Soil Microbial Community Function Research Articles

Effects of micronutrient fertilization on soil carbon pools and microbial community functioning

Fertilization with macronutrients, e.g., nitrogen (N) and phosphorus (P), has wide-ranging and well-characterized effects on terrestrial ecosystem functions. In contrast, influences of other elements, e.g., sodium (Na), calcium (Ca), and potassium (K), hereafter, ‘micronutrients’, are poorly understood. To determine effects of macronutrients, micronutrients, and their interactions on soil carbon (C) cycling, we conducted a full factorial experiment where treatments consisted of fertilizing experimental plots with Na, Ca, and K (each manipulated individually) and macronutrients (N + P added together). Each year of the experiment we measured aboveground plant biomass and sampled soils to quantify mineralizable C pools and active microbial biomass. To further explore micronutrient effects on microbial-mediated soil C cycling, in the final year of the experiment we assessed microbial C cycle functions using a catabolic profiling technique and quantified multiple additional soil C pools: particulate (POM-C), mineral-associated (MAOM-C), and total (TC). Macronutrients (N + P) affected nearly all measured variables – when N + P was added, active microbial biomass increased, catabolic profiles were altered, and mineralizable C, POM-C, and TC pools all increased. Micronutrients also had effects on soil C cycling that were generally smaller than effects of macronutrients – Ca addition reduced mineralizable C pools relative to the other treatments and K addition increased POM-C and TC pools. Further, Ca + K addition altered microbial catabolic profiles, but only when N + P was also added. Our study reveals several influences of micronutrients on soil C cycling – specifically, that Ca and K may influence the size of soil C pools by influencing the C cycle functions of soil microbial communities.

Effect of Soil Aggregate Size on Vineyard Bacterial Communities under Organic and Conventional Agro-Managements

Soil microorganisms are an indispensable component of natural ecosystems and play an important role in agro-management ecosystems. However, the function of soil microbial communities is still a black box. The present study aimed to investigate the effect of organic and conventional agro-management practices in a vineyard on the soil’s bacterial community and its composition in three different soil aggregate sizes using functional profiles derived using 16S rDNA metagenomics analysis for elucidating the metabolic capabilities of soil microbial communities. Soil samples were compared in terms of community composition and functionality. A clear distinction was found between the two managements. The soil samples contained 12 phyla and 45 orders, where Proteobacteria was the most common phylum in all treatments. Twenty-three functional profiles were obtained for both treatments and three aggregate sizes, showing similarity in their function, suggesting that functionality is due to the community’s composition and environmental conditions. The results indicate that organic farming systems have a beneficial effect on microbial diversity and encourage ecosystem multifunctionality.

Recovery of soil microbial diversity and functions along a tropical montane forest disturbance gradient

Logging and forest conversion are occurring at alarming rates in tropical forests. These disturbances alter soil microbial community structure and functions. While direct links between changes in soil properties, such as pH and microbial community structure are well established, the indirect effects of logging and forest conversion on soil microbial community structure and functions are poorly understood. We used a space-for-time substitution to investigate the changes in soil microbial diversity and functions across a forest recovery gradient in the tropical montane forests of northern Borneo. We used surface (top 5 cm) soil to assess soil physicochemical and microbial (next-generation DNA sequencing) properties, and standardized litterbags (Tea Bag Index) to assess litter decomposition and stabilization. Our results show that bacterial and fungal diversity increases with recovery time and reaches pre-disturbance levels between 60- and 80-years post-disturbance. Litter decomposition rate constants increased linearly with increasing bacterial and fungal diversity. Litter stabilization also increased linearly with fungal diversity, but was highest at intermediate levels of bacterial diversity. Our results provide insights on the effects of forest logging and conversion on soils and highlight the tight coupling between soil microbial diversity and soil functions in tropical montane forests.

Responses of soil microbial communities to concentration gradients of antibiotic residues in typical greenhouse vegetable soils

To explore the responses of soil microbial communities to concentration gradients of antibiotic residues in soil, 32 soil samples were collected from a typical greenhouse vegetable production base in Northern China in 2019. The total concentrations of 26 antibiotic residues in these soil samples was 83.24–4237.93 μg·kg−1, of which metabolites of tetracyclines were 23.34–1798.80 μg·kg−1. The total concentrations in 32 samples were clustered into three levels (L: <100 μg·kg−1, M: 100–300 μg·kg−1, H: >300 μg·kg−1) to elucidate the impacts of antibiotic residues on the diversity, structure, composition, function and antibiotic resistome of soil microbial community. Results showed that higher concentration of antibiotic residues in soil was prone to decrease the diversity and shift the structure and composition of soil microbial community. Antibiotic resistome occurred in soils with antibiotic residues exceeding 300 μg·kg−1. Interactions among soil bacteria followed the order of H > L > M, consistent with the relative abundances of mobile genetic elements. Bacteroidetes and Firmicutes were the top attributors impacting the profile of antibiotics in soil. According to weighted comprehensive pollution index of risk quotient, in 28.1 % of soil samples the residual antibiotics presented high ecological risk, whereas in the rest of soil samples the ecological risk is medium. The results will enrich the database and provide references for antibiotic contamination control in soils of the region and alike.

Tillage intensity and plant rhizosphere selection shape bacterial-archaeal assemblage diversity and nitrogen cycling genes

Agroecosystem management practices, plant-microbe interactions, and climate are all factors that influence soil microbial community diversity and functionality. Herein, we assessed diversity of soil bacterial-archaeal assemblages and denitrification gene markers in a long-term tillage field experiment. We evaluated bulk and rhizosphere soils from two crop years (corn and soybean) of a three-year rotation of corn-soybean-small grain + cover crop. Soil samples were collected at three growth stages from corn and soybean plants and across three tillage practices that had been applied every year for 40 years. Tillage practices represented three levels of disturbance intensity ranging from low (no-till) to intermediate (chisel-disk) to high (moldboard plow) intensities. Bacterial assemblage diversity differed in soils having contrasting tillage histories and from bulk or rhizosphere soil (compartments), crop year, and growth stage. Compared to plowed and chisel-disked soils, no-till soils had lower abundances of denitrification genes, higher abundances of genes for dissimilatory nitrate reduction to ammonium (DNRA), and higher abundances of family-level taxa associated with archaeal nitrification and anammox. Soybean rhizospheres exerted stronger selection on bacterial-archaeal composition and diversity relative to corn rhizospheres. Abundances of N genes were grouped by factors related to weather, as well as management and soil compartment, which could impact activity related to denitrification and DNRA. Low intensity tillage may provide an option to reduce potential ‘hot spots’ or ‘hot moments’ for N losses in agricultural soils, although weather and crop type are also important factors that can influence how tillage affects microbial assemblages and microbial N use.

Effects of Biochar and Plant Growth-Promoting Rhizobacteria on Plant Performance and Soil Environmental Stability

(1) Background: Biochar and plant growth-promoting rhizobacteria (PGPR) are widely used as amendments to increase the availability of nutrients and the diversity of the bacterial community within soil. (2) Methods: In this study, we investigated the effects of biochar and PGPR amendments on plant performance, soil physicochemical property, and soil microbial diversity, as well as their relationship in a Eucalyptus (clone DH32−29) plantation in Guangxi, China. We determined the microbial AWCD, Simpson, Shannon, and McIntosh indices, and soil inorganic nitrogen (NH4+, NO3−), total phosphorus (TP), total potassium (TK), total nitrogen (TN), and plant growth and nutrient concentrations; (3) Results: Biochar-only had a significant impact on soil microbial community function, although the effects on plant performance were limited. PGPR plus biochar was found to significantly increase the diversity indices of soil microbes, as well as soil TK and TP. Besides, soil microbes displayed a preference for carbohydrates rather than other carbon sources. (4) Conclusion: Soil microbial functional diversity responded to changes in plant performance and, therefore, it could indicate soil ecological stability and ecosystem productivity. These findings may suggest that biochar and PGPR could potentially maintain ecological sustainability in the soil and improve plant performance through altering soil physicochemical properties in a eucalyptus plantation.

Land use intensification in a dry-hot valley reduced the constraints of water content on soil microbial diversity and multifunctionality but increased CO2 production

Conversion of abandoned land (mainly savanna) into cropland generally occurs in fragile ecosystems such as dry-hot valleys (DHVs) in southwest China, with the intent of increasing land productivity and conducting ecological restoration. However, the effects of conversion on soil microbial communities and carbon turnover of savanna ecosystems remain unclear, since savannas could be a vital but overlooked carbon sink. To illustrate the ecological consequences of land-use change (LUC) for savanna ecosystems, a 1-year field experiment was conducted in DHVs of southwest China. The soil properties, microbial respiration, and metagenomics from two different land-use types (grassland and mango plantation) were examined to reveal the effects of regional LUC on soil C turnover and microbial traits. Conversion from degraded grassland into cropland increased the contribution of soil microclimate to the microbial community composition, reduced the constraints of soil water content (SWC), and further decreased nutrient availability. LUC reshaped the composition and structure of soil bacterial communities. Specifically, soil dominant microbes that belonged to Actinobacteria and Proteobacteria were significantly enriched by conversion, while rare microbes that belonged to a wider range of phyla were generally depleted, leading to an overall decrease in community diversity. In addition, LUC-induced changes in soil characteristics and microbial communities further decreased soil multifunctionality as well as the carbon use efficiency of microbes. Intensified microbial respiration and a significant increase in the soil CO2 efflux were observed following LUC, which could drive changes in soil microbial community composition and functions (such as growth and regeneration). In summary, through simultaneously reducing constraints on SWC and decreasing nutrient availability, conversion from degraded grassland to cropland in a DHV decreased soil microbial diversity and multifunctionality, and increased microbial respiration and soil CO2 efflux. Our study provides new insights for understanding the role and mechanisms of LUC in soil carbon turnover in ecologically fragile areas such as DHVs.

Land-use-driven change in soil labile carbon affects microbial community composition and function

The conversion of natural forests to plantations can lead to a substantial loss of soil organic carbon (SOC) and threaten the function of soil microbial communities. However, the effect of forest conversion on the relationship between SOC dynamics and shifts in the composition and function of the microbial community remain poorly understood, although such information is critical for predicting the long-term effect of land-use change on global SOC dynamics and storage. To fill this knowledge gap, our study investigated the influence of two decades of converting natural forest to a tea plantation on SOC storage, microbial community composition, C-degrading enzyme activity and the abundance of C-degrading microbial functional genes in a subtropical region in China. Two decades after converting natural forest to tea plantation, SOC storage decreased by 30%, and labile SOC [including easily mineralized C (Cmin), readily oxidizable C (ROC), dissolved organic C (DOC), and microbial biomass C (MBC)] decreased by 21–71%. Land-use change decreased the relative abundance of copiotrophic bacteria but increased the relative abundance of oligotrophic bacteria and lignin-degrading fungi. This resulted in a decrease in cellulase activity and cbhI gene abundance involved in cellulose degradation and conversely an increase in ligninase activity involved in lignin degradation after the conversion. Such shifts in microbial community composition and function associated with land-use change were mediated by the decrease in the labile C pool rather than the total SOC. Our study provided new insights into not only shifts in microbial communities but also specific C functional genes and related enzymes after forest conversion. These findings highlight that labile SOC, as an important functional soil component for microbial communities, significantly affects SOC dynamics and storage.

A field study of nano-FeS loaded lignin hydrogel application for Cd reduction, nutrient enhancement, and microbiological shift in a polluted paddy soil

Cadmium (Cd) pollution in paddy soil has caused serious harm to human health. Nano-ferrous sulfide@lignin hydrogel (FeS@LH) composites could be an ideal material for paddy soil Cd removal due to the excellent adsorption performance and mechanical strength. But the FeS@LH’s performance in a paddy field remains unclear. In this study, FeS@LH was applied to a Cd-contaminated paddy field when planting water spinach (Ipomoea aquatica Forssk). The results showed that FeS@LH effectively removed Cd from the soil (37.6 %) and water spinach (34.5 %) after 30 days. The concentrations of Pb, Zn, Cu, and other metals in soil and water spinach were co-reduced. When the FeS@LH dosage was 30 g·m−2, the effective functional distance was within 30 cm. FeS@LH application had a positive effect on soil nutrients. The soil nitrogen and organic matter contents increased by 16.1 % and 13.8 %, respectively. No significant effect on soil total phosphorus and potassium contents was presented. The survival rate of zebrafish in the acute toxicity test of FeS@LH was 98.9 %, indicating its biosafety. In addition, FeS@LH application decreased soil microbial community diversity probably due to the decreased pH. The microbial metabolism tended to enhance, suggesting a restoration of soil microbial community function after Cd removal.

One or many? Multi-species livestock grazing influences soil microbiome community structure and antibiotic resistance potential

Soil health has been highlighted as a key dimension of regenerative agriculture, given its critical importance for food production, carbon sequestration, water filtration, and nutrient cycling. Microorganisms are critical components of soil health, as they are responsible for mediating 90% of soil functions. Multi-species rotational grazing (MSRG) is a promising strategy for maintaining and improving soil health, yet the potential effects of MSRG on soil microbiomes are poorly understood. To address this knowledge gap, we collected soil microbial samples at three timepoints during the 2020 grazing season for 12 total paddocks, which were equally split into four different grazing treatments—cattle only, sheep only, swine only, or multi-species. Shallow shotgun metagenomic sequencing was used to characterize soil microbial community taxonomy and antibiotic resistome. Results demonstrated broad microbial diversity in all paddock soil microbiomes. Samples collected early in the season tended to have greater archaeal and bacterial alpha diversity than samples collected later for all grazing treatments, while no effect was observed for fungi or viruses. Beta diversity, however, was strongly influenced by both grazing treatment and month for all microbial kingdoms, suggesting a pronounced effect of different livestock on microbial composition. Cattle-only and swine-only paddocks were more dissimilar from multi-species paddocks than those grazed by sheep. We identified a large number of differentially abundant taxa driving community dissimilarities, includingMethanosarcinaspp.,Candidatus Nitrocosmicus oleophilus, Streptomycesspp.,Pyriculariaspp.,Fusariumspp., andTunggulvirus Pseudomonas virusϕ-2. In addition, a wide variety of antibiotic resistance genes (ARGs) were present in all samples, regardless of grazing treatment; the majority of these encoded efflux pumps and antibiotic modification enzymes (e.g., transferases). This novel study demonstrates that grazing different species of livestock, either separately or together, can impact soil microbial community structure and antibiotic resistance capacity, though further research is needed to fully characterize these impacts. Increasing the knowledge base about soil microbial community structure and function under real-world grazing conditions will help to construct metrics that can be incorporated into traditional soil health tests and allow producers to manage livestock operations for optimal soil microbiomes.

Pecan plantation age influences the structures, ecological networks, and functions of soil microbial communities

AbstractUnderstanding the changes in microbial communities with increasing plantation age will benefit the maintenance of forest health and productivity and the sustainable development of forest ecosystems. It was not clear before this study whether the microbial communities of pecan (Carya illinoinensis) plantations would be affected by their age. Based on MiSeq sequencing, we studied the effects of pecan age on microbial communities in rhizosphere and bulk soils of pecan plantations for the first time. The results showed that the bacterial alpha diversity of bulk soil increased significantly with plantation age (p &lt; 0.05), while fungal alpha diversity was less influenced by pecan age in both rhizosphere soil and bulk soil. Pecan age significantly influenced bacterial and fungal community structure in both rhizosphere soil and bulk soil (p &lt; 0.01). The fungal community composition was significantly altered by pecan age as reflected by the increase (22% in bulk soil and 18.4% in rhizosphere soil) and decrease (25.4% in bulk soil and 22.7% in rhizosphere soil) in the relative abundances of Basidiomycetes and Ascomycota, respectively. The pH value and available phosphorus (AP) content drove microbial community structure and composition. The bacterial network was more complex than the fungal network, and simpler and more stable microbial network structures occurred in the rhizosphere soil than in the bulk soil. With increasing plantation age, the risk from plant pathogenic fungi increased, and the functional profile of the microbial community shifted from the nitrogen cycle to carbon utilization.

Effects of Land Use Conversion on the Soil Microbial Community Composition and Functionality in the Urban Wetlands of North-Eastern China

Urban wetlands are undergoing intensive conversion from natural wetlands to farmlands, woodlands, and even alkaline land. This study aimed to determine the effects of land conversion on soil microbial communities of urban wetlands in the hinterland of Songnen Plain, Northeastern China. Soil samples were collected from various sites of Longfeng wetland, including swamp wetland (SW), meadow wetland (MW), woodland (WL), farmland (FL), and alkaline land (AL). High-throughput sequencing followed by bioinformatic analysis was conducted to evaluate the structure, composition, and function of soil bacterial and fungal communities. The most dominant bacterial and fungal phylum among the land-use types were Proteobacteria and Ascomycota, respectively. In addition, the bacterial diversity and functions varied significantly across different land-use types. However, no remarkable differences in fungal communities were observed under various land-use types. Edaphic parameters, including exchange sodium percent (ESP) and total nitrogen (TN), remarkably influenced the abundance and diversity of soil microbial communities. These results show that land-use type shapes various aspects of soil microbial communities, including soil physicochemical properties, microbial taxa structure, potential functional genes, and correlation with environmental factors. This study provides reliable data to guide land use management and supervision by decision-makers in this region.

Shifts in Soil Microbial Community Composition, Function, and Co-occurrence Network of Phragmites australis in the Yellow River Delta.

Soil microorganisms play vital roles in regulating biogeochemical processes. The composition and function of soil microbial community have been well studied, but little is known about the responses of bacterial and fungal communities to different habitats of the same plant, especially the inter-kingdom co-occurrence pattern including bacteria and fungi. Herein, we used high-throughput sequencing to investigate the bacterial and fungal communities of five Phragmites australis habitats in the Yellow River Delta and constructed their inter-kingdom interaction network by network analysis. The results showed that richness did not differ significantly among habitats for either the bacterial or fungal communities. The distribution of soil bacterial community was significantly affected by soil physicochemical properties, whereas that of the fungal community was not. The main functions of the bacterial and fungal communities were to participate in the degradation of organic matter and element cycling, both of which were significantly affected by soil physicochemical properties. Network analysis revealed that bacteria and fungi participated in the formation of networks through positive interactions; the role of intra-kingdom interactions were more important than inter-kingdom interactions. In addition, rare species acted as keystones played a critical role in maintaining the network structure, while likely played an important role in maintaining the network topological properties. Our findings provided insights into the inter-kingdom microbial co-occurrence network and response of the soil microbial community composition and function to different P. australis habitats in coastal wetlands, which will deepen our insights into microbial community assembly in coastal wetlands.

Structural and functional characteristics of soil microbial community in a Pinus massoniana forest at different elevations.

Shifts in forest soil microbial communities over altitudinal gradients have long been attracting scientific interest. The distribution patterns of different soil microbial communities along altitudinal gradients in subtropical mountain forest ecosystems remain unclear. To better understand the changes in soil microbial communities along an altitude gradient, we used Illumina MiSeq metagenome sequencing technology to survey the soil microbial communities in a Pinus massoniana forest at four elevations (Mp1000, Mp1200, Mp1400, Mp1600) and in a tea garden in Guizhou Leigong Mountain in Southwestern China. We observed that the richness of bacteria, fungi, and viruses in the soil microbial community changed in a unimodal pattern with increasing elevation while that of Archaea first increased significantly, then decreased, and finally increased again. Euryarchaeota and Thaumarchaeota were the predominant Archaea, Proteobacteria and Acidobacteria were the predominant bacterial groups, Ascomycota and Basidiomycota were the predominant fungal groups, and Myoviridae, Podoviridae, and Siphoviridae were the predominant virus groups. Amino acid transport and metabolism, energy production and conversion, signal transduction mechanisms, and DNA replication, restructuring and repair were the predominant categories as per NOG function gene-annotation. Carbohydrate metabolism, global and overview map, amino acid metabolism, and energy metabolism were predominant categories in the KEGG pathways. Glycosyl transferase and glycoside hydrolase were predominant categories among carbohydrate enzyme-functional genes. Cluster, redundancy, and co-occurring network analyses showed obvious differences in the composition, structure, and function of different soil microbial communities along the altitudinal gradient studied. Our findings indicate that the different soil microbial communities along the altitudinal gradient have different distribution patterns, which may provide a better understanding of the mechanisms that determine microbial life in a mid-subtropical mountain forest ecosystem.

Adaptive multi-paddock grazing increases soil nutrient availability and bacteria to fungi ratio in grassland soils

Grasslands are used extensively for grazing livestock, and variation in grazing management may affect the soil microbial community and ecosystem functions, such as nutrient cycling, in grasslands. In particular, adaptive multi-paddock (hereafter ‘multi-paddock’) grazing is considered a regenerative grazing management practice that can improve the sustainability of grasslands. However, little is known about how multi-paddock grazing affects the soil microbial community, which plays an importance role in global biogeochemical cycling. In this study, grassland soils were collected from 15 ranch pairs located across the Canadian prairie, where, in each pair, one ranch practiced multi-paddock grazing while the other practiced conventional grazing (varying from continuous to slow to fast rotational grazing). We used soil phospholipid fatty acid (PLFA) profiles to quantify microbial functional groups, and measured microbial biomass C and soil properties. Our data show that microbial PLFA abundances and microbial biomass C was not different between the two grazing systems. However, multi-paddock grazing resulted in lower ratios of microbial biomass C: N (MBC:MBN), fungi: bacteria (F:B) and Gram-positive: Gram-negative bacteria in grassland soils compared to conventional grazing. Further investigation of specific management metrics revealed that MBC:MBN and F:B ratios were most affected by cattle stocking rate and stocking density, respectively. Thus, there is potential to affect soil function by altering the composition of soil microbial communities through multi-paddock grazing.

Soil microbes-mediated enzymes promoted the secondary succession in post-mining plantations on the Loess Plateau, China

The diversity of vegetation configuration is the key to ecological restoration in open-pit coal mine dump. However, the recovery outcomes of different areas with the same vegetation assemblage pattern are completely different after long-term evolution. Therefore, understanding the causes of differential vegetation recovery and the mechanism of plant succession is of great significance to the ecological restoration of mines. Three Pinus tabulaeformis plantations with similar initial site conditions and restoration measures but with different secondary succession processes were selected from the open-pit coal mine dump that has been restored for 30 years. Soil physicochemical properties, enzyme activities, vegetation and microbial features were investigated, while the structural equation models were established to explore the interactions between plants, soil and microbes. The results showed that original vegetation configuration and soil nutrient conditions were altered due to secondary succession. With the advancement of the secondary succession process, the coverage of plants increased from 34.8% to 95.5% (P < 0.05), soil organic matter increased from 9.30 g kg−1 to 21.13 g kg−1 (P < 0.05), and total nitrogen increased from 0.38 g kg−1 to 1.01 g kg−1 (P < 0.05). The activities of soil urease and β-glucosidase were increased by 1.7-fold and 53.26%, respectively. Besides, the secondary succession also changed the soil microbial community structure and function. The relative abundance of Nitrospira genus which dominates the nitrification increased 5.2-fold. The results showed that urease and β-glucosidase promoted the increase of vegetation diversity and biomass by promoting the accumulation of soil organic matter and nitrate nitrogen, which promoted the ecological restoration of mine dumps.

The activity and functions of soil microbial communities in the Finnish sub-Arctic vary across vegetation types.

Due to climate change, increased microbial activity in high-latitude soils may lead to higher greenhouse gas (GHG) emissions. However, microbial GHG production and consumption mechanisms in tundra soils are not thoroughly understood. To investigate how the diversity and functional potential of bacterial and archaeal communities vary across vegetation types and soil layers, we analyzed 116 soil metatranscriptomes from 73 sites in the Finnish sub-Arctic. Meadow soils were characterized by higher pH and lower soil organic matter (SOM) and carbon/nitrogen ratio. By contrast, dwarf shrub-dominated ecosystems had higher SOM and lower pH. Although Actinobacteria, Acidobacteria, Alphaproteobacteria and Planctomycetes were dominant in all communities, there were significant differences at the genus level between vegetation types; plant polymer-degrading groups were more active in shrub-dominated soils than in meadows. Given that climate-change scenarios predict the expansion of shrubs at high latitudes, our results indicate that tundra soil microbial communities harbor potential decomposers of increased plant litter, which may affect the rate of carbon turnover in tundra soils. Additionally, transcripts of methanotrophs were detected in the mineral layer of all soils, which may moderate methane fluxes. This study provides new insights into possible shifts in tundra microbial diversity and activity due to climate change.

Interactive effects of microplastics, biochar, and earthworms on CO2 and N2O emissions and microbial functional genes in vegetable-growing soil

Soil carbon dioxide (CO2) and nitrous oxide (N2O) emissions are two main greenhouse gases that play important roles in global warming. Studies have shown that microplastics, biochar, and earthworms can significantly affect soil greenhouse gas emissions. However, few studies have explored how their interactions affect soil CO2 and N2O emissions. A mesocosm experiment was conducted to investigate their interactive effects on soil greenhouse gases and soil microbial functional genes in vegetable-growing soil under different incubation times. Biochar alone or combined with microplastics significantly decreased soil CO2 emissions but had no effect on soil N2O emissions. Microplastics and biochar inhibited CO2 emissions and promoted N2O emissions in the soil with earthworms. The addition of microplastics, biochar, and earthworms had significant effects on soil chemical properties, including dissolved organic carbon, ammonia nitrogen, nitrate nitrogen, total nitrogen, and pH. Microplastics and earthworms selectively influenced microbial abundances and led to a fungi-prevalent soil microbial community, while biochar led to a bacteria-prevalent microbial community. The interactions of microplastics, biochar, and earthworms could alleviate the reduction of the bacteria-to-fungi ratio and the abundance of microbial functional genes caused by microplastics and earthworms alone. Microplastics significantly inhibited microorganisms as well as C and N cycling functional genes in earthworm guts, while biochar obviously stimulated them. The influence of the addition of exogenous material on soil greenhouse gas emissions, soil chemical properties, and functional microbes differed markedly with soil incubation time. Our results indicated that biochar is a promising amendment for soil with microplastics or earthworms to simultaneously mitigate CO2 emissions and regulate soil microbial community composition and function. These findings contribute to a better understanding of the interaction effects of microplastics, biochar, and earthworms on soil carbon and nitrogen cycles, which could be used to help conduct sustainable environmental management of soil.

Response of the Soil Microbe Community to Maize Residue Management Strategies Under Double-Cropping Systems

Sustainable agriculture has become a common trend in countries around the world. This includes returning straw to the field as part of sustainable crop production. However, it is not known whether changing the amount of straw returned to the field will lead to changes in the microbial community during decomposition and subsequent nutrient use by the next season's crop. The design included three treatments: (1) all the summer maize stalks returned to the field (SR); (2) half the summer maize stalks returned to the field (HSR); and (3) no summer maize stalks returned to the field (control: CK), base on all the winter wheat stalks were returned to the field. Compared with CK, the annual yield of SR treatment and HSR treatment increased by 18.8 and 17.3%, respectively. However, there are no significant difference in crop yield between the SR and HSR treatments. Compared with CK, the Proteobacteria increased by 29.9% in SR and 31.2% in HSR, which is the second most common bacterium during the maturity stage of maize season. Different crops season have an important impact on soil microbial community function (ANOSIM, R = 0.5209, P = 0.001). The PCoA analysis of the Faprotax function prediction found that the functional composition in the wheat planting period (wheat jointing and wheat harvest) was more similar, and the functional composition of maize planting period (maize tasseling and maize harvest) was more similar. The HSR can significantly increase the diversity of species in the soil to meet the nutritional demands for crop growth for achieve high and stable crop yield.

Maize root exudate composition alters rhizosphere bacterial community to control hotspots of hydrolase activity in response to nitrogen supply

Improving nitrogen (N) acquisition by crops from soil is essential to reduce fertilization rates whilst maintaining yields. Plants can adapt their nutrient acquisition strategies according to N availability, which also affects soil microbial community structure, functions and activities and relies on the supply of carbon (C) for energy. We hypothesized that N deprivation would create hotspots of N- and C-acquiring hydrolase activities in maize rhizosphere through the effects of altered root exudation on the rhizosphere bacterial community. We grew maize under three N fertilization rates and combined soil zymography with the identification of rhizosphere microbial communities and non-targeted metabolic profiling of root exudates to explore enzyme hotspot formation. The rhizosphere extents of β-1,4-glucosidase (BG) and β-N-acetylglucosaminidase (NAG) activities decreased after N fertilization, narrowing by 48% and 39%, respectively, under typical field N application rates compared to zero application. Rhizosphere extents of enzyme activities were more sensitive to altered N supply than changes in the rates of enzyme activities: BG activity decreased by ∼10%, while NAG activity was unaffected. Decreases in the activities of both hydrolases and their rhizosphere extents caused by N addition correlated with reduced abundances of oligotrophs. The relative abundances of oligotrophic bacteria (e.g., Acidobacteria) decreased, while copiotrophs (e.g., Pseudomonadota and Patescibacteria) increased under the highest N application rate. Co-occurrence networks of the rhizosphere bacterial community revealed that functional units increased with BG activity, while an efficient and denser co-occurrence network supported expansion of its rhizosphere extent. The metabolic profiles of root exudates changed according to the N application rate, suggesting that their chemistry was regulated by the plant in response to N supply. The composition of root exudates and dissolved organic C and nitrate contents explained the largest variations in NAG hotspots in the rhizosphere. In summary, maize actively adjusts the composition of root exudates to increase interactions with rhizosphere bacteria, thereby stimulating hydrolase production and activities, and altering their rhizosphere extents to mobilize N and energy (C) in a larger soil volume, under conditions of N deficiency.