Soil Bacterial Populations Research Articles

Effects of plastic film mulching on soil microbial carbon metabolic activity and functional diversity at different maize growth stages in cool, semi-arid regions.

Plastic film mulching has been widely used to enhance soil hydrothermal conditions and increase crop yields in cool, semi-arid areas. However, its impact on soil microbial carbon metabolic activity and functional diversity during plant growth remains unclear despite their important roles in nutrient cycling and soil quality evaluation. This study used the Biolog EcoPlate technique to investigate the dynamics and driving factors of soil microbial carbon metabolic activity and functional diversity at different maize growth stages following plastic film mulching. The results revealed that film mulching significantly increased microbial carbon metabolic activities [represented by average well color development (AWCD)] by 300% at the seedling stage and by 26.8% at maturity but decreased it by 47.4% at the flowering stage compared to the control (without mulching). A similar trend was observed for the microbial functional diversity index. Redundancy analysis identified soil moisture (SM), soil temperature (ST), dissolved organic carbon (DOC), microbial biomass carbon (MBC), and bacteria amounts as the primary factors influencing changes in soil microbial carbon source utilization. The mulch treatment significantly increased SM at all growth stages, while its warming effect disappeared at the flowering stage. Soil DOC, MBC, and bacterial populations were notably higher under mulching at the seedling and maturity stages but lower at the flowering stage. Pearson correlation analysis showed that changes in SM, ST, DOC, MBC, and bacterial populations positively correlated with the utilization of all carbon source classes, AWCD, and functional diversity indexes after film mulching. Furthermore, maize grain yield and water use efficiency increased by 142 and 129%, respectively, following film mulching. In conclusion, plastic film mulching enhanced soil microbial carbon metabolic activity and functional diversity at the seedling and maturity stages, improving crop yields in cool, semi-arid areas. Furthermore, the decrease in soil carbon metabolic capacity at flowering stage highlights that supplementing soil carbon sources should be considered after continuous film mulching to sustain or enhance farmland productivity and soil quality.

Influence of phosphate and potassium solubilizing bacteria on performance of crop, endophytic and rhizosphere microbial population in chamomile

Phosphate (Bacillus megaterium) and potassium (Frateuria aurantia) solubilizing bacteria (PSB and KSB) were assessed for their agronomic impact on chamomile performance in a pot experiment at CSIR-CIMAPRC, Bengaluru. Results demonstrated that 75% recommended dose of fertilizer (RDF) combined with PSB and KSB significantly improved chamomile performance, enhancing plant height (41.4 cm), stem diameter (1.10 mm), number of flowers (348.67), flower: leaf ratio (1.24), and flower dry weight (4.28 g plant-1) compared to control, RDF alone, and sole solubilizer application. The combined application with 100% RDF synergistically increased rhizosphere bacterial population from 25 × 104 Cfu g-1 to 57 × 104 cfu g-1, while 75% RDF + PSB + KSB resulted in 53 × 104 cfu g-1. Morphological and biochemical analyses revealed diverse variations in chamomile endophytes and rhizosphere soil bacterial populations, mainly Bacillus and Streptococcus genera. PSB and KSB, whether applied individually or combined, significantly influenced chamomile growth and yield, with microbial dynamics enhancing nutrient solubilization and availability.

Phacelia and Buckwheat Cover Crops’ Effects on Soil Quality in Organic Vegetable Production in a High Tunnel System

Cover crops (CCs) are regarded as beneficial to agricultural practice as an option for soil quality improvement in field production systems. The main goal of this study was to assess the impact of spring phacelia (Phacelia tanacetifolia Benth.) and buckwheat (Fagopyrum Mill.) in a crop rotation (CC–leek–parsley, 2020–2021) on the physicochemical and biological properties of the soil in an organic high tunnel system. Soil analyses involved measurements of bulk density, water capacity, soil aggregation, soil organic carbon (SOC), available soil nutrients, as well as microbial abundance and diversity. Phacelia generated more aboveground biomass (58.2 t fresh matter ha−1) than buckwheat (33.0 t ha−1), and their biomass contained 161 kg N ha−1 and 67 kg N ha−1, respectively. A large quantity of elements, such as N, Ca, P, S, B, and Cu, were found in phacelia biomass. More Mg and Na were found in buckwheat plants. The results showed that CC biomass significantly improved some of the soil physical and chemical properties, such as soil organic carbon stock and wet aggregate stability, and decreased soil bulk density. Cover crop treatments changed the dynamics of soil bacterial and fungus populations in a high tunnel system. Phacelia increased the quantity of ammonifiers and nitrifiers in the soil substantially. Further research with a long-term focus is needed to assess the impact of cover crops on soil properties, soil quality, and subsequent crop yields in high tunnel crop rotation and management systems.

Effects of soil moisture on soil viral reproductive strategies in an agricultural soil

AbstractGenomic evidence suggests that lysogenic viruses significantly influence the evolution of their host communities and soil microbial ecology and functionality. However, the response of soil viral reproductive strategies (VRS) to environmental factors, in particular soil water stress, remains poorly understood. We investigated this by employing a laboratory microcosm incubation system with different soil moisture levels (30%, 60% and 90% field capacity). Our study focused on soil biochemical properties, bacterial and viral populations, lysogenic fractions and virus/bacteria ratio (VBR). The results showed that soil moisture significantly affected bacterial and viral counts, lysogenic fractions and VBR (p < 0.01), with bacterial counts increasing and viral counts decreasing with increasing soil moisture. The lysogenic fraction peaked at low moisture, suggesting a shift in viral strategy under hydration stress, which may affect virus‐bacteria interactions and nutrient dynamics, enhancing host adaptability. Analyses using correlation, random forest and structural equation modelling identified soil moisture as the dominant factor shaping VRS by altering nutrient availability and host population. These findings provide a new insight into microbial regulation of feedback to environmental change from the life history strategies of soil viruses.

PREVALENCE OF PESTICIDE TOLERANCE IN SOIL BACTERIA FROM DARJEELING HIMALAYAS: A GROWING CONCERN OF GRASSHOPPER EFFECT

Agricultural development involves the use of pesticides that have ended up in the soil or water bodies. These chemicals can accumulate and control microbial population by imposing tolerance to them. Pesticides can accumulate in soil or water by a multi-hopping phenomenon, termed the ‘Grasshopper effect’ that requires one or more volatilization-migration-deposition cycles. This study is an attempt at assessing the possible occurrence of this phenomenon in the Darjeeling Himalayas. A total of 39 sites of varied biotopes were sampled and their soil bacterial populations assessed based on the acquired degree of tolerance against pesticides. Soil microbial consortia isolated from all the regions showed total tolerance against the volatile pesticides emamectin benzoate, thiamethoxam, quinalphos, deltamethrin, spiromesifen and flubendiamide. Out of 47 isolates obtained, 29 exhibited full tolerance against them. Based on altitudinal zones, all the isolates from below <2000 ft depicted no inhibition zones against the tested pesticides while some inhibition was observed for the isolates from 2000-4000 ft (57.14%), 4000-6000 ft (28.57%), 8000-10000 ft (14.29%) and >10000 ft (75%). This work provides evidence for the occurrence of the ‘Grasshopper effect’ in the Darjeeling Himalayas facilitating the long-range transport, deposition and accumulation of harmful volatile pesticides in the region.

Examining the Effect of Agrochemicals on Soil Microbiological Activity, Micronutrient Availability, and Uptake by Maize (Zea mays L.) Plants

Agricultural practices profoundly influence soil microbial populations and physicochemical properties, vital for crop growth and quality. This study aims to explore the impact of diverse agrochemical applications on soil microbial dynamics, physicochemical properties, and maize yield and proximate properties. Topsoil samples, collected at depths of 1 to 15 cm, were transported to Jimma University for maize cultivation. Over 120 days, soil and maize samples were collected at specified intervals for analysis, including soil pH, microbial populations, and nutrient content. Statistical analysis using one-way ANOVA (p < 0.05) was conducted. Soil bacterial and fungal populations were measured on days 5, 10, 20, 40, 80, and 120. The highest total mesophilic bacterial count (TMBC) was in compost-treated pots (G) and the lowest in those receiving macronutrient fertilizers and glyphosates (B). The highest total mesophilic fungal count (TMFC) was in pots with glyphosates and compost (F), and the lowest was in pots treated with macronutrient fertilizers and glyphosates (B). Pots treated with macronutrient fertilizers and glyphosates (B), macronutrient fertilizers (A), and micronutrient fertilizers (C) showed the lowest Fe and Zn levels. Maize in pots treated with macronutrient fertilizer combined with glyphosate (B) exhibited the lowest protein, fats, and carbohydrates. Notably, compost-treated soils showed the highest bacterial and fungal counts, Fe, and Zn concentrations, while micro-mineral fertilizer combined with glyphosate (B) depleted the soil. Agrochemical treatments negatively affected maize yield quality, indicating complex treatment-related changes in soil parameters.

Spatial Patterns of Soil Bacterial Communities and N-cycling Functional Groups Along an Altitude Gradient in Datong River Basin

The altitude distribution patterns of soil microorganisms and their driving mechanisms are crucial for understanding the consequences of climate change on terrestrial ecosystems. There is an obvious altitude difference in Datong River Basin in the Qilian Mountains. Two spatial scale transections were set up along the mountain slope (with altitude spanning 1 000 m) and the mainstream direction (with altitude spanning 300-500 m), respectively. The distribution characteristics of the soil bacterial community structure and diversity along the altitude gradients were examined using high-throughput sequencing technology. Based on the FAPROTAX database, the altitude distribution patterns of nitrogen cycling functional groups were analyzed to investigate the major environmental factors influencing the altitude distribution patterns of soil bacterial communities. The findings revealed that:① Soil physicochemical characteristics varied significantly with altitude. The content of total nitrogen (TN) and nitrate nitrogen (NO3-) were positively correlated with the altitude (P < 0.01), whereas the soil bulk density and pH were negatively connected (P < 0.001). ② The abundance of OTU increased significantly along the altitude (P < 0.01), and the richness and diversity indices increased along the altitude, although the trend was not statistically significant (P > 0.05). ③ The predominant bacterial communities were Acidobacteria, Proteobacteria, and Bacteroidetes, and as altitude climbed, their relative abundances varied between increasing, decreasing, and slightly decreasing, respectively. ④ The nitrogen cycling processes involved 13 functional groups, primarily nitrification, aerobic ammonia oxidation, aerobic nitrite oxidation, etc. As the altitude increased, the response law changed, with an increase in the abundance of nitrobacteria (P < 0.01), a slight increase in the abundance of aerobic ammonia-oxidizing bacteria and nitrite-oxidizing bacteria, and a hump-back tendency in bacteria abundance for nitrogen respiration. ⑤ Redundancy analysis revealed that the key determinants influencing soil bacterial populations at the phylum level were altitude, pH, and the content of NH4+. Mantel analysis showed that the dominant groups of soil bacterial nitrogen cycling were all statistically and significantly driven by altitude (P < 0.01). ⑥ The α-diversity of the bacterial community with increasing altitude were both increased along the mountain slope and the mainstream direction, but the soil properties, the abundance of N-cycling functional groups, and the main environmental factors differed. Therefore, it is of great significance to explore the altitude distribution pattern of soil microorganisms at different spatial scales.

Effects of Different Conditioners on Soil Microbial Community and Labile Organic Carbon Fractions under the Combined Application of Swine Manure and Straw in Black Soil

The return of straw and manure to agricultural fields can impact soil organic carbon (SOC) and biological properties. However, there is a lack of research on how to use swine manure, maize straw, and various conditioners together affects soil bacterial and fungal populations. This study aimed to investigate six treatments, namely, only maize straw (S00), maize straw combined with swine manure (S0Z), maize straw combined with biochar and swine manure (SCZ), maize straw combined with boron slag and swine manure (SBZ), maize straw combined with biological agent and swine manure (SJZ), and maize straw combined with bio-organic fertilizer and swine manure (SFZ). The results showed that after the two-year return, all treatments increased the SOC content in 2023, which was 12.55–26.89% higher than S00. And the SCZ treatment significantly increased the soil organic carbon (SOC), dissolved organic carbon (DOC), easily oxidizable carbon (EOC), particulate organic carbon (POC), and microbial biomass carbon (MBC) content by 26.89%, 25.44%, 56.88%, 16.08%, and 43.54%, compared to S00. A redundancy analysis (RDA) showed that the continuous application of manure, maize straw, and conditioners has a positive impact on the diversity and abundance of soil microbial communities, enhancing the accumulation of soil carbon. Furthermore, our research revealed that soil fungi exhibited higher sensitivity in soil carbon composition following the addition of manure, straw, and conditioners to agricultural fields than bacteria. In conclusion, the addition of different conditioners to the fields is beneficial to biodiversity conservation from the perspective of achieving soil carbon storage and soil protection. Our findings suggested that the combination of maize straw, biochar, and swine manure was been proven to be the most effective treatment for increasing labile organic carbon fractions and enhancing the microbial community.

Alterations of bacterial community related C cycle by affecting soil carbon fractions under aged biochar application

AbstractBiochar is a beneficial substance for sequestering organic carbon in soil. Application of fresh biochar (FB) to the soil leads to an increase in soil organic carbon (SOC). However, the effects of aged biochar on SOC stabilization in acidic soils are unclear. A 90‐day incubation study was assessed to evaluate the impact of adding rice straw biochar on acid soil. The study aimed to assess the alterations in carbon fractions, enzyme activity and bacterial communities in soil. We used different ageing processes (water‐washed biochar [WB] and H2O2 oxidation biochar [OXB]) at a rate of 2%, with control at 0% of biochar. The results indicated that aged biochar reduced CO2 efflux and increased microbial biomass carbon (MBC), reducing the microbial metabolic quotient (qCO2). The SOC and its fractions increased with ageing relative to the FB treatment. Compared with the FB treatment, the carbon pool management index (CPMI) also increased with the OXB application. Additionally, the application of OXB stimulated the soil enzymes involved in carbon cycling, specifically β‐1,4‐glucosidase (βG), β‐1,4‐xylosidase (βX) and cellobiohydrolase (CBH) relative to the FB and WB treatments. Moreover, biochar applications improved the structure and functions of the bacterial population in soil with high acidity. Proteobacteria, Acidobacteria, Actinobacteria and Chloroflexi were the most prevalent species in all treatments, as shown by their relative abundances. The redundancy analysis revealed that the DOC (dissolved organic carbon) and MBC significantly impacted on the microbial community. Furthermore, adding OXB altered the Bacterial community involved in the C cycle by affecting SOC. These findings help us learn more about how applying fresh or aged rice straw biochar changes different carbon fractions and microbial communities in soil. It may serve as an instance for studying the provision of soil organic carbon after applying biochar in acidic soil.

Compost and Beneficial Pseudomonas Populations Promote Enzyme Activity, Amino Acids and Polymers Utilization Patterns in Heavy Metal Contaminated Soils

PGPR-assisted phytoremediation is a biotechnology offering opportunities to improve the state of contaminated soil ecosystems. The present study has investigated the potential of six beneficial isolates tolerant to Cd, Pb, and Zn and identified through 16S rDNA sequential analysis as Bacillus cereus, Pseudomonas putida, and Pseudomonas fluorescens to stimulate spinach growth and soil microbial community development in heavy metal-contaminated soil with or without the addition of compost. We found improved plant growth in all treatments with compost, but especially applying consortiums of isolates. Microbial enzyme activities and basal soil respiration were significantly higher in the rhizosphere and in amended treatments than in non-rhizosphere and control. The microbial community-level physiological profiles in the rhizosphere studied with the Ecoplates of BiologTM system showed increased metabolic potential in treatments with compost and beneficial bacteria. Principal component analysis revealed domination of amino acids and polymers utilizing communities in compost and bacterial consortium amended soils, carbohydrates and amino acids in compost and single strains application, and the lowest representation of amines and amides and phenolic compounds utilizers. Thus, may conclude that the use of quality organic amendments together with beneficial soil bacterial populations is a suitable and promising approach for the phytostabilization of soils contaminated with heavy metals.

RHIZOSPHERE MICROBIOME, SOIL ENZYMES AND GROUNDNUT YIELD AS INFLUENCED BY ADDITION OF BIOCHAR AND FERTILIZERS IN IRRIGATED ALFISOL OF NORTH COASTAL ANDHRA PRADESH

The field experiment was conducted in irrigated Alfisols of North coastal Andhra Pradesh tostudy the effect of biochar and chemical fertilizers on rhizosphere microbiome, soil enzymes andyield performance of groundnut crop (variety K-6) during rabi, 2018-19. Biochar application tosoil significantly increased soil bacterial, fungal and actinomycetes population. At pod developmentstage, the highest number of bacterial count (39.0 x106 CFU g-1 soil) was observed in T5 (100%RDF + biochar @ 6 t ha-1) which was on par with all the biochar applied treatments (T3, T4, T6, T7,T8). The Biochar applied @ 6 t ha-1 (T5 & T8) significantly increased the bacterial population ascompared to non-biochar applied treatments (T1 & T2). Fungal and actinomycetes populationfollowed the similar trend of bacterial count. Soil urease activity was significantly superior inbiochar applied treatments (T3, T4, T5, T6, T7, T8) compared to non biochar applied treatments (T1and T2). With increased rates of biochar application the urease activity markedly increased insoil. Similar trend was noticed with respect to dehydrogenase, acid phosphatase and alkalinephosphatase enzymes in soil in response to addition of biochar. At pod development stage, thehighest leaf area index (3.16) was recorded with 100% RDF + biochar @ 6 t ha-1(T5) which wassignificantly higher than T1 (control), T2 (100% RDF) and T6 (75% RDF + biochar @ 2 t ha-1). Thehighest drymatter accumulation of 2951 kg ha-1 at peg penetration and 6428 kg ha-1 at poddevelopment was observed in T5 (100% RDF + biochar @ 6 t ha-1) which was on par with T3(100% RDF + biochar @ 2 t ha-1), T4 (100% RDF + biochar @ 4 t ha-1), T8 (75% RDF + biochar @6 t ha-1) treatments. Groundnut pod yield was highest (4019.58 kg ha-1) in treatment received100% RDF + biochar @ 6 t ha-1, which was on par with T4 (100% RDF + biochar @ 6 t ha-1) and T8(75% RDF + biochar @ 6 t ha-1).

Depth-Wise Distribution of Soil Chemical Properties, Micro-nutrients Status, and Bacterial Population under Quercus leucotrichophora and Shorea robusta Forest of Chakrata and Thano Region of Uttarakhand

Forest trees have an appreciable demand for nutrients as they have longer rotation than crops and this is easily replenished by the constant release of nutrients resulting from weathering under favorable conditions in the soils developed from parent material rich in nutrient-bearing minerals. A study was undertaken to assess the chemical properties, micro-nutrient status, and bacterial population; two sites were taken for the collection of soil samples: the oak forest of Chakrata and the Sal forest of Thano. Soils were drawn at three depths viz. 0-30 cm, 30-60 cm, 60-90 cm. All soil parameters examined at three depths viz. 0-30 cm, 30-60 cm, 60-90 cm. Oak (Quercus Leucotrichophora) forests have higher microbial activity than Sal forests. The soil in both the studied areas was rich in nutrients, where, the maximum mean standard deviation values of pH (6.85), soil organic carbon (5.9 %), available nitrogen (0.04 %) reported in the Oak forest of Chakrata, and available phosphorus were almost similar in both forest regions. Oak forests have higher organic carbon, water-holding capacity, and nutrient availability compared to Sal forests. However, it is concluded that, for better conditions of these forests for soil and carbon-storing potential, the forest needs good management practices, especially in community forest areas to avoid illegal felling, impact of fire, and over-exploitation of fuel and fodder. Good management practices would help mitigate the impact of climate change and sustainable outcomes of the resources for the community's benefit.

Assessment of the impact of spent mushroom substrate on biodiversity and activity of soil bacterial and fungal populations based on classical and modern soil condition indicators

Assessment of the impact of spent mushroom substrate on biodiversity and activity of soil bacterial and fungal populations based on classical and modern soil condition indicators

Enhanced phytoremediation of metal contaminated soils aimed at decreasing the risk of antibiotic resistance dissemination

The enhanced phytoremediation of metal contaminated soils holds great promise for the recovery of soil health and functionality, while providing a range of co-benefits, from an environmental and human health perspective, derived from the revegetation of the degraded sites and the concomitant delivery of ecosystem services. Due to diverse evolutionary co-selection mechanisms between metal resistance and antibiotic resistance in bacteria, metal contaminated soils are considered potential reservoirs of antibiotic resistant bacteria (ARB) which can contribute to the existing antibiotic resistance crisis. During the enhanced phytoremediation of metal contaminated soils, the application of organic wastes (e.g., manure, slurry, sewage sludge) as soil amendments can aggravate the risk of antibiotic resistance spread, because they often contain ARB which harbor antibiotic resistance genes (ARGs) that can then be propagated among soil bacterial populations through horizontal gene transfer (HGT). Due to the magnitude and criticality of the antibiotic resistance crisis, as well as the higher risk of spread and dispersal of ARB and ARGs (they make copies of themselves) compared to metals, it is proposed here to aim enhanced phytoremediation strategies towards decreasing the soil resistome (and, hence, the risk of its potential link with the human resistome), while reducing total and/or bioavailable metal concentrations and restoring soil health and the delivery of ecosystem services. To this purpose, a decalogue of practices is tentatively suggested. Finally, a proper management of plant and soil microbial compositions is a most crucial aspect, together with the selection of the right organic wastes and phytoremediation practices.

Land spreading of olive mill wastewater (OMW): Biodegradation of organic matter and polyphenols in soil and effect on the activity of the total soil microflora

Abstract Agricultural spreading of olive mill wastewater (OMW) can represent a promising alternative solution, provided that the operation is controlled and the doses applied are respected. However, a reserve toward OMW spreading remains, for fears of possible microbiological negative incidences on the soil. To contribute to assessing this area, we have tried to study their microbiological impact and the fate of OMW polyphenols in soil in a greenhouse. In comparison with untreated soil with OMW (control), the application of 50, 100, and 200 m3/ha was studied for two months. The results obtained revealed that phenolic extracts from raw OMW showed five major peaks by HPLC at 280 nm, which were present only in trace amounts after 2 weeks of treatment at neutral pH. The phenols and organic matter (OM) from OMW were biodegraded or reorganized, and the bacterial population of soil treated with 50 and 100 m3/ha OMW was significantly higher compared to the soil that received water. However, a dose of 200 m3/ha did not affect soil microflora. Consequently, using OMW by direct spreading can be recommended at doses of 50 and 100 m3/ha. Doses higher than those studied, which are considered excessive and not recommended, could have undesirable repercussions.

The impact of utilizing oyster shell soil conditioner on the growth of tomato plants and the composition of inter-root soil bacterial communities in an acidic soil environment.

The objective of this study is to examine the impact of various oyster shell soil conditioners, which are primarily composed of oyster shells, on the growth of tomatoes in acidic soil. Moreover, the aim of this investigation is to analyze the variety and structure of soil bacterial populations in close proximity to tomato roots while also contributing to the understanding of the physical, chemical, and biological mechanisms of oyster shell soil conditioners. Tomato plants were grown in acidic red soil in three groups: a control group and a treatment group that used two types of oyster shell soil conditioners, OS (oyster shell powder) and OSF (oyster shell powder with organic microbial fertilizer). A range of soil physicochemical properties were measured to study differences in inter-soil physicochemical parameters and the growth of tomato plantings. In addition, this study utilized the CTAB (Cetyltrimethylammonium Bromide) technique to extract DNA from the soil in order to investigate the effects of oyster shell soil conditioner on the composition and diversity of bacterial populations. Utilizing high-throughput sequencing technologies and diversity index analysis, the composition and diversity of bacterial populations in the soil adjacent to plant roots were then evaluated. Ultimately, correlation analysis was used in this study to explore the relationship between environmental factors and the relative abundance of soil bacteria in the inter-root zone of tomato plants. The findings indicated that the oyster shell soil conditioners were capable of modifying the physicochemical characteristics of the soil. This was evidenced by significant increases in soil total nitrogen (16.2 and 59.9%), soil total carbon (25.8 and 27.7%), pH (56.9 and 55.8%), and electrical conductivity (377.5 and 311.7%) in the OS and OSF groups, respectively, compared to the control group (p < 0.05). Additionally, data pertaining to tomato seed germination and seedling growth biomass demonstrated that both oyster shell soil conditioners facilitated the germination of tomato seeds and the growth of seedlings in an acidic red clay soil (p < 0.05). On the other hand, the application of two oyster shell soil conditioners resulted in a modest reduction in the diversity of inter-root soil bacteria in tomato plants. Specifically, the group treated with OSF exhibited the most substantial fall in the diversity index, which was 13.6% lower compared to the control group. The investigation carried out on the soil between tomato plant roots yielded findings about the identification of the ten most abundant phyla. These phyla together represented 91.00-97.64% of the overall abundance. In the inter-root soil of tomatoes, a study identified four major phyla, namely Proteobacteria, Bacteroidetes, Acidobacteria, and Actinobacteria, which collectively accounted for up to 85% of the total abundance. At the general level, the relative abundance of Massilia increased by 2.18 and 7.93%, Brevundimonas by 5.43 and 3.01%, and Lysobacter by 3.12 and 7.49% in the OS and OSF groups, respectively, compared to the control group. However, the pathogenic bacteria unidentified_Burkholderiaceae decreased by 5.76 and 5.05%, respectively. The correlation analysis yielded conclusive evidence indicating that, which involved the use of CCA (Canonical Correlation Analysis) graphs and Spearman correlation coefficients, pH exhibited a positive correlation (p < 0.05) with Shewanella and a negative correlation (p < 0.05) with Bradyrhizobium. The relative abundance of Lysobacter and Massilia exhibited a positive correlation with the levels of total soil nitrogen. The utilization of oyster shell soil conditioner on acidic red soil resulted in several positive effects. Firstly, it raised the pH level of the inter-root soil of tomato plants, which is typically acidic. This pH adjustment facilitated the germination of tomato seeds and promoted the growth of seedlings. In addition, the application of oyster shell soil conditioner resulted in changes in the structure of the bacterial community in the inter-root soil, leading to an increase in the relative abundance of Proteobacteria and Bacteroidetes and a decrease in the relative abundance of Acidobacteria. Furthermore, this treatment fostered the proliferation of genera of beneficial bacteria like Massilia, Brevundimonas, and Lysobacter, ultimately enhancing the fertility of the red soil.

Prevalence of trace gas-oxidizing soil bacteria increases with radial distance from Polloquere hot spring within a high-elevation Andean cold desert.

High-elevation arid regions harbor microbial communities reliant on metabolic niches and flexibility to survive under biologically stressful conditions, including nutrient limitation that necessitates the utilization of atmospheric trace gases as electron donors. Geothermal springs present "oases" of microbial activity, diversity, and abundance by delivering water and substrates, including reduced gases. However, it is unknown whether these springs exhibit a gradient of effects, increasing their impact on trace gas-oxidizers in the surrounding soils. We assessed whether proximity to Polloquere, a high-altitude geothermal spring in an Andean salt flat, alters the diversity and metabolic structure of nearby soil bacterial populations compared to the surrounding cold desert. Recovered DNA and metagenomic analyses indicate that the spring represents an oasis for microbes in this challenging environment, supporting greater biomass with more diverse metabolic functions in proximal soils that declines sharply with radial distance from the spring. Despite the sharp decrease in biomass, potential rates of atmospheric hydrogen (H2) and carbon monoxide (CO) uptake increase away from the spring. Kinetic estimates suggest this activity is due to high-affinity trace gas consumption, likely as a survival strategy for energy/carbon acquisition. These results demonstrate that Polloquere regulates a gradient of diverse microbial communities and metabolisms, culminating in increased activity of trace gas-oxidizers as the influence of the spring yields to that of the regional salt flat environment. This suggests the spring holds local importance within the context of the broader salt flat and potentially represents a model ecosystem for other geothermal systems in high-altitude desert environments.

Resistance of various soil geosystem bacteria to enzymatic lysis at different pH

Bacteria appear to be an inevitable element of soil geochemistry because they participate actively in chemical transformations of soil media components. One of the factors determining the composition of bacterial population in soil is resistance of bacteria to enzymes which hydrolyze cell walls. In the following research, resistance of bacteria (Priestia megaterium, Micrococcus luteus and Escherichia coli) to lysozyme in the pH range appropriate for soils is investigated. All the three species are proved to be most sensitive to lysozyme in slightly alkaline conditions (P. megaterium is least resistant at pH 8.0, M. luteus at pH 8.3, E. coli at pH 8.5), and resistance of all the three microorganisms in the range of pH values of 6.0—7.0 changes insignificantly. A possible factor defining the pH optimum for lysozyme activity in relation to these bacteria is the structure of negatively charged components of their cell walls and outer membranes.

Resistance mechanisms of cereal plants and rhizosphere soil microbial communities to chromium stress.

Agricultural soils contaminated with heavy metals poison crops and disturb the normal functioning of rhizosphere microbial communities. Different crops and rhizosphere microbial communities exhibit different heavy metal resistance mechanisms. Here, indoor pot studies were used to assess the mechanisms of grain and soil rhizosphere microbial communities on chromium (Cr) stress. Millet grain variety 'Jingu 21' (Setaria italica) and soil samples were collected prior to control (CK), 6 hours after (Cr_6h), and 6 days following (Cr_6d) Cr stress. Transcriptomic analysis, high-throughput sequencing and quantitative polymerase chain reaction (qPCR) were used for sample determination and data analysis. Cr stress inhibited the expression of genes related to cell division, and photosynthesis in grain plants while stimulating the expression of genes related to DNA replication and repair, in addition to plant defense systems resist Cr stress. In response to chromium stress, rhizosphere soil bacterial and fungal community compositions and diversity changed significantly (p<0.05). Both bacterial and fungal co-occurrence networks primarily comprised positively correlated edges that would serve to increase community stability. However, bacterial community networks were larger than fungal community networks and were more tightly connected and less modular than fungal networks. The abundances of C/N functional genes exhibited increasing trends with increased Cr exposure. Overall, these results suggest that Cr stress primarily prevented cereal seedlings from completing photosynthesis, cell division, and proliferation while simultaneously triggering plant defense mechanisms to resist the toxic effects of Cr. Soil bacterial and fungal populations exhibited diverse response traits, community-assembly mechanisms, and increased expression of functional genes related to carbon and nitrogen cycling, all of which are likely related to microbial survival during Cr stress. This study provides new insights into resistance mechanisms, microbial community structures, and mechanisms of C/N functional genes responses in cereal plants to heavy metal contaminated agricultural soils. Portions of this text were previously published as part of a preprint (https://www.researchsquare.com/article/rs-2891904/v1).

Improving productivity, nutrient efficiency and economics of chamomile (Matricaria chamomilla L.) using phosphate and potassium solubilizing bacteria

Chamomile (Matricaria chamomilla L.) is a vital medicinal and aromatic plant, widely recognized for its industrial applications. However, sustainable cultivation of chamomile faces challenges due to the excessive use of chemical fertilizers, which can negatively impact soil health and the environment. There is a growing need to explore alternative agricultural practices that enhance nutrient use efficiency while minimizing environmental harm. Field experiments were conducted from 2022 to 2024 at the CSIR-CIMAP Research Centre in Bengaluru to evaluate the effects of phosphate solubilizing bacteria (PSB) and potassium solubilizing bacteria (KSB) on the performance and nutrient use efficiency of chamomile. Various treatment combinations of Recommended Dose of Fertilizers (RDF: 100 kg N, 60 kg P2O5, and 40 kg K2O ha-1) with PSB and KSB were tested, including co-inoculation and sole applications, to determine their impact on plant growth, yield and economic returns. Co-inoculating PSB and KSB with 100% RDF significantly increased plant height (48.09 cm) and branch count (15.43), outperforming RDF alone and other treatments. Sole applications of PSB or KSB with 100% RDF were comparable to 75% RDF combinations. The highest agronomic use efficiency (27.28%) and microbial response (37.49%) were achieved with 100% RDF+PSB+KSB, leading to a 137.49% yield increase. The highest concentrations of key compounds, α-bisabolol oxide B and α-bisabolol, were observed with 75% RDF+PSB+KSB. α-bisabolol peaked in the RDF-alone treatment. The 100% RDF+PSB+KSB treatment achieved the highest net monetary returns (US$ 5110 ha-1) and a benefit-to-cost ratio of 2.41, similar to 75% RDF+PSB+KSB. Overall, 75% RDF with PSB and KSB significantly enhances chamomile performance, increases soil bacterial populations, boosts nutrient mineralization, reduces chemical fertilizer use, and minimizes environmental impact. This approach offers a promising pathway for sustainable chamomile cultivation, leading to higher yields, improved economic returns, and reduced environmental impact.