Catalytic efficiency of soil enzymes explains temperature sensitivity: Insights from physiological theory

Recycled wheat straw biochar enhances nutrient-poor soil: Enzymatic kinetics of carbon, nitrogen, and phosphorus cycling

The recycling of waste wheat straw into biochar for soil improvement is a promising, sustainable strategy to enhancing nutrient-poor soils. Biochar application to soil has been shown to enhances the activity of key enzymes involved in nutrient cycling, such as invertase (INV), urease (URE), and alkaline phosphatase (ALP), which play roles in carbon (C), nitrogen (N), and phosphorus (P) cycling, as well as catalase (CAT), an enzyme with redox properties. However, the kinetic behavior of these enzymes remains largely unexplored. A 36-week laboratory study was conducted to evaluate the effects of biochar on enzyme kinetics in grey desert and aeolian soils including Michaelis-Menten constant (Km), maximum reaction velocity (Vmax), and catalytic efficiency (Vmax/Km). Results indicated that biochar application significantly increased soil pH, available phosphorus (AP), ammonium nitrogen (NH4+-N), dissolved organic carbon (DOC), and microbial biomass carbon (MBC) while reducing nitrate nitrogen (NO3--N), which were identified as dominant factors influencing enzyme kinetic parameters. Enzyme activities related to C, N, and P cycling (excluding catalase) increased significantly at a biochar application rate of 4 % by mass. Changes in Km and Vmax for URE, INV, ALP, and CAT suggest that biochar influences enzyme kinetics through mechanisms such as adsorption, microenvironmental shifts, and allosteric modulation. An economic assessment identified 4 % biochar application as the optimal rate, yielding soil quality index (SQI) values of 0.53 and 0.65 for grey desert and aeolian soils, respectively. These findings suggest that biochar-amended soils exhibit improved fertility, highlighting the potential of biochar to enhance soil health.

Carbon-based materials from waste PVC/iron chips dechlorination as peroxidase mimics for total antioxidant capacity biosensing

The monitoring of antioxidant capacity is very important to evaluate the quality of antioxidant foods or drugs for market regulation. Herein, dechlorination treatment of waste PVC/scrap irons were conducted in subcritical water to obtain carbon-based Fe composites (CM-Fe-dPVC) with peroxidase-like activity. The electron bonding of C 2p and Fe 3d orbital led to strong electron migration ability. CM-Fe-dPVC exhibited excellent activity of simulated peroxidase. Vitamin C (VC) and CM-Fe-dPVC had competitive behaviors on •OH generation in TMB oxidation reaction. A portable paper based colorimetric test kit was developed for monitoring total antioxidant capacity of beverages and pharmaceuticals on the market (with the detection limit of 0.1 μM for Vc). The results of life cycle assessment (LCA) revealed that the proposed strategy had low global warming potential. This research could provide important reference for high value recycling of organic solid wastes.

Mobility inhibition of arsenic in the soil: the role of green synthesized silica nanoparticles

The studies showed the effectiveness of green-synthesized SiO2NPs in mitigating the toxicity of Arsenic. Density Functional Theory (DFT) is a computational method used to determine electronic structure, energy gap, and toxicity prediction. Experimentally, silicon nanoparticles of 0 (S0) and 100% v/v (S100) were applied to the surface of the soil. 150 mL of Arsenic trioxide was applied twice at a rate of 0 (As0) and 3.2 g/mL (As3.2) at an interval of three weeks. Green synthesized SiO2NPs possessed a higher chemical potential (µ) and electrophilicity index; consequently, charges could be transferred and easily polarized. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels of the green synthesized SiO2NPs enable them to donate electrons and complex with arsenic, reducing their bioavailability and toxicity. Evidence from the studies further showed that SiO2NPs had buffered the soil acidity and electric conductivity, posing a high binding site and reactivity with exchangeable cations and micronutrients due to their smaller energy gap. Furthermore, the catalytic activities of the soil enzymes dehydrogenase (DHA) and peroxidase (POD) were greatly increased, which enhanced the electrostatic interaction between the SiO2NPs and As.

Mineral-mediated stability of organic carbon in soil and relevant interaction mechanisms

Soil, the largest terrestrial carbon reservoir, is central to climate change and relevant feedback to environmental health. Minerals are the essential components that contribute to over 60% of soil carbon storage. However, how the interactions between minerals and organic carbon shape the carbon transformation and stability remains poorly understood. Herein, we critically review the primary interactions between organic carbon and soil minerals and the relevant mechanisms, including sorption, redox reaction, co-precipitation, dissolution, polymerization, and catalytic reaction. These interactions, highly complex with the combination of multiple processes, greatly affect the stability of organic carbon through the following processes: (1) formation or deconstruction of the mineral-organic carbon association; (2) oxidative transformation of the organic carbon with minerals; (3) catalytic polymerization of organic carbon with minerals; and (4) varying association stability of organic carbon according to the mineral transformation. Several pieces of evidence related to the carbon turnover and stability during the interaction with soil minerals in the real eco-environment are then demonstrated. We also highlight the current research gaps and outline research priorities, which may map future directions for a deeper mechanisms-based understanding of the soil carbon storage capacity considering its interactions with minerals.

pH-Activated Scallop-Type Nanoenzymes for Oxidative Stress Amplification and Photothermal Enhancement of Antibacterial and Antibiofilm Effect

Ferric phosphate (FePOs) nanoenzymes can express peroxidase (POD) activity under the dual stimulation of an acidic environment and high H2O2 concentrations. In living organisms, this generates reactive oxygen species (ROS) in sites of lesion infection, and thus FePOs nanoenzymes can act as antimicrobial agents. Here, CeO2 and ZnO2 were immobilized in a scallop-type FePOs nanoenzyme material loaded with a photosensitizer, indocyanine green, to synthesize a multifunctional cascade nanoparticle system (FePOs-CeO2-ZnO2-ICG, FCZI NPs). H2O2 concentrations could be adjusted through the ZnO2 self-activation response to the slightly acidic environment in biofilms, further promoting the release of ROS from the POD-like reaction of FePOs, achieving amplification of oxidative stress, DNA and cell membrane damage, and exploiting the photodynamic/photothermal effects of indocyanine green to enhance the antibiofilm effects. CeO2 can remove redundant ROS by switching from Ce4+ to Ce3+ valence, enhancing its ability to fight chronic inflammation and oxidative stress and thus promoting the regeneration of tissues around infection. By maintaining the redox balance of normal cells, increasing ROS at the infection site, eliminating redundant ROS, and protecting normal tissues from damage, the synthesized system maximizes the elimination of biofilms and treatment at the infection site. Therefore, this work may pave the way for the application of biocompatible nanoenzymes.

Amoxicillin degradation and high-value extracellular polymer recovery by algal-bacterial symbiosis systems

Algal-bacterial symbiosis systems have emerged as sustainable methods for the treatment of new pollutants and the recovery of resources. However, the bio-refinery of biomass derived from microalgae is inefficient and expensive. In order to simultaneously degrade antibiotic and recover resources efficiently, two algal-bacterial symbiosis systems were constructed using Pseudomonas aeruginosa (alginate overproduction) and Bacillus subtilis (poly-γ-glutamic acid overproduction) with amoxicillin-degrading-microalga Prototheca zopfii W1. The optimal conditions for W1 to degrade amoxicillin are 35 °C, pH 7, and 180 rpm. In the presence of 5-50 mg/L of amoxicillin, W1-P. aeruginosa and W1-B. subtilis exhibit higher amoxicillin degradation and produce more extracellular polymers than W1 or bacteria alone. The metabolomic analysis demonstrates that the algal-bacterial symbiosis enhances the tolerance of W1 to amoxicillin by altering carbohydrate metabolism and promotes the production of biopolymers by upregulating the precursors synthesis. Moreover, the removal of amoxicillin (10 mg/L) from livestock effluent by W1-P. aeruginosa and W1-B. subtilis is greater than 90 % in 3 days, and the maximum yields of alginate and poly-γ-glutamate are 446.1 and 254.3 mg/g dry cell weight, respectively. These outcomes provide theoretical support for the application of algal-bacterial symbiosis systems to treatment of amoxicillin wastewater and efficient production of biopolymers.

Flooding duration affects the temperature sensitivity of soil extracellular enzyme activities in a lakeshore wetland in Poyang Lake, China

Extracellular enzymes play central roles in the biogeochemical cycles in wetland ecosystems. Their activities are strongly impacted by hydrothermal conditions. Under the ongoing global change, many studies reported the individual effects of flooding and warming on extracellular enzyme activities, however, few researches investigated their interactive effects. Therefore, the current study aims to determine the responses of extracellular enzyme activities to warming in wetland soils under divergent flooding regimes. We investigated the temperature sensitivity of seven extracellular enzymes related to carbon (α-glucosidase, AG; β-glucosidase, BG; cellobiohydrolase, CBH; β-xylosidase, XYL), nitrogen (β-N-acetyl -glucosaminidase, NAG; leucine aminopeptidase, LAP), and phosphorus (Phosphatase, PHOS) cycling along the flooding duration gradient in a lakeshore wetland of Poyang Lake, China. The Q₁₀ value, calculated using a temperature gradient (10, 15, 20, 25, and 30 °C), was adopted to represent the temperature sensitivity. The average Q₁₀ values of AG, BG, CBH, XYL, NAG, LAP, and PHOS in the lakeshore wetland were 2.75 ± 0.76, 2.91 ± 0.69, 3.34 ± 0.75, 3.01 ± 0.69, 3.02 ± 1.11, 2.21 ± 0.39, and 3.33 ± 0.72, respectively. The Q₁₀ values of all the seven soil extracellular enzymes significantly and positively correlated with flooding duration. The Q₁₀ values of NAG, AG and BG were more sensitive to the changes in flooding duration than other enzymes. The Q₁₀ values of the carbon, nitrogen, and phosphorus-related enzymes were mainly determined by flooding duration, pH, clay, and substrate quality. Flooding duration was the most dominant driver for the Q₁₀ of BG, XYL, NAG, LAP, and PHOS. In contrast, the Q₁₀ values of AG and CBH were primarily affected by pH and clay content, respectively. This study indicated that flooding regime was a key factor regulating soil biogeochemical processes of wetland ecosystems under global warming.

Low carbon availability in paleosols nonlinearly attenuates temperature sensitivity of soil organic matter decomposition

Temperature sensitivity (Q₁₀ ) of soil organic matter (SOM) decomposition is an important parameter in models of the global carbon (C) cycle. Previous studies have suggested that substrate quality controls the intrinsic Q₁₀ , whereas environmental factors can impose large constraints. For example, physical protection of SOM and its association with minerals attenuate the apparent Q₁₀ through reducing substrate availability and accessibility ([S]). The magnitude of this dampening effect, however, has never been quantified. We simulated theoretical Q₁₀ changes across a wide range of [S] and found that the relationship between Q₁₀ and the log₁₀ -transformed [S] followed a logistic rather than a linear function. Based on the unique Holocene paleosol chronosequence (7 soils from ca. 500 to 6900 years old), we demonstrated that the Q₁₀ decreased nonlinearly with soil age up to 1150 years, beyond which Q₁₀ remained stable. Hierarchical partitioning analysis indicated that an integrated C availability index, derived from principal component analysis of DOC content and parameters reflecting physical protection and mineral association, was the main explanatory variable for the nonlinear decrease of Q₁₀ with soil age. Microbial inoculation and ¹³ C-labelled glucose addition showed that low C availability induced by physical protection and minerals association attenuated Q₁₀ along the chronosequence. A separate soil incubation experiment indicated that Q₁₀ increased exponentially with activation energy (E_a ) in the modern soil, suggesting that SOM chemical complexity regulates Q₁₀ only when C availability is high. In conclusion, organic matter availability strongly decreased with soil age, whereas Michelis-Menten kinetics defines the Q₁₀ response depending on C availability, but Arrhenius equation describes the effects of increasing substrate complexity.