The long-term effects of microplastics on soil organomineral complexes and bacterial communities from controlled-release fertilizer residual coating.

Controlled-release fertilizer (CRF) was applied widely in China as an efficient utilization strategy for improving grain yield and reducing the nitrogen contamination. However, it was indeterminate to know the impacts of inevitably imported plastic into the soil on sustainable development. After ten-year fixed-site experiment, the visible residual coating microplastics were separated from the soil to measure their changes, then the long-term effects of CRF application (theoretical microplastic content 0.018-0.151 g kg-1 soil) on soil architecture and bacterial communities were evaluated. Based on soil organomineral complexes (OMC) distribution experiments and soil 16S rRNA sequence analysis, residual coating microplastics had no significant impact on soil architecture and limited effects on soil bacteria, but became the specific microbial habitat. The nitrogen rate and nitrogen release mode affected sand- and silt-grade OMC, and nitrogen rate impacted soil bacteria communities. The residual coating, small inert particles, is safe for soil OMC and bacterial communities in agricultural soil. Due to the effectiveness of CRF on reducing environmental pollution, CRF is considered as a favorable measure to the sustainable agricultural development in Shandong Province, China.

Molecular Composition of Size-Fractionated Fulvic Acid-Like Substances Extracted from Spent Cooking Liquor and Its Relationship with Biological Activity.

The treatment of spent cooking liquor is critical for clean production of pulp and paper industry. There is a compelling need to develop a cost-effective and green technology for reuse of organic matter in spent cooking liquor to mitigate the negative impacts on the environment. The objective of this study is to examine the chemical structure of fulvic acid-like substances extracted from spent cooking liquor (PFA) and their relationship with bioactivity in plant growth. Compared with the benchmark Pahokee peat fulvic acid (PPFA), PFA has less aromatic structure, but higher content of lignin, carbohydrates, and amino acid. After fractionation, protein/amino proportion decreased with increasing molecular weight, but the aromaticity increased. Under salt stress, rice seedling growth was promoted by PFA with low molecular weight (<5 kDa), but inhibited by fraction with high molecular weight (>10 kDa). Principal component analysis suggested that promoted growth was more related with chemical structure (O- and N-alkyl moieties) than with molecular weight. This study provided the theoretical basis for development of an innovative green technology of sustainable reuse of spent cooking liquor in agriculture.

Controlled-release urea reduced nitrogen leaching and improved nitrogen use efficiency and yield of direct-seeded rice.

The use of controlled-release urea (CRU) has become one of best management practices for increasing crop yield and improving nitrogen (N) use efficiency (NUE). However, the effects of CRU on direct-seeded rice are not well understood while direct-seeding has gradually replaced transplanting due to increasing labor cost and lack of irrigation water. The objective of this two-year field experiment was to compare the effects of the CRU at four rates (120, 180, 240 and 360 kg N ha-1, CRU1, CRU2, CRU3 and CRU4, respectively) with a conventional urea fertilizer (360 kg N ha-1; U) and a control (no N fertilizer applied; CK) on yield, biomass, NUE of direct-seeded rice and soil nutrients. The results indicated that the successive release rates of N from CRU corresponded well to the N requirements of rice. The use of CRU3 and CRU4 increased rice grain yields by 20.8 and 28.7%, respectively, compared with U. In addition, the NUEs were improved by all CRU treatments compared to the U treatment. Concentrations of NO3--N and NH4+-N in the soil were increased, especially during the later growth stages of the rice, and the leaching of N was reduced with CRU treatments. In conclusion, applying CRU on direct-seeded rice increased the crops yields and NUE, increased nitrogen availability at the late growth stages, and reduced N leaching.

Gene Expression, Enzyme Activity, Nitrogen Use Efficiency, and Yield of Rice Affected by Controlled-Release Nitrogen.

Controlled- or slow-release urea can improve crop nitrogen use efficiencies and yields in many agricultural production systems. The effect of controlled-release urea on the relationships between levels of gene expression and yields has not been adequately researched. We conducted a 2 year field study with direct-seeded rice, which included treatments of controlled-release urea at four rates (120, 180, 240, and 360 kg N ha-1), a standard urea treatment (360 kg N ha-1), and a control treatment without applied nitrogen. Controlled-release urea improved the inorganic nitrogen concentrations of root-zone soil and water, functional enzyme activities, protein contents, grain yields, and nitrogen use efficiencies. Controlled-release urea also improved the gene expressions of nitrate reductase [NAD(P)H] (EC 1.7.1.2), glutamine synthetase (EC 6.3.1.2), and glutamate synthase (EC 1.4.1.14). With the exception of glutamate synthase activity, there were significant correlations among these indices. The results showed that controlled-release urea improved the content of inorganic nitrogen within the rice root zone. Compared with urea, the average enzyme activity of controlled-release urea increased by 50-200%, and the relative gene expression was increased by 3-4 times on average. The added soil nitrogen increased the level of gene expression, allowing enhanced synthesis of enzymes and proteins for nitrogen absorption and use. Hence, controlled-release urea improved the nitrogen use efficiency and the grain yield of rice. Controlled-release urea is an ideal nitrogen fertilizer showing great potential for improving rice production.

Development of multifunctional copper alginate and bio-polyurethane bilayer coated fertilizer: Controlled-release, selenium supply and antifungal.

Bio-based controlled release fertilizers (BCRFs) are cost-effective and renewable thus gradually replacing petroleum-based controlled release fertilizers (CRFs). However, most of the study mainly focused on modifying BCRFs to improve controlled-release performance. It is necessary to further increase the functionality of BCRF for expanding the application. A multifunctional double layered bio-based CRF (DCRF) was prepared. Urea was used as the core of fertilizer, bio-based polyurethane was used as the inner coating, and sodium alginate and copper ions formed the hydrogel as the outer coating. In addition, mesoporous silica nanoparticles loaded with sodium selenate was used to modify the sodium alginate hydrogel (MSN@Se hydrogel). The results showed that the nitrogen longevity of the DCRF was much better than that of urea and BCRF. The selenium nutrient longevity of the DCRF was 40 h, much longer than that of sodium selenate. The DCRF improved the yield and nutritive value of cherry radish (Raphanus sativus L. var.radculus pers) with the elevated contents of selenium, an essential trace element. Moreover, the DCRF showed inhibitory effect on Fusarium oxysporum Schltdl. and could resist soil-borne fungal diseases continuously. Overall, this multifunctional fertilizer has great potential for expanding the use of BCRFs for sustainable development of agriculture.

Efficiencies of different microbial parameters as indicator to assess slight metal pollutions in a farm field near a gold mining area.

In order to monitor changes in the concentrations of metals in the soil, different microbial indices such as BIOLOG, microbial carbon (C(mic)), basal respiration, and culturable microbe's most probable number were used. We compared these methods and wanted to discover which method was the best at measuring slight changes in the amounts of heavy metals. Factor analyses were applied to the BIOLOG data and metal concentrations so the combined effects of heavy metals on microbes could be analyzed via statistical data reduction and the distribution patterns of metal concentration could also be revealed. The results showed that the BIOLOG method could barely detect subtle characteristic changes in the soil samples, while the C(mic) method was more sensitive. Furthermore, different heavy metals did not have the same origin/source, and their effects on microbial indices should be analyzed separately. Significant positive correlations between C(mic) and metals were observed and suggested the limitation of using traditional microbial parameters as metal pollution indicators. Among all the soil characteristics in our study, pH seemed to be the most active abiotic factor that affected microorganisms.

Transcriptome sequencing analysis reveals silver nanoparticles antifungal molecular mechanism of the soil fungi Fusarium solani species complex.

Silver nanoparticles (AgNPs) have been widely used in various fields due to their antimicrobial activities. However, the antimicrobial mechanisms of AgNPs against fungi, especially on transcriptional level, are still unclear. In this study, the inhibitory property of AgNPs against Fusarium solani species complex was investigated. Transmission electron microscopes were used to observe the alterations in morphology and cellular structure of fungal hyphae treated with AgNPs. Disturbances in the cell walls and membranes, as well as empty space in the cytoplasm were observed. The transcriptome sequencing of F. solani species complex mycelia was performed using the Illumina NextSeq 500 ribonucleic acid sequencing (RNA-Seq) platform. In the RNA-Seq study, AgNPs treatment resulted in 2503 differentially expressed genes (DEGs). Gene Ontology (GO) analysis revealed that the DEGs were mainly involved in 6 different terms. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis also revealed that energy and substance metabolism, signal transduction and genetic information processing were the most highly enriched pathways for these DEGs. In addition, RNA-seq results were validated by quantitative polymerase chain reactions (qPCRs). Our findings enhanced the understanding of the antifungal activities of AgNPs and the underlying molecular mechanisms, and provided a new perspective for investigating this novel antifungal agent.

Self-Assembly of Hydrophobic and Self-Healing Bionanocomposite-Coated Controlled-Release Fertilizers.

Self-healing materials have received increased attention because of their automatic detecting and repairing damage function. In this paper, a novel self-assembly and self-healing bionanocomposite was developed as a coating material for controlled release fertilizers. This nanotechnology-enabled coating is environmentally friendly and highly efficient and possesses a tunable nutrient-releasing characteristic. In the synthesis process, bio-based polyurethane coated urea (BPCU) was prepared by the reaction of bio-polyols with isocyanate. The BPCU was then modified by the layer-by-layer technology to prepare self-assembling modified BPCU (SBPCU). Last, hollow nano-silica (HNS) particles loaded with the sodium alginate (SA) were used to modify SBPCU to fabricate of self-assembling and self-healing BPCU (SSBPCU). The results show that the self-assembled materials were synthesized through electrostatic adsorption. The self-healing was observed through scanning electron microscopy and 3D-X-ray computed tomography, revealing the mechanism was that the repair agent released from HNS reacted with the curing agent to block the pore channels and cracks of the coating. As a result, the SSBPCU exhibited the highest hydrophobicity and surface roughness and thus the slowest release rate. For the first time, this work has designed a novel strategy to solve the bottleneck problem that restricts the development of a controlled-release fertilizer.

Long-term effects of untreated wastewater on soil bacterial communities.

For 46 years (1957-2002), irrigation with wastewater has increased the amount of heavy metal and organic contaminants in soils and altered bacterial communities in Shenyang, northeastern China. There has been characterization of the different heavy metal and petroleum contaminants in two types of land uses (cornfields and paddy fields). The Nemerow composite indices of heavy metal contaminants have been higher in cornfields (1.17-4.73) than those in paddy fields (0.57-1.64). Molecular-based techniques and biochemical-based techniques were used to analyze soil microbial diversity in our study. The metabolic activity of soil microbe communities was higher in paddy sites than that in cornfields. Organic pollutants such as saturated and polycyclic aromatic hydrocarbons have significantly affected soil bacterial compositions. Heavy metals differed in how they disturbed the microbial communities. Arsenic (As) and lead (Pb) shifted the community composition and decreased microbial diversity; copper (Cu) reduced bacterial abundance in soil; and cadmium (Cd) and chromium (Cr) lowered the metabolic capabilities of bacteria.

Bio-based Large Tablet Controlled-Release Urea: Synthesis, Characterization, and Controlled-Released Mechanisms.

To improve nitrogen (N) use efficiency and minimize environmental pollution caused by fertilizer overuse, novel bio-based large tablet controlled-release urea (LTCRU) was prepared using bio-based coating materials to coat large tablet urea (LTU) derived from urea prills (U). Nano fumed silica (NFS) was added to the bio-based coating materials to improve the slow-release properties. The surface area of the LTU and U was measured by three-dimensional scanning. In comparison to U, LTU had a smaller surface area/weight ratio, which can reduce the coating materials. Scanning electron microscopy analysis showed that the addition of NFS in bio-based coating materials reduced the porosity of the coating shells of LTCRUs and, thus, enhanced the N release longevity of the controlled-released fertilizer. Dependent upon the pores on the coating shells of LTCRU, two N release patterns were revealed. Because of the good release characteristics, the novel LTCRU shows great potential to support sustainable agricultural production.

Responses of the terrestrial ammonia-oxidizing archaeon Ca. Nitrososphaera viennensis and the ammonia-oxidizing bacterium Nitrosospira multiformis to nitrification inhibitors.

Nitrification inhibitors have been used for decades to improve nitrogen fertilizer utilization in farmland. However, their effect on ammonia-oxidizing Archaea (AOA) in soil is little explored. Here, we compared the impact of diverse inhibitors on nitrification activity of the soil archaeon Ca. Nitrososphaera viennensis EN76 and compared it to that of the ammonia-oxidizing bacterium (AOB) Nitrosospira multiformis. Allylthiourea, amidinothiourea, and dicyandiamide (DCD) inhibited ammonia oxidation in cultures of both N. multiformis and N. viennensis, but the effect on N. viennensis was markedly lower. In particular, the effective concentration 50 (EC50) of allylthiourea was 1000 times higher for the AOA culture. Among the tested nitrification inhibitors, DCD was the least potent against N. viennensis. Nitrapyrin had at the maximal soluble concentration only a very weak inhibitory effect on the AOB N. multiformis, but showed a moderate effect on the AOA. The antibiotic sulfathiazole inhibited the bacterium, but barely affected the archaeon. Only the NO-scavenger carboxy-PTIO had a strong inhibitory effect on the archaeon, but had little effect on the bacterium in the concentrations tested. Our results reflect the fundamental metabolic and cellular differences of AOA and AOB and will be useful for future applications of inhibitors aimed at distinguishing activities of AOA and AOB in soil environments.