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The soluble components of rhizodeposition-root exudates-are the most important sources of readily available carbon (C) for rhizosphere microorganisms. The first steps of exudate utilization by microorganisms define all further flows of root C in the soil, including recycling and stabilization. Nevertheless, most studies have traced root exudates C much later after its initial uptake by microorganisms. To understand microbial uptake and utilization of rice root exudates, we traced C incorporated into microbial groups by C profiles of phospholipid fatty acids (PLFAs) within a short time (6 h) after CO pulse labeling. Labeling was conducted five times during three growth stages: active root growth (within the 21 days after transplanting), rapid shoot growth (37 and 45 days), and rapid reproduction (53 and 63 days). C was quickly assimilated throughout the rhizosphere microorganism, and the incorporation rate increased with rice maturity. Despite low redox conditions in paddy soil, fungi outcompeted bacteria in utilizing the root exudates. At all growth stages, fungal PLFAs (18:2 w6, 9c/18:0) showed the highest C levels, whereas actinomycete PLFAs (16:0 10-methyl) showed the lowest C incorporation. Principal component analysis revealed that the rhizosphere microbial community differed among rice growth stages, whereas the whole microbial community remained stable. In conclusion, the rapid incorporation of carbon from root exudates into microorganisms in paddy soils depends on the growth stage of the rice plant and is the first step of C utilization in rice rhizosphere, further defining C utilization and stabilization. [ABSTRACT FROM AUTHOR]

Highlights: [•] Adsorbed Fe(II) reactivity affected by dissolved organic matter (DOM). [•] DOM affect adsorbed Fe(II) density and peak oxidation potential of active species. [•] High molecular weight DOM fractions have stronger electron transfer capacities. [•] A lower peak oxidation potential indicates a higher reduction rate. [•] A higher electron transfer capacities value indicates a higher reduction rate. [ABSTRACT FROM AUTHOR]

Highlights: [•] Interfacial reduction rates of 2-nitrophenol affected by Fe(II)/Cu(II) interaction. [•] Fe(II)/Cu(II) interaction affect peak oxidation potential of active species. [•] Fe(II)/Cu(II) molar ratio affect mineral-sorbed Fe(II) density. [•] A lower peak oxidation potential indicates a higher reduction rates. [•] A higher normalized sorbed Fe(II) density indicates a higher reduction rates. [Copyright &y& Elsevier]

Microorganisms regulate soil organic matter (SOM) formation through accumulation and decomposition of microbial necromass, which is directly and indirectly affected by elevated CO2 and N fertilization. We investigated the role of microorganisms in SOM formation by analyzing 13C recovery in microorganisms and carbon pools in paddy soil under two CO2 levels, with and without N fertilization, after continuous 13CO2 labelling was stopped. Microbial turnover transferred 13C from living microbial biomass (determined by the decrease in phospholipid fatty acids) to necromass (determined by the increase in amino sugars). 13C incorporation in fungal living biomass and necromass was higher than that in bacteria. Bacterial turnover was faster than necromass decomposition, resulting in net necromass accumulation over time; fungal necromass remained stable. Elevated CO2 and N fertilization increased the net accumulation of bacterial, but not fungal, necromass. CO2 levels, but not N fertilization, significantly affected 13C incorporation in SOM pools. Elevated CO2 increased 13C in particulate organic matter via the roots, and in the mineral-associated organic matter (MAOM) via bacterial, but not fungal, necromass. Overall, bacterial necromass plays a dominant role in the MAOM formation response to elevated CO2 because bacteria are sensitive to elevated CO2. [ABSTRACT FROM AUTHOR]

Nitrogen (N) and phosphorus (P) availability plays a crucial role in carbon (C) cycling in terrestrial ecosystems. However, the C:N:P stoichiometric regulation of microbial mineralization of plant residues and its impact on the soil priming effect (PE), measured as CO 2 and CH 4 emission, in paddy soils remain unclear. In this study, the effect of soil C:N:P stoichiometry (regulated by the application of N and P fertilizers) on the mineralization of 13 C-labelled rice straw and the subsequent PE was investigated in a 100-day incubation experiment in flooded paddy soil. N and P additions increased straw mineralization by approximately 25% and 10%, respectively. Additions of both N and P led to higher CO 2 efflux, but lower CH 4 emission. With an increase in the ratios of DOC:NH 4 + -N, DOC:Olsen P, and microbial biomass C:N, 13 CO 2 efflux increased exponentially to a maximum. Compared with sole straw addition, exclusive N addition led to a weaker PE for CO 2 emission, whereas exclusive P addition induced a stronger PE for CO 2 emission. In contrast, CH 4 emitted from native soil organic matter (SOM) was reduced by 7.4% and 46.1% following P and NP application, respectively. Structural equation models suggest that available N had dominant and direct positive effects, whereas microbial biomass stoichiometry mainly exerted negative indirect effects on PE. The stoichiometry of soil enzyme activity directly down-regulated CH 4 emission from SOM. Microbes obviously regulate soil C turnover via stoichiometric flexibility to maintain an elemental stoichiometric balance between resources and microbial requirements. The addition of straw in combination with N and P fertilization in paddy soils could therefore meet microbial stoichiometric requirements and regulate microbial activity and extracellular enzyme production, resulting in co-metabolism of fresh C and native SOM. [ABSTRACT FROM AUTHOR]

Many studies have shown that the microbial biomass content in paddy soils is much higher than that in upland soils, but a comprehensive review of the underlying mechanisms and processes is lacking. We conducted a meta-analysis of published literature on the microbial biomass content in continuous paddy soils (>1700 data pairs) and paddy-upland rotation soils (>1100 data pairs) as compared to that in adjacent upland soils (>360 data pairs), measured by the fumigation extraction or fumigation incubation method. The microbial biomass carbon (MBC) content in paddy soils was double that in upland soils. This MBC surplus in paddy soils compared to upland soils was explained by (1) higher input of root C and rhizodeposits by rice plants compared with upland crops; (2) lower oxygen availability and consequently slower microbial turnover; (3) higher microbial C assimilation efficiency in paddy soils; and (4) additional C stabilization on iron (oxyhydr)oxides in paddy soils. The proportion of MBC in total soil organic C in paddy-upland rotation, paddy, and upland soils was 3.5%, 2.5%, and 2.1%, respectively. The higher microbial biomass C/N ratio in paddy soils (12.4 ± 0.11) compared to upland soils (9.9 ± 0.21) reflects greater N losses (through nitrate leaching and denitrification) in relation to slower C losses under anoxic conditions. Despite higher temperature and better water availability, microbial biomass turnover was 1.1–1.6 times slower in paddy soils than in upland soils because of oxygen limitation. Multiple stepwise regression and redundancy analyses showed that microbial biomass in continuous paddy and paddy-upland rotation soils was affected by similar soil factors (such as total N and organic C), whereas microbial biomass in upland soils was mainly affected by pH and the organic C content. Paddy-upland rotation soils undergo oxic–anoxic cycles and consequently can absorb and coprecipitate organic compounds with iron (oxyhydr)oxides as an additional advantage for C stabilization. We conclude that the reduced microbial activity and slower microbial turnover under oxygen-limited conditions lead to nearly two times higher microbial biomass content in paddy than in upland soils. • Microbial biomass (MB) content in paddy soils is twice more than that in upland soils. • Lower O 2 availability leads to slow decomposition of organic matter and MB turnover. • Fe and Mn oxidation-reduction dynamics stabilize C in paddy and paddy-rotation soils. • High MB content in paddy soils is because of high microbial substrate use efficiency. [ABSTRACT FROM AUTHOR]

Introduction: The relationships among microelements and soil microbial communities are essential for understanding the maintenance of soil's ecological functions and their effects on fruit quality in orchards. However, these relationships have not been adequately studied, despite the importance of microelements for the growth of microorganisms and plants., Methods: To address this research gap, we investigated the relationships among microelements (K, Ca, Na, Mg, Fe, Mn, Zn, and Cu), the diversity and composition of soil microbiomes, and fruit quality in loquat orchards., Results: We found that microelements explained more variations in microbial community structures than geographic position, basic soil properties, and macroelements, with 19.6-42.6% of bacterial, 4.3-27.7% of fungal, and 5.9-18.8% of protistan genera significantly correlated with microelements. Among the microelements, AMg and ACu were the most influential in determining the soil microbiome. The soil microbes exhibited varied threshold values for environmental breadth among the microelements, with the broadest range for AMg and the narrowest for AZn. Additionally, the microbes showed significant phylogenetic signals for all microelements, with an increasing divergence of soil microelements. The dominant community assembly shifted from homogeneous selection to stochastic, and then to heterogeneous selection. Moreover, microelements and the microbiome were the top two factors individually explaining 11.0 and 11.4% of fruit quality variation, respectively., Discussion: These results highlight the importance of microelement fertilization in orchard management and provide scientific guidance for improving fruit quality., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The author(s) declared that they were an editorial board member of Frontiers, at the time of submission. This had no impact on the peer review process and the final decision., (Copyright © 2024 Wang, Wang, Wu, Yuan, Zhong, Qi, Wang, Wu, Ge and Zhu.)

Microbial mineralization of dissolved organic matter (DOM) plays an important role in regulating C and nutrient cycling. Viruses are the most abundant biological agents on Earth, but their effect on the density and activity of soil microorganisms and, consequently, on mineralization of DOM under different temperatures remains poorly understood. To assess the impact of viruses on DOM mineralization, we added soil phage concentrate (active vs. inactive phage control) to four DOM extracts containing inoculated microbial communities and incubated them at 18 °C and 23 °C for 32 days. Infection with active phages generally decreased DOM mineralization at day one and showed accelerated DOM mineralization later (especially from day 5 to 15) compared to that with the inactivated phages. Overall, phage infection increased the microbially driven CO 2 release. Notably, while higher temperature increased the total CO 2 release, the cumulative CO 2 release induced by phage infection (difference between active phages and inactivated control) was not affected. However, higher temperatures advanced the response time of the phages but shortening its active period. Our findings suggest that bacterial predation by phages can significantly affect soil DOM mineralization. Therefore, higher temperatures may accelerate host-phage interactions and thus, the duration of C recycling., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Soil C inputs and its priming effect (PE) are important in regulating soil C accumulation and mitigating climate change; however, the factors that control the direction and intensity of PE remains unclear. Soil C accumulation is strongly affected by the reductive iron status in paddy fields, while the addition of organic substances increases the emission of certain gases (CO 2 /CH 4 ) under the PE, contributing to climate change. Here, we elucidated the mechanism by which Fe reduction, measured by Fe(II) production, regulates PE for CO 2 and CH 4 in paddy soils. Specifically, we quantified PE induced by 13 C-labeled straw in anaerobic paddy soil, augmented by ferrihydrite and/or biochar, over 150 days in a laboratory experiment. The PE of CO 2 was initially negative (-15.3 to -41.5 mg C kg -1 ) before 20 days of incubation and subsequently became positive. PE intensity for both gases depended on ferrihydrite or biochar application. Straw+biochar had the highest PEs (CO 2 , 116.5 mg C kg -1 ; CH 4 , 309.4 mg C kg -1 ), while straw+ferrihydrite produced the lowest PEs (CO 2 , 41.3 mg C kg -1 ; CH 4 , 107.8 mg C kg -1 ). Fe reduction was approximately three times higher with straw+ferrihydrite than with straw alone and was further stimulated by additional biochar. Thus, biochar appeared to accelerate Fe reduction, destabilize mineral-bound organic C, and increase nutrient availability to microbes. Enhanced microbial C and N mining led to a positive PE for CO 2 . Cumulative PE for CH 4 was 2-3 times higher than that for CO 2 , indicating conversion via methanogenesis. Biochar acted as an electron shuttle, increasing Fe reduction and stimulating interspecies electron transfer, and increased CH 4 production. Therefore, Fe reduction and biochar jointly increased PE intensity for CH 4 . In conclusion, water and fertilizer management of paddy soil could contribute toward mitigating climate change., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Optimization of clays as adsorbent for low concentration phosphorus removal from wastewater has received increasing attention in recent years. This study explored the feasibility of using bentonite as an adsorbent for phosphate (P) removal from synthetic wastewater, by assessing the performance of thermally treated bentonite for P removal and elucidating the mechanisms of P adsorption. Natural bentonite (B25) was thermally treated at 100-1000 °C (B100-B1000) for 2 h. Physical and chemical properties were measured by the SEM, XRD, pore size distribution, EDX, and cation exchange capacity (CEC) methods. Thermal treatment increased P sorption capacity of bentonite and that B800 had a higher P sorption capacity (6.94 mg/g) than B25 (0.237 mg/g) and B400 (0.483 mg/g) using the Langmuir isotherm equation. Study of sorption kinetics indicated that B800 rapidly removed 94% of P from a 10 mg P/L solution and the pseudo-second-order equation fitted the data well. The Ca 2+ release capacity of B800 (1.31 mg/g) was significantly higher than that of B25 (0.29 mg/g) and B400 (0.40 mg/g) (p < 0.05). The initial pH level had a smaller impact on P removal efficiency for B800 than that of B25 and B400. Ca-P was the main fraction of P adsorbed onto B800, and Ca 10 -P was the main species (41.4%). The main factors affecting the phosphorous adsorption capacity of B800 were changed crystal structure, strong calcium release capacity, and improved stability in different pH solutions. The results demonstrated that thermally treated bentonite (B800) has the potential to be an efficient adsorbent for removal of low-concentration phosphorus from wastewater.