Maize Rhizosphere Research Articles

Establishment and Effect of a Protist Consortium on the Maize Rhizosphere

Protists are abundant in the rhizosphere, and protist inoculation onto plants has revealed protists’ roles in plant growth and development, disease suppression, and relationships with plant-beneficial bacteria. In this study, we evaluated the establishment of an 18-member defined protist consortium after inoculation onto germinated maize seedlings, along with the effects on the bacterial populations in the rhizosphere. Inoculated protists established a community that could be detected in the rhizosphere 3 weeks after inoculation. Plants inoculated with the protist consortium developed a bacterial community structure similar to that of plants inoculated with protist-free rhizosphere bacteria but different from that of uninoculated plants. This indicates that the protist cultures introduced rhizosphere-competent bacteria to the seedling. We also observed a plant growth phenotype, as inoculation with rhizosphere bacteria suppressed plant growth in the absence, but not the presence, of protists. Maize inoculated with an antibiotic-treated protist had lower biomass than plants inoculated with an untreated protist, indicating that growth promotion by protists depended on bacteria in the protist culture microbiome. This study shows that inoculation of germinated seeds establishes protist and bacterial communities on maize roots and that plant-detrimental effects of rhizosphere bacteria can be mitigated by the presence of protists.

Prospects of iron solubilizing Bacillus species for improving growth and iron in maize (Zea mays L.) under axenic conditions

Iron (Fe) deficiency in calcareous soils is a significant agricultural challenge, affecting crop productivity and nutritional quality. This study aimed to isolate, characterize, and evaluate Fe solubilizing rhizobacterial isolates from maize rhizosphere in calcareous soils as potential biofertilizers. Forty bacterial isolates coded as SG1, SG2, …, SG40 were isolated and screened for siderophore production, with ten showing significant Fe solubilizing capabilities. These isolates were further assessed for phosphate solubilization and exopolysaccharides production. The selected bacterial isolates were also screened under axenic conditions for their ability to improve maize growth. The isolates SG8, SG13, SG24, SG30 and SG33 significantly enhanced growth parameters of maize. Notably, SG30 showed highest increment in shoot length (58%), root length (54%), root fresh and dry biomass (67% and 76%), SPAD value (67%), relative water contents (69%), root surface area (61%), and Fe concentration in shoots (79%) as compared to control. The biochemical characterization of these strains showed that all these strains have capability to solubilize insoluble phosphorus, produce indole-3-acetic acid (IAA), and ammonia with catalase, urease and protease activity. Molecular identification through 16s rRNA gene sequencing confirmed high similarity (99.7–100%) of the selected isolates to various Bacillus species, including B. pyramidoids, B. firmicutes, and B. cereus. The study provides a strong base for developing eco-friendly, cost-effective biofertilizers to address Fe deficiency in crops and promote sustainable agriculture.

Deciphering Nitrogen Stress Responses in Maize Rhizospheres: Comparative Transcriptomics of Monocropping and Intercropping Systems

A well-developed rhizospheric system is crucial for maize to adapt to environmental stresses, thereby enhancing yield and quality. However, nitrogen (N) stress significantly impedes rhizospheric development and growth in maize. The genetic responses of maize’s rhizosphere to N stress under monocropping systems with exogenous inorganic N fertilization and intercropping systems reliant on biological N fixation are not well understood, especially regarding common and specific response genes. Therefore, through transcriptomic analysis, this study systematically investigated the gene expression and molecular responses of maize’s rhizosphere under two N supply regimes to N stress. The results showed that N stress generated 196 common and 3350 specific differentially expressed genes across the two systems, with the intercropping system exhibiting a stronger specific response. KEGG analysis revealed that the common genes, though few, are involved in key pathways essential for crop growth. Maize monocropping specific differentially expressed genes (MM) were enriched in pathways related to membrane lipids, cell wall formation, and intracellular signaling, while maize/alfalfa intercropping specific differentially expressed genes (MA) were linked to stress resistance through the glutathione metabolic pathway. WGCNA analysis identified five co-expression modules (CM). MA significantly increased the transcription factor families and structural domains directly targeting rhizospheric growth and development genes, including AP2, GRAS, Cys2His2 Zinc Finger, and LBD in CM blue. Conversely, MM significantly increased the transcription factor families and NAC structural domain targeting the promoters of N transporter protein genes in CM pink. This study emphasizes the importance of both common and specific genes in maintaining maize growth under suboptimal N supply in monocropping and intercropping systems.

Cover crop monocultures and mixtures enhance bacterial abundance and functionality in the maize root zone

Abstract Cover cropping is an effective method to protect agricultural soils from erosion, promote nutrient and moisture retention, encourage beneficial microbial activity, and maintain soil structure. Re-utilization of winter cover crop root channels by maize roots during summer allows the cash crop to extract resources from distal regions in the soil horizon. In this study, we investigated how cover cropping during winter followed by maize (Zea mays L.) during summer affects the spatiotemporal composition and function of the bacterial communities in the maize rhizosphere and surrounding soil samples using quantitative PCR, 16S rRNA gene amplicon sequencing, and metaproteomics. We found that the bacterial community differed significantly among cover crop species, soil depths, and maize growth stages. Bacterial abundance increased in reused root channels, and it continued to increase as cover crop diversity changed from monocultures to mixtures. Mixing Fabaceae with Brassicaceae or Poaceae enhanced the overall contributions of several steps of the bacterial carbon (C) and nitrogen (N) cycles, especially glycolysis and the pentose phosphate pathway. The deeper root channels of Fabaceae and Brassicaceae as compared to Poaceae corresponded to higher bacterial 16S rRNA gene copy numbers and improved community presence in the subsoil regimes, likely due to the increased availability of root exudates secreted by maize roots. In conclusion, root channel reuse improved the expression of metabolic pathways of the C and N cycles and the bacterial communities, which is beneficial to the soil and to the growing crops.

Bacillus velezensis B105-8, a potential and efficient biocontrol agent in control of maize stalk rot caused by Fusarium graminearum.

Maize stalk rot (MSR), caused by Fusarium graminearum, is the most serious soil borne disease in maize production, seriously affecting maize yield and quality worldwide. Microbial biocontrol agents are the best means of controlling MSR and reducing the use of chemical fungicides, such as Bacillus spp. In the study, a soil-isolated strain B105-8 was identified as B. velezensis (accession No. PP325775.1 and No. PP869695.1), demonstrated a broad spectrum against various pathogens causing maize diseases, which effectively controlled MSR, exhibited a high control efficacy of more than 60% and growth-promoting effect in the pot plant. B105-8 could effectively improve soil urease (S-UE), invertase (S-SC), and catalase (S-CAT) activities. S-NP activity showed an initial increase with a peak of 20,337 nmol/h/g, followed by a decrease, but activity remained significantly better than control treatment with chemical fungicides. The application of B105-8 repaired the damage caused by F. graminearum on soil activity. The antifungal compound B-1, extracted from B105-8, was purified using a protein purifier, revealing inhibitory effects against F. graminearum. Mass spectrometry analysis indicated the potential presence of C14 Bacillomycin, C15 Iturin, C15 Mycosubtilin, C17, and C15 fengycin in B-1. In pot experiments, a 5 μL/mL concentration of B-1 exhibited 69% control on MSR, enhancing maize root elongation, elevation, and fresh weight. At 10 μL/mL, B-1 showed 89.0 and 82.1% inhibition on spore production and mycelial growth, causing hyphal deformities. This study presents the innovative use of B. velezensis, isolated from maize rhizosphere in cold conditions to effectively control MSR caused by F. graminearum. The findings highlight the remarkable regional and adaptive characteristics of this strain, making it an excellent candidate to fight MSR in diverse environments. In conclusion, B. velezensis B105-8 demonstrated potential as a biocontrol agent for MSR.

Trichoderma Rhizosphere Soil Improvement: Regulation of Nitrogen Fertilizer in Saline–Alkali Soil in Semi-Arid Region and Its Effect on the Microbial Community Structure of Maize Roots

In order to reduce the actual impact of a saline–alkali environment on maize production in semi-arid areas, it is particularly important to use the combined fertilization strategy of Trichoderma microbial fertilizer and nitrogen fertilizer. The purpose of this study was to investigate the effects of different concentrations of nitrogen fertilizer combined with Trichoderma on improving the structural characteristics and ecological functions of maize rhizosphere microbial community in semi-arid saline–alkali soil. Through the microbiome analysis of maize rhizosphere soil samples with 60 kg N·ha−1 (N1) and 300 kg N·ha−1 (N2) nitrogen fertilizer combined with Trichoderma (T1) and without Trichoderma (T0), we found that the combination of Trichoderma and different concentrations of nitrogen fertilizer significantly affected the structure of bacterial and fungal communities. The results of this study showed that the combination of Trichoderma and low-concentration nitrogen fertilizer (N1T1) could improve soil nutritional status and enhance its productivity potential, revealing the relationship between beneficial and harmful fungal genera, microbial diversity and abundance, and crop biomass, which is of great significance for improving agricultural production efficiency and sustainable development.

Intercropping of tobacco and maize at seedling stage promotes crop growth through manipulating rhizosphere microenvironment.

Changes in the rhizosphere microbiome and metabolites resulting from crop intercropping can significantly enhance crop growth. While there has been an increasing number of studies on various crop combinations, research on the intercropping of tobacco and maize at seedling stage remains limited. This study is the first to explore rhizosphere effects of intercropping between tobacco and maize seedling stages, we analyzed the nitrogen, phosphorus and potassium nutrients in the soil, and revealed the important effects on soil microbial community composition and metabolite profiles, thereby regulating crop growth and improving soil balance. Compared with mono-cropping, intercropping increased the biomass of the two crops and promoted the nutrient absorption of nitrogen, phosphorus and potassium. Under intercropping conditions, the activities of sucrase, catalase and nitrate reductase in tobacco rhizosphere soil and the content of available potassium, the activities of nitrate reductase and acid phosphatase in maize rhizosphere soil were significantly increasing. Rhizosphere soil bacterial and fungal communities such as Sphingomonas, Massilia, Humicola and Penicillium respond differently to crop planting patterns, and soil dominant microbial communities are regulated by environmental factors such as pH, Organic Matter, Available Potassium, Nitrate Reductase, and Urease Enzyme. Network analysis showed that soil microbial communities were more complex after intercropping, and the reciprocal relationship between bacteria and fungi was enhanced. The difference of metabolites in soil between intercropping and monocropping system was mainly concentrated in galactose metabolism, starch and sucrose metabolism pathway, and the content of carbohydrate metabolites was significantly higher than that of monocropping soil. Key metabolites such as D-Sucrose, D-Fructose-6-Phosphate, D-Glucose-1-Phosphatel significantly influence the composition of dominant microbial communities such as Sphingomonas and Penicillium. This study explained the effects of intercropping between flue-cured tobacco and maize on the content of soil metabolites and soil microbial composition in rhizosphere soil, and deepened the understanding that intercropping system can improve the growth of flue-cured crops seedlings through rhizosphere effects.

Decoupled fungal and bacterial functional responses to biochar amendment drive rhizosphere priming effect on soil organic carbon mineralization

The application of biochar to soil is widely recognized as a promising strategy for enhancing the accumulation and stability of soil organic carbon (SOC), which is crucial in mitigating climate change. However, the influence of interactions between plants and biochar on soil microbial communities and their involvement in SOC mineralization and stability remains unclear. This understanding is essential for optimizing carbon (C) sequestration in systems involving plants, soil, and biochar. In this study, employing a 13C natural abundance approach, we investigated the effect of biochar on the maize rhizosphere priming effect (RPE) in paddy soil. We also examined alterations in microbial communities and functional genes related to C degradation and fixation. Over the 99 days of maize growth, biochar application increased RPE and total SOC while decreasing dissolved organic C. It also elevated soil pH, resulting in shifts in fungal and bacterial community structure, favoring oligotrophic species. Fungal and bacterial assemblies were dominated by deterministic and stochastic processes, respectively. While the abundance of fungal guilds varied irregularly, bacterial guilds were uniformly enriched under biochar-plant interactions. Functional traits such as ecoenzymatic activities, bacterial guilds, and functional genes predominantly affected RPE under biochar application. Bacterial functional genes associated with C degradation and fixation were concurrently enhanced with biochar application. Our results indicate that interactions between plants and biochar can enhance native SOC mineralization and accumulation in a short timeframe by modulating functional traits of soil microorganisms, particularly the bacterial community involved in C degradation and fixation.Graphical

Optimizing nitrogen fertilization in maize: the impact of nitrification inhibitors, phosphorus application, and microbial interactions on enhancing nutrient efficiency and crop performance.

Despite the essential role of nitrogen fertilizers in achieving high crop yields, current application practices often exhibit low efficiency. Optimizing nitrogen (N) fertilization in agriculture is, therefore, critical for enhancing crop productivity while ensuring sustainable food production. This study investigates the effects of nitrification inhibitors (Nis) such as Dimethyl Pyrazole Phosphate (DMPP) and Dimethyl Pyrazole Fulvic Acid (DMPFA), plant growth-promoting bacteria inoculation, and phosphorus (P) application on the soil-plant-microbe system in maize. DMPFA is an organic nitrification inhibitor that combines DMP and fulvic acid for the benefits of both compounds as a chelator. A comprehensive rhizobox experiment was conducted, employing varying levels of P, inoculant types, and Nis, to analyze the influence of these factors on various soil properties, maize fitness, and phenotypic traits, including root architecture and exudate profile. Additionally, the experiment examined the effects of treatments on the bacterial and fungal communities within the rhizosphere and maize roots. Our results showed that the use of Nis improved plant nutrition and biomass. For example, the use of DMPFA as a nitrification inhibitor significantly improved phosphorus use efficiency by up to 29%, increased P content to 37%, and raised P concentration in the shoot by 26%, compared to traditional ammonium treatments. The microbial communities inhabiting maize rhizosphere and roots were also highly influenced by the different treatments. Among them, the N treatment was the major driver in shaping bacterial and fungal communities in both plant compartments. Notably, Nis reduced significantly the abundance of bacterial groups involved in the nitrification process. Moreover, we observed that each experimental treatment employed in this investigation could select, promote, or reduce specific groups of beneficial or detrimental soil microorganisms. Overall, our results highlight the intricate interplay between soil amendments, microbial communities, and plant nutrient dynamics, suggesting that Nis, particularly DMPFA, could be pivotal in bolstering agricultural sustainability by optimizing nutrient utilization.

Impact of arbuscular mycorrhizal fungi on maize rhizosphere microbiome stability under moderate drought conditions.

With an alarming increase in global greenhouse gas emissions, unstable weather conditions are significantly impacting agricultural production. Drought stress is one of the frequent consequences of climate change that affects crop growth and yield. Addressing this issue is critical to ensure stable crop productivity under drought conditions. Arbuscular mycorrhizal fungi (AMF) establish symbiotic relationships with plants and enhance their resistance to adverse conditions. Effects of arbuscular mycorrhizal associations on the rhizosphere microbiome and root transcriptome under drought conditions have not been explored. Here, we investigated the effects of AMF and drought stress on rhizosphere microorganisms and root transcriptome of maize plants grown in chernozem soil. We used high-throughput sequencing data of bacterial 16S rRNA and fungal internal transcribed spacer regions (ITS) to identify rhizosphere microorganisms. Transcriptomic data were used to assess gene expression in maize plants under different treatments. Our results show that AMF maintains the composition of maize rhizosphere microorganisms under drought stress. In particular, the bacterial and fungal phyla maintained were Actinomycetes and Ascomycota, respectively. Transcriptomic data indicated that AMF influenced gene expression in maize plants under drought stress. Under drought stress, the expression of SWEET13, CHIT3, and RPL23A was significantly higher in the presence of AMF than it was without AMF inoculation, indicating better sugar transport, reduced malondialdehyde accumulation, and improved water use efficiency in AMF-inoculated maize plants. These findings suggest that AMF can enhance the resistance of maize to moderate drought stress by stabilising plant physical traits, which may help maintain the structure of the rhizosphere microbial community. This study provides valuable theoretical insights that should aid the utilization of AMF in sustainable agricultural practices.

Pb pollution altered bacterial community assembly and predicted functions in aggregate-size fractions of agricultural soil near a smelter

In order to investigate the impact of Pb smelter pollution on bacterial community structure, diversity and function at the microenvironment scale, the maize rhizosphere soils subjected to long-term (over 20 years) Pb smelter pollution were collected, and bacterial communities and putative functions associated with different aggregate-size fractions were identified by 16S rRNA sequencing, KEGG and FAPROTAX. The results showed that Pb pollution significantly diminished bacterial diversity, and prompted a shift in the bacterial communities toward more oligotrophic taxa, including Firmicutes, Chloroflexi, and Gemmatimonadetes. Furthermore, the functional subcategories related to cell motility and energy metabolism, as well as the functional groups involved in carbon (C), nitrogen (N), and sulfur (S) cycles, exhibited a marked decline under Pb pollution. At the aggregate scale, distinct differences were observed in the composition of bacterial communities across silt and clay (<250 μm), micro-aggregates (250∼1000 μm), and macro-aggregates (1000∼2000 μm and >2000 μm) in uncontaminated soils. However, Pb pollution disrupted these original distinctions among bacterial communities in various aggregate-size fractions, with a decreased abundance of dominant Proteobacteria and an increased abundance of Firmicutes in large aggregates. While the differences in bacterial functional groups in aggregate-size fractions were also detected. The functional groups associated with carbon (C) and nitrogen (N) cycles were significantly enriched in the macro-aggregates (1000∼2000 μm) in uncontaminated soils. However, similar with the change of bacterial community structure, most functional groups (except for chemoheterotrophy) in aggregate-size fractions exhibited no significant differences under Pb exposure. Our results suggested that Pb pollution altered bacterial community structure and predicted functions at the aggregate level, and showed greater negative effects on bacterial functions in macro-aggregates (1000∼2000 μm). This study can provide a new perspective for the influence of Pb smelter pollution on soil aggregate microenvironment.

Auxin-Mediated Modulation of Maize Rhizosphere Microbiome: Insights from Azospirillum Inoculation and Indole-3-Acetic Acid Treatment

Auxin-Mediated Modulation of Maize Rhizosphere Microbiome: Insights from Azospirillum Inoculation and Indole-3-Acetic Acid Treatment

Maize/soybean intercropping with nitrogen supply levels increases maize yield and nitrogen uptake by influencing the rhizosphere bacterial diversity of soil.

Intercropping practices play a crucial role in enhancing and maintaining the biodiversity and resiliency of agroecosystems, as well as promoting stable and high crop yields. Yet the relationships between soil nitrogen, microbes, and yield in maize cultivated under maize/soybean intercropping systems remain unclear. To fill that knowledge gap, here we collected maize rhizosphere soil at the staminate stage after 6 consecutive years of maize/soybean intercropping, to investigate how intercropping and nitrogen application rates affected nitrogen utilization by crops and soil microbial community composition and function. We also examined correlations of those responses with yields, to clarify the main ways that yield is enhanced via intercropping and by nitrogenous fertilizer gradient changes generated by different nitrogen application rates. The amount of applied fertilizer was 240 kg N ha-1 was best for obtaining a high maize yield and also led to the greatest nitrogen-use efficiency and bacterial diversity. Under the same N application rate, intercropping increased the maize yield by 31.17% and soil nitrogen (total, ammonium and nitrate nitrogen) by 14.53%, on average, in comparison to monocropping. The enrichment of Gemmatimonas and Bradyrhizobium significantly increased the soil nitrogen content, and a greater relative abundance of Sphingomonas and Gemmatimonas increased the maize yield, whereas enrichment of Candidatus_Udaeobacter and Bradyrhizobium decreased it. The benefits of intercropping mainly arise from augmenting the abundance of beneficial microorganisms and enhancing the efficiency of N use by crop plants. This study's findings are of key importance to bolster the stability of agro-ecosystems, to guide the scientific rational use of nitrogen fertilizers, and to provide a sound theoretical basis for achieving the optimalmanagement of intensive crop-planting patterns and green sustainable development.

Rhizosphere flavonoids alleviates the inhibition of soybean nodulation caused by shading under maize-soybean strip intercropping

The flavonoids produced by legume roots are signal molecules that induce nod genes for symbiotic rhizobium. Nevertheless, the promoting effects of flavonoids in root exudates in intercropping system on soybean nodulation are still unknown. A two years of field experiments was carried with maize soybean strip intercropping, i.e., the interspecific row spacing of 30 cm (MS30), 45 cm (MS45), 60 cm (MS60), and sole soybean/maize:SS/MM, and root interaction, i.e., root no barrier (NB) and root polythene-plastic barrier (PB), to evaluate relationships between flavonoids in root exudates and nodulation. We found that root-root interaction between soybean and maize enhances the nodules number and fresh weight in intercropped soybean. This enhancement increase gradually with expansion of interspecific distance. Proportion of nodules with diameter greater than 0.4cm was higher in intercropped soybean with NB than with PB. The expressions of nodules-related genes (GmENOD40, GmNIN2b and GmEXPB2) were up-regulated. Furthermore, compared with monocropping, isoflavones secretion of soybean roots reduced, flavonoids and flavonols secretion of maize and soybean roots increased under intercropping. The secretion of differential metabolites of flavonoids in the rhizosphere of maize and soybean declined with root barrier. The expressions of GmCHS8 and GmIFS1 in soybean roots were up-regulated and GmICHG was down-regulated under root interaction. The most of the flavonoids and flavonol compounds were positively correlated with nodule diameter. The nodules number, the nodules fresh weight and the proportion of nodules with a diameter greater than 0.2 cm increased in different genotypes of soybean treated with maize root exudate, which promoted the improvement of nitrogen fixation capacity. Therefore, maize-soybean strip intercropping combined with reasonable spacing to enhance the positive effect of underground root interaction, and improve the nodulation and nitrogen fixation capacity of intercropping soybean.

Novel insights into the factors influencing rhizosphere reactive oxygen species production and their role in polycyclic aromatic hydrocarbons transformation

Reactive oxygen species (ROS) are recognised as pivotal biogeochemical process drivers. However, the factors influencing ROS production in the rhizosphere and their role in pollutant transformation remain elusive. We investigated ROS with a focus on spatiotemporal variations in superoxide radicals (O2•−), hydrogen peroxide (H2O2), and hydroxyl radicals (•OH) in the rhizosphere of maize during root development, and elucidated the impact of environmental conditions on ROS production. In-situ visualisation by fluorescence imaging showed that ROS hotspots gradually shifted from seminal to lateral roots during maize growth, indicating that newly developed roots are the major contributors to ROS production. The three types of ROS contents changed with root growth, suggesting that root development regulates ROS production. The ROS contents reached a maximum at 25 °C and 45% maximum field capacity. Both ambient temperature and soil moisture indirectly influenced ROS production by regulating the release of root exudates to induce changes in water-soluble phenols and dissolved organic carbon (DOC). In contrast, ROS content gradually increased with oxygen availability, which directly mediated ROS generation by acting as a precursor. More interestingly, the presence of polycyclic aromatic hydrocarbons (PAHs) significantly enhanced ROS generation, which further promoted PAH removal with a contribution of 31.4–43.3%. These findings provide new insights into the occurrence, distribution, and environmental effects of ROS in the rhizosphere.

Benefit and risk: Keystone biomes in maize rhizosphere associated with crop yield under different fertilizations

The highly diverse beneficial and deleterious microbes in the rhizosphere influence plant growth and crop production in agricultural ecosystems. However, our understanding of the relationships between beneficial and risky phylotypes in the rhizosphere, and plant growth, in addition to their potentially varied response to different fertilization treatments in black soils, remains poor. Here, we investigated variations in multitrophic (e.g., bacteria, fungi, invertebrates, and protists) community composition and diversity under different five-year fertilization treatments, and identified the potential beneficial and potential risky keystone multitrophic biota in maize rhizosphere and bulk soils based on ecological networks and soil food web structure. Bacteria and protist community compositions exhibited greater variations under different fertilization regimes when compared with those of fungi and invertebrates. In addition, two keystone phylotype groups associated with crop yield and soil function were detected, and the potential beneficial keystone phylotypes exhibited higher relative abundances in C-fixation, N-fixation, and P-mineralization genes; conversely, the potential risky keystone phylotypes were associated with denitrification and nitrate reduction genes, and included more potential fungal pathogens. Furthermore, structural equation modeling results indicated that organic amendments, particularly cow manure, could improve crop yield by enriching beneficial keystone phylotypes and suppressing risky keystone phylotypes. Altogether, the results of the present study highlight the critical roles of rhizosphere biota in food production, and identify keystone phylotypes that are beneficial or harmful to crop production and soil function, which could facilitate the conservation of beneficial biota and the early detection of potential pathogens, as well as the exploitation of beneficial biota to increase crop yield.

Differential recruitment of plant growth-promoting bacteria community by soybean rhizosphere in no-tillage and integrated crop-livestock

Agricultural practices influence plant-microbe interactions in the rhizosphere and, particularly can drive the recruitment of plant growth-promoting bacteria (PGPB). This study assessed the PGPB community in soil under no-tillage (NT) and in the rhizosphere of maize and grass under integrated cro-livestock (ICL) to evaluate their influence on the recruitment of PGPB in the rhizosphere of soybean. Soil samples from the soybean rhizosphere under NT and ICL were collected and compared to samples collected from bulk soil and the rhizosphere of maize and grass in ICL, using the 16 S rRNA approach. The structure of the PGPB community differed (21.8% of variation) when comparing the rhizosphere of soybean in NT and ICL. The soybean rhizosphere in NT enriched distinct PGPB compared to those observed in ICL. The proportion of specialist PGPB was higher in the rhizosphere of soybean in ICL (33.8%) than in NT (26.5%). Regardless of the agricultural system, the rhizosphere of soybean showed a similar number of nodes, but ICL promoted a higher number of edges in the soybean rhizosphere. Bacillus and Mycobacterium were identified as the main keystone taxa in the rhizosphere of soybean in NT. In contrast, Streptomyces and Sphingomonas were keystone taxa in the rhizosphere of soybean in ICL. This study demonstrated distinct recruitment of PGPB by the rhizosphere of soybean based on agricultural systems, i.e., NT and ICL.

Maize-Soybean Rotation and Intercropping Increase Maize Yield by Influencing the Structure and Function of Rhizosphere Soil Fungal Communities.

Soil-borne diseases are exacerbated by continuous cropping and negatively impact maize health and yields. We conducted a long-term (11-year) field experiment in the black soil region of Northeast China to analyze the effects of different cropping systems on maize yield and rhizosphere soil fungal community structure and function. The experiment included three cropping systems: continuous maize cropping (CMC), maize-soybean rotation (MSR), and maize-soybean intercropping (MSI). MSI and MSR resulted in a 3.30-16.26% lower ear height coefficient and a 7.43-12.37% higher maize yield compared to CMC. The richness and diversity of rhizosphere soil fungi were 7.75-20.26% lower in MSI and MSR than in CMC. The relative abundances of Tausonia and Mortierella were associated with increased maize yield, whereas the relative abundance of Solicoccozyma was associated with decreased maize yield. MSI and MSR had higher proportions of wood saprotrophs and lower proportions of plant pathogens than CMC. Furthermore, our findings indicate that crop rotation is more effective than intercropping for enhancing maize yield and mitigating soil-borne diseases in the black soil zone of Northeast China. This study offers valuable insights for the development of sustainable agroecosystems.

Analysis of Bacterial Community Characteristics in Maize Root Zones Under Maize-soybean Compound Planting Mode

Maize-soybean compound intercropping has the potential to increase yield and is being tested for spreading in Huang-Huai-hai Plain. However, the main regulatory regions of this cropping pattern on soil microbial communities have not been clarified. In the present study, the tested samples were collected from three maize root zones of bulk soil, rhizosphere soil, and roots under mono- and intercropping planting modes, respectively. The non-rhizosphere soil chemical properties and enzyme activities were determined, and bacterial communities were characterized using high-throughput sequencing of the 16S rRNA gene V3-V4 region. Compared with monocropping, the maize bulk soil electric conductivity （EC）, soil organic matter （SOM）, available potassium （AK）, available phosphorus （AP）, total nitrogen （TN）, and enzyme activities of intercropping were significantly increased. The α diversities and β diversity of the bacterial community in rhizosphere soil were significantly different between the two planting modes. There were 11 bacteria genera with significantly higher abundance in the rhizosphere soil of compound planting than that of monoculture, and TN, AP, and catalase were the three most important factors contributing to their distribution. The abundances of 8 genera among the 11 genera mentioned above, unclassified Vicinamibacterales, unclassified Geminicoccaceae, MND1, unclassified Gemmatimonadaceae, Acidibacter, unclassified Vicinamibacteraceae, Sphingomonas, and unclassified Comamonadaceae were significantly positively correlated with TN. As for the bacteria distribution in maize root, AK contributed the most and had a significantly negative correlation with unclassified Rhizobiaceae and unclassified Microscillaceae and a positive correlation with Haliangium. Maize-soybean compound intercropping affected mainly the bacterial community of maize rhizosphere and had an evident effect on soil fertilizer cultivation and microbial diversity regulation, which provides a theoretical basis and practical guidance for rational intercropping to maintain agroecosystem biodiversity.

The lactonase BxdA mediates metabolic specialisation of maize root bacteria to benzoxazinoids

Root exudates contain specialised metabolites that shape the plant’s root microbiome. How host-specific microbes cope with these bioactive compounds, and how this ability affects root microbiomes, remains largely unknown. We investigated how maize root bacteria metabolise benzoxazinoids, the main specialised metabolites of maize. Diverse and abundant bacteria metabolised the major compound in the maize rhizosphere MBOA (6-methoxybenzoxazolin-2(3H)-one) and formed AMPO (2-amino-7-methoxy-phenoxazin-3-one). AMPO forming bacteria were enriched in the rhizosphere of benzoxazinoid-producing maize and could use MBOA as carbon source. We identified a gene cluster associated with AMPO formation in microbacteria. The first gene in this cluster, bxdA encodes a lactonase that converts MBOA to AMPO in vitro. A deletion mutant of the homologous bxdA genes in the genus Sphingobium, did not form AMPO nor was it able to use MBOA as a carbon source. BxdA was identified in different genera of maize root bacteria. Here we show that plant-specialised metabolites select for metabolisation-competent root bacteria. BxdA represents a benzoxazinoid metabolisation gene whose carriers successfully colonize the maize rhizosphere and thereby shape the plant’s chemical environmental footprint.