Soil Carbon Cycling Research Articles

Impact of a warmer cold season on soil nitrogen and carbon cycling in High Arctic wet sedge tundra

Soil available nitrogen (N) pools in the High Arctic are expected to increase due to permafrost thaw and elevated microbial activity stimulated by atmospheric warming and subsequent changes in soil moisture regimes. The cold season, or the period between soil freeze-up in fall and thaw in spring, is warming relatively faster compared to the growing season, which may increase the insulating snow cover and microbial degradation of soil organic matter. Changes in temperature and available N levels can stimulate soil CO₂, CH4, and N₂O flux rates which could trigger further warming. Despite the potential importance of the cold season, the influence of variability in cold season temperatures on the release and accumulation of inorganic N and greenhouse gases is poorly understood in High Arctic environments. We conducted a 50-day laboratory incubation study that mimics the annual soil temperature cycle to investigate the effects of different minimum cold season temperatures (- 10˚C, −15˚C, −20˚C, −25˚C) on spring and growing season N and carbon (C) cycling in the soil.We measured inorganic N pools, net N cycling rates, and CO₂, CH4, and N₂O fluxes throughout the study. Over the coldest period of the annum, the warmest and coldest soils displayed greatest net N mineralization rates (-0.035 mg kg−1 d-1 and −0.049 mg kg−1 d-1 respectively). During the thaw period, we found that soils treated with −10˚C resulted in a spring NO3–-N flush that was ∼ 700% larger than −15 ˚C, −20 ˚C, −25 ˚C treatments, which were relatively consistent with each other, suggesting a cold-temperature inhibition of nitrification. Although cold season fluxes of CH4 and CO₂ differed with temperature, there was no treatment effect on subsequent flux rates during the growing season. We conclude that changes in cold season temperatures can play a crucial role in soil N biogeochemistry in High Arctic wet-sedge communities and have a potential to disrupt surrounding downstream ecosystems. The impact of cold season warming, however, does not appear to be linear for all processes with temperature change.

Metagenomics combined with metabolomics reveals the effect of Enterobacter sp. inoculation on the rhizosphere microenvironment of Bidens pilosa L. in heavy metal contaminated soil

Metagenomics analysis was performed to determine the effects of Enterobacter sp. FM-1 (FM-1) on key genera as well as functional genes in the rhizosphere of Bidens pilosa L. (B. pilosa L.). Moreover, metabolomics was used to reveal the differences among rhizosphere metabolites after FM-1 inoculation. FM-1 inoculation significantly increased the activity of enzymes associated with the carbon cycle in soil; among them, invertase activity increased by 5.52 units compared to a control. Specifically, the relative abundance of beneficial genera increased significantly, such as Lysobacter (0.45–2.58 unit increase) in low-contamination soils (LC) and Pseudomonas (31.17–45.99 unit increase) in high-contamination soils (HC). Comparison of different transformation processes of the C cycle revealed that inoculation of FM-1 increased the abundance of functional genes related to the carbon cycle in LC soil. In contrast, the nitrogen cycling pathway was significantly elevated in both the LC and HC soils. FM-1 inoculation reduced HM resistance gene abundance in the rhizosphere soil of B. pilosa L. in the LC soil. Moreover, FM-1 and B. pilosa L. interactions promoted the secretion of rhizosphere metabolites, in which lipids and amino acids played important roles in the phytoremediation process. Overall, we explored the rhizosphere effects induced by plantmicrobe interactions, providing new insights into the functional microbes and rhizosphere metabolites involved in phytoremediation.

Using enzyme activities as an indicator of soil fertility in grassland - an academic dilemma.

Grasslands play an important role in conserving natural biodiversity and providing ecosystem functions and services for societies. Soil fertility is an important property in grassland, and the monitoring of soil fertility can provide crucial information to optimize ecosystem productivity and sustainability. Testing various soil physiochemical properties related to fertility usually relies on traditional measures, such as destructive sampling, pre-test treatments, labor-intensive procedures, and costly laboratory measurements, which are often difficult to perform. However, soil enzyme activity reflecting the intensity of soil biochemical reactions is a reliable indicator of soil properties and thus enzyme assays could be an efficient alternative to evaluate soil fertility. Here, we review the latest research on the features and functions of enzymes catalyzing the biochemical processes that convert organic materials to available plant nutrients, increase soil carbon and nutrient cycling, and enhance microbial activities to improve soil fertility. We focus on the complex relationships among soil enzyme activities and functions, microbial biomass, physiochemical properties, and soil/crop management practices. We highlight the biochemistry of enzymes and the rationale for using enzyme activities to indicate soil fertility. Finally, we discuss the limits and disadvantages of the potential new molecular tool and provide suggestions to improve the reliability and feasibility of the proposed alternative.

Global biogeographic distribution of Bathyarchaeota in paddy soils.

Bathyarchaeota, known as key participants of global elements cycling, is highly abundant and diverse in the sedimentary environments. Bathyarchaeota has been the research spotlight on sedimentary microbiology; however, its distribution in arable soils is far from understanding. Paddy soil is a habitat similar to freshwater sediments, while the distribution and composition of Bathyarchaeota in paddy soils have largely been overlooked. In this study, we collected 342 in situ paddy soil sequencing data worldwide to illuminate the distribution patterns of Bathyarchaeota and explore their potential ecological functions in paddy soils. The results showed that Bathyarchaeota is the dominant archaeal lineage, and Bathy-6 is the most predominant subgroup in paddy soils. Based on random forest analysis and construction of a multivariate regression tree, the mean annual precipitation and mean annual temperature are identified as the factors significantly influencing the abundance and composition of Bathyarchaeota in paddy soils. Bathy-6 was abundant in temperate environments, while other subgroups were more abundant in sites with higher rainfall. There are highly frequent associations between Bathyarchaeota and methanogens and ammonia-oxidizing archaea. The interactions between Bathyarchaeota and microorganisms involved in carbon and nitrogen metabolism imply a potential syntrophy between these microorganisms, suggesting that members of Bathyarchaeota could be important participants of geochemical cycle in paddy soils. These results shed light on the ecological lifestyle of Bathyarchaeota in paddy soils, and provide some baseline for further understanding Bathyarchaeota in arable soils.IMPORTANCEBathyarchaeota, the dominant archaeal lineage in sedimentary environments, has been the spotlight of microbial research due to its vital role in carbon cycling. Although Bathyarchaeota has been also detected in paddy soils worldwide, its distribution in this environment has not yet been investigated. In this study, we conducted a global scale meta-analysis and found that Bathyarchaeota is also the dominant archaeal lineage in paddy soils with significant regional abundance differences. Bathy-6 is the most predominant subgroup in paddy soils, which differs from sediments. Furthermore, Bathyarchaeota are highly associated with methanogens and ammonia-oxidizing archaea, suggesting that they may be involved in the carbon and nitrogen cycle in paddy soil. These interactions provide insight into the ecological functions of Bathyarchaeota in paddy soils, which will be the foundation of future studies regarding the geochemical cycle in arable soils and global climate change.

A Comprehensive Analysis of Machine Learning-Based Assessment and Prediction of Soil Enzyme Activity

Different soil characteristics in different parts of India affect agriculture growth. Crop growth and crop production are significantly impacted by healthy soil. Soil enzymes mediate almost all biochemical reactions in the soil. Understanding the biological processes of soil carbon and nitrogen cycling requires defining the significance of prospective elements at the play of soil enzymes and evaluating their activities. A combination of Multiple Linear Regression (MLR), Random Forest (RF) models, and Artificial Neural Networks (ANN) was employed in this study to assess soil enzyme activity, including amylase and urease activity, soil physical properties, such as sand, silt, clay, and soil chemical properties, including organic matter (SOM), nitrogen (N), phosphorus (P), soil organic carbon (SOC), pH, and fertility level. Compared to other methods for estimating soil phosphatase, cellulose, and urease activity, the RF model significantly outperforms the MLR model. In addition, due to its ability to manage dynamic and hierarchical relationships between enzyme activities, the RF model outperforms other models in evaluating soil enzyme activity. This study collected 3972 soil samples from 25 villages in the Bhandara district of Maharashtra, India, with chemical, physical, and biological parameters. Overall, 99% accuracy was achieved for cellulase enzyme activity and 94% for N-acetyl-glucosaminidase enzyme activity using the Random Forest model. Crops have been suggested based on the best performance accuracy algorithms and evaluation performance metrics.

Response of Cellulose Decomposition and Nodulation in Soils Amended with Biochar for Peri-Urban Agriculture

Peri-urban agriculture is becoming a potential step to promote sustainable and environmental food production systems. Our aim was to study the effect of biochar application at various rates on faba bean growth, cellulose decomposition, nodulation, and selected enzyme activities associated with carbon cycling in clay and sandy soils collected from peri-urban agricultural areas near the city of El-Minia, Egypt. To achieve this aim, incubation and pot experiments were conducted under controlled greenhouse conditions using clay and sandy soil. Among the studied treatments, using biochar at the rate of 3 kg/sq·m was the most effective soil amendment followed by biochar at the rate of 2 kg/sq·m. At 60 days of incubation, the count of cellulose-decomposing microorganisms reached a high level in both clay and sandy soil, and then decreased after 90 days, regardless of the biochar rate. The response of the cellulose-decomposer ratio (Fcd/Bcd) was positively correlated with biochar rates and incubation time. The obtained results showed significant increases in fresh and dry weight in clay soil compared to sandy soil. In any case, the use of biochar as a soil amendment enhanced soil health, soil microbial communities, and increased cellulose-decomposing microorganisms, thus improving faba bean nodulation and growth.

Fire effects on soil carbon cycling pools in forest ecosystems: A global meta-analysis

Changes in soil carbon (C) pools driven by fire in forest ecosystems remain equivocal, especially at a global scale. In this study we analyzed data from 232 studies consisting of 1702 observations to investigate whether ecosystem type, climate zone, stand age, soil depth, slope, elevation, and the time since fire in influence of forest soil carbon pools to fire regime (fire type, fire season, fire intensity). Additionally, we explored the potential mechanisms of the relationships between multiple response variables to the fire using linear regression and random forest models. On aggregate, fires significantly increased the mean effect sizes of several key soil carbon cycling components-including microbial biomass carbon (MBC), dissolved organic carbon (DOC), total carbon (TC), pyrogenic carbon (PyC), soil organic matter (SOM), soil organic carbon (SOC) by 0.77, 0.89, 0.87, 1.22, 0.97 and 0.93, respectively, compared to unburned forests ecosystems. However, the fire effects on soil C pools vary widely between environmental factors and duration, and are mediated by factors such as tree species, fire type, and soil layer. A correlation analysis displayed the effects of fire on MBC and DOC were significantly and negatively correlated with elevation. Fire effects on the forest floor and mineral soil indicated significantly increased PyC. SOC and TC in coniferous tree species are the most sensitive to fires, thereby altering important feedback relationships with the fire-vegetatale-climate system. Interestingly, latitude has a stronger influence on SOC than mean annual precipitation or elevation, indicating that variations in latitude play a significant role in regulating the amount of SOC in forest ecosystems. Overall, the results illustrated geographic variation in fire effects on soil C cycling underscores the need for region-specific fire management plans, and help us understand the responses of soil C cycling to fire in forest ecosystems, and facilitate decision-making to forest fire management.

The core microbiota as a predictor of soil functional traits promotes soil nutrient cycling and wheat production in dryland farming

Abstract Host plants and the microbiota living in the rhizosphere are interdependent, mutually reinforced and mutually beneficial but the assembly, functions and microbial interactions of the host‐associated microbiota are still unclear. Herein, winter wheat was selected as a test plant to explore the assembly process of total bacteria from bulk soil (BS) and rhizosphere soil (RS), and phoD‐harbouring bacteria in RS at a long‐term (14 years) trial site. We also identified core microbes that are potentially relevant to soil carbon (C), nitrogen (N) and phosphorus (P) cycling genes and soil biogeochemical properties, and investigated the relationships between soil variables, functional genes and wheat productivity. The results showed that the microhabitat of the plant, rather than P fertilizer input, was the main factor affecting the microbial diversity, composition and co‐occurrence networks. The BS bacterial community was driven by deterministic processes but the RS and phoD bacterial communities were dominated by stochastic processes. The influence of deterministic processes decreased with increasing soil nutrient content. A core microbial community consisted of 10 OTUs in different microhabitats and was significantly related to soil functional genes and properties. In the rhizosphere soil, significant correlations were found between soil variables, soil functional bacteria and genes, and crop productivity. Synthesis and applications. This study provides empirical evidence that the assembly process of the microbial community is governed by environmental factors in various soil environments and provides new perspectives on the sustainable improvement of crop productivity. Read the free Plain Language Summary for this article on the Journal blog.

Soil microbe-mediated carbon and nitrogen cycling during primary succession of biological soil crusts in tailings ponds

Tailings ponds resulting from mining operations have led to serious environmental hazards, and their bioremediation is an area of ongoing exploration. Primary succession represents the starting point of biotic community establishment and development, with soil carbon and nitrogen cycling being critical to this process. To investigate the soil microbial-mediated carbon and nitrogen cycling patterns accompanying primary succession, we selected three types of tailings ponds as study areas and set up sampling sites for different stages of primary succession. The results showed that primary succession promoted microbe-mediated carbon and nitrogen cycling. It also led to improvements in soil nutrient availability and enzyme activity. In primary succession, the main pathways of carbon cycling are 3HP and rTCA, and nitrogen cycling is nitrate assimilation. In the early stages, microbes mediated more anaerobic and microaerobic processes. As succession proceeded, the pattern of microbial contributions to the carbon and nitrogen cycles changed. As succession proceeds, the functional metabolic potential of the carbon cycle gradually rises, while the nitrogen cycle shows a dramatic increase after the accumulation of autotrophic biomass. In addition, we found a positive coupling pattern between the carbon and nitrogen cycles. These findings support the optimization of bioremediation strategies for tailings ponds.

Viral community structure and functional potential vary with lifestyle and altitude in soils of Mt. Everest

More and more focus has been placed on the processes by which viruses interact with bacteria to influence the biogeochemical cycles. The intricacy of soil matrix and the incompleteness of databases, however, constrains the investigation on the mechanisms of soil viruses exerting ecological functions. The modification of ICTV classification system in 2021 was also a huge shock to the results of the existing studies on virome. We used viral metagenomes combined with soil properties to investigate the viral community composition and auxiliary metabolic genes (AMGs) profiles of various lifestyles in soils of Mount Everest at different altitudes. Viral lifestyles and soil nutrient levels were found to significantly influence the diversity and composition of viral communities. Temperate virus lifestyle dominated in high-altitude soils with lower level of nutrients because of its stronger survival adaptability, and the structural and functional diversity of viral communities was positively correlated with the contents of nutrients (total carbon and total nitrogen). The primary types of AMGs carried by temperate and virulent viruses differed, while a variety of genes involved in carbon metabolism highlighted the potential importance of viruses in the soil carbon cycle of Mount Everest. Moreover, the abundance of AMGs encoding carbohydrate-active enzymes had a significant and positive correlation with soil C/N ratio. Overall, these findings provide a context for further exploration on the regulatory mechanisms of viruses in carbon cycle via interactions with microorganisms.

Positive responses of soil nutrients and enzyme activities to AM fungus under interspecific and intraspecific competitions when associated with litter addition

Arbuscular mycorrhizal fungi mediated-litter decomposition is essential for soil carbon and nutrient cycling. Plant competition profoundly influences soil C, nutrients, glomalin-related soil protein, and enzymes. However, it is unclear how a combined AM fungus and litter addition affects soil properties under interspecific and intraspecific competitions. With 170-day-old Broussonetia papyrifera and Carpinus pubescens seedlings, three treatments of intraspecific or interspecific plant competition, AMF Claroideoglomus etunicatum inoculation or not, and leaf litter addition to soil substrate or not were examined to address differences in plant biomass production, soil organic carbon, total nitrogen and total phosphorus, EE-GRSP, DE-GRSP and T-GRSP, and activity of alkaline phosphatase, catalase and urease. The results were as follows: Root, shoot and total biomass increased in B. papyrifera but decreased in C. pubescens under AM mycorrhization in both intraspecific and interspecific competitions. Under mycorrhization, intraspecific, not interspecific, competition increased SOC and ratios of C/N, C/P, DE-GRSP and T-GRSP. Mycorrhization plus litter addition increased SOC, ratios of C/N, C/P and N/P, EE-GRSP, DE-GRSP, T-GRSP, and alkaline phosphatase activity under intraspecific competition, while soil TN, TP, and catalase and urease activities. Soil C, N, P, EE-GRSP or T-GRSP positively associated with catalase, urease or alkaline phosphatase activities. These results showed that alterations in intra- and interspecific competition induced by AM fungus positively respond to soil C, nutrient, GRSP, and enzyme activities, thus plant competition is a key factor in regulating soil properties. Overall, we suggest that interspecific competition enables AMF to increase soil N and P accumulations and related enzyme activities, while intraspecific competition confers more significant benefits than interspecific competition in improving soil C and GRSP accumulations under a combined AMF and litter addition. The findings highlight the importance of plant competition in improving soil function through AM fungus, which is conducive to understand the mechanisms of plant restoration and nutrient cycling in degraded ecosystems.

Mutual feeding mechanism of carbon, nitrogen and enzyme activity in Northeast China black soil under snow cover change

Projected future changes in snow cover patterns associated with global warming in cold zone ecosystems could affect soil biochemical cycling. However, the effects of snow cover changes on soil available carbon, nitrogen and enzyme activities and their potential response mechanisms have not been clarified. Therefore, from November 2021 to April 2022, this study conducted a snow depth manipulation test of four treatments in the northeast black soil region, and divided the test period into five stages to measure soil temperature and humidity, microbial biomass, enzyme activity, and available carbon and nitrogen. The results showed that the decrease of snow cover increased the freeze-thaw cycle frequency and freezing temperature of soil, but decreased the soil water content. Soil total organic carbon and inorganic nitrogen contents were increased in early and deep snow periods, while snow treatment was on the contrary. Due to the release of soluble nutrients caused by frequent freeze-thaw processes, Soil soluble organic carbon and Soil soluble organic nitrogen contents increased with the decrease of snow depth in deep snow period, snowmelt period and subsequent early crop growth period. Snow treatment increased soil microbial carbon and nitrogen content in early winter and early spring because snow provided heat insulation. Soil enzyme activities increased with the increase of snow cover. Compared with the control, soil urease activities and sucrase activities increased by 18.5 % and 11.5 % under snow treatment, and decreased by 23.2 % and 10.8 % under snow reduction treatment. In addition, soil soluble organic matter was a controlling factor for soil microbial biomass and enzyme activity throughout winter. The direct effect of soil soluble organic carbon and nitrogen on soil enzymes will make soil enzymes participate in the cyclic transformation process of available carbon, thus forming a closed loop of mutual feedback between soil available carbon and nitrogen and enzymes. These results demonstrated that the changes of snow cover in the future will have certain effects on soil carbon and nitrogen cycles and enzyme activities and hence biogeochemical cycling in terrestrial system of earth.

Effects of Vegetation Types on Carbon Cycle Functional Genes in Reclaimed Soil from Open Pit Mines in the Loess Plateau

Vegetation restoration can effectively improve the ecological environment of mining areas, enhance the ecological service function, and promote the carbon sequestration and sink increase in the ecosystem. The soil carbon cycle plays an important role in the biogeochemical cycle. The abundance of functional genes can predict the material cycling potential and metabolic characteristics of soil microorganisms. Previous studies on functional microorganisms have mainly focused on large ecosystems such as farmland, forest, and wetland, but relatively little attention has been paid to complex ecosystems with great anthropogenic interference and special functions, such as mines. Clarifying the succession and driving mechanism of functional microorganisms in reclaimed soil under the guidance of vegetation restoration is helpful to fully explore how functional microorganisms change with the change in abiotic and biotic conditions. Therefore, 25 topsoil samples were collected from grassland (GL), brushland (BL), coniferous forests (CF), broadleaf forests (BF), and mixed coniferous and broadleaf forests (MF) in the reclamation area of the Heidaigou open pit waste dump on the Loess Plateau. The absolute abundance of soil carbon cycle functional genes was determined using real-time fluorescence quantitative PCR to explore the effect of vegetation restoration on the abundance of carbon cycle-related functional genes in soil and its internal mechanism. The results showed that:① the effects of different vegetation restoration types on the chemical properties of reclaimed soil and the abundance of functional genes related to the carbon cycle were significantly different (P<0.05). GL and BL showed significantly better accumulation of soil organic carbon, total nitrogen, and nitrate nitrogen (P<0.05) than that in CF. ② The gene abundance of rbcL, acsA, and mct was the highest among all carbon fixation genes. The abundance of functional genes related to carbon cycle in BF soil was higher than that in other types, which was closely related to the high activity of ammonium nitrogen and BG enzymes and the low activity of readily oxidized organic carbon and urease in BF soil. The functional gene abundance of carbon degradation and methane metabolism was positively correlated with ammonium nitrogen and BG enzyme activity and negatively correlated with organic carbon, total nitrogen, readily oxidized organic carbon, nitrate nitrogen, and urease activity (P<0.05). ③ Different vegetation types could directly affect soil BG enzyme activity or affect soil nitrate nitrogen content, thus indirectly affecting BG enzyme activity, in turn manipulating the abundance of functional genes related to the carbon cycle. This study is helpful to understand the effects of different vegetation restoration types on the functional genes related to the carbon cycle in the soil of mining areas on the Loess Plateau and provides a scientific basis for ecological restoration and ecological carbon sequestration and sink enhancement in mining areas.

Drought intensity alters productivity, carbon allocation and plant nitrogen uptake in fast versus slow grassland communities

Abstract Grasslands face more frequent and extreme droughts; yet, their responses to increasing drought intensity are poorly understood. Increasing drought intensity likely triggers abrupt shifts (thresholds) in grassland ecosystem functioning which can implicate recovery trajectories. Here, we determined how drought intensity affects plant productivity, and plant–soil carbon (C) and nitrogen (N) cycling. We exposed model grassland plant communities with contrasting resource acquisition strategies (a fast‐ vs a slow‐strategy plant community), to a gradient of drought intensity. The drought gradient ranged from well‐watered to severely water‐limited conditions. We identified thresholds of plant community productivity (above‐ground biomass) at peak drought and 2 months after re‐wetting, and measured net ecosystem exchange and ecosystem respiration of C throughout the drought and recovery phases. At peak drought and 1 week after re‐wetting, we traced recently acquired C from plants to the soil and into microbial biomass and fatty acids using 13C pulse labelling, and measured plant and soil N. At peak drought, slow‐strategy plant communities were more drought resistant than fast‐strategy communities, as the threshold in plant productivity occurred at a higher drought intensity for the slow‐ than the fast‐strategy community. Shortly after re‐wetting, microbial uptake of recent plant‐assimilated C increased with increasing past drought intensity, coinciding with an increase in soil N availability and leaf N. Threshold responses to drought intensity at peak drought translated into non‐linear recovery responses, with greater compensatory growth in the fast‐strategy community. At peak drought, increasing drought intensity reduced C uptake and increased relative C partitioning to leaves and microbial biomass. Upon re‐wetting, plant community strategy mediated drought intensity effects on plant and soil C and N dynamics and plant recovery trajectories. The fast‐strategy community recovered quickly, with higher leaf N than the slow community, while the slow community increased C allocation to microbial biomass. Synthesis. Our findings highlight that C and N dynamics in the plant–soil system display non‐linear responses to increasing drought intensity both during and after drought, which has implications for plant community recovery trajectories.

Metaproteomics reveals functional partitioning and vegetational variation among permafrost-affected Arctic soil bacterial communities.

Microbial activity in Arctic soils controls the cycling of significant stores of organic carbon and nutrients. We studied in situ processes in Alaskan soils using original metaproteomic methods in order to relate important heterotrophic functions to microbial taxa and to understand the microbial response to Arctic greening. Major bacterial groups show strong metabolic specialization in organic topsoils. α-/β-/γ-Proteobacteria specialized in the acquisition of small, soluble compounds, whereas Acidobacteria, Actinobacteria, and other detritosphere groups specialized in the degradation of plant-derived polymers. α-/β-/γ-Proteobacteria dominated the expression of transporters for common root exudates and limiting nitrogenous compounds, supporting an ecological model of dependence upon plants for carbon and competition with plants for nitrogen. Detritosphere groups specialized in distinct substrates, with Acidobacteria producing the most enzymes for hemicellulose depolymerization. Acidobacteria was the most active group across the three plant ecotypes sampled-the largely nonvascular, lower biomass intertussock and the largely vascular, higher biomass tussock and shrub. Functional partitioning among bacterial groups was stable between plant ecotypes, but certain functions associated with α-/β-/γ-Proteobacteria were more strongly expressed in higher biomass ecotypes. We show that refined metaproteomic approaches can elucidate soil microbial ecology as well as biogeochemical trajectories of major carbon stocks. IMPORTANCE The Arctic is warming twice as fast as the rest of the planet, and Arctic soils currently store twice as much carbon as the entire atmosphere-two facts that make understanding how Arctic soil microbial communities are responding to climate change particularly urgent. Greening of vegetation cover across the Arctic landscape is one of the most prominent climate-driven shifts in Arctic terrestrial ecology, with potentially profound effects on biogeochemical cycling by the soil microbiome. Here we use metaproteomics to document microbial metabolic functions that drive soil carbon and nutrient cycling processes in an Arctic tundra landscape. We identify functional roles among bacterial taxonomic groups that are largely stable across vegetation types, with certain functions strongly expressed by rhizosphere groups reflecting a community metabolic response to greening.

Molecular composition and possible transformations of labile soil organic matter fractions in Mediterranean arable soils: Relevance and implications

With the increased global interest in sequestering carbon in soil, it is necessary to understand the composition of different pools of soil organic matter (SOM) that cycle over suitably short timeframes. To explore in detail the chemical composition of agroecologically relevant yet distinct fractions of SOM, the light fraction of SOM (LFOM), the 53-μm particulate organic matter (POM), and the mobile humic acid (MHA) fractions were sequentially extracted from agricultural soils and characterized using both 13C cross polarization magic angle spinning nuclear magnetic resonance (CPMAS NMR) spectroscopy and also Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). The NMR results showed a decrease in the O-alkyl C region assigned to carbohydrates (51–110 ppm) and an increase in the aromatic region (111–161 ppm) proceeding from the LFOM to the POM and then to the MHA fraction. Similarly, based on the thousands of molecular formulae assigned to the peaks detected by FT-ICR-MS, condensed hydrocarbons were dominant only in the MHA, while aliphatic formulae were abundant in the POM and LFOM fractions. The molecular formulae of the LFOM and POM were mainly grouped in the high H/C lipid-like and aliphatic space, whereas a portion of the MHA compounds showed an extremely high (17–33, average of 25) double bond equivalent (DBE) values, corresponding to low H/C values of 0.3–0.6, representative of condensed hydrocarbons. The labile components appeared most pronounced in the POM (93% of formulae have H/C ≥ 1.5) similar to the LFOM (89% of formulae have H/C ≥ 1.5) but in contrast to the MHA (74% of formulae have H/C ≥ 1.5). The presence of both labile and recalcitrant components in the MHA fraction suggests that the stability and persistence of soil organic matter is influenced by a complex interaction of physical, chemical, and biological factors in soil. Understanding the composition and distribution of different SOM fractions can provide valuable insights into the processes that govern carbon cycling in soils, which can help inform strategies for sustainable land management and climate change mitigation.

Metagenomics insights into the functional profiles of soil carbon, nitrogen, and phosphorus cycles in a walnut orchard under various regimes of long-term fertilisation

Soil microbial functional potential is important for productivity and sustainable agricultural development; however, the potential response of soil nutrient cycling to different fertilisation regimes remains unclear, especially in perennial tree soils. Here, metagenomic sequencing was applied to investigate the soil microbial functional profiles of carbon (C), nitrogen (N), and phosphorus (P) cycling after seven years of chemical, organic, and biofertiliser fertilisation in walnut (Juglans regia L.) orchard. Microbial communities balanced their elemental requirements through selective degradation. The highest relative abundance of genes for labile C-degradation (amyA, malZ, and xylH) was found under chemical fertilisation (F), whereas the metabolic potential for soil N and P cycling was less affected by F. Compared with CK and F, the addition of organic and/or biofertiliser significantly reduced the relative abundances of labile and recalcitrant C-degradation genes (e.g., chi, and xylH) but promoted the processes of N degradation (GDH1, GDH2, ureA, glnA, and arcC), DNRA (nrfA, napB, and napC), organic P mineralisation (phy), P solubilisation (gcd), and P uptake and transport (phnD) in walnut soils. At the phylum level, most C, N, and P cycle-related microbes were similar, and applying biofertiliser remarkably improved the relative abundances of Proteobacteria and Firmicutes involved in C, N, and P cycling processes. Furthermore, soil TN and AP were key limiting macronutrients for regulating the pathways of soil C, N, and P cycles and microbial taxa. C, N, and P cycle-related genes were tightly coupled through synergetic or antagonistic interactions, especially metabolic pathways encoded by glnA, mmsA, phy, and appA. Overall, our results provide a biological perspective on the microbial genetic potential of soil C, N, and P cycles in perennial crops and explore their interactions under different long-term fertilisation regimes in a walnut orchard.

Nano-Nd2O3 reduced soil bacterial community function by altering the relative abundance of rare and sensitive taxa.

Nanoparticulate-Nd2O3 (nano-Nd2O3) has been excessively utilized in agriculture, industry, and medicine. Hence, nano-Nd2O3 can have environmental implications. However, the impact of nano-Nd2O3 on alpha diversity, composition, and function of soil bacterial communities has not been thoroughly evaluated. We amended soil to achieve different concentrations of nano-Nd2O3 (0, 10, 50, and 100mgkg-1 soil) and incubated the mesocosms for 60days. On days 7 and 60 of the experiment, we measured the effect of nano-Nd2O3 on alpha diversity and composition of soil bacterial community. Further, the effect of nano-Nd2O3 on the function of soil bacterial community was assessed based on changes in the activities of the six potential enzymes that mediate the cycling of nutrients in the soil. Nano-Nd2O3 did not alter the alpha diversity and composition of the soil bacterial community; however, it negatively affected community function in a dose-dependent manner. Specifically, the activities of β-1,4-glucosidase and β-1,4-n-acetylglucosaminidase that mediate soil carbon and nitrogen cycling, respectively, were significantly affected on days 7 and 60 of the exposure. The effect of nano-Nd2O3 on the soil enzymes correlated with changes in relative abundances of the rare and sensitive taxa, viz., Isosphaerales, Isosphaeraceae, Ktedonobacteraceae, and Streptomyces. Overall, we provide information for the safe implementation of technological applications that use nano-Nd2O3.

Long-term N addition leads to microbial C, but not N limitation of poplar plantation soils in eastern China

Soil extracellular enzymes are vital to regulating soil carbon (C) and nutrient cycling, and hence affecting soil function. However, how soil enzymes activity will respond to increasing global nitrogen (N) deposition, remains poorly understood. In this study, we applied five N addition treatments (0, 5, 10, 15, and 30 g m−2 yr−1) at a coastal China poplar plantation to explore the activity of the five soil enzymes associated with C, N, and phosphorus (P) cycling and nutrient limitation of soil microbes from 2018 to 2020. We found that N addition significantly increased C, decreased N and showed no significant impact on P acquisition enzyme activity. We also found that N addition aggravated soil microbial C limitation but did not significantly change the N limitation. Both soil microbial C and N limitation were eased with time (year). Best subset regression analysis (BSS) showed that dissolved organic C, soil pH, and microbial biomass C were the dominant drivers of C, N, and P acquisition enzyme activity, respectively. Also, BSS showed that soil available N explained the greatest proportion of variation in positive soil microbial C and negative N limitation. Our study provides evidence for changes in soil enzymes activity and microbial nutrients limitation, as well as contributes to the theoretical basis for soil microbial nutrient cycling with elevated N deposition.

Soils at the temperate forest edge: An investigation of soil characteristics and carbon dynamics

Global proliferation of forest edges through anthropogenic land-use change and forest fragmentation is well documented, and while forest fragmentation has clear consequences for soil carbon (C) cycling, underlying drivers of belowground activity at the forest edge remain poorly understood. Increasing soil C losses via respiration have been observed at rural forest edges, but this process was suppressed at urban forest edges. We offer a comprehensive, coupled investigation of abiotic soil conditions and biotic soil activity from forest edge to interior at eight sites along an urbanization gradient to elucidate how environmental stressors are linked to soil C cycling at the forest edge. Despite significant diverging trends in edge soil C losses between urban and rural sites, we did not find comparable differences in soil % C or microbial enzyme activity, suggesting an unexpected decoupling of soil C fluxes and pools at forest edges. We demonstrate that across site types, soils at forest edges were less acidic than the forest interior (p < 0.0001), and soil pH was positively correlated with soil calcium, magnesium and sodium content (adj R2 = 0.37), which were also elevated at the edge. Compared to forest interior, forest edge soils exhibited a 17.8 % increase in sand content and elevated freeze-thaw frequency with probable downstream effects on root turnover and decomposition. Using these and other novel forest edge data, we demonstrate that significant variation in edge soil respiration (adj R2 = 0.46; p = 0.0002) and C content (adj R2 = 0.86; p < 0.0001) can be explained using soil parameters often mediated by human activity (e.g., soil pH, trace metal and cation concentrations, soil temperature), and we emphasize the complex influence of multiple, simultaneous global change drivers at forest edges. Forest edge soils reflect legacies of anthropogenic land-use and modern human management, and this must be accounted for to understand soil activity and C cycling across fragmented landscapes.