the host plant.

The Effects of Drainage on the Soil Fungal Community in Freshwater Wetlands

Wetland drainage has been intensively implemented globally, and it has exerted significant effects on wetland ecosystems. The effects of wetland drainage on the soil fungal community remain to be clarified. Soil samples were collected at depths of 0–5 and 5–10 cm in freshwater Phragmites australis wetlands to investigate changes in the fungal community before and after drainage (termed FW and DFW, respectively) using high-throughput sequencing of the fungal-specific internal transcribed spacer 1 (ITS1) gene region. No significant differences in the α diversity of the soil fungal community were found in 0–10 cm soils between FW and DFW (p &gt; 0.05), except for the abundance-based coverage estimator (ACE) and Chao1 indices in 5–10 cm soils. Significantly higher values of ACE and Chao1 in 5–10 cm soils in FW than in DFW indicated that wetland drainage may reduce fungal community richness in 5–10 cm soils. Ascomycota, Sordariomycetes, and Cephalothecaceae were the dominant fungal phylum, class, and family, respectively, in 0–5 and 5–10 cm soils of both FW and DFW, representing as high as 76.17, 58.22, and 45.21% of the fungal community in 5–10 FW soils, respectively. Saprotrophic fungi predominated in both FW and DFW. Drainage altered both the fungal community structure and some edaphic factors. Mantel tests and Spearman correlation analyses implied that edaphic factors [i.e., soil organic matter (SOM), electronic conductivity (EC), pH, and clay] also affected soil fungal community structure. Overall, wetland drainage altered the community structure of the fungal community in the freshwater wetlands.

Bacillus atrophaeus WZYH01 and Planococcus soli WZYH02 Improve Salt Tolerance of Maize (Zea mays L.) in Saline Soil

With the increasing shortage of land resources and people's attention to the ecological environment, the application of microbial fertilizer with natural soil microorganisms as the main component has attracted increasing attention in saline agriculture. In this study, two salt-tolerant strains, YL07 (Bacillus atrophaeus) and YL10 (Planococcus soli), were isolated from maize (Zea mays L.) rhizosphere soil with a saturated conductivity (EC_e) of 6.13 dS/m and pH of 8.32 (Xinjiang, China). The effects of B. atrophaeus WZYH01 (YL07) and Planococcus soli WZYH02 (YL10) on the growth and development of maize (Zea mays L.) under salt stress (EC_e = 5.9 dS/m) were further studied. The results showed that compared with uninoculation, inoculation with B. atrophaeus WZYH01 and Planococcus soli WZYH02 significantly improved maize growth performance, biomass yield, and antioxidant levels under salt stress, and the effect of Planococcus soli WZYH02 was more prominent than the effect of B. atrophaeus WZYH01. Moreover, inoculation with B. atrophaeus WZYH01 and Planococcus soli WZYH02 protected maize from salt stress by regulating plant hormone [IAA and abscisic acid (ABA)] levels and increasing nutrient acquisition. In addition, the tested strains were most efficient for maize growth and health, increasing the content of K⁺ accompanied by an effective decrease in Na⁺ in maize tissues. The transcription levels of salt tolerance genes (ZMNHX1, ZMNHX2, ZMHKT, ZMWRKY58, and ZMDREB2A) in inoculated maize were also dramatically higher than the transcription levels of the specified salt tolerance genes in uninoculated maize. In conclusion, B. atrophaeus WZYH01 and Planococcus soli WZYH02 can alleviate the harmful effects of salt stress on crop growth, thereby promoting sustainable agricultural development.