Soil Functions Research Articles

Specific responses in soil metabolite alteration and fungal community decline to the long-term monocropping of lisianthus

Continuous cropping obstacle (CCO) is becoming a serious threat to the quality production of lisianthus (Eustoma grandiflorum). However, investigations of the causal mechanism of CCO in lisianthus are still lacking. To this end, soil biotic dynamics and metabolites alterations were illuminated using metagenomic sequencing and metabolomic profiling along a chronosequence that has cultivated lisianthus from 2 weeks to 6 years. Soil EC and nutrient contents increased significantly as the cultivation duration prolonged. Fungal community has undergone significant decline in their diversity and biomass. Nevertheless, no apparent accumulation of pathogenicity-related microbes was observed along the investigated chronosequence. The alterations of soil metabolites along the chronosequence reflect the decline of microbial activity, the accumulation of phytotoxic compounds and the loss of metabolite involved in beneficial plant-microbe interactions. As a result, lisianthus plants in the longer continuous cropping soil experienced stressful condition as evidenced by the increasing trend of stress responsive metabolites and the overall soil function deterioration as indicated by soil enzymes. Hierarchical partitioning analysis showed that the investigated factors can explain a total of 92.25 % of the variations in the soil function degradation. Of which, soil metabolite alteration was the most important factor in explaining the CCO development, covering 24.55 % of the explainable variations. Spearman's correlation results further implied that soil metabolite alteration is the main driver in the development of CCO in lisianthus, especially by mediating the plant-microbes interactions. Our findings revealed a general pattern of soil biotic and abiotic response to the continuous monocropping of lisianthus and suggest that the overcome of the CCO in lisianthus requires further studies focusing on the crucial metabolites and their interactions with microbes.

A meta-analysis to compare the sensitivities of earthworms and enchytraeids to different stressors

Earthworms and enchytraeids are soil organisms involved in key soil functions, such as organic matter turnover and soil structure, at different scales. In natural soils, these organisms are exposed and sensitive to different abiotic factors (e.g., climate, land use and management) and are often used as bioindicators of human disturbances, particularly chemical stress. However, the sensitivity of these two groups of Oligochaeta (Annelida) to different stressors has never been compared. Using data from 49 publications and 330 observations, we performed a meta-analysis to compare the sensitivities of earthworms and enchytraeids to all kinds of stressors under similar test conditions. Earthworms and enchytraeids were found to be equally sensitive to chemical stressors (mean effect size −0.61 [-2.53; 1.30]) regardless of the studied endpoint (mortality or reproduction). Most of the observations dealt with the effects of pesticides (42 %) and heavy metals (40 %) on both organisms. No difference in sensitivity was revealed when these two stressors were considered separately. Regarding the two most studied species of enchytraeids and earthworms, the mean effect sizes of all the possible combinations of Eisenia fetida (41 % of the studies) or Eisenia andrei (48 %) or Enchytraeus crypticus (73 % of the studies) or Enchytraeus albidus (27 %) did not reveal any differences in sensitivity. This study also highlights the lack of studies on environmentally relevant (i.e., representative of natural soils) enchytraeid and earthworm species. We also revealed that mostly ecotoxicologists have compared the sensitivities of these two key soil organisms when they are exposed to and threatened by other important factors, such as agricultural practices and climate change.

Enhanced Soil Fertility and Carbon Dynamics in Organic Farming Systems: The Role of Arbuscular Mycorrhizal Fungal Abundance.

Arbuscular mycorrhizal fungi (AMF) are critical for soil ecosystem services as they enhance plant growth and soil quality via nutrient cycling and carbon storage. Considering the growing emphasis on sustainable agricultural practices, this study investigated the effects of conventional and organic farming practices on AMF diversity, abundance, and ecological functions in maize, pepper, and potato-cultivated soils. Using next-generation sequencing and quantitative PCR, we assessed AMF diversity and abundance in addition to soil health indicators such as phosphorus content, total nitrogen, and soil organic carbon. Our findings revealed that, while no significant differences in soil physicochemical parameters or AMF diversity were observed across farming systems when all crop data were combined, organic farming significantly enhances AMF abundance and fosters beneficial microbial ecosystems. These ecosystems play vital roles in nutrient cycling and carbon storage, underscoring the importance of organic practices in promoting robust AMF communities that support ecosystem services. This study not only deepens our understanding of AMF's ecological roles but also highlights the potential of organic farming to leverage these benefits for improving sustainability in agricultural practices.

Trees support functional soils in a dryland agricultural area

Trees provide multiple ecosystem services such as carbon sequestration, hydrological regulation and habitat for arboreal animals. However, they are often removed to support agricultural enterprises. Despite the importance of tree remnants, we know relatively little about how soils differ across sites of varying condition. Here, we describe a study where we examined the relative effects of trees, compared with unvegetated interspaces, on soil functions in remnant patches at sites in good and poor condition in two eucalypt communities in an irrigation area in eastern Australia. We found that, in general, carbon and nutrient cycling were relatively greater beneath trees, and in surface soils, but there were no clear trends in relation to site condition. The values of most soil attributes (e.g., soluble and exchangeable cations, nitrogen, phosphorus) were greater beneath trees, indicating strong fertile island effects in both communities. Overall, our study confirms the importance of trees in remnant patches in agricultural landscapes, particularly those in sites of poor condition. It also suggests that soil processes may still be relatively intact, even in sites in poor condition. Our study reinforces the need to protect trees in remnant woodland reserves to maintain critical ecosystem functions related to nutrient retention. These remnants are important for achieving sustainable management of agricultural systems.

Impacts of soil de-sealing practices on urban land-uses, soil functions and ecosystem services in French cities

Soil sealing has been recognised as one of the main causes of urban soil degradation in Europe. To tackle this issue, de-sealing measures have recently been promoted in cities to increase the sustainability of soil ecosystem services. To our knowledge, very few evaluations of de-sealing projects have as yet been done to assess the current framework of these urban planning practices. Therefore, we conducted an online survey to collect and analyse soil de-sealing projects throughout mainland France. A 60-question survey was run over a 4-month-period, and data about 57 projects were collected. The answers covered a diversity of projects, structures and stakeholders and included data such as the location / objectives / costs and benefits of the projects implemented in cities of various sizes. A typology of urban land-uses before and after de-sealing was defined. Among the diverse objectives of de-sealing, rainwater management, reducing urban heat, and greening were most frequent. More than half of the respondents (64%) indicated that ecosystem services were used to drive their de-sealing project. The methods usually required excavation of the sealing cover and road layers being replaced by newly imported fertile materials. Recent de-sealing projects have reused derelict materials from the site (soil-material inventory) and/or local urban waste for soil construction, which can help minimise both the economic and environmental costs of urban greening projects. The results of this study provide quite an exhaustive view of current French de-sealing practices and could provide guidelines for improving soil functions by applying soil engineering processes to construct sustainable fertile soils for urban greening.

Variation of soil pore structure and predication of the related functions following land‐use conversion identified by multi‐scale X‐ray tomography

AbstractLand‐use conversion profoundly influences the soil pore structure, consequently modifying the soil functions. Investigating the variation of multiscale soil pore structure and their associated functions following land‐use change is critical for evaluating land management strategies. However, this topic has not yet been extensively explored in recent studies. In this study, the pore structure of soil following land‐use conversion was quantitatively investigated by multiscale X‐ray tomography. Intact soil aggregates and undisturbed soil cores were collected from paddy fields (PF) and from vegetable fields were converted from paddy fields for 5 years (VF‐5), 13 years (VF‐13), and 20 years (VF‐20), respectively. Results revealed that the connected porosity of both aggregates and soil cores was significantly increased after land‐use conversion. The isolated porosity of soil aggregates increased, while, conversely, it decreased for soil cores. The variance in pore structure was attributed to the development of new pores, including channels created by vegetable roots, fissures, earthworm holes, and packing pores resulting from the decomposition of soil organic matter and the rearrangement of soil particles. The altered pore structure influenced the soil exchangeability and reservation ability. For aggregates, the isolated porosity of PF and VF‐5 accounted for over 70% of the total imaged porosity. These aggregates displayed a larger water and carbon reservation ability, but limited exchangeability of air, water, and nutrients. The isolated porosity of VF‐13 and VF‐20 aggregates accounted for approximately 50% of the total imaged porosity, suggesting they could effectively balance the exchange and storage of air, water, and nutrients. As for soil cores, isolated pores became negligible (<0.2%) following land‐use conversion, leading to the emergence of a drainable pore system suitable for vegetable plantation. These findings offer insights into the development of pore structures and the prediction of soil function variations at multiple scales, both of which are crucial for optimizing soil management protocols.

Mycobiota of revegetated post‐mining and adjacent unmined sites 10 years after mining decommissioning

Although overlooked in post‐mining rehabilitation, soil mycobiota constitute an important fraction of biodiversity, playing pivotal functions in soil that contribute to the revegetation process and soil stability in post‐mining environments. Evaluating the rehabilitation progress requires comparing it, when possible, with a reference site, preferably identical or similar to pre‐mining characteristics. Here, we investigated the mycobiota from a reference site, comparable to pre‐mining characteristics, and a post‐mining revegetated site 10 years after decommissioning and revegetation, during rainy and dry seasons. We combined the metabarcoding approach with functional traits from fungal operational taxonomic units and complemented our results with traditional techniques for arbuscular mycorrhizal fungi (AMF) surveys using spore morphology and mycorrhizal colonization. Our findings demonstrated that the composition of the fungal community exhibited more differences between the two sites studied than the intra‐annual periods assessed, even though the sites were under the same climatic conditions, spatially nearby, and without barriers between them. The mycobiota composition displayed differences between sites from phylum to genus levels. However, the predictive trophic modes (pathotrophs, saprotrophs, and symbionts) were equivalent in the two sites. All roots of plants assessed had AMF colonization, and AMF spore densities were similar. While many fungal taxa were present at both sites, the spatial connectivity between both sites was insufficient for equivalence of fungal community structure and composition. Differences in chemical and physical soil characteristics may have shaped the fungal communities. This study highlights the need to comprehend the fungal community from mining environments, considering concepts of landscape connectivity.

Long-term legacy of phytoremediation on plant succession and soil microbial communities in petroleum-contaminated sub-Arctic soils

Abstract. Phytoremediation can be a cost-effective method of restoring contaminated soils using plants and associated microorganisms. Most studies follow the impacts of phytoremediation solely across the treatment period and have not explored long-term ecological effects. In 1995, a phytoremediation study was initiated near Fairbanks, Alaska, to determine how the introduction of annual grasses and/or fertilizer would influence degradation of petroleum hydrocarbons (PHCs). After 1 year, grass and/or fertilizer-treated soils showed greater decreases in PHC concentrations compared to untreated plots. The site was then left for 15 years with no active site management. In 2011, we re-examined the site to explore the legacy of phytoremediation on contaminant disappearance, as well as on plant and soil microbial ecology. We found that the recruited vegetation and the current bulk soil microbial community structure and functioning were all heavily influenced by initial phytoremediation treatment. The number of diesel-degrading microorganisms (DDMs) was positively correlated with the percentage cover of vegetation at the site, which was influenced by initial treatment. Even 15 years later, the initial use of fertilizer had significant effects on microbial biomass, community structure, and activity. We conclude that phytoremediation treatment has long-term, legacy effects on the plant community, which, in turn, impact microbial community structure and functioning. It is therefore important to consider phytoremediation strategies that not only influence site remediation rates in the short-term but also prime the site for the restoration of vegetation over the long-term.

The effects of agricultural practices on earthworm communities in Estonia

Earthworms support and mediate the provision of many processes in the soil. They are therefore important in maintaining soil functioning and contribute towards the sustainability of soil management systems. Assessment of earthworm communities can provide answers regarding the land management conservation efforts and insight on soil quality. The main aim of this study was to assess the impact of farming (organic vs conventional) and tillage (no-tillage vs minimum tillage vs conventional tillage) systems on earthworm communities under varying soil conditions in arable fields across Estonia. To achieve this, we compiled data from studies carried out over a period of 21 years on Estonian arable fields. While organic farming and conventional farming showed a similar earthworm abundance, earthworm diversity was significantly higher (p < 0.05) under the organic system. Higher abundance, species richness, and the proportion of anecic species suggest that a no-tillage system creates the most favourable habitat conditions for earthworms. Soil texture further influenced the effect of management system on earthworm abundance and diversity indexes. For example, the differences in earthworm abundance and diversity between the management systems increased from lighter textured to heavier textured soils. Our results suggest that soil texture is a major factor influencing earthworm communities in Estonian agricultural fields and emphasizes the importance of including different soil texture classes when assessing the effects of agricultural management practices in field-scale studies.

Benefit and risk: Keystone biomes in maize rhizosphere associated with crop yield under different fertilizations

The highly diverse beneficial and deleterious microbes in the rhizosphere influence plant growth and crop production in agricultural ecosystems. However, our understanding of the relationships between beneficial and risky phylotypes in the rhizosphere, and plant growth, in addition to their potentially varied response to different fertilization treatments in black soils, remains poor. Here, we investigated variations in multitrophic (e.g., bacteria, fungi, invertebrates, and protists) community composition and diversity under different five-year fertilization treatments, and identified the potential beneficial and potential risky keystone multitrophic biota in maize rhizosphere and bulk soils based on ecological networks and soil food web structure. Bacteria and protist community compositions exhibited greater variations under different fertilization regimes when compared with those of fungi and invertebrates. In addition, two keystone phylotype groups associated with crop yield and soil function were detected, and the potential beneficial keystone phylotypes exhibited higher relative abundances in C-fixation, N-fixation, and P-mineralization genes; conversely, the potential risky keystone phylotypes were associated with denitrification and nitrate reduction genes, and included more potential fungal pathogens. Furthermore, structural equation modeling results indicated that organic amendments, particularly cow manure, could improve crop yield by enriching beneficial keystone phylotypes and suppressing risky keystone phylotypes. Altogether, the results of the present study highlight the critical roles of rhizosphere biota in food production, and identify keystone phylotypes that are beneficial or harmful to crop production and soil function, which could facilitate the conservation of beneficial biota and the early detection of potential pathogens, as well as the exploitation of beneficial biota to increase crop yield.

The Effect of Climate Change on Soil Health: A Review

The phrase &amp;quot;soil health&amp;quot; mentions to the entire functionality of the soil as determined by the biological, chemical, and physical characteristics of the soil that are necessary for long-term, sustainable agricultural production by little impact on the environment. The ability of soil to carry out environmental and agronomic tasks, such as biomass productivity, sensitivity to management inputs, and resilience to biotic and abiotic stressors, is referred to as soil health. Since it is impossible to assess directly, soil fertility status and other specific soil parameters, including organic matter content, might be utilized in order to infer the state of the soil. Climate change may have an effect on soil health through temperature changes, salinity, hydrology, and the availability of organic matter. Main characteristics of the soil that are crucial for preserving its health are its desirable texture, structure, and tilt. The impact of several anticipated global change drivers, such as increasing atmospheric carbon dioxide levels, rising temperatures, changed precipitation patterns, as well as nitrogen in the atmosphere accumulation, on the environmental, substance, and organic functions of soil, should be taken into account when describing the condition of soils in connection with changes in the climate.

Core Bacterial Taxa Determine Formation of Forage Yield in Fertilized Soil.

Understanding the roles of core bacterial taxa in forage production is crucial for developing sustainable fertilization practices that enhance the soil bacteria and forage yield. This study aims to investigate the impact of different fertilization regimes on soil bacterial community structure and function, with a particular focus on the role of core bacterial taxa in contributing to soil nutrient content and enhancing forage yield. Field experiments and high-throughput sequencing techniques were used to analyze the soil bacterial community structure and function under various fertilization regimes, including six treatments, control with no amendment (CK), double the standard rate of organic manure (T01), the standard rate of organic manure with nitrogen input equal to T04 (T02), half the standard rate of inorganic fertilizer plus half the standard rate of organic manure (T03), the standard rate of inorganic fertilizer reflecting local practice (T04), and double the standard rate of inorganic fertilizer (T05). The results demonstrated that organic manure treatments, particularly T01, significantly increased the forage yield and the diversity of core bacterial taxa. Core taxa from the Actinomycetota, Alphaproteobacteria, and Gammaproteobacteria classes were crucial in enhancing the soil nutrient content, directly correlating with forage yield. Fertilization significantly influenced functions relating to carbon and nitrogen cycling, with core taxa playing central roles. The diversity of core microbiota and soil nutrient levels were key determinants of forage yield variations across treatments. These findings underscore the critical role of core bacterial taxa in agroecosystem productivity and advocate for their consideration in fertilization strategies to optimize forage yield, supporting the shift towards sustainable agricultural practices.

Managing both overstory and understory vegetation mitigates the impact of drought on soil nematode communities in a Mediterranean pine forest

Forest management strategies can effectively mitigate the impacts of drought on tree species, but their effects on soil fauna remain largely unexplored. Among soil organisms, soil nematodes can serve as valuable bioindicators to assess the impact of forest management on soil biodiversity and soil functioning. Consequently, we investigated two related questions in a Mediterranean Pinus halepensis Mill. forest located in southeastern France. First, how do soil nematodes respond to forest management practices? Second, can forest management practices help modulate the effects of Mediterranean summer drought on these soil organisms? We conducted a field experiment in which we explored the influence of two forest management techniques—tree thinning (intense, moderate, or absent) and understory removal (shrubs present or absent)—on soil nematodes before and after the summer drought. We found that only total and bacterivorous nematode abundances were positively influenced by the forest management practices. The highest values were observed under conditions of intense thinning combined with shrub presence, with an average of 97,509 individuals per kg of dry soil. In contrast, the abundances of all nematodes, with the exception of predaceous nematodes, were lower after the summer drought with a reduction ranging from −55 % to −82 %. Total, bacterivorous, and fungivorous nematode abundances were less negatively affected by the summer drought under conditions of moderate thinning when shrubs were present versus absent. More generally, we discovered that bacterivorous and fungivorous nematodes were particularly sensitive to the forest management practices and the summer drought. It is thus apparent that habitat alterations induced by forest management can strongly affect nematode community structure and could therefore prompt shifts in ecosystem functioning. Finally, this study highlights that, in forests, understory vegetation can have significant positive impacts on soil nematode populations when severe dry periods occur.

Insight into the short-term effects of TiO2 nanoparticles on the cultivation of medicinal plants: Comprehensive analysis of Panax ginseng physiological indicators, soil physicochemical properties and microbiome

To meet societal needs, a large number of medicinal plants are cultivated artificially. However, issues such as diseases and continuous cropping obstacles (CCO) have severely impacted their quality and yield. Exploring and innovating the cultivation technology for medicinal plants is essential to meet their high demand and ensure sustainable development. The role of titanium dioxide nanoparticles (nano-TiO2) in medicinal plant cultivation remains unclear. To advance the application of nanotechnology in this field, a comprehensive exploration of its potential benefits is necessary. In this study, nano-TiO2 was applied to ginseng (Panax ginseng C.A. Meyer) to acquire a holistic comprehension of its impact on ginseng growth, rhizosphere, and ginseng-used soil. Our findings reveal that nano-TiO2 significantly enhances ginseng root activity and has notable effects on antioxidant enzyme systems. The two concentrations of nano-TiO2 markedly influenced the structure and composition of microbial communities in the rhizosphere and ginseng-used soil, including key microorganisms such as Chloroflexi and Acidobacteriota, which are closely involved in soil function. Furthermore, nano-TiO2 altered the competitive and cooperative relationships within microbial networks. Nano-TiO2 application significantly increased soil organic matter (SOM) content in rhizosphere and ginseng-used soils and affected the activities of several important soil enzymes. Environmental factors, such as EC, pH, and soil nutrients, were found to be the main factors influencing the microbial community. In conclusion, our findings illuminate the complex effects of nano-TiO2 on the “plant-microbial-soil” system in the context of ginseng cultivation. This work offers novel strategies for optimizing medicinal plant growth and development, as well as improving cultivated soil by using nanomaterials.

Synergistic changes in bacterial community composition, function, and soil characteristics of tomato rhizosphere soil under long-term monoculture conditions

Tomato is widely cultivated all over the world, and long-term monoculture has resulted in decreased tomato yields and stunted plant growth. Soil bacterial communities have a profound effect on plant growth and health, and the effect of different planting years on rhizosphere soil microorganisms of tomato is not clear. In this study, metagenomic sequencing was used to analyze the rhizosphere soil microorganisms of tomatoes cultivated continuously for 3, 6 years (short-term continuous cropping), 9, and 12 years (long-term continuous cropping) (LZ3, LZ6, LZ9, LZ12). The results showed that the pH in LZ9 was significantly higher than that in the other treatments, the relative abundance of Planctomycetes and Candidatus Rokubacteria in LZ3 were higher than those in the other treatments, the relative abundance of Proteobacteria was significantly higher in LZ6 and LZ9 than that in the other treatments, and the relative abundance of Chloroflexi and Bacteroidetes in LZ12 were higher than those in the other treatments. At the genus level, the relative abundance of Nocardioides, Sphingomonas, Pseudolabrys were lower in LZ3 than that in other treatments, and the relative abundance of Gaiella was significantly higher in short-term continuous cropping than that in LZ9. The pH, hydrolyzable nitrogen (HN), and available potassium (AK) were the most important factors driving the changes in microbial communities. The relative abundance of amino acid metabolism, terpenoid and polyketide metabolism decreased significantly with years of continuous cropping, and that total nitrogen (TN), HN, and available phosphorus (AP) were significantly correlated with translation, amino acid metabolism, and cell growth and death. Continuous cropping leads to nutrient imbalance in tomato soils, which affects the structure and functional composition of soil microbial communities, providing insights into microbial community response to continuous tomato cropping, but further in-depth studies are needed.

Labile not stable SOC fractions constitute the manageable drivers of soil health advances in carbon farming

The assessment of soil health and the determination of carbon stability in soils are current challenges that have gained momentum through initiatives at national as well as international scales. However, inferring universally valid soil health parameters that are directly linked to carbon permanence remains challenging. Our aim was to evaluate the potential of simultaneous thermal analysis (STA) for an improved monitoring of soil health advances in the context of carbon farming strategies. For this purpose, an on-farm comparison of soil health in ten conservation agricultural systems with adjacent conventional farms was performed based on STA and thermal measures were related to key biological and physical indicators for monitoring soil functions. Using an autocorrelation-based approach, we identified independent thermal indicators, revealing that carbon farming efforts predominantly increased labile soil organic matter fractions in the range of 300–400 °C, while thermally more recalcitrant fractions did not respond to farming system transformation. Similarly, most soil health indicators revealed highest correlation with temperature ranges of mass loss of labile organic matter fractions. The relation of STA with commonly used soil health indicators was highest for soil organic carbon (SOC, r=0.971) and total nitrogen (TN, r=0.981). However, also inference on microbial activity parameters such as dimethylsulfoxid reduction, microbial biomass carbon and substrate-induced respiration could be demonstrated with r>0.663. The results thus highlight key temperature ranges of organic matter stability for future soil monitoring tasks of climate change mitigation potentials of carbon farming and related advances in soil health.

Relationship between Plant-Available Water and Soil Compaction in Brazilian Soils

The capacity of soil to retain water and make it available to plants is an essential soil functions for the sustainability of terrestrial ecosystems. A lot of progress has been made in estimating water retention and availability as a function of soil texture. On the other hand, a lower effort has been dedicated to seeking correlations between plant-available water (AW) and soil compaction. In this study, we compiled a dataset with 2479 records from experiments conducted in Brazilian soils to evaluate the relationship between AW and bulk density (BD). The dataset was split into sub-datasets defined by soil textural classes to reduce the effect of texture on AW–BD relationships. In each sub-dataset, AW–BD relationships were described by linear regression. In general, there was a weak association between AW and BD. The strongest correlations were found in the Silty Loam (R2 = 0.26) and Loam (R2 = 0.13) classes. However, the partitioning of the overall dataset by textural classes was not effective to eliminate the effect of texture on AW–BD relationships. Still, the data showed that soil compaction may increase or reduce AW. Nevertheless, more experimental research is needed to bring a better understanding of how AW is affected by changes in BD.

Nitrogen utilization efficiency assessment during bioremediation of petroleum-contaminated loess soils: insights from metagenomic analysis

Nitrogen addition is commonly used to remediate total petroleum hydrocarbons (TPH) in petroleum-contaminated soils. However, acceptable exogenous nitrogen dosages and their utilization efficiency for the degradation of hydrocarbons in oil-polluted soils are not well understood. This study compared the hydrocarbon bioremediation capacity by applying different doses of NH4Cl as a stimulant in soils contaminated with TPH at 8553 and 17090 mg/kg. The results showed acceptable exogenous nitrogen levels ranging from 60 to 360 mg N/kg soil, and the optimal nitrogen dosage for TPH remediation was 136 mg N/kg in soils with different TPH concentrations. The nitrogen availability efficiency (NAE) and nitrogen polarization factor availability (NPFA) in the 136 mg N/kg addition treatments were 6.69 and 20.47 mg/mg in 8533 mg/kg TPH-polluted soil, and 6.03 and 31.11 mg/mg in 17090 mg/kg TPH-polluted soil, respectively. Metagenomic analysis revealed that the application of 136 mg/kg nitrogen facilitated ammonia oxidation and nitrite reduction to nitric oxide, and induced soil microorganisms to undergo regulatory or adaptive changes in energy supply and metabolic state, which could aid in restoring the ecological functions of petroleum-contaminated soils. These findings underscore that 136 mg/kg of nitrogen dosage application is optimal for remediation of petroleum-contaminated soils irrespective of the TPH concentrations. This exogenous nitrogen application dosage for TPH remediation aligns with the nitrogen requirements for crop growth in agriculture.

Hyperspectral characterization of vegetation in hemiboreal, boreal and Arctic peatlands using a geographically extensive field dataset

Northern peatlands store up to 25% of global soil organic carbon and function as important hotspots for biodiversity. However, they are facing degradation from climate change driven by human activities as well as anthropogenic land use changes, up to the point of endangering the ecosystems' functioning and the storage of soil organic carbon entailed within them. The surface vegetation of northern peatlands is an important indicator of the ecosystem's functioning and ecohydrology, highlighting the importance of its large-scale, continuous monitoring. Approaches utilizing hyperspectral data for monitoring vegetation health and species composition can also be applied to peatland vegetation. To support the development of methods for interpreting hyperspectral satellite data from peatlands, we conducted a comprehensive in situ study of hemiboreal, boreal, sub-Arctic and Arctic peatland vegetation. We measured the reflectance spectra (350–2500 nm), soil moisture, and various vegetation-related attributes from a total of 446 vegetation plots in Estonia and Finland, from a 1500 km south-north interval. We then investigated (i) the spectral variation in surface vegetation of hemiboreal, boreal, sub-Arctic and Arctic peatlands and (ii) explored its connection to plant functional types (PFTs) and soil moisture, as well as evaluated the potential of hyperspectral data in estimating PFT cover using simple vegetation indices and partial least square (PLS) regression. Our results indicate that (i) the best spectral regions to retrieve information regarding the PFT vary greatly especially between vascular plants and bryophytes, (ii) the reflectance at an individual wavelength as well as simple vegetational index can, to some extent, predict the PFT, and that (iii) the PLS regression can predict the PFT with good accuracy. Overall, our findings demonstrate the potential of using hyperspectral data in monitoring PFTs in northern peatlands. The spectral library and the ancillary data from the peatland sites collected for this study are available as open data.

BIOAUGMENTATION AS BIOREMEDIATION APPROACH FOR CONTAMINATED SOIL: A REVIEW

The inevitable impacts by the emerging urbans developments towards the quality and function of soil have raised concerns for future environment consequences. Pollutants that evolved from the anthropogenic activities including heavy metals, pesticides, petroleum hydrocarbons (TPH) and polycyclic aromatic hydrocarbons (PAHs) tend to be persistent within the soil and hence, contribute to long term effects towards the environment and human’s health. Researchers discovered the success of bioaugmentation as part of bioremediation as an approach towards degrading the pollutants by employing microorganisms (i.e., bacteria or fungi) to enhance the removal of pollutants. The concept, mechanism, method, and factors affecting bioaugmentation is studied for the past years to explore the thorough process of bioaugmentation. It is claimed that bioaugmentation is directly related to the microbial activity and have three different approaches (autochthonous, allochthonous, and genetically engineering microorganisms). pH, temperature, moisture, and oxidation reduction potential are the key prospects towards bioaugmentation efficiency. The application of bioaugmentation towards each targeted pollutant are studied to certify its capability of degrading, removing, and transforming pollutants into less toxic components.