Abundance Of Soil Microorganisms Research Articles

Response of soil microbial glycoside hydrolase family 6 cellulolytic population to lignocellulosic biochar reveals biochar stability toward microbial degradation.

Biochar produced from lignocellulosic biomass offers an opportunity to recycle waste into a valuable soil amendment. The application of biochar has been proposed to mitigate climate change by sequestering carbon in the soil. However, the field impact of biochar treatment on the cellulolytic microbial populations involved in the earlier steps of cellulose degradation is poorly understood. A field trial spanning three consecutive crop cycles of Zea mays was conducted in a degraded tropical Ultisol of Peninsular Malaysia. The soil was amended with two contrasting biochar made from oil palm kernel shells (pyrolyzed at 400°C) and rice husks (gasified at 800°C) with or without fertilizer supplementation. Soil samples were taken at each harvesting stage and analyzed for total organic carbon, labile active organic carbon, total cellulase, and β-glucosidase. Microbial glycoside hydrolase family 6 (GH6) cellulase genes and transcripts, involved in the early steps of cellulose degradation, were quantified from the extracted soil deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), respectively. Total organic carbon, labile active organic carbon, and β-glucosidase activity were significantly increased, while no effect on total cellulase activity was found. Both biochars stimulated the total population (DNA-derived) abundance of soil microorganisms harboring the GH6 cellulase genes. The biochar amendment did not affect the active population (RNA-derived) of the GH6 cellulolytic community, showing no significant changes in transcript expression. This indirectly corroborates the role of biochar as a potential carbon sequester in the soil.

Tea and Pleurotus ostreatus intercropping modulates structure of soil and root microbial communities.

Intercropping with Pleurotus ostreatus has been demonstrated to increase the tea yield and alleviate soil acidification in tea gardens. However, the underlying mechanisms remain elusive. Here, high-throughput sequencing and Biolog Eco analysis were performed to identify changes in the community structure and abundance of soil microorganisms in the P. ostreatus intercropped tea garden at different seasons (April and September). The results showed that the soil microbial diversity of rhizosphere decreased in April, while rhizosphere and non-rhizosphere soil microbial diversity increased in September in the P. ostreatus intercropped tea garden. The diversity of tea tree root microorganisms increased in both periods. In addition, the number of fungi associated with organic matter decomposition and nutrient cycling, such as Penicillium, Trichoderma, and Trechispora, was significantly higher in the intercropped group than in the control group. Intercropping with P. ostreatus increased the levels of total nitrogen (TN), total phosphorus (TP), and available phosphorus (AP) in the soil. It also improved the content of secondary metabolites, such as tea catechins, and polysaccharides in tea buds. Microbial network analysis showed that Unclassified_o__Helotiales, and Devosia were positively correlated with soil TN and pH, while Lactobacillus, Acidothermus, and Monascus were positively correlated with flavone, AE, and catechins in tea trees. In conclusion, intercropping with P. ostreatus can improve the physical and chemical properties of soil and the composition and structure of microbial communities in tea gardens, which has significant potential for application in monoculture tea gardens with acidic soils.

Analysis of Tobacco Straw Return to the Field to Improve the Chemical, Physical, and Biological Soil Properties and Rice Yield

Straw incorporation into soil contributes significantly to the sustainable development of agriculture. To investigate the impact of tobacco straw returns on a tobacco–rice replanting system, we designed an experiment with two straw return levels and a control group: T1 (full return), T2 (root return), and CK (no straw return). Over a three-year field experiment in rice fields in South China, we assessed the effects of tobacco straw return on soil quality, microbial diversity, dry matter accumulation, and yield composition of rice. The results demonstrated that returning tobacco straw to the field effectively enhanced rice yield by positively influencing various soil physical, chemical, and biological properties. Compared to those in the CK treatment, as the soil porosity increased from 9.0% to 12.4%, the mean weight diameter of the soil aggregates substantially increased, ranging from 28.7% to 45.2%. There were significant increases in soil organic matter, total nitrogen, and alkaline dissolved nitrogen. Soil sucrase activity increased between 29.8% and 44.9%, and urease activity increased between 4.3% and 62.2% over the three consecutive years of straw return. The diversity index of soil fungi significantly increased. Additionally, rice yield increased markedly, ranging from 1.8% to 5.1%. Overall, the enhancement effect of T1 surpassed that of T2. According to our comprehensive analysis, the incorporation of tobacco straw into the field was found to enhance the physical properties of the soil, elevate soil enzyme activity, and increase the abundance of soil microorganisms. Consequently, this practice led to improved rice yield and a reduction in agricultural waste output. Overall, the return of tobacco straw to the field represents a clean and dependable approach in rice-cultivated tobacco areas to improve soil health and rice productivity.

The impact of desertification on soil health stability in Semi-Arid alpine Regions: A case study of the Qilian Mountains in the northeastern Tibetan Plateau, China

Desertification poses a serious threat to ecosystem health, and with global changes, the variability and uncertainty of ecological functions in semi-arid alpine regions are increasing. A pressing issue is quantifying how desertification affects the soil system functions in these areas. However, empirical evidence is still lacking in exploring the interaction between desertification degradation gradients and soil functions under natural conditions by coupling soil physicochemical properties, soil microbiota, and vegetation. For this purpose, we conducted a survey sampling of soil and vegetation at five sites with no, light, moderate, severe and extremely severe desertification in Qinghai Area of Qilian Mountains National Park, China. We introduced a new concept soil health stability (SHS) to represent the actual health status of soil systems in semi-arid alpine regions and assessed the impact of desertification on this stability. We observed that the intensification of desertification has led to a significant decrease in soil organic matter, relative abundance of soil microorganisms, and plant factors. The contributions of plant factors and soil microbiota to SHS showed a negative correlation with the degradation gradient. SHS varied across different degradation gradients, rather than following a single linear relationship, with a relatively rapid decline in the transition from non-desertification to moderate desertification. Our work emphasizes that the coupled contributions of soil physicochemical properties, soil microbiota, and vegetation to SHS. It calls for intensified prevention and treatment of mild and moderate desertification, while providing new methods and deeper scientific understanding for accurately evaluating soil system functions in semi-arid alpine regions.

Effects of fire smoke on soil microorganisms: results of a modelling experiment

ABSTRACT Wildfires are widespread and have major effects on ecosystems. The sensitivity of soil microorganisms to smoke was studied in experimental conditions using smoke generated from burning pine sawdust. High concentrations of toxicants such as NO (40 mg/m3), NO2 (60 mg/m3), CO (3570 mg/m3), C2H4O (241 mg/m3), CH2O (9.5 mg/m3), C6H6O (4.4 mg/m3), and C6H14 (238 mg/m3) were measured in the smoke. Reduced abundance of Azotobacter chroococcum by 9–62% and of microscopic fungi by 25–57% was found when the soil was treated with smoke for 30–120 min. The abundance of soil microorganisms after exposure to smoke depended on time. Several species of soil fungi (Fusarium oxysporum, Venturia inaequalis, Fusarium moniliforme, Fusarium graminearum, Cladosporium cucumerinum, Penicillium chrysogenum, Rhodotorula rubra, Lipomyces starkeyi), and bacteria (Acinetobacter calcoaceticus, Streptomyces violaceus, Kocuria rosea) were studied. The lowest smoke exposure time at which growth inhibition was registered was 1–5 min. The effect of smoke on the enzymatic activity of Haplic Chernozem soils was also evaluated. Catalase activity was found to decrease by 25%, and peroxidase and polyphenol oxidase by 15% and 33%, respectively. High smoke toxicity contributed to changes in microbial abundance and enzymatic activity.

Soil Microorganisms in Agricultural Fields and Agronomic Regulation Pathways

Agricultural soil microorganisms play a crucial role in farmland ecosystems and are integral to the material cycle in these environments. The composition and abundance of soil microorganisms are influenced by agronomic measures that alter the soil microenvironment. These changes are pivotal to enhancing crop resistance, maximizing yield, and facilitating nutrient cycling in farmlands. Drawing on prior research advancements, this study systematically examined the functions of soil microorganisms, the effects of various agronomic measures on their populations, and the ways in which agronomic measures regulate soil microorganisms, and this article offers a comprehensive study of agricultural influences on microorganisms. Additionally, it outlines key areas for future research on soil microorganisms in farmlands, aiming to provide valuable insights for the sustainable development of farmland ecosystems.

Seasonal changes of soil microbiota and its association with environmental factors in coal mining subsidence area

As a special type of wetland, the new wetland in the coal mining subsidence area is highly sensitive to environmental changes. In recent years, more and more attention has been paid to the studies of soil microbial diversity in newly born wetlands in coal mining subsidence areas. However, there are few reports on the seasonal variation of soil microbial diversity and its relationship with soil physical and chemical properties. In this study, 16S rRNA gene sequencing technology was used to analyze the seasonal changes of soil microbial composition and functional diversity in newly formed wetlands in coal mining subsidence areas, and to determine the seasonal changes of soil nutrient elements and physical and chemical properties in coal mining subsidence areas, so as to analyze the correlation between soil microbial diversity and soil nutrient elements and physical and chemical properties in newly formed wetlands in coal mining subsidence areas. A total of 16,050 OTUs were obtained after sample gene noise reduction. Proteobacteria, Acidobacteriota and Bacteroidota were the highest abundance in the coal mining subsidence area of Jining. The two seasons gathered separately, and temperature (Temp), total phosphorus (TP), available phosphorus (AP), total organic carbon (TOC) and dry matter content (DMC) were the key factors for the seasonal change of soil microbial community in the wetland of the coal mining subsidence area of Jining. The contents of Temp, AP and TP were significantly correlated with the abundance of soil microorganisms in summer subsidence area, while the contents of DMC and TOC were significantly correlated with the abundance of soil microorganisms in winter subsidence area. Soil microbial diversity in coal mining subsidence area was correlated with the seasons. Temp, TP, AP, TOC and DMC were the key factors for the seasonal change of soil microbial community in the wetland of the coal mining subsidence area of Jining.

Similarities and differences in the microbial structure of surface soils of different vegetation types.

Soil microbial community diversity serves as a highly sensitive indicator for assessing the response of terrestrial ecosystems to various changes, and it holds significant ecological relevance in terms of indicating ecological alterations. At the global scale, vegetation type acts as a major driving force behind the diversity of soil microbial communities, encompassing both bacterial and fungal components. Modifications in vegetation type not only induce transformations in the visual appearance of land, but also influence the soil ecosystem's material cycle and energy flow, resulting in substantial impacts on the composition and performance of soil microbes. In order to examine the disparities in the structure and diversity of soil microbial communities across distinct vegetation types, we opted to utilize sample plots representing four specific vegetation types. These included a woodland with the dominant tree species Drypetes perreticulata, a woodland with the dominant tree species Horsfieldia hainanensis, a Zea mays farmland and a Citrus reticulata fields. Through the application of high-throughput sequencing, the 16S V3_V4 region of soil bacteria and the ITS region of fungi were sequenced in this experiment. Subsequently, a comparative analysis was conducted to explore and assess the structure and dissimilarities of soil bacterial and fungal communities of the four vegetation types were analyzed comparatively. Our findings indicated that woodland soil exhibit a higher richness of microbial diversity compared to farmland soils. There were significant differences between woodland and farmland soil microbial community composition. However, all four dominant phyla of soil fungi were Ascomycota across the four vegetation types, but the bacterial dominant phyla were different in the two-farmland soil microbial communities with the highest similarity. Furthermore, we established a significant correlation between the nutrient content of different vegetation types and the relative abundance of soil microorganisms at both phyla and genus levels. This experiment serves as a crucial step towards unraveling the intricate relationships between plants, soil microbes, and soil, as well as understanding the underlying driving mechanism.

Bacterial abundance of cacao agroforestry, cacao monoculture and secondary forest land uses in north Luwu, South Sulawesi

Expanding the agricultural sector in North Luwu influences land use modification to enhance plantation output. Continuous land use and clearance can jeopardize the survival of native land vegetation, altering C and N cycles, community composition, population, and soil microbial activity. Microorganisms are essential for maintaining the health and quality of the soil. The abundance of soil microorganisms significantly impacts ecosystem function, so it can help boost agricultural output. This demonstrates that data on the abundance and diversity of soil microorganisms can be used to determine soil fertility. However, more information is needed about the diversity of soil microbes in North Luwu. This study seeks to determine the abundance of soil microorganisms, particularly for various land uses. Random soil samples were collected from cacao monoculture, cacao agroforestry, and secondary forest. The C: N ratio and the total number of microorganisms were then measured in the collected soil samples. Cacao agroforestry with the highest C: N ratio had 1.8 x 108 CFU/g of total soil bacterial, the highest bacterial abundance among the three land covers, followed by secondary forest and cacao monoculture with the lowest C: N ratio and lowest bacterial abundance 2 x 107 CFU/g. These results indicated that the soil C: N ratio influences the bacterial abundance of various land uses. The highest abundance of nitrate-fixing bacteria was found in secondary forests and the lowest in cacao agroforestry, even though the %N indicated by both was the same.

Effects of Modified Biochar-Supported Zero-Valent Iron on the Removal of Trichloroethylene and Responses of Microbial Community in Soil

Trichloroethylene is a typical organic contaminant that has widely existed in industry sites and groundwater. Biochar-supported zero-valent iron material has been used to remove trichloroethylene in groundwater; however, it could affect the microbial communities in aquifer soil, leading to changes in the environmental behavior of trichloroethylene. In this study, biochar was prepared under oxygen-limited conditions and modified by NaOH and HNO3 agents. Then, a modified biochar-supported zero-valent iron composite (BC composites) was synthesized using ball milling technology. The effects of BC composites on the removal of trichloroethylene and the responses of the microbial community were investigated under the condition of simulated aquifer soil. The results showed that the specific surface areas of BC composites were increased after the modification with NaOH. The highest removal rate of trichloroethylene was observed in the BC_2 treatment, up to 90.01%. Except in the BC_1 treatment, the diversity and abundance of soil microorganisms were increased, and the microbial community structure was changed after the addition of different BC composites, in which Bacillus, Thiobacillus, and Pseudomonas might have been the potential degrading bacteria of trichloroethylene. The abundance of Thiobacillus and Pseudomonas increased under the BC_2 treatment, which was favorable to the removal of trichloroethylene. The stabilization of the microbial community structure was probably maintained by Nocardioideas, Thermincola, Lysobacter, Gemmatimonas, Microvirga, and Pseudomonas. According to the predictive analysis of microbial metabolic pathways, the abundance of xenobiotics biodegradation and metabolism genes and the folding, sorting, and degradation of genes were the highest under the BC_2 treatment. Thus, the NaOH-modified BC composite could prompt the removal of trichloroethylene in simulated aquifer soil, probably due to the increase in the abundance of soil-degrading bacteria and the expression of degradation genes, demonstrating that the NaOH-modified BC composite could be used for the remediation of the organic-contaminated industry sites as a new composite material.

The effects of adding exogenous lignocellulose degrading bacteria during straw incorporation in cold regions on degradation characteristics and soil indigenous bacteria communities.

Low temperature is one of the bottleneck factors that limits the degradation of straw during rice straw incorporation. Determining strategies to promote the efficient degradation of straw in cold regions has become a highly active research area. This study was to investigate the effect of rice straw incorporation by adding exogenous lignocellulose decomposition microbial consortiums at different soil depths in cold regions. The results showed that the lignocellulose was degraded the most efficiently during straw incorporation, which was in deep soil with the full addition of a high-temperature bacterial system. The composite bacterial systems changed the indigenous soil microbial community structure and diminished the effect of straw incorporation on soil pH, it also significantly increased rice yield and effectively enhanced the functional abundance of soil microorganisms. The predominant bacteria SJA-15, Gemmatimonadaceae, and Bradyrhizobium promoted straw degradation. The concentration of bacterial system and the depth of soil had significantly positive correlations on lignocellulose degradation. These results provide new insights and a theoretical basis for the changes in the soil microbial community and the application of lignocellulose-degrading composite microbial systems with straw incorporation in cold regions.

The rice–edible mushroom pattern promotes the transformation of composted straw-C to soil organic carbon

The application of composted straw in conventional rice cultivation patterns can enhance soil organic carbon (SOC); however, it increases methane (CH4) emission, thereby reducing its net carbon sequestration efficiency in paddy fields. The rice–edible mushroom pattern may improve this phenomenon because edible mushrooms can promote straw decomposition and soil aggregate formation. Here, we investigated the effect of four inoculation amounts of edible mushroom on the transformation of composted straw-C in paddy fields using 13C tracer technology under rice–edible mushroom pattern. The results indicated that the inoculation of edible mushrooms increased the abundance of soil microorganisms and fungal mycelium, reduced SOC aromaticity, and promoted the formation of macroaggregates. Inoculation of edible mushrooms stimulated the transformation of composted straw-C to SOC and reduced its conversion to CH4. The sequestration efficiency of composted straw-C in the soil increased as the inoculation amounts of edible mushrooms increased. When the edible mushroom inoculation amount was 3000 kg ha–1, the highest amount of composed straw-C was sequestrated in soil. With more inoculation amount, more fungal mycelium was produced, which enhanced the physical protection of composted straw-C by promoting the formation of soil aggregates. This study indicated that under the rice–edible mushroom pattern, transformation of composted straw-C to the soil carbon was favored compared with its transformation to CH4, and this conversion efficiency increased with the increasing inoculation amounts of edible mushrooms.

Effects of dibutyl phthalate on microbial community and the carbon cycle in salinized soil

Dibutyl phthalate (DBP), a typical persistent organic pollutant, is of extensive attention because of its universal detection in soils and its impact on soil ecology. However, the ecological effects of DBP on ecologically fragile salinized soils are unclear, especially as soil salinization can result in soil degradation and thus affect the soil carbon cycle. Therefore, in this study, a typical salinized soil (agricultural soil in the Yellow River Delta) was selected and treated with DBP at different doses (1.0, 10, and 50 mg kg−1) and incubated for 30 d. The results revealed that DBP exposure significantly decreased the abundance of soil microorganisms. Molecular ecological network analysis showed that some taxa related to the carbon cycle gradually became key taxa in the network, changing the composition and structure of the bacterial community. The decrease of cbbLG, cbbLR and cex, and the increase of sga, glx and mcrA functional gene abundance affected carbon conversion. Molecular docking indicated that DBP could bind to soil invertase and β-glucosidase proteins, and change the enzyme activity. These results emphasized the critical impact of DBP on microbial communities and carbon cycling in salinized soils, and will play an essential role in DBP ecological risk assessment.

Effects of walnut/Rosa roxburghii compound planting on growth, fruit yield, quality of Rosa roxburghii and soil properties.

Walnut and Rosa roxburghii are important arbor and shrub fruit trees cultivated in the southwest mountainous area of China. Furthermore, those two species are compound cultivated in this area. In this study, we investigated the growth, yield, fruit quality, photosynthesis, and soil fertility of R. roxburghii in a 7-year typical 'Qianhe 7'/ 'Guinong 5' compound planting pattern in Guizhou. The results showed that compared with the monoculture, photosynthetic pigment content and photosynthetic rate of R. roxburghii leaves were significantly lower in the compound plantation. The growth and yield of R. roxburghii decreased significantly, with a 77.7% reduction of yield. Fruit quality of R. roxburghii was improved. The content of ascorbic acid (Vc), total phenol, carbohydrate, K, Ca, Mg, Fe, Mn, Zn, and other substances increased significantly. Fruit Vc and Mn content increased by 34.1% and 64.1%, respectively. The contents of total N, available N and K in the soil increased by 45.8%, 34.8% and 67.8%, respectively. The abundance of soil microorganisms and functional bacteria increased significantly, with the increase of bacteria and fungi being more than 36.0%. The increase of potassium bacteria and nitrogen fixing bacteria was 71.3% and 124.8%, respectively. However, the contents of organic matter, carbon-nitrogen ratio, total P, total K, available mineral nutrient (P, Ca, Mg, Fe, Mn, Cu, Zn) contents decreased. While the activities of soil urease and catalase were increased, the activities of other soil enzymes (sucrase, cellulase, protease, phosphatase) were significantly reduced. In summary, with continuous growth of walnuts in the walnut/R. roxburghii compound plantation, there was obvious shade and soil fertility competition for R. roxburghii, which affected its yield, but had a improvement effect on fruit quality.

Deep mowing rather than fire restrains grassland Miscanthus growth via affecting soil nutrient loss and microbial community redistribution.

Fire and mowing are crucial drivers of grass growth. However, their effects on soil properties, microbial communities, and plant productivity in dry-alkaline grasslands have not been well investigated. This study evaluated the effects of mowing (slightly and deeply) and fire on vegetation traits (Tiller number per cluster and plant height) and biomass (plant dry weight), and soil availability of N, P, and K, as well as soil microorganism abundance in a Miscanthus system. We designed one control and three experimental grass plots (slightly and deeply mowed, and burned) in 2020-2021 in the Xi'an Botanical Garden of Shaanxi Province, Xi'an, China. Tiller number, plant height per cluster, and soil N, P, and K availability during Miscanthus growth decreased significantly (p < 0.05) in all treatments compared to the control. However, this effect was much greater in the deep-mowing plot than in the other plots. After harvest, deep mowing induced the greatest effect on biomass among all treatments, as it induced a 5.2-fold decrease in dry biomass relative to the control. In addition, both fire and mowing slightly redistributed the community and diversity of the soil bacteria and fungi. This redistribution was significantly greater in the deep-mowing plot than in other plots. In particular, relative to the control, deep mowing increased the abundance of Firmicutes and especially Proteobacteria among soil bacterial communities, but significantly (p < 0.05) decreased Basidiomycota and increased Ascomycota abundance among soil fungal communities. We conclude that nutrient limitation (N, P, and K) is crucial for Miscanthus growth in both mowing and fire grasslands, whereas deep mowing can induce soil nutrient loss and microorganism redistribution, further restraining grass sustainability in dry-alkaline grasslands.

Role of Halotolerant Plant Growth-Promoting Rhizobacteria in Mitigating Salinity Stress: Recent Advances and Possibilities

Soil salinity is one of the major abiotic constraints in agricultural ecosystems worldwide. High salinity levels have negative impacts on plant growth and yield, and affect soil physicochemical properties. Salinity also has adverse effects on the distribution and abundance of soil microorganisms. Salinity problems have previously been addressed in research, but most approaches, such as breeding for salt tolerant varieties and soil amelioration, are expensive and require years of efforts. Halotolerant plant growth-promoting rhizobacteria (HT-PGPR) secrete secondary metabolites, including osmoprotectants, exopolysaccharides, and volatile organic compounds. The importance of these compounds in promoting plant growth and reducing adverse effects under salinity stress has now been widely recognised. HT-PGPR are emerging as effective biological strategies for mitigating the harmful effects of high salinity; improving plant growth, development, and yield; and remediating degraded saline soils. This review describes the beneficial effects and growth-promoting mechanisms of various HT-PGPR, which are carried out by maintaining ion homeostasis, increasing nutrient availability, and the producing secondary metabolites, osmoprotectants, growth hormones, and volatile organic compounds. Exploring suitable HT-PGPR and applications in agriculture production systems can play a crucial role in reducing the adverse impacts of salinity stress and sustainable crop productivity.

Effect of Nitrogen Fertilization in the Sour Cherry Orchard on Soil Enzymatic Activities, Microbial Population, and Fruit Quality

Sour cherry (Prunus cerasus L.) is one of the most important fruit crops in Poland and ‘Łutówka’ is the dominant cultivar in commercial orchards. The experiment was carried out in 2007–2013 in three orchards; in each of them, three levels of fertilization were applied: 0 N kg ha−1, 60 kg N ha−1, and 120 kg N ha−1. The activity of dehydrogenase and protease in the soil was studied depending on nitrogen fertilization. The abundance of soil microorganisms was assessed: bacteria, fungi, actinomycetes, and nitrogenous bacteria (Azospirillum and Azotobacter) in the years during the experiments carried out with fertilization of 60 kg N ha−1 in all orchards. The enzyme activity of dehydrogenases increased after the use of 60 kg N ha−1 from 3.8 to 6.7 (cm3 H2 24 h−1 kg−1 DW soil), but a further increase in the dose to 120 kg N ha−1 caused a decrease in activity to 5.1 (cm3 H2 24 h−1 kg−1 DW soil). The activity of proteases was dependent on nitrogen fertilization, but to a large extent it was related to the course of climatic conditions. There is no relationship between the growth and the activity of proteases. The yield and selected quality parameters of the cherry fruits were associated with both dehydrogenases and proteases. The use of lower doses of nitrogen fertilizers allows for maintaining biological balance in the soil and a more efficient use of nutrients, contributing to less environmental pollution.

Effects of long-term fertilization with contemporary Danish human urine, composted household waste and sewage sludge on soil nematode abundance and community structure

It is desirable to recycle the urban waste products human urine, composted household waste and sewage sludge as fertilizers to agricultural fields. This could minimize the use of NPK fertilizer, improve soil structure and store carbon. However, waste products may contain heavy metals, persistent organic pollutants (POP) and plastics, and there are concerns that long-term build-up of these substances will cause unwanted effects on soil health.Nematodes are ubiquitous and numerous in soil ecosystems. Abundance and community structure of soil nematodes can be used as indicators of soil health, as some species are vulnerable to pollution. There are well-developed methods for detecting environmental changes based on nematode community structure.At the long-term CRUCIAL field experiment, where alternative fertilizer products have been applied since 2003, we measured effects of long-term fertilization with human urine, composted household waste and sewage sludge on soil properties (pH, soil organic matter and nitrogen availability), abundance of soil microorganisms (bacteria, fungi, small protozoa and ciliates) and nematode trophic groups compared to plots with unfertilized, NPK and cattle manure treatment. Sampling and assessments were done three times during a growth season. Further, we assessed the composition of nematode communities using metabarcoding.Treatments with a high input of organic matter (cattle manure, composted household waste and sewage sludge) had high abundances of bacteria and thus bacterial grazers (small protozoa, ciliates, and bacterial feeding nematodes). We found a significant correlation between nematode community structure and pH and organic matter. We calculated the nematode Maturity Index 2–5 (pollution indicator) based on metabarcoding data, which did not differ significantly between the treatments.We conclude that long-term fertilization with different types of contemporary Danish urban waste products affects both soil properties and abundance of soil organisms, the latter largely reflecting the organic matter input of the fertilizer treatments. We found no adverse effect on nematode communities that could indicate pollution-induced stress on nematofauna or decreased soil fertility.

Effects of Applying Arbuscular Mycorrhizal Fungi to Nitrogen Cycle Microorganisms in Soils with Coffee Plantations

Abstract: Mycorrhizae are associations between plants and beneficial fungi. They are the most active components of the plant’s nutrient absorption organs. On the other hand, soil microorganisms are fundamental for their functioning and dynamics as a living system. This research aimed to evaluate the effects of applying arbuscular mycorrhizal fungi (AMF) to the abundance of functional groups associated with the nitrogen cycle of soils with coffee plantations in Sasaima, Cundinamarca, Colombia. The soil samples were collected from four study plots during months 0, 2, and 8 and handled as follows: Plot 1. Application of liquid AMF (75-80 spores/gram of dry powder); Plot 2. Application of AMF in solid formulation (300 spores/gram); Plot 3. Application of native AMF, extracted from the soil under study (25 spores/gram); and Plot 4. Control, no application of AMF . The abundance of soil microorganisms associated with the nitrogen cycle was estimated using the most probable number technique to quantify ammonifying, proteolytic, ammonium-oxidizing, nitrite-oxidizing, and denitrifying microorganisms. The standard physicochemical parameters of the soil were measured. Afterward, univariate and multivariate analyses of the data were performed. The results showed a positive correlation between the application of AMF, organic carbon, and phosphorus, higher in the plots with native AMF. However, the abundance of functional groups of the nitrogen cycle did not show significant differences among the treatments; still, the principal components analysis showed a correlation between the plots with liquid and solid AMF, ammonifying microorganisms, and ammonium-oxidizing bacteria.

Soil depth and agricultural irrigation activities drive variation in microbial abundance and nitrogen cycling

Understanding the vertical diversity and abundance of soil microorganisms in shifting environments is crucial for the improvement of crop yield, tackling climate change and optimizing biogeochemical cycles in the Earth’s critical zone. In this study, a comprehensive survey of soil microbial communities was conducted in fields in an irrigated area and an abandoned area in western China. In total, 40 soil cores (600 cm deep) were taken from land under irrigation–fertilization management (IL; 34 cores) and abandoned land (AL; six cores) from July 2013 to April 2018. Spatiotemporal variation in the abundance of soil bacteria, fungi and nitrogen (N)-cycling microbes was evaluated. Soil depth was found to drive soil microbial abundance, but not diversity, throughout the vertical soil profile. The results suggest that in winter, the abundances were mainly driven by environmental variables (depth and temperature), but in summer, by depth, temperature and nutrient status. Depth had strong direct effects, and indirect impacts via temperature and TN, on microbial abundance in summer. The sequence counts for some prokaryotic taxa presented clear, mid-profile peaks in the vertical soil profiles. These distributions may be partially explained by soil texture. Consequently, the environmental filtering associated with depth controls local microbial abundance along resource gradients in the soil profile. Other factors, including temperature, moisture, pH and nutrients, were secondary regulators of microbial abundance. Further, irrigated agriculture land use could accelerate N cycling, increase nitrate leaching, and N2O and N2 production. Such findings, which enhance our understanding of how soil microbial communities respond to environmental changes and N-cycling pathways in the deeper soil profile, could improve field nitrogen management.