Effects of Modification and Co-Aging with Soils on Cd(II) Adsorption Behaviors and Quantitative Mechanisms by Biochar

In this study, original rice straw biochar and two KMnO4-modified biochars (pre- and postmodification) were prepared, which were all pyrolysed at 400℃. Premodified biochar had the largest Cd adsorption capacity, strongest acid and solute buffering capacity, which benefited from the increase of carbonate content, specific surface area and the emergence of Mn(II) and MnOx through modification. Original and premodified biochars were then conducted four types of aging process, namely, aging without soil, co-aging with acid (pH=5.00), neutral (pH=7.00) and alkaline (pH=8.30) soils, using an improved three-layer mesh method. The adsorption capacities of modified biochar were always larger than those of original biochar after aging processes. After four aging processes, Cd(II) adsorption capacities were basically in the order of aged biochar without soil > biochar co-aged with alkaline soil > biochar co-aged with neutral soil > biochar co-aged with acid soil, and KMnO4-modified biochar was always better than original biochar after co-aging with soils. The dominant adsorption mechanism of original and premodified biochars (fresh and aged) for Cd(II) was all the precipitation and adsorption with minerals (accounted for 58.55%~85.55%). In this study, we highlighted that biochar remediation for Cd should be evaluated by co-aging with soil instead of aging without soil participation.

Effect of DC Currents and Strain on Corrosion of X80 Steel in a Near-Neutral Environment

The corrosion behavior of X80 steel in a near-neutral soil-simulated solution under various DC stray currents and applied strains was investigated using electrochemical measurements (open circuit potential, linear polarization, and electrochemical impedance spectroscopy) and surface analysis techniques. Our results show that a DC stray current has a substantially greater effect on steel corrosion compared to applied strain. However, strain could slow down the corrosion rate in specific conditions by affecting the composition of corrosion products and the structure of the corrosion scale on the surface of the steel. Although the porosity of the corrosion scale of steel without an applied strain will increase with increasing DC currents, once strain is applied, the corrosion scale will become denser. Furthermore, both DC currents and strain can promote steel pitting, and the number and size of pitting holes will increase significantly with an increase in current densities.

Intra-Soil Milling for Stable Evolution and High Productivity of Kastanozem Soil

The long-term field experiment on the Kastanozem showed that the standard moldboard plowing to a depth of 22 cm (control), chiseling to a depth of 35 cm, and three-tier plowing (machine type PTN–40) to a depth of 45 cm was incapable of providing a stable soil structure and aggregate system. The transcendental Biogeosystem Technique (BGT*) methodology for intra-soil milling of the 20–45 cm layer and the intra-soil milling PMS–70 machine were developed. The PMS–70 soil processing provided the content of 1–3 mm sized aggregate particle fraction in the illuvial horizon of about 50 to 60%, which was 3-fold higher compared to standard plowing systems. Soil bulk density reduced in the layer 20–40 cm to 1.35 t m−3 compared to 1.51 t m−3 in the control option. In the control, the rhizosphere developed only in the soil upper layer. There were 1.3 roots per cm−2 in 0–20 cm, and 0.2 roots per cm−2 in 20–40 cm. The rhizosphere spreads only through the soil crevices after chilling. After three-tier plowing (PTN–40), the rhizosphere developed better in the local comfort zones of the soil profile between soil blocks impermeable for roots. After intra-soil milling PMS–70, the rhizosphere developed uniformly in the whole soil profile: 2.2 roots per cm−2 in 0–20 cm; 1.7 roots per cm−2 in 20–40 cm. Matric water potential was higher, soil salinization was lower, and the pH was close to neutral. Soil organic matter (SOM) content increased to 3.3% in 0–20 cm and 2.1% in 20–40 cm compared to the control (2.0% in the 0–20 cm soil layer and 1.3% in the 20–40 cm layer). The spring barley yield was 53% higher compared to the control. The technology life cycle profitability was moldboard 21.5%, chiseling 6.9%, three-tier 15.6%, and intra-soil milling 45.6%. The new design of the intra-soil milling machine provides five times less traction resistance and 80% increased reliability, halving energy costs.

Linking meta-omics to the kinetics of denitrification intermediates reveals pH-dependent causes of N2O emissions and nitrite accumulation in soil

Soil pH is a key controller of denitrification. We analysed the metagenomics/transcriptomics and phenomics of two soils from a long-term liming experiment, SoilN (pH 6.8) and un-limed SoilA (pH 3.8). SoilA had severely delayed N2O reduction despite early transcription of nosZ (mainly clade I), encoding N2O reductase, by diverse denitrifiers. This shows that post-transcriptionally hampered maturation of the NosZ apo-protein at low pH is a generic phenomenon. Identification of transcript reads of several accessory genes in the nos cluster indicated that enzymes for NosZ maturation were present across a range of organisms, eliminating their absence as an explanation for the failure to produce a functional enzyme. nir transcript abundances (for NO2− reductase) in SoilA suggest that low NO2− concentrations in acidic soils, often ascribed to abiotic degradation, are primarily due to biological activity. The accumulation of NO2− in neutral soil was ascribed to high nar expression (nitrate reductase). The -omics results revealed dominance of nirK over nirS in both soils while qPCR showed the opposite, demonstrating that standard primer pairs only capture a fraction of the nirK pool. qnor encoding NO reductase was strongly expressed in SoilA, implying an important role in controlling NO. Production of HONO, for which some studies claim higher, others lower, emissions from NO2− accumulating soil, was estimated to be ten times higher from SoilA than from SoilN. The study extends our understanding of denitrification-driven gas emissions and the diversity of bacteria involved and demonstrates that gene and transcript quantifications cannot always reliably predict community phenotypes.

The Possibilities of Using Common Buckwheat in Phytoremediation of Mineral and Organic Soils Contaminated with Cd or Pb

The results of this study provided accurate guidance on the possibility of using common buckwheat (Fagopyrum esculentum Moench) in phytoremediation practices for mineral soil or organic soils contaminated with Cd or Pb. Based on a model pot experiment, the tolerance of buckwheat to elevated contents of cadmium and lead in organic and mineral soils was examined. The soils were differentiated into neutral and acidic, and amended with metals at doses of 10 mg Cd kg−1 DM and 100 mg Pb kg−1 DM of soil. The growth, development, biomass, translocation coefficient, and tolerance index (TI) of the tested plants were examined. The use of metals caused a weakening of plant growth and development, as well as intensified chlorotic and necrotic changes to the buckwheat leaves. The application of Cd caused a statistically significant decrease in shoot biomass. The plants growing in organic acidic soil were most vulnerable to Cd toxicity. The (TI) values confirm the generally low tolerance of buckwheat to Cd, except for the treatment in organic neutral soil, and the high tolerance of this plant to Pb in all the studied soils.

Soil and plant δ¹⁵N have a different response to experimental warming: A global meta-analysis

The 15N natural abundance composition (δ15N) in soils or plants is a useful tool to indicate the openness of ecosystem N cycling. This study was aimed to evaluate the influence of the global warming on soil and plant δ15N. We applied a global meta-analysis method to synthesize 79 and 76 paired observations for soil and plant δ15N from 20 published studies, respectively. Results showed that the mean effect sizes of the soil and plant δ15N under experimental warming were −0.524 (95 % CI: −0.987 to −0.162) and 0.189 (95 % CI: −0.210 to 0.569), respectively. This indicated that soil and plant δ15N had negative and positive responses to warming at the global scale, respectively. Experimental warming significantly (p < 0.05) decreased soil δ15N in Alkali soil, grassland/meadow, and under air warming, whereas it significantly (p < 0.05) increased soil δ15N in neutral soil. Plant δ15N significantly (p < 0.05) increased with increasing temperature in neutral soil and significantly (p < 0.05) decreased in alkali soil. Latitude did not affect the warming effects on both soil and plant δ15N. However, the warming effect on soil δ15N was positively controlled by the mean annual temperature, which is related to the fact that the higher temperature can strengthen the activity of soil microbes. The effect of warming on plant δ15N had weaker relationships with environmental variables compared with that on soil δ15N. This implied that soil δ15N tended to be more efficient in indicating the openness of global ecosystem N cycling than plant δ15N.

Self-healing of bio-cementitious mortar incubated within neutral and acidic soil

The efficiency of bio self-healing of pre-cracked mortar specimens incubated in sand was investigated. The investigation examined the effect of soil pH representing industrially recognised classes of exposure, ranging from no risk of chemical attack (neutral pH ≈ 7) to very high risk (pH ≈ 4.5). Simultaneously, the soil was subjected to fully and partially saturated cycles for 120 days to resemble groundwater-level fluctuation. Bacillus subtilis with nutrients were impregnated into perlite and utilised as a bacterial healing agent. The healing agent was added to half of the mortar specimens for comparison purposes. Mineral precipitations were observed in both control and bio-mortar specimens, and the healing products were examined by SEM–EDX scanning. The healing ratio was evaluated by comparing (1) the repair rate of the crack area and (2) by capillary water absorption and sorptivity index—before and after incubation. The results indicated that bacteria-doped specimens (bio-mortar) exhibited the most efficient crack-healing in all incubation conditions i.e. different chemical exposure classes. In the pH neutral soil, the average healing ratios for the control and bio-mortar specimens were 38% and 82%, respectively. However, the healing ratio decreased by 43% for specimens incubated in acidic soil (pH ≈ 4) compared with specimens incubated in neutral soil (pH ≈ 7). The study implies that bio self-healing is generally beneficial for concrete embedded within soil; however, aggressive ground conditions can inhibit the healing process.

Can we improve soil properties and plant biomass using rock powder as soil amendment?

&lt;p&gt;The application of rock powder is an option to improve soil fertility while valorising the overburden material produced by industries. The &amp;#8220;enhanced weathering&amp;#8221; of silicate rock has also gained recent interest in the scientific community for its potential to mitigate climate change. However, the effect of rock powder on the soil physical properties remains unclear, especially under climate change (e.g., increasing drought events). Prior to any large scale application of rock powder, it is crucial to disentangle the potential effects of rock powder application on its environment. In a mesocosm experiment, we explored the effect of three rock powders on plant biomass, soil aggregation and organic carbon (OC) allocation within aggregates, in two soils with clayey and sandy textures, under regular watering or severe drought conditions. We demonstrate that the rock powder was the third factor after drought and soil texture significantly affecting the plant growth, resulting in a significant plant biomass decrease ranging from - 13 % to - 42 % compared with the control. We mainly attribute this effect to the increase of the already neutral soil pH, along with the release of excessive heavy metal amounts at a toxic range for the plant. Yet, we found that adding rock powder to the soil resulted in an increase of the relative amount of microaggregates in the soil by up to + 70 %, along with a re-distribution of OC within the fine fractions of the soil (up to + 32 % of OC in &lt; 250 &amp;#181;m fractions). The new mineral-mineral and organo-mineral interactions promoted by the rock powder addition could potentially favour OC persistence in soil on the long term. With our results, we insist on the potential risks for plant growth associated to the application of rock powder when not handled properly. In addition to the current enthusiasm around the capacity of rock powder to enhance carbon sequestration in the inorganic form, we also encourage scientists to focus their research on its effect on soil structure properties and OC storage.&lt;/p&gt;