Glycine-chelated zinc rather than glycine-mixed zinc has lower foliar phytotoxicity than zinc sulfate and enhances zinc biofortification in waxy corn.

To determine whether high spraying concentrations of Zn sources increase the Zn concentration in waxy corn (Zea mays L. var. ceratina Kulesh) seeds without compromising agronomic performance, field experiments were conducted between 2018 and 2020. Excess ZnSO4 application caused foliar burn, barren ear tip, and grain yield loss. ZnEDTA and Glycine-chelated Zn (ZnGly) caused less foliar burn, but Glycine-mixed Zn caused more foliar burn than ZnSO4. The seed Zn concentration increased with spraying Zn concentration. ZnEDTA (≤0.8%) had a higher threshold concentration than ZnGly (≤0.4%). Nevertheless, Zn biofortification efficacy did not significantly differ between 0.4% ZnGly and 0.8% ZnEDTA, and the grain Zn recovery rate of 0.4% ZnGly was much higher than that of 0.8% ZnEDTA. Additionally, dual-isotope labelling tests confirmed that 15N-glycine and 68Zn in ZnGly interacted. In the future, chelating technology is essential for developing new Zn fertilizers to optimize Zn biofortification efficacy.

Nano zero-valent iron-induced changes in soil iron species and soil bacterial communities contribute to the fate of Cd.

Nano zero-valent iron (nZVI) is used for soil remediation; however, the impact of nZVI on soil solid iron phases and its interactions with soil microorganisms in relation to the fate of Cd in soil remains unclear. In the current study, we investigated the mechanisms underlying the change in mobility of Cd in exogenous Cd-contaminated soil with nZVI and γ radiation treatments. The results showed that nZVI treatment decreased Cd availability but also increased the soil pH and dissolved Mn and poorly crystalline Fe contents. However, the increased poorly crystalline Fe(II) levels contributed to a reduction in Cd availability in soils treated with nZVI by immobilizing Cd associated with Fe oxides, rather than by increasing pH or Mn oxide levels. Moreover, Cd stabilization efficiency was higher in γ-irradiated soils than in non-irradiated soils regardless of the Cd level, with noticeable differences in bacterial community composition between the non-irradiated and irradiated soils. The genera Bacillus, Pullulanibacillus, and Alicyclobacillus are important in the redox of poorly crystalline Fe(II)-containing minerals in non-irradiated soil. This research provides a new method for further improving the Cd stabilization efficiency of nZVI in combination with microbial iron oxidization inhibitors.

Substrate control of sulphur utilisation and microbial stoichiometry in soil: Results of 13C, 15N, 14C, and 35S quad labelling.

Global plant sulphur (S) deficiency is increasing because of a reduction in sulphate-based fertiliser application combined with continuous S withdrawal during harvest. Here, we applied 13C, 15N, 14C, and 35S quad labelling of the S-containing amino acids cysteine (Cys) and methionine (Met) to understand S cycling and microbial S transformations in the soil. The soil microorganisms absorbed the applied Cys and Met within minutes and released SO42- within hours. The SO42- was reutilised by the MB within days. The initial microbial utilisation and SO42- release were determined by amino acid structure. Met released 2.5-fold less SO42- than Cys. The microbial biomass retained comparatively more C and S from Met than Cys. The microorganisms decomposed Cys to pyruvate and H2S whereas they converted Met to α-ketobutyrate and S-CH3. The microbial stoichiometries of C, N, and S derived from Cys and Met were balanced after 4 d by Cys-derived SO42- uptake and Met-derived CO2 release. The microbial C:N:S ratio dynamics showed rapid C utilisation and loss, stable N levels, and S accumulation. Thus, short-term organic S utilisation by soil microorganisms is determined by amino acid structure whilst long-term organic S utilisation by soil microorganisms is determined by microbially controlled stoichiometry.

The inhibition effect of tea polyphenols on soil nitrification is greater than denitrification in tea garden soil.

Tea polyphenols are the most widely distributed class of secondary metabolites (Camellia sinensis) and account for a considerable proportion of the pruning residues of tea. A large amount of tea polyphenols have fallen down over soil with prunning residues every year. However, the effect of tea polyphenols on soil nitrogen cycle, especially the denitrification process and its related microbial communities, remains unclear. Epigallocatechin gallate (EGCG), the most abundant component of tea polyphenols, was selected to simulate the effects of tea polyphenols on soil nitrification, denitrification, related functional genes and microbial community. The results indicated that addition of EGCG can significantly (p < 0.05) inhibit soil nitrification. Copy numbers of bacterial and archaeal ammonia monooxygenase genes (amoA) decreased as EGCG concentration increased. Further, the ammonia oxidisers exhibited a significantly (p < 0.05) greater niche differentiation under the effect of EGCG compared with the control treatment (no EGCG addition). However, the inhibition effect of EGCG over soil denitrification was most significant at 34 and 36 day of incubation period, and such inhibitory effect was more apparent on nitrification compared with denitrification. EGCG addition increased the diversity of bacterial community. The composition of bacterial community was significantly altered and community variation was primary explained by EGCG, NH4+-N, NO3--N, soil organic carbon contents and potential denitrification rates. EGCG addition significantly increased relative abundance of Proteobacteria and Bacteroidetes phyla whereas decreased Actinobacteria. Overall, tea polyphenols can inhibit soil nitrification to a larger extent than denitrification by reducing the abundance of microorganisms carrying the related functional genes. Our results can serve as important basis of reducing the nitrogen pollution risk in tea orchards and could be considered as a powerful natural nitrification inhibitor to reduce the environmental risks caused by unreasonable nitrogen fertiliser adaptation.