Soil Microorganism Community Research Articles

Influence of thinning on carbon storage mediated by soil physicochemical properties and microbial community composition in large Chinese fir timber plantation

BackgroundThinning practices are useful measures in forest management and play an essential role in maintaining ecological stability. However, the effects of thinning on the soil properties and microbial community in large Chinese fir timber plantations remain unknown. The purpose of this study was to investigate the changes in soil physicochemical properties and microbial community composition in topsoil (0–20 cm) under six different intensities (i.e., 300 (R300), 450 (R450), 600 (R600), 750 (R750) and 900 (R900) trees per hectare and 1650 (R1650) as a control) in a large Chinese fir timber plantation.ResultsCompared with the CK treatment, thinning significantly altered the contents of soil organic carbon (SOC) and its fractions but not in a linear fashion; these indicators were highest in R900. In addition, thinning did not significantly affect the soil microbial community diversity indices but significantly affected the relative abundance of the core microbial community. Proteobacteria, Acidobacteria, and Actinobacteria were the dominant bacterial phyla; the relative abundances of Proteobacteria and Acidobacteria were highest in R900, and that of Actinobacteria was lowest in R900. The dominant fungal phyla were Ascomycota, Basidiomycota and Mucoromycota; the relative abundance of Ascomycota was lowest in R900, and that of Mucoromycota was highest in R900. The fungal microbial community composition was more sensitive than the bacterial community composition. The activity of the carbon-cycling genes was not linearly correlated with thinning, and the abundance of C-cycle genes was highest in R900.ConclusionsThese findings are important because they show that SOC and its fractions and the abundance of the soil microorganism community in large Chinese fir timber plantations can be significantly altered by thinning, thus affecting the capacity for carbon storage. These results may advance our understanding of how the density of large timber plantations could be modified to promote soil carbon storage.

The regulating mechanisms of Triton X-100 affected oxidation of PAHs in site soil aggregates using sodium citrate assisted Fe2+-persulfate

Here, we present a first investigation of the inhibition mechanism of surfactant Triton X-100 (TX-100) on the oxidation degradation of polycyclic aromatic hydrocarbons (PAHs) in site soil aggregates using sodium citrate assisted Fe2+-activated persulfate (SC/Fe2+/PS). First, TX-100 was not only competed the adsorption sites of soil aggregates with PS, but also consumed PS, which inhibit the PAHs remediation rate in the TX-100 elution followed by the SC/Fe2+/PS oxidation system from 55.6 % in the oxidation system to 50.3 %. Furthermore, in the oxidation followed by elution system, PAHs was adsorbed on the iron minerals produced during the oxidation, which would be form a bound PAHs that was difficult to react with PS, and then re-eluted to the soil by the TX-100. Additionally, it was found that the oxidative and the elution efficiency of PAHs exhibited negative correlations with aggregate particle sizes. Finally, soil microorganism communities were more strongly changed by SC/Fe2+/PS oxidation and PAHs concentration than that of TX-100 elution, with obvious alterations bacteria than fungi, the effects of SC/Fe2+/PS and PAHs concentration on microorganism communities were opposite. This study provided a proof of regulating mechanisms for the site soil remediation using surfactants combined with the iron-PS system.

Effects of N levels on land productivity and N2O emissions in maize-soybean relay intercropping.

Relay intercropping of maize and soybean can improve land productivity. However, the mechanism behind N2O emissions in this practice remains unclear. A two-factor randomized block field trial was conducted to reveal the mechanism of N2O emissions in a full additive maize-soybean relay intercropping. Factor A was three cropping systems - that is, monoculture maize (Zea mays L.), monoculture soybean (Glycine max L. Merr.) and maize-soybean relay intercropping. Factor B was different N supply, containing no N, reduced N and conventional N. Differences in N2O emissions, soil properties, rhizosphere bacterial communities and yield advantage were evaluated. The land equivalent ratio was 1.55-2.44, and the cumulative N2O emission ( ) was notably lower by 60.2% in intercropping than in monoculture, respectively. Reduced N declined without penalty on the yield advantages. The relay intercropping shifted soil properties - for example, soil organic matter, total N, and protease activity - and improved the soil microorganism community - for example, Proteobacteria and Acidobacteria. Intercropping reduced by directly suppressing nirS- and amoA-regulated N2O generation during soil N cycling, or nirS- and amoA-mediated soil properties shifted to reduce indirectly. Reduced N directly reduced by decreasing soil N content and reducing soil microorganism activities to alleviate N2O produced in soil N cycling. Conducting a full additive maize-soybean relay intercropping with reduced nitrogen supply provides a way to alleviate N2O emissions without the penalty on the yield advantage by changing rhizosphere bacterial communities and soil N cycling. © 2024 Society of Chemical Industry.

Tourmaline-enhanced bioremediation of Cd/BDE-153 co-contaminated soil: Migration, soil microorganism structure and enzyme activities

The efficient remediation of the soil co-contaminated with heavy metals and polybrominated diphenyl ethers (PBDEs) from electronic disassembly zones is a new challenge. Here, we screened a fungus of F. solani (F.s) can immobilize Cd and remove PBDEs. wIt combined with tourmaline enhances the remediation of co- pollutants in the soil. Furthermore, the environment risks of the enhanced technology were assessed through the amount of Cd/BDE-153 in Amaranthus tricolor L. (amaranth) migrated from soil, as well as the changes of soil microorganism communities and enzyme activities. The results showed the combined treatment of tourmaline and F.s made the removal percentage of BDE-153 in rhizosphere soil co-contaminated with BDE-153 and Cd reached 46.5%. And the weak acid extractable Cd in rhizosphere soil decreased by 33.7% compared to control group. In addition, the combined remediation technology resulted in a 32.5% (22.8%), 45.5% (37.2%), and 50.7% (38.1%) decrease in BDE-153 (Cd) content in the roots, stems, and leaves of amaranth, respectively. Tourmaline combined with F.s can significantly increase soil microorganism diversity, soil dehydrogenase and urease activities, further improving the remediation rate of Cd and BDE-153co-pollutants in soil and the biomass of amaranth. This study provides the remediation technology of soil co-contaminated with heavy metal and PBDEs and ensure the maintenance of food security.

Motivating organic farmers to adopt practices that support the pest-suppressive microbiome relies on understanding their beliefs

Abstract Certified organic farming is a suite of regulated practices that can support social, economic, and ecological sustainability in agriculture. Despite the standardization and regulation of certifying bodies, practices adopted by organic farmers vary with potential heterogeneous effects on environmental outcomes. While it is accepted that beliefs can enable or constrain the adoption of farming practices, it remains unclear if variation in organic farmer beliefs mediates observed heterogeneity in practices and the ecology of farms. Communities of soil microorganisms that induce plant resistance and regulate insect herbivores offer a lens to explore the relationship between beliefs and practice adoption. Variation in insect herbivores across organic farms is common but none have studied the role of farmer beliefs in regulating pests through the soil microbiome. Herein, we hypothesized that variation in adoption of microbiome-supportive practices by organic farmers is driven by heterogeneity in their microbiome beliefs. We also investigate the importance of demographic variables and farm characteristics, compared to farmer beliefs, for adoption of practices that support the microbiome. To test our hypothesis, we surveyed the microbiome beliefs, farming practices, and motivations of 85 organic farmers in New York State, USA. We used affinity propagation to cluster farmers by their beliefs, and statistical models to evaluate variation in farming practice adoption and farmer motivations. Our survey received a 30.5% response rate, most organic farmers (≈96%) believed the soil microbiome was important for supporting plant defenses and reducing pests, and <16% believed their farming practices were unimportant for promoting beneficial microbiomes. Seven clusters of farmers were identified that varied in their microbiome beliefs. Among the clusters ≈42% of farmers believed on-farm management and external factors (e.g., climate change) were important for promoting the microbiome. These farmers used fewer pesticides and synthetic mulches, more pre-planting practices (e.g., solarization), and were more motivated to adopt new practices to support the microbiome than their peers. The most important factors motivating adoption were reductions in pests, increased yields, and biodiversity benefits. Beliefs, demographics, and farm characteristics (e.g., time in organic management) were correlated with similar suites of farming practices, but only beliefs predicted farmer motivations. Our study suggests beliefs are key to understanding farmer motivations and promoting organic farming system sustainability via the pest-suppressive microbiome. More broadly, we suggest the need for socio-ecological approaches that account for farmer beliefs when studying the adoption of conservation practices in agroecosystems.

Dazomet fumigation modification of the soil microorganism community and promotion of Panax notoginseng growth.

Panax notoginseng, a medicinal herb in China, is attacked by several pathogens during its cultivation. Dazomet (DZ) is a soil fumigant that is effective in controlling soil-borne pathogens, but its long-term effects on P. notoginseng growth and soil properties are unknown. We conducted field experiments over two consecutive years to assess the impact of three concentrations of DZ fumigation (35 kg/666.7 m2, 40 kg/666.7 m2, and 45 kg/666.7 m2) on soil physicochemical properties, microbial diversity, and P. notoginseng growth. Correlation analyses were performed between microbial community changes and soil properties, and functional predictions for soil microorganisms were conducted. DZ fumigation increased total nitrogen, total phosphorus, total potassium, available phosphorus, available potassium, and ammonia nitrogen levels in the soil. DZ fumigation promoted the nutrient accumulation and improvement of agronomic traits of P. notoginseng, resulted in a 2.83-3.81X yield increase, with the highest total saponin content increasing by 24.06%. And the 40 kg/666.7 m2 treatment had the most favorable impact on P. notoginseng growth and saponin accumulation. After DZ fumigation, there was a decrease in the relative abundance of pathogenic fungi such as Fusarium, Plectosphaerella, and Ilyonectria, while beneficial bacteria such as Ramlibacter, Burkholderia, and Rhodanobacteria increased. The effects of fumigation on soil microorganisms and soil physicochemical properties persisted for 18 months post-fumigation. DZ fumigation enhanced the relative abundance of bacteria involved in the biosynthesis of secondary metabolites and arbuscular mycorrhizal fungi, reduced the relative abundance of plant-animal pathogenic fungi, reduced the occurrence of soil-borne diseases. In conclusion, DZ fumigation enhanced soil physicochemical properties, increased the proportion of beneficial bacteria in the soil, and rebalanced soil microorganism populations, consequently improving the growth environment of P. notoginseng and enhancing its growth, yield, and quality. This study offers a theoretical foundation for DZ fumigation as a potential solution to the continuous cropping issue in perennial medicinal plants such as P. notoginseng.

Effect of carbon nanomaterials on functional diversity and structure of soil microbial community under single and repeated exposures.

The extensive application of carbon nanomaterials (CNMs) has attracted increasing studies concerned about its environmental impact. These studies focus on single exposure to CNMs, but repeated exposures with relatively low concentration are more likely to occur under actual exposure scenario. In this study, we studied the metabolic functional and structure of soil microorganism community under single and repeated exposures to multiwalled carbon nanotubes (MW), graphene (GR), and fullerene (C60) by Biolog EcoPlates and high-throughput sequencing. Our findings revealed that repeated exposures to CNMs significantly increase the metabolic activity and diversity of the soil microbial community as compared with single exposure. Principal component and similarity analysis not only indicated that GR exerted a stronger effect on soil microbial diversity among three exposures compared to C60 and MW, but also revealed that the metabolic activity of the soil microbial community was more affected by the exposure scenarios of CNMs than the type of CNMs. These findings elucidated the effect of CNMs under different exposure scenarios on soil microorganism community, providing a new perspective on the risk assessment of nanomaterials.

Soil microbial biomass carbon and Jatropha curcas yield intecropping with forages and crop species

The domestication of Jatropha curcas L. in the Brazilian territory has been boosted by its great potential in the production of grains, oil and, in particular, its adaptation in different soil and climatic conditions. The aim of this research was evaluate the soil biological quality through the soil microbial biomass carbon and its indices derivate (metabolic and microbial quotient) under J. curcas intercropping with many forages species, legumes and annual crop rotation systems, as well as the accumulated production of J. curcas grains and oil. The experiment was conducted in a commercial area in the randomized blocks experimental design with the treatments arranged in a 12 x 2 factorial design, with four repetitions, resulting in 12 treatments with cropping systems and 2 sampling times (February 2012 and May 2012). Soil sampling was performed in February and May 2012, at 0 at 10 cm layer and four composite samples were collected in each cropping system, from five subsamples in each plot. J. curcas intercropping with B. ruziziensis, favors the maintenance of the community of soil microorganisms compared to the treatment with the species P. maximum cv. Massai and Cajanus cajan, which promoted decreasing in soil organic matter dynamics, when compared to the other cropping systems. The monocropping systems of J. curcas and intercropping in rotation systems 2 and 3 achieved higher yields of J. curcas grains and oil over three seasons.

Allelochemicals and soil microorganisms jointly mediate sex-specific belowground interactions in dioecious Populus cathayana.

Little is known about how sex differences in root zone characteristics, such as contents of allelochemicals and soil microbial composition, mediate intra- and intersexual interactions in dioecious plants. We examined the processes and mechanisms of sex-specific belowground interactions mediated by allelochemicals and soil microorganisms in Populus cathayana females and males in replicated 30-yr-old experimental stands insitu and in a series of controlled experiments. Female roots released a greater amount and more diverse phenolic allelochemicals into the soil environment, resulting in growth inhibition of the same sex neighbors and deterioration of the community of soil microorganisms. When grown with males, the growth of females was consistently enhanced, especially the root growth. Compared with female monocultures, the presence of males reduced the total phenolic accumulation in the soil, resulting in a shift from allelopathic inhibition to chemical facilitation. This association was enhanced by a favorable soil bacterial community and increased bacterial diversity, and it induced changes in the orientation of female roots. Our study highlighted a novel mechanism that enhances female performance by males through alterations in the allelochemical content and soil microbial composition. The possibility to improve productivity by chemical mediation provides novel opportunities for managing plantations of dioecious plants.

Rhizobium Soaking Promoted Maize Growth by Altering Rhizosphere Microbiomes and Associated Functional Genes.

Rhizobium is a Gram-negative bacterium, which dissolves minerals, produces growth hormones, promotes root growth, and protects plants from different soil-borne pathogens. In the present study, roots, stalks, and fresh weight of maize (Zea mays L.) were significantly increased after soaking in Bradyrhizobium japonicum compared with the control. Subsequently, transcriptome sequencing results of the whole maize plant soaked in B. japonicum showed that multiple growth and development-related genes were up-regulated more than 100-fold compared to the control. Furthermore, the abundance of plant growth promoting bacteria, such as Acidobacteria Subgroup_6 and Chloroflexi KD4-96, were increased significantly. On the contrary, the abundance of multiple pathogens, such as Curvularia, Fusarium and Mycocentrospora, were significantly decreased. Moreover, inoculation with B. japonicum could inhibit the infection of the pathogen Fusarium graminearum in maize. These results suggest that soaking seeds in B. japonicum may affect the expression of maize growth and development-related genes as the bacteria changes the soil microorganism community structure. These findings may help to expand the application of B. japonicum in crop production and provide new opportunities for food security.

Structure of Microbial Communities and Biological Activity in Tundra Soils of the Euro-Arctic Region (Rybachy Peninsula, Russia).

The relevance of the Arctic regions' study is rapidly increasing due to the sensitive response of fragile ecosystems to climate change and anthropogenic pressure. The microbiome is an important component that determines the soils' functioning and an indicator of changes occurring in ecosystems. Rybachy Peninsula is the northernmost part of the continental European Russia and is almost completely surrounded by Barents Sea water. For the first time, the microbial communities of the Entic Podzol, Albic Podzol, Rheic Histosol and Folic Histosol as well as anthropogenically disturbed soils (chemical pollution and human impact, growing crops) on the Rybachy Peninsula were characterized using plating and fluorescence microscopy methods, in parallel with the enzymatic activity of soils. The amount and structure of soil microbial biomass, such as the total biomass of fungi and prokaryote, the length and diameter of fungal and actinomycete mycelium, the proportion of spores and mycelium in the fungal biomass, the number of spores and prokaryotic cells, the proportion of small and large fungal spores and their morphology were determined. In the soils of the peninsula, the fungal biomass varied from 0.121 to 0.669 mg/g soil. The biomass of prokaryotes in soils ranged from 9.22 to 55.45 μg/g of soil. Fungi predominated, the proportion of which in the total microbial biomass varied from 78.5 to 97.7%. The number of culturable microfungi ranged from 0.53 to 13.93 × 103 CFU/g in the topsoil horizons, with a maximum in Entic Podzol and Albic Podzol soils and a minimum in anthropogenically disturbed soil. The number of culturable copiotrophic bacteria varied from 41.8 × 103 cells/g in a cryogenic spot to 5551.3 × 103 cells /g in anthropogenically disturbed soils. The number of culturable oligotrophic bacteria ranged from 77.9 to 12,059.6 × 103 cells/g. Changes in natural soils because of anthropogenic impact and a change in vegetation types have led to a change in the structure of the community of soil microorganisms. Investigated tundra soils had high enzymatic activity in native and anthropogenic conditions. The β-glucosidase and urease activity were comparable or even higher than in the soils of more southern natural zone, and the activity of dehydrogenase was 2-5 times lower. Thus, despite the subarctic climatic conditions, local soils have a significant biological activity upon which the productivity of ecosystems largely depends. The soils of the Rybachy Peninsula have a powerful enzyme pool due to the high adaptive potential of soil microorganisms to the extreme conditions of the Arctic, which allows them to perform their functions even under conditions of anthropogenic interference.

Rhizospheric soil organic carbon accumulated but its molecular groups redistributed via rhizospheric soil microorganisms along multi-root Cerasus humilis plantation chronosequence at the karst rocky desertification control area.

Though the relationships between the microorganism communities and the edaphic factors in rhizosphere soil along the plantation chronosequence have been widely reported, few researches have appeared on the interrelationship about rhizospheric soil microorganism community and soil organic carbon (SOC) under multi-root Cerasus humilis plantations of different age. In our study, the rhizospheric soil microbial communities, soil physicochemistry, and SOC molecular groups in plantations of 1-, 3-, and 5-year-old Cerasus humilis were investigated in karst rocky desertification control area of southwest China. It was found that karst rhizospheric soil moisture, total nitrogen, available potassium, and 46-60ppm N-alkyl/methoxyl C decreased; however, SOC and fungal:bacterial ratio decreased along multi-root Cerasus humilis plantation chronosequence. Proteobacteria, Actinobacteriota, Acidobacteriota, and Ascomycota were recognized as the top 4 phyla in the karst rhizospheric soil microbial co-occurrence network. Moreover, Cerasus humilis plantations exerted significantly direct effect on rhizospheric soil microbial communities and soil physicochemical properties exerted significantly direct effects on SOC molecular groups. Our results suggested that the increased Cerasus humilis plantation years will promote C sequestration (e.g., SOC) with the continued input of root litter, root exudates, and plant litter. The inputted and activated C can be preferentially consumed by rhizospheric soil microorganisms and converted into microbial-derived compounds, which are finally incorporated into recalcitrant SOC pools. Hence, Cerasus humilis redistributed SOC molecular groups via rhizospheric soil microorganisms, and increased ratio of fungi:bacteria in rhizosphere was associated with C sequestration which could not be regarded as a widespread rule. Though our study is the first attempt to recognize the interaction between rhizospheric soil microbial community and SOC molecular groups at the karst rocky desertification control area, it provides a baseline for further research that ecological restoration can promote soil C sequestration via soil microorganisms in the early period of eco-restoration at karst area.

Biochar derived from hydrolysis of sewage sludge influences soil properties and heavy metals distributed in the soil.

Sewage sludge contains a large number of nutrients and dangerous substances, when sludge was processed into sludge hydrochar that was added to the soil, which not only solve the problem of sludge disposal, but also amend the soil and fix pollutants in the soil. However, it was lack of report on the effect of the sludge hydrochar on soil compositions and soil microorganism community structures until now. In the present study, the hydrothermal carbonization method is used to prepare hydrochar from sewage sludge at temperatures of 180℃ and 240℃ at durations of 6h and 15h in this paper. The effects of the prepared sludge hydrochar on soil-derived dissolved organic matter (DOM), the content of total dissolved nitrogen (TDN) and NO3--N in soil, and the community structure of soil bacteria and fungi were evaluated. Furthermore, the change rules in heavy metal speciation in soils treated with sludge hydrochar were investigated. With the increase in the preparation temperature and dosage of sludge hydrochar, the main components of DOM changed from soluble microbial byproducts to fulvic acid-like and humic acid-like fractions through UV and fluorescence characterization. The sludge hydrochar prepared at low temperature could significantly increase the contents of TDN and NO3--N in the soil. Affected by sludge hydrochar, the dominant phylum of the bacterial community changed from Proteobacteria to Actinobacteria, and the dominant phylum in the fungal community did not change, but its relative abundance increased. Finally, the sludge hydrochar obtained when the carbonization time was 15h was more beneficial to reduce the total amount and available content of heavy metals in the soil. The study provides a basis for sludge hydrochar application for the soil amendment.

Influence of soil management for soybean production under microbial diversity in amazon soils

The tropical Amazon has a unique biodiversity that has been affected by the development of pastures and economically important crops, such as soybeans. In the Amazon soil, the communities of microorganisms are diverse and act in different biogeochemical activities relevant to their adaptation to the environment. The assessment of changes in soil microorganism communities is essential to consider the impact of agribusiness action in one of the wealthiest regions in diversity in the world. Thus, the soil microbial diversity of the Amazon forest, the north region of Brazil, was evaluated regarding the influence of soybean farming with regions with periods of two and 14 years of exploitation, with regions of pasture and forest area, through the metagenomics approach with new generation sequencing technology, in addition, it was considered chemical characteristics such as pH value, organic matter content, macronutrients, micronutrients, and cations. High microbial diversity was identified at all collection sites and, despite this, bacterial, archaeal, and virus communities were very diverse between sites, with higher identification of Enterobacter cloacae and species of Pseudomonas, Pseudoplusia includens, Methanosarcina barkeri in the farmed and pasture, whose microbial diversity is influenced by the presence of cations and the interaction of organic matter with clay. It was evident that there is a change in the communities of native microorganisms for others adapted in the areas that had their vegetal cover eliminated.

A less complex but more specialized microbial network resulted in faster fine-root decomposition in young stands of Robinia pseudoacacia

Microorganisms play an important role in litter decomposition. Bacteria and fungi colonize litter during the decomposition process; therefore, understanding the interactions of bacterial and fungal communities can yield insight into litter decomposition dynamics. Most studies have focused on leaf litter decomposition, but thus far, there has been little information on the dynamic changes in soil microbial composition at the different stages of fine-root decomposition. Therefore, we conducted a 210-day incubation experiment on the fine roots of Robinia pseudoacacia to explore how the temporal dynamics of soil enzyme activities and microbial communities are related to the decomposition of R. pseudoacacia at four different stand ages (15, 25, 35 and 45 years) during vegetation restoration. The results showed that the fine-root decomposition rate was higher for young stands of R. pseudoacacia. We found that the oxidase activity was significantly higher in the young stands (15 and 25 years) than in the old stands (35 and 45 years), while the hydrolase activity showed the opposite trend. The main reason for the higher decomposition rate in young stands of R. pseudoacacia was the high oxidase enzyme activities and less complex but more specialized microbial network of younger stands. The occurrence network was used to identify the keystone taxa by statistical analysis, and the key taxa changed from Acidobacteria to Proteobacteria during vegetation restoration. These findings demonstrate that vegetation restoration alters the soil microorganism community and network structure during fine-root decomposition of R. pseudoacacia. This finding is of great significance for understanding the role of microorganisms in regulating fine-root decomposition dynamics.

Soil microbial communities under wheat and maize straw incorporation are closely associated with soil organic carbon fractions and chemical structure

The incorporation of different types of crop straw may lead to distinct forms and chemical structures of soil organic matter (SOM), which are closely associated with the communities of soil microorganisms in agricultural ecosystems. However, the relationships between the physiochemical composition of SOM and soil microbial communities in response to the incorporation of different types of crop straw remain largely unknown. In this study, we sought to gain insights into these relationships based on a long-term (10 year) field experiment, in which we examined the effects of five treatments [no fertilizer (control), mineral fertilizer (F), mineral fertilizer and wheat straw return (WF), mineral fertilizer and maize straw return (MF), and mineral fertilizer with wheat and maize straw (WMF)]. Using advanced solid-state 13carbon (C) nuclear magnetic resonance and high-throughput sequencing techniques, we investigated the associations between SOM physical fractions and chemical composition and the compositions of soil fungal and bacterial communities Our observations indicated that compared with treatment MF, the long-term incorporation of wheat straw increased the proportions of carbohydrate carbons in light-fraction and coarse-particulate organic matter (cPOM), which were significantly correlated with soil bacterial community composition. Long-term maize straw incorporation was found to increase the proportions of course and fine-POM fractions relative to the WF treatment, as well as the proportions of their aromatic carbons, which were significantly correlated with soil fungal community composition. Collectively, the findings of this study revealed that bacterial and fungal communities are characterized by two distinct responses to wheat and/or maize straw incorporation, which are strongly associated with the physical fractions and chemical structure of SOM, particularly in the case of POM. These findings provide valuable insights for understanding the associations between soil microbial communities and SOM fractions following crop straw incorporation, which will contribute to the development of optimal strategies for crop straw management.

Antibiotic properties of Satureja montana L. hydrolate in bacteria and fungus of clinical interest and its impact in non-target environmental microorganisms

The aim of this study was to analyse the microbicidal and microbiostatic activity of S. montana hydrolate L., the water-soluble fraction of the hydro-distillation process used to obtain the essential oil, on 14 Gram-positive and Gram-negative bacteria and a fungus of clinical interest. To consider whether this hydrolate is a more environmentally friendly alternative to traditional antibiotics, its effect on non-target microorganisms in the aquatic and terrestrial environment was analysed using natural soil and river microorganism communities, characterized through 16S rRNA gene sequencing. Results showed that S. montana hydrolate was especially effective (25% v/v concentration) against Pasteurella aerogenes, Streptococcus agalactiae and Acinetobacter baumannii (priority 1, WHO). It was also a microbicide for a further 7 bacterial strains and the fungus Candida albicans (50% v/v concentration). The river and soil communities exposed to the hydrolate showed a decrease in their growth, as well as a decrease in their ability to metabolize polymers and carbohydrates (soil microorganisms) and polymers, carboxylic and ketone acids (river microorganisms). Hydrolates could be an alternative to conventional antibiotics, but their impact on the environment must be taken into account.

Substituting Sargassum sp. Compost for Inorganic Fertilizer Improves the Growth and Yield of Shallot (Allium cepa L. Aggregatum Group)

Fertilizers derived from natural materials, such as Sargassum sp. (seaweed), are a promising technique to overcome the negative impact of overuse of inorganic fertilizers. Groundwater contamination, soil degradation, and changes in the soil microorganism community are problems related to overdosing on inorganic fertilizer during crop production. The use of Sargassum compost (SC) as a substitute inorganic fertilizer was tested by evaluating the growth and yield of shallot grown on sandy soil. The research was arranged in a randomized complete block design consisting of four treatments and three blocks of replications. The treatments involved substituting SC for inorganic fertilizer, which were 100% inorganic, 25% SC + 75% inorganic, 50% SC + 50% inorganic, and 75% SC + 25% inorganic, respectively. The compositions of nitrogen (N), phosphorus (P), potassium (K), sodium (Na), sulfur (S), auxin, gibberellin, cytokinin, and kinetin in SC, as well as the growth and yield of shallot, were analyzed by analysis of variance followed by the least significant difference test. The results showed that the SC contained high organic matter (45.78%), nitrogen (4.1%), phosphate (0.5%), potassium (0.8%), sodium (7.2%), sulfur (0.2%), and plant growth hormones, such as auxin (8.14 mg.g−1), gibberellin (15.97 mg.g−1), cytokinin (7.70 mg.g−1), and kinetin (2.78 mg.g−1). Interestingly, all substitution levels of the SC for inorganic fertilizer improved nutrient absorption in the leaves, roots, and bulbs. Moreover, the growth and yield of shallot were not significantly different among the treatments. Therefore, to provide sufficient nutrients and growth hormones, SC could be substituted for up to 75% of organic fertilizers for shallot plants.

Bacterial, fungal, and mycorrhizal communities in the soil differ between clearcuts and insect outbreaks in the boreal forest 50 years after disturbance

Soil microorganisms influence the functions and processes of forest ecosystems, and their composition is affected by natural and anthropogenic disturbances. Timber harvesting disturbs boreal soil microbiomes, most notably ectomycorrhizal communities which are reportedly less diverse in the first decade following a clearcut. However, the long-term impact of harvesting on forest soil microorganism communities have rarely been investigated nor compared with natural disturbances. Our objective was to compare the composition and diversity of bacterial, fungal, and mycorrhizal communities between boreal old-growth and nearby 50–year–old stands regenerating after either an insect outbreak or a clearcut. Our main hypothesis was that the nature of the stand–replacing disturbance influences the composition of the soil microbiome, and that the effect is still detectable 50 years later. We collected 90 samples from 30 plots across six forest stands dominated by Abies balsamea. We sequenced the genome regions 16S rRNA v3v4 for bacteria and ITS1 for fungi and we constructed distance matrices to evaluate changes in community composition with permutational analyses of variance. Results show that 10.2 % to 12.4 % of the variability in community composition can be explained by stand type alone for bacteria, fungi, and mycorrhizae. The composition of soil microbiomes did not vary with soil physicochemical properties. Stands regenerating after a clearcut had a greater alpha diversity (H’) of fungi and mycorrhizae than stands regenerating after an insect outbreak, while old–growth stands were intermediate. Our data indicate that soil microbiomes associated with natural disturbance dynamics differ from those of clearcutted stands, although the mechanisms underlying this pattern remain unclear. Therefore, we suggest that forest managers spare the largest possible tracts of unmanaged forests across the harvested landscape, including areas affected by natural disturbances, so that benchmark soil communities remain available for future studies.

Responses of soil microorganisms to simulated climate change in desert grassland in northern China

Abstract The study evaluates how simulated climate change affects microorganism communities in the desert grassland of Ningxia Autonomous Region, China. It explores the soil microorganism community and relationships among the soil microorganism community, chemical properties, soil respiration (SR), and plant biomass under climate change. We established a field experiment with five levels of rainfall using rainout shelters and two levels of temperature by the Open-Top Chamber (OTC). The results show that in fungal communities, normal precipitation will promote the number and base number of valid sequences the most, and R66 will significantly promote the mean length of the valid sequence. In the bacterial communities, the interaction of increasing temperature and R133 will promote the number of valid sequences and R166 will promote the length of valid sequences. Neither rainfall nor rising temperature promotes not only the soil community α-diversity but also the soil microorganism community β-diversity. Soil microorganism communities show resistance to rainfall. SR will limit the soil microorganism diversity. Soil organic carbon (SOC), soil total nitrogen (STN), and soil total phosphorus (STP) will promote soil microorganism abundance (SMA) and soil microorganism diversity (SMS). Aboveground living biomass (ALB) and soil temperature (ST) will promote soil α-diversity, whereas the effect of root biomass (RB) on the soil α-diversity is the opposite.