The rhizosphere effect of native legume Albizzia julibrissin on coastal saline soil nutrient availability, microbial modulation, and aggregate formation

Comparative analysis of crab growth performance, enzyme activity, and microbiota between rice-crab coculture and pond farming systems

Introduction

To support the sustainable development of rice and aquaculture industries, various rice-animal coculture systems have been developed. One such system, the rice-crab coculture system (RCC), has been practiced for decades in northern China. However, studies on the crab physiological status in RCC remain limited. Microorganisms play a crucial role in aquaculture by influencing animal nutrition, health, nutrient cycling, water quality, and environmental impact. Research on the gut and environmental microbiota in RCC is scarce.

Methods

This study compared the growth performance, immune and digestive enzyme activities of crabs between RCC and traditional pond farming system (PF). In addition, the microbiota in crab guts, water, and sediment from both systems was investigated using 16S rRNA gene sequencing.

Results

Crabs in RCC exhibited superior growth performance and higher enzymatic activities, including acid phosphatase (ACP), alkaline phosphatase (AKP), lipase (LPS), and trypsin (TRY). Significant differences were observed in microbiota composition across crab gut, water, and sediment samples, respectively. RCC crabs had a lower abundance of Bacteroidota and a higher abundance of Firmicutes in their gut microbiota. The RCC environment was enriched with beneficial bacteria such as Rhizobiales, Methylococcales, KD4-96, C39, Xanthomonadales, and Nitrosomonadaceae. Microbial function predictions confirmed enhanced methanotrophy and nitrogen fixation in the RCC.

Discussion

The RCC enhances the growth rate and immune capability of crabs. Crabs from RCC consume more animal-based nutrition, which results in distinct differences in gut microbiota composition and higher levels of LPS and TRY compared to those in PF. Additionally, RCC supports environmentally beneficial bacteria that contribute to greenhouse gas reduction, carbon and nitrogen fixation, organic matter decomposition, and ammonia oxidation, benefiting both the crabs and their ecosystem. These findings enhance our understanding of crab physiology and microbial communities in RCC and PF systems.

The Growth and Ion Absorption of Sesbania (Sesbania cannabina) and Hairy Vetch (Vicia villosa) in Saline Soil Under Improvement Measures

Soil salinization is a serious threat to the ecological environment and sustainable agricultural development in the arid regions of northwest China. Optimal soil salinization amelioration methods were eagerly explored under different soil salinity levels. Sesbania and hairy vetch are salt-tolerant plants, and green manure improved the saline environment. In this study, two leguminous halophytic crops, sesbania (Sesbania cannabina) and hairy vetch (Vicia villosa), were planted under different salinity levels, combined with three saline soil improvement measures, namely gravel mulching, manure application, and straw returning. No improvement measures and no salinity treatment was set as the control (CK). This study was conducted to analyze the effects of soil salinization improvement measures on the growth and ion uptake of sesbania and hairy vetch as biological measures under different soil salinity levels. Sesbania under manure application absorbed the highest soil Na+ (2.71 g kg-1) and Cl- (2.66 g kg-1) amounts at a soil salinity of 3.2 g kg-1, which was 14.7% and 10.95% higher than under gravel mulching and straw returning, respectively. Na+ and Cl- absorption of hairy vetch under manure application reached the highest value of 1.39 g kg-1 and 1.38 g kg-1 at a soil salinity of 1.6 g kg-1, which was 24.46% and 22.31% higher than under gravel mulching and straw returning, respectively. Plant height and stem diameter as well as root growth and development of sesbania and hairy vetch were limited at soil salinities greater than 1.6 g kg-1 and 0.8 g kg-1. Overall, sesbania and hairy vetch effectively absorbed both soil Na+ and Cl- under manure application, thus regulating soil salinity and reducing soil salinization. However, soil salinity levels greater than 3.2 g kg-1 and 1.6 g kg-1 not only weakened the ionic absorption capacity but also inhibited the growth and development of sesbania and hairy vetch. This study provides evidence that soil salt ion absorption by sesbania and hairy vetch is promoted effectively, ameliorating soil salinity, under manure application as compared to under gravel mulching and straw returning.

Mangrove afforestation as an ecological control of invasive Spartina alterniflora affects rhizosphere soil physicochemical properties and bacterial community in a subtropical tidal estuarine wetland

Background

The planting of mangroves is extensively used to control the invasive plant Spartina alterniflora in coastal wetlands. Different plant species release diverse sets of small organic compounds that affect rhizosphere conditions and support high levels of microbial activity. The root-associated microbial community is crucial for plant health and soil nutrient cycling, and for maintaining the stability of the wetland ecosystem.

Methods

High-throughput sequencing was used to assess the structure and function of the soil bacterial communities in mudflat soil and in the rhizosphere soils of S. alterniflora, mangroves, and native plants in the Oujiang estuarine wetland, China. A distance-based redundancy analysis (based on Bray-Curtis metrics) was used to identify key soil factors driving bacterial community structure.

Results

S. alterniflora invasion and subsequent mangrove afforestation led to the formation of distinct bacterial communities. The main soil factors driving the structure of bacterial communities were electrical conductivity (EC), available potassium (AK), available phosphorus (AP), and organic matter (OM). S. alterniflora obviously increased EC, OM, available nitrogen (AN), and NO3 --N contents, and consequently attracted copiotrophic Bacteroidates to conduct invasion in the coastal areas. Mangroves, especially Kandelia obovata, were suitable pioneer species for restoration and recruited beneficial Desulfobacterota and Bacilli to the rhizosphere. These conditions ultimately increased the contents of AP, available sulfur (AS), and AN in soil. The native plant species Carex scabrifolia and Suaeda glauca affected coastal saline soil primarily by decreasing the EC, rather than by increasing nutrient contents. The predicted functions of bacterial communities in rhizosphere soils were related to active catabolism, whereas those of the bacterial community in mudflat soil were related to synthesis and resistance to environmental factors.

Conclusions

Ecological restoration using K. obovata has effectively improved a degraded coastal wetland mainly through increasing phosphorus availability and promoting the succession of the microbial community.

Ameliorative effect of poly-γ-glutamic acid biopreparation on coastal saline soil

To investigate the effect of poly-γ-glutamic acid (γ-PGA) biopreparation on ameliorating coastal saline soil, three treatments were established: soil salt washed treatment (CK), soil salt washed with added γ-PGA (PGA), soil salt washed with added γ-PGA biopreparation (PGAB). This study determined the effects of γ-PGA on coastal saline soil by analyzing soil aggregate, soil evaporation, soil vertical water and salt distribution, and soil cation content, soil pH, soil nutrient content and soil microorganism quantity. Results showed that γ-PGA had an ameliorative effect on saline soil, with the PGAB treatment exhibiting the most pronounced ameliorative effect compared to CK. Adding PGAB reduced soil evaporation by 30.45 %, soil salt content by 27.91 %, meanwhile increasing plant height by 33.86 %, plant fresh weight by 98.54 %, soil aggregate diameter by 6.68 times, soil water content by 26.47 % (P < 0.05). Additionally, soil total nitrogen was increased by 50.0 % in PGAB treatment, and available nitrogen and phosphorus contents were increased by 1.68 times and 85.83 % (P < 0.05), respectively. Populations of soil-culturable bacteria and fungi of PGAB treatment increased by 65.96 % and 1.23 times, respectively (P < 0.05). After salt-washing process, adding PGAB improved soil physicochemical properties, which altered the ecological environment of rhizosphere soil and promoted plant growth. The results can provide a practical approach for ameliorating coastal saline soils.

The effect of AMF combined with biochar on plant growth and soil quality under saline-alkali stress: Insights from microbial community analysis

Arbuscular mycorrhizal fungi (AMF) and biochar application individually can enhance plant tolerance to saline-alkali stress and promote plant growth efficiency. However, little is known about the potential synergistic effects of their combination on improving plant growth and soil quality under saline-alkali stress. This experiment adopted the potted method to explore the effects of four treatments on switchgrass growth and soil quality: biochar (BC), Rhizophagus irregularis (Ri), biochar + Ri (BR) and a control without biochar or Ri (CK). Compared to the CK treatment, the switchgrass biomass increased by 92.4 %, 148.6 %, and 177.3 % in the BC, Ri, and BR treatment groups, respectively. Similarly, the rhizosphere soil quality index increased by 29.33 %, 22.7 %, and 49.1 % in the respective treatment groups. The BR treatment significantly altered the rhizosphere soil microbial composition and diversity. Notably, compared to the other treatments, the archaeal α-diversity in the BR group showed a significant decrease. BR treatment significantly increased the relative abundance of bacteria, fungi and archaea at the genus level (e.g., Bacillus, Trichome and candidatus_methanopenens). Network analysis showed that the complexity and closeness of interactions between different microbial taxa were stronger in the BC, Ri and BR treatments than in the CK treatment, with BR being the more prominent. In summary, biochar combined with Ri has a better effect on promoting the growth of switchgrass under saline-alkali stress, improving the quality of saline-alkali soil, and increasing soil microbial diversity. This study provides a new approach for the efficient development and utilization of saline-alkali land.

A Comparative Analysis of Bacterial and Fungal Communities in Coastal and Inland Pecan Plantations

Pecan forests (Carya illinoinensis) are significant contributors to both food and oil production, and thrive in diverse soil environments, including coastal regions. However, the interplay between soil microbes and pecan forest health in coastal environments remains understudied. Therefore, we investigated soil bacterial and fungal diversity in coastal (Dafeng, DF) and inland (Guomei, GM) pecan plantations using high-throughput sequencing. The results revealed a higher microbial diversity in the DF plantation than in the GM plantation, significantly influenced by pH and edaphic factors. The dominant bacterial phyla were Proteobacteria, Acidobacteriota and Bacteroidota in the DF plantation, and Acidobacteriota, Proteobacteria, and Verrucomicrobiota in the GM plantation. Bacillus, Nitrospira and UTCFX1 were significantly more abundant bacterial genera in DF soil, whereas Candidatus Udaeobacter, HSB_OF53-F07 and ADurbBin063-1 were more prevalent in GM soil. Basidiomycota dominated fungal sequences in the GM plantation, with a higher relative abundance of Ascomycota in the DF plantation. Significant differences in fungal genus composition were observed between plantations, with Scleroderma, Hebeloma, and Naucoria being more abundant in DF soil, and Clavulina, Russula, and Inocybe in GM soil. A functional analysis revealed greater carbohydrate metabolism potential in GM plantation bacteria and a higher ectomycorrhizal fungi abundance in DF soil. Significantly positive correlations were detected between certain bacterial and fungal genera and pH and total soluble salt content, suggesting their role in pecan adaptation to coastal environments and saline-alkali stress mitigation. These findings enhance our understanding of soil microbiomes in coastal pecan plantations, and are anticipated to foster ecologically sustainable agroforestry practices and contribute to coastal marshland ecosystem management.

Analysis of small-scale soil CO2 fluxes in an orange orchard under irrigation and soil conservative practices

The quantification of soil carbon dioxide (CO2) flux represents an indicator of the agro-ecosystems sustainability. However, the monitoring of these fluxes is quite challenging due to their high spatially-temporally variability and dependence on environmental variables and soil management practices.In this study, soil CO2 fluxes were measured using a low-cost accumulation chamber, that was realized ad hoc for the surveys, in an orange orchard managed under different soil management (SM, bare versus mulched soils) and water regime (WR, full irrigation versus regulated deficit irrigation) strategies. In particular, the soil CO2 flux measurements were acquired in discontinuous and continuous modes, together with ancillary agrometeorological and soil-related information, and then compared to the agrosystem scale CO2 fluxes measured by the eddy covariance (EC) technique.Overall significant differences were obtained for the soil CO2 discontinuous fluxes as function of the WR (0.16 ± 0.01 and 0.14 ± 0.01 mg m-2 s-1 under full irrigation and regulated deficit irrigation, respectively). For the continuous soil CO2 measurements, the response observed for the SM factor varied from year to year, indicating for the overall reference period 2022-23 higher soil CO2 flux under the mulched soils (0.24 ± 0.01 mg m-2 s-1) than under bare soil conditions (0.15 ± 0.00 mg m-2 s-1). Inter-annual variations were also observed as function of the day-of-year (DOY), the SM and their interactions, resulting in higher soil CO2 flux under the mulched soils (0.24 ± 0.02 mg m-2 s-1) than under bare soil (0.15 ± 0.01 mg m-2 s-1) in certain periods of the years, according to the environmental conditions.

Results

suggest the importance of integrating soil CO2 flux measurements with ancillary variables that explain the variability of the agrosystem and the need to conduct the measurements using different operational modalities, also providing for night-time monitoring of CO2. In addition, the study underlines that the small-scale chamber measurements can be used to estimate soil CO2 fluxes at orchard scale if fluxes are properly scaled.

Plastic footprint deteriorates dryland carbon footprint across soil-plant-atmosphere continuum

Plastic fragments are widely found in the soil profile of terrestrial ecosystems, forming plastic footprint and posing increasing threat to soil functionality and carbon (C) footprint. It is unclear how plastic footprint affects C cycling, and in particularly permanent C sequestration. Integrated field observations (including 13C labelling) were made using polyethylene and polylactic acid plastic fragments (low-, medium- and high-concentrations as intensifying footprint) landfilling in soil, to track C flow along soil-plant-atmosphere continuum (SPAC). The result indicated that increased plastic fragments substantially reduced photosynthetic C assimilation (p < 0.05), regardless of fragment degradability. Besides reducing C sink strength, relative intensity of C emission increased significantly, displaying elevated C source. Moreover, root C fixation declined significantly from 21.95 to 19.2 mg m-2, and simultaneously root length density, root weight density, specific root length and root diameter and surface area were clearly reduced. Similar trends were observed in the two types of plastic fragments (p > 0.05). Particularly, soil aggregate stability was significantly lowered as affected by plastic fragments, which accelerated the decomposition rate of newly sequestered C (p < 0.05). More importantly, net C rhizodeposition declined averagely from 39.77 to 29.41 mg m-2, which directly led to significant decline of permanent C sequestration in soil. Therefore, increasing plastic footprint considerably worsened C footprint regardless of polythene and biodegradable fragments. The findings unveiled the serious effects of plastic residues on permanent C sequestration across SPAC, implying that current C assessment methods clearly overlook plastic footprint and their global impact effects.

Techno-economic analysis of phytoremediation: A strategic rethinking

Phytoremediation is a cost-effective and environmentally sound approach, which uses plants to immobilize/stabilize, extract, decay, or lessen toxicity and contaminants. Despite successful evidence of field application, such as natural attenuations, and self-purification, the main barriers remain from a "promising" to a "commercial" approach. Therefore, the ultimate goal of this paper is to examine factors that contribute to phytoremediation's underutilization and discuss the real costs of phytoremediation when the time and land values are considered. We revisit mechanisms and processes of phytoremediation. We synthesize existing information and understanding based on previous works done on phytoremediation and its applications to provide the technical assessment and perspective views in the commercial acceptance of phytoremediation. The results show that phytoremediation is the most suitable for remote regions with low land values. Since these regions allow a longer period to be restored, land vegetation covers can be established in more or less time like natural attenuation. Since the length of phytoremediation is an inherent limitation, this inherent disadvantage limits its adoption in developed business regions, such as growing urban areas. Because high land values could not be recovered in the short term, phytoremediation is not cost-effective in those regions. We examine the potential measures that can enhance the performance of phytoremediation, such as soil amendments, and agricultural practices. The results obtained through review can clarify where/what conditions phytoremediation can provide the most suitable solutions at a large scale. Finally, we identify the main barriers and knowledge gaps to establishing a vegetation cover in large-scale applications and highlight the research priorities for increased acceptance of phytoremediation.

Effect of planting salt-tolerant legumes on coastal saline soil nutrient availability and microbial communities

Soil salinization is a serious global environmental problem affecting sustainable development of agriculture. Legumes are excellent candidates for the phytoremediation of saline soils; however, how soil microbes mediate the amelioration of coastal saline ecosystems is unknown. In this study, two salt-tolerant legumes, Glycine soja and Sesbania cannabina were planted in coastal saline soil for three years. Soil nutrient availability and microbiota structure (including bacteria, fungi, and diazotrophs) were compared between the phytoremediated soils and control soil (barren land). Planting legumes reduced soil salinity, and increased total carbon, total nitrogen, and NO3--N contents. Among the soil microbiota, some nitrogen-fixing bacteria (e.g., Azotobacter) were enriched in legumes, which were probably responsible for soil nitrogen accumulation. The complexity of the bacterial, fungal, and diazotrophic networks increased significantly from the control to the phytoremediated soils, suggesting that the soil microbial community formed closer ecological interactions during remediation. Furthermore, the dominant microbial functions were chemoheterotrophy (24.75%) and aerobic chemoheterotrophy (21.97%) involved in the carbon cycle, followed by nitrification (13.68%) and aerobic ammonia oxidation (13.34%) involved in the nitrogen cycle. Overall, our findings suggested that G. soja and S. cannabina legumes were suitable for ameliorating saline soils as they decreased soil salinity and increased soil nutrient content, with microorganisms especially nitrogen-fixing bacteria, playing an important role in this remediation process.

Characterization of endophytic bacteriome diversity and associated beneficial bacteria inhabiting a macrophyte Eichhornia crassipes

Introduction

The endosphere of a plant is an interface containing a thriving community of endobacteria that can affect plant growth and potential for bioremediation. Eichhornia crassipes is an aquatic macrophyte, adapted to estuarine and freshwater ecosystems, which harbors a diverse bacterial community. Despite this, we currently lack a predictive understanding of how E. crassipes taxonomically structure the endobacterial community assemblies across distinct habitats (root, stem, and leaf).

Methods

In the present study, we assessed the endophytic bacteriome from different compartments using 16S rRNA gene sequencing analysis and verified the in vitro plant beneficial potential of isolated bacterial endophytes of E. crassipes.

Results and discussion

Plant compartments displayed a significant impact on the endobacterial community structures. Stem and leaf tissues were more selective, and the community exhibited a lower richness and diversity than root tissue. The taxonomic analysis of operational taxonomic units (OTUs) showed that the major phyla belonged to Proteobacteria and Actinobacteriota (> 80% in total). The most abundant genera in the sampled endosphere was Delftia in both stem and leaf samples. Members of the family Rhizobiaceae, such as in both stem and leaf samples. Members of the family Rhizobiaceae, such as Allorhizobium- Neorhizobium-Pararhizobium-Rhizobium were mainly associated with leaf tissue, whereas the genera Nannocystis and Nitrospira from the families Nannocystaceae and Nitrospiraceae, respectively, were statistically significantly associated with root tissue. Piscinibacter and Steroidobacter were putative keystone taxa of stem tissue. Most of the endophytic bacteria isolated from E. crassipes showed in vitro plant beneficial effects known to stimulate plant growth and induce plant resistance to stresses. This study provides new insights into the distribution and interaction of endobacteria across different compartments of E. crassipes Future study of endobacterial communities, using both culture-dependent and -independent techniques, will explore the mechanisms underlying the wide-spread adaptability of E. crassipesto various ecosystems and contribute to the development of efficient bacterial consortia for bioremediation and plant growth promotion.

Improved effects of combined application of nitrogen-fixing bacteria Azotobacter beijerinckii and microalgae Chlorella pyrenoidosa on wheat growth and saline-alkali soil quality

Soil salinization seriously affects crop yield and soil productivity. The application of bacteria and microalgae has been considered as a promising strategy to alleviate soil salinization. However, the effect of bacteria-microalgae symbiosis on saline-alkali land is still unclear. This study evaluated the effects of Azotobacter beijerinckii, Chlorella pyrenoidosa, and their combined application on the wheat growth and saline-alkali soil improvement. The results showed that, among all the treatments, A. beijerinckii + live C. pyrenoidosa combined inoculation group (BA) had the best effect on increasing wheat plant biomass, improving salt tolerance, and improving soil fertility. The dry weight of wheat plant in the BA group increased by 66.7%, 17.4%, and 35.0%, respectively, compared with the control group (CK), A. beijerinckii inoculation group (B), and live C. pyrenoidosa inoculation group (A). The total nitrogen content of wheat plant in the BA group increased by 69.5%, 76.7%, and 71.1%, compared with the CK, B, and A group. The proline content of wheat plant in the BA group was 100% higher than that in the CK group. The N/P ratio and K/Na ratio of wheat plant increased by 157% and 12.9% in the BA group compared with the CK group, respectively, which was more conducive to alleviating nitrogen limitation and salt stress. The A. beijerinckii + live C. pyrenoidosa inoculation treatment better reduced soil pH and improved the availability of phosphorus in soil. This study illustrated the comprehensive application prospects of bacteria-microalgae interactions on wheat growth promotion and soil improvement in saline-alkali land, and provided a new effective strategy for improving saline-alkali soil quality and increasing crop productivity.

The altered metabolites contributed by dysbiosis of gut microbiota are associated with microbial translocation and immune activation during HIV infection

Background

The immune activation caused by microbial translocation has been considered to be a major driver of HIV infection progression. The dysbiosis of gut microbiota has been demonstrated in HIV infection, but the interplay between gut microbiota and its metabolites in the pathogenesis of HIV is seldom reported.

Methods

We conducted a case-controlled study including 41 AIDS patients, 39 pre-AIDS patients and 34 healthy controls. Both AIDS group and pre-AIDS group were divided according to clinical manifestations and CD4 + T cell count. We collected stool samples for 16S rDNA sequencing and untargeted metabolomics analysis, and examined immune activation and microbial translocation for blood samples.

Results

The pre-AIDS and AIDS groups had higher levels of microbial translocation and immune activation. There were significant differences in gut microbiota and metabolites at different stages of HIV infection. Higher abundances of pathogenic bacteria or opportunistic pathogen, as well as lower abundances of butyrate-producing bacteria and bacteria with anti-inflammatory potential were associated with HIV severity. The metabolism of tryptophan was disordered after HIV infection. Lower level of anti-inflammatory metabolites and phosphonoacetate, and higher level of phenylethylamine and polyamines were observed in HIV infection. And microbial metabolic pathways related to altered metabolites differed. Moreover, disrupted metabolites contributed by altered microbiota were found to be correlated to microbial translocation and immune activation.

Conclusions

Metabolites caused by dysbiosis of gut microbiota and related metabolic function are correlated to immune activation and microbial translocation, suggesting that the effect of microbiota on metabolites is related to intestinal barrier disruption in HIV infection.

Seasonal changes driving shifts of aquatic rhizosphere microbial community structure and the functional properties

Ecological floating beds could enable roots to become suspended and this allowed submerged roots to harbour various types of microbes. But, there was a lack of systematic research on microbial community structure changes and the influencing mechanisms. In this study, the ecological floating beds were constructed using selected plants [Cyperus involucratus Rottboll (Cyp), Thalia dealbata Fraser (Tha) and Iris tectorum Maxim (Iri)] that was compared with a control group [static water (S)]. The results showed that the highest abundance and diversity of root microbial communities were found in autumn, with the dominant taxa being Proteobacteria, Actinobacteriota, Cyanobacteria, Chloroflexi, Firmicutes, Bacteroidota, and Acidobacteriota. The microbial communities of Tha and Cyp groups greatly overlapped, while the Iri and control groups exhibited distinctly diverse communities. The root microbial populations of the same plant also reflected a large change in different seasons. Conversely, photosynthetic autotrophs and specialized anaerobes were more inclined to thrive at higher temperatures and lower DO concentrations and then they gradually became the dominant species. Microbial co-occurrences of the Tha and control groups were complex and showed both cooperation and competition. In addition, TOC was an important environmental factor that shaped the microbial community structures and DO changed the microbial community by affecting the abundance of aerobic and anaerobic bacteria. Microorganisms showed potential for degradation and metabolism of non-food substances with low/no corresponding metabolic pathways.

Halophytes increase rhizosphere microbial diversity, network complexity and function in inland saline ecosystem

Salinization is an important global environmental problem influencing sustainable development of terrestrial ecosystems. Salt-tolerant halophytes are often used as a promising approach to remedy the saline soils. Yet, how rhizosphere microbes' association and functions vary with halophytes in saline ecosystems remains unclear, restricting our ability to assess the role of halophytes in remedying saline ecosystems. Herein, we examined bacterial and fungal diversities, compositions, and co-occurrence networks in the rhizospheres of six halophytes and bulk soils in a semiarid inland saline ecosystem, and related these parameters to microbial functions. The microbiomes were more diverse and complex and microbial activity and residues were higher in rhizospheres than bulk soils. The connections of taxa in the rhizosphere microbial communities increased with fungi-fungi and bacteria-fungi connections and fungal diversity. The proportion of the fungi-related central connections were larger in rhizospheres (13-73%) than bulk soils (3%). Moreover, microbial activity and residues were significantly correlated with microbial composition and co-occurrence network complexity. These results indicated that enhanced association between fungi and bacteria increased microbial co-occurring network complexity in halophytes rhizosphere, which contributed to the higher microbial functions (microbial activities and residue) in this inland saline ecosystem.

Regulating Root Fungal Community Using Mortierella alpina for Fusarium oxysporum Resistance in Panax ginseng

Plant-associated microbes play important roles in plant health and disease. Mortierella is often found in the plant rhizosphere, and its possible functions are not well known, especially in medical plants. Mortierella alpina isolated from ginseng soil was used to investigate its effects on plant disease. The promoting properties and interactions with rhizospheric microorganisms were investigated in a medium. Further, a pot experiment was conducted to explore its effects on ginseng root rot disease. Physicochemical properties, high-throughput sequencing, network co-occurrence, distance-based redundancy analysis (db-RDA), and correlation analysis were used to evaluate their effects on the root rot pathogen. The results showed that Mortierella alpina YW25 had a high indoleacetic acid production capacity, and the maximum yield was 141.37 mg/L at 4 days. The growth of M. alpina YW25 was inhibited by some probiotics (Bacillus, Streptomyces, Brevibacterium, Trichoderma, etc.) and potential pathogens (Cladosporium, Aspergillus, etc.), but it did not show sensitivity to the soil-borne pathogen Fusarium oxysporum. Pot experiments showed that M. alpina could significantly alleviate the diseases caused by F. oxysporum, and increased the available nitrogen and phosphorus content in rhizosphere soil. In addition, it enhanced the activities of soil sucrase and acid phosphatase. High-throughput results showed that the inoculation of M. alpina with F. oxysporum changed the microbial community structure of ginseng, stimulated the plant to recruit more plant growth-promoting bacteria, and constructed a more stable microbial network of ginseng root. In this study, we found and proved the potential of M. alpina as a biocontrol agent against F. oxysporum, providing a new idea for controlling soil-borne diseases of ginseng by regulating rhizosphere microorganisms.

Effects of Temperature and Nitrogen Application on Carbon and Nitrogen Accumulation and Bacterial Community Composition in Apple Rhizosphere Soil

Malus sieversii grows on the slopes of the Tianshan Mountains in Xinjiang where the difference in daily temperature is significant. In recent years, the rhizosphere soil health of Malus sieversii has been severely impacted by anthropogenic disturbance and pathogenic infestation. The soil nutrient content and soil microorganism diversity are the main components of soil health. Low temperature has negative effects on soil bacterial community structure by inhibiting the accumulation of carbon and nitrogen. However, the effects of temperature and nitrogen application on soil carbon and nitrogen accumulation and the bacterial community composition in the rhizosphere soil of Malus sieversii are unclear. We set two temperature levels, i.e., low temperature (L) and room temperature (R), combined with no nitrogen (N0) and nitrogen application (N1) to explore the response of plant carbon and nitrogen uptake, rhizosphere soil carbon and nitrogen accumulation and bacterial community composition to temperature and nitrogen fertilization. At the same temperature level, plant 13C abundance (P-Atom13C), plant 15N absolute abundance (P-Con15N), soil 15N abundance (S-Atom15N) and soil urease, protease and glutaminase activities were significantly higher under nitrogen application compared with the no-nitrogen application treatment. The bacterial community diversity and richness indices of the apple rhizosphere soil in the N1 treatment were higher than those in the N0 treatment. The relative abundances of Actinobacteria, Rhodopseudomonas, and Bradyrhizobium were higher in the LN1 treatment than in the LN0 treatment. Redundancy analysis (RDA) showed that plant 13C absolute abundance (P-Con13C) and plant 15N absolute abundance (P-Con15N) were the main factors affecting the soil bacterial community composition. In summary, Nitrogen application can alleviate the effects of low temperature stress on the soil bacterial community and is of benefit for the uptakes of carbon and nitrogen in Malus sieversii plants.