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The global environment is constantly changing and our planet is getting warmer at an unprecedented rate. The study of the carbon cycle, and soil respiration, is a very active area of research internationally because of its relationship to climate change. It is crucial for our understanding of ecosystem functions from plot levels to global scales. Although a great deal of literature on soil respiration has been accumulated in the past several years, the material has not yet been synthesized into one place until now. This book synthesizes the already published research findings and presents the fundamentals of this subject. Including information on global carbon cycling, climate changes, ecosystem productivity, crop production, and soil fertility, this book will be of interest to scientists, researchers, and students across many disciplines. * A key reference for the scientific community on global climate change, ecosystem studies, and soil ecology* Describes the myriad ways that soils respire and howthis activity influences the environment* Covers a breadth of topics ranging from methodologyto comparative analyses of different ecosystem types* The first existing \"treatise\" on the subject

Petroleum hydrocarbon (TPH) contamination at industrial sites poses severe ecological and health risks to humans. However, conventional persulfate oxidation suffers from low efficiency and high oxidant demand requirements. To address this limitation, we employed citric acid-FeSO₄-modified sodium persulfate (FNS) for soil remediation.In this study, the petroleum hydrocarbon (TPH)-contaminated soil of a chemically contaminated site was used as the test object, and sodium persulfate modified by citric acid-FeSO 4 (FNS) was selected as the oxidant. Based on laboratory tests, quantifying TPH degradation efficiency, soil pH variation, and sulfate leaching concentrations, the effects of oxidant dosage, oxidant dosage times, and CaO dosage on the remediation effect of petroleum hydrocarbon-contaminated soil were systematically investigated. The results demonstrated that citric acicd-FeSO 4 significantly enhanced sodium persulfate activation (p < 0.01), achieving within 28 days a 36% higher TPH degradation efficiency than unmodified persulfate at 2% dosage. This modification amplified oxidation intensity and efficiency by up to 2.3-fold over the remediation period.For the contaminated soil with a petroleum hydrocarbon content of 16524 mg/kg, after a 28-day remediation period,FNS amendment achieved significant TPH reductions of 76.9% (to 3820 mg/kg) at 4% dosage-below Class II construction land in China’s soil environmental quality standard (4500 mg/kg). At a 6% dosage, after the same 28-day remediation period,reduction efficiency reached 95.5% (to 750 mg/kg) lower than the screening value of soil contamination risk for Class I construction land in China’s Soil Environmental Quality Standard (826 mg/kg). The FNS agent can significantly improve the oxidation strength and efficiency of sodium persulfate, but it causes soil acidification and exceeds the SO 4 2- leaching concentration standard, among other things. The restored soil needs to be conditioned with CaO neutralization. In addition, FNS must be applied at one time and cannot be applied separately.

Background Submerged soils are globally important both in natural and agricultural ecosystems and cover 5–7% of the global land surface. Therefore, processes in submerged soils are important for global biogeochemical cycles. These processes are strongly influenced by oxygen availability, i.e. redox potential. Scope This review aims to provide an overview of the role of redox potential in nutrient cycling, soil organic matter turnover and the effect of plants on nutrient cycling processes in submerged soil. Conclusion In submerged soils, the active terminal electron acceptor for reduction processes follows the sequence O 2 , NO 3 − , MnO 2, Fe 3+ , SO 4 2− and CO 2 where, in most cases organic matter, is the electron donor. Depletion of available organic matter during this sequence can limit the subsequent processes. Drying and rewetting of previously submerged soils have complex effects on nutrient cycling. Submerged soils often have higher organic matter content than aerobic soils which is due to chemical, metabolic and physical mechanisms. Plants have complex effects on processes in wetland soils resulting from release of oxygen from roots which can induce iron and methane oxidation around roots. However, plants can also increase methane release due to transport of methane via aerenchyma to the shoots. For a better understanding of processes in submerged soils, future investigations across scales, ranging from microscale to macroscale, are needed.

To improve the coupling of in situ chemical oxidation and in situ bioremediation, a systematic analysis was performed of the effect of chemical oxidation with Fenton's reagent, modified Fenton's reagent, permanganate, or persulfate, on microbial diversity and activity during 8 weeks of incubation in two diesel-contaminated soils (peat and fill). Chemical oxidant and soil type affected the microbial community diversity and biodegradation activity; however, this was only observed following treatment with Fenton's reagent and modified Fenton's reagent, and in the biotic control without oxidation. Differences in the highest overall removal efficiencies of 69 % for peat (biotic control) and 59 % for fill (Fenton's reagent) were partially explained by changes in contaminant soil properties upon oxidation. Molecular analysis of 16S rRNA and alkane monooxygenase (alkB) gene abundances indicated that oxidation with Fenton's reagent and modified Fenton's reagent negatively affected microbial abundance. However, regeneration occurred, and final relative alkB abundances were 1–2 orders of magnitude higher in chemically treated microcosms than in the biotic control. 16S rRNA gene fragment fingerprinting with DGGE and prominent band sequencing illuminated microbial community composition and diversity differences between treatments and identified a variety of phylotypes within Alpha-, Beta-, and Gammaproteobacteria. Understanding microbial community dynamics during coupled chemical oxidation and bioremediation is integral to improved biphasic field application.

Hexavalent Chromium (Cr(VI)) contamination in soils poses significant ecological risks due to its mobility and toxicity, with retention mechanisms governed by interactions between soil properties and Cr(VI). However, the quantitative roles of key soil parameters in Cr(VI) retention remain poorly resolved, particularly across diverse soil types. This study investigated Cr(VI) retention behaviors in 16 Chinese soils (15 types) through batch experiments, isothermal adsorption model, correlation analysis and path analysis. The results showed that the retention of Cr(VI) in acidic soils was significantly higher than in alkaline soils. Acidic soils (pH < 5.4) with higher concentrations of exchangeable Fe(II) (Exch-Fe(II)) exhibited strong Cr(VI) holding capabilities,while Alkaline soils (pH > 7.3) with highest content of CaCO 3 show negligible Cr(VI) reactions.Cr(VI) retention was high at soil pH values below approximately 5.5, but declined sharply at higher pH values. The Langmuir model was only suitable for describing acidic soils (pH < 5.4), while the Freundlich equation was applicable to all soils. Correlation analysis revealed that soil pH, the content of soil organic matters(SOM), Exch-Fe(II), complexed iron (Com-Fe), and clay were significantly related to the Cr(VI) retention ( p < 0.01), whereas the CaCO 3 content was negatively related to the Cr(VI) retention ( p < 0.05).Path analysis revealed that soil pH was the most important direct factor, followed by Exch-Fe(II), Com-Fe, clay, in determining Cr(VI) retention in natural soil. CEC and CaCO 3 content had only limited directly effects on the Cr(VI) retention. Additionally, The content of SOM, Amorphous iron oxides(Amo-Fe), and Easily reducible manganese(Er-Mn) content had little directly effect on Cr(VI) retention. To validate these findings, Cr(VI) retention was measured in all soils after adjusting their pH to 4.3, 6, and 8. The results highlighted soil pH and Exch-Fe(II) content were the most decisive factors for evaluating Cr(VI) retention in natrual soils,whereas SOM content was an unreliable parameter for assessing this process.

Background Salinization damages the health of soil systems and reduces crop yields. Responses of microbial communities to salinized soils and their functional maintenance under high salt stress are valuable scientific problems. Meanwhile, the microbial community of the salinized soil in the plateau environment is less understood. Here, we applied metagenomics technology to reveal the structure and function of microorganisms in salinized soil of the Tibetan Plateau. Results The diversity of composition and function of microbial community in saline soil have changed significantly. The abundances of chemoautotrophic and acidophilic bacteria comprising Rhodanobacter , Acidobacterium , Candidatus Nitrosotalea, and Candidatus Koribacter were significantly higher in saline soil. The potential degradation of organic carbon in the saline soil, as well as the production of NO and N 2 O via denitrification, and the production of sulfate by sulfur oxidation were significantly higher than the non-saline soil. Both types of soils were rich in genes encoding resistance to environmental stresses (i.e., cold, ultraviolet light, and hypoxia in Tibetan Plateau). The resistance of the soil microbial communities to the saline environment is based on the absorption of K + as the main mechanism, with cross-protection proteins and absorption buffer molecules as auxiliary mechanisms in our study area. Network analysis showed that functional group comprising chemoautotrophic and acidophilic bacteria had significant positive correlations with electrical conductivity and total sulfur, and significant negative correlations with the total organic carbon, pH, and available nitrogen. The soil moisture, pH, and electrical conductivity are likely to affect the bacterial carbon, nitrogen, and sulfur cycles. Conclusions These results indicate that the specific environment of the Tibetan Plateau and salinization jointly shape the structure and function of the soil bacterial community, and that the bacterial communities respond to complex and harsh living conditions. In addition, environmental feedback probably exacerbates greenhouse gas emissions and accelerates the reduction in the soil pH. This study will provide insights into the microbial responses to soil salinization and the potential ecological risks in the special plateau environment.

Extended soil contamination by polychlorinated biphenyls (PCBs) represents a global environmental issue that can hardly be addressed with the conventional remediation treatments. Rhizoremediation is a sustainable alternative, exploiting plants to stimulate in situ the degradative bacterial communities naturally occurring in historically polluted areas. This approach can be enhanced by the use of bacterial strains that combine PCB degradation potential with the ability to promote plant and root development. With this aim, we established a collection of aerobic bacteria isolated from the soil of the highly PCB-polluted site \"SIN Brescia-Caffaro\" (Italy) biostimulated by the plant Phalaris arundinacea. The strains, selected on biphenyl and plant secondary metabolites provided as unique carbon source, were largely dominated by Actinobacteria and a significant number showed traits of interest for remediation, harbouring genes homologous to bphA, involved in the PCB oxidation pathway, and displaying 2,3-catechol dioxygenase activity and emulsification properties. Several strains also showed the potential to alleviate plant stress through 1-aminocyclopropane-1-carboxylate deaminase activity. In particular, we identified three Rhodococcus strains able to degrade in vitro several PCB congeners and to promote lateral root emergence in the model plant Arabidopsis thaliana in vivo. In addition, these strains showed the capacity to colonize the root system and to increase the plant biomass in PCB contaminated soil, making them ideal candidates to sustain microbial-assisted PCB rhizoremediation through a bioaugmentation approach.

Background Saline and alkaline stresses damages the health of soil systems. Meanwhile, little is known about how saline or alkaline stress affects soil nitrifier and denitrifier communities. Therefore, we compared the responses of gene-based nitrifier and denitrifier communities to chloride (CS), sulfate (SS), and alkaline (AS) stresses with those in a no-stress control (CK) in pots with a calcareous desert soil. Results Compared with CK, saline and alkaline stress decreased potential nitrification rate (PNR) and NO 3 -N; increased pH, salinity, water content, and NH 4 -N; and decreased copy numbers of amoA -AOA and amoA -AOB genes but increased those of denitrifier nirS and nosZ genes. Copies of nirK increased in SS and AS but decreased in CS. There were more copies of amoA -AOB than of amoA -AOA and of nirS than of nirK or nosZ . Compared with CK, SS and AS decreased operational taxonomic units (OTUs) of amoA -AOB but increased those of nirS and nosZ , whereas CS decreased nirK OTUs but increased those of nosZ . The numbers of OTUs and amoA -AOB genes were greater than those of amoA -AOA. There were positive linear relations between PNR and amoA -AOA and amoA -AOB copies. Compared with CK, the Chao 1 index of amoA -AOA and amoA -AOB decreased in AS, that of nirK increased in CS and SS, but that of nirS and nosZ increased in all treatments. The Shannon index of amoA -AOB decreased but that of nirS increased in CS and SS, whereas the index of nirK decreased in all treatments. Saline and alkaline stress greatly affected the structure of nitrifier and denitrifier communities and decreased potential biomarkers of nirS -type; however, AS increased those of nirK - and nosZ -type, and SS decreased those of nosZ -type. Soil water content, pH, and salinity were important in shaping amoA -AOA and denitrifier communities, whereas soil water and pH were important to amoA -AOB communities. Conclusion These results indicate that the nitrifier and denitrifier communities respond to saline and alkaline stresses conditions. Communities of amoA -AOA and amoA -AOB contribute to nitrification in alluvial gray desert soil, and those of nirS are more important in denitrification than those of nirK or nosZ .

Aims The invasion of Spartina alterniflora has a significant influence on soil biogeochemistry cycling in coastal wetlands. However, the roles of the S. alterniflora invasion chronosequence in regulating soil dissimilatory NO3− reduction processes (denitrification (DNF), anaerobic ammonium oxidation (ANA) and dissimilatory nitrate reduction to ammonium (DNRA)) remains unclear. The objective of this study was therefore to reveal the effects of S. alterniflora invasion on the soil NO3− reduction processes and associated gene abundance. Methods We investigated plant biomass, soil properties, NO3− reduction processes and associated gene abundance of NO3− reduction pathways following S. alterniflora invasion chronosequences of 6, 10, and 14 years compared to Cyperus malaccensis in a coastal wetland of southeastern China. Results The S. alterniflora invasion generally increased plant biomass, soil water content, available substrates, nirS, anammox bacterial 16S rRNA and nrfA gene abundance, but it decreased soil bulk density. Soil DNF, ANA and DNRA rates in stands of S. alterniflora ranged from 1.52 to 17.58, 0.31 to 1.27 and 0.14 to 2.01 nmol N g−1 h−1, respectively, which were generally higher than the values in stands of C. malaccensis. The soil NO3− reduction rates generally increased with the increasing chronosequence of invasion by S. alterniflora, while the changes in DNF and ANA rates were less pronounced than changes in DNRA. DNF was the dominant pathway (70.00–92.41%), and the ANA and DNRA contributed 2.49–15.27% and 5.10–20.75% to the total NO3− reduction, respectively. The contributions of DNF and ANA to the total NO3− reduction decreased slightly, while the contribution of DNRA increased remarkably after S. alterniflora invasion. Soil NO3− reduction processes were influenced by available substrates and associated microbial activities. It is estimated that an N loss of approximately 520.97 g N m−2 yr.−1 in C. malaccensis and 794.46 g N m−2 yr.−1 in S. alterniflora were linked to both DNF and ANA processes. Conclusions The S. alterniflora invasion altered soil NO3− reduction processes by increasing soil microbial activities and available substrates and thus may further mediate the soil N availability in the coastal wetlands.

In semi-arid and arid regions, mulching with various materials is one of the highly significant ways to keep soil surface coverage. This approach helps efficiently reduce drought stress and soil erosion, thus preserving soil composition and ecosystem. The research aimed to pinpoint the physicochemical alterations and fungal diversity brought on by food waste mulch (FWM) in the desert soil. An experimental field assessment was conducted from early April (spring) to late August (summer) 2021 in the soil of the Jupar desert, the main watershed of the Central Plateau, southeastern Iran. The mulch was made from a combination of clay (70%), food waste (15%), and water and sprayed in 3 plots on the Jupar desert soil surface as a case group. Moreover, 3 plots of the Jupar desert soil and clay were selected as a non-mulch-controlled surface (control groups). The physicochemical changes were studied in all groups including FWM, desert soil, and clay. Besides, the samples were cultured and checked daily to determine the growth of fungal colonies. All fungal isolates were characterized to the species level by phenotypical and molecular methods. Sequence analysis of the ITS1, 5.8S, and ITS2 regions was done. The statistical findings displayed that the physical and chemical characteristics of FWM (case group) were significantly different compared to clay and soil samples (control groups) (P<0.05). Phenotypic and genotypic analysis of the fungal consortium showed that the most frequent filamentous and yeast fungi belonged to the Alternaria and Naganishia genera, respectively. Identified fungi are classified as growth-inducing and anti-pest fungi. This study showed that adding FWM of organic matter can cause partial variety in soil fungal diversity and stabilize the desert soil due to enriching the organic matter in eroding soils.