Glomalin-related soil protein (GRSP) contributes to the formation and maintenance of soil aggregates, it is however remains unclear whether long-term intensive manure amendments alter soil aggregates stability and whether GRSP regulates these changes. Based on a three-decade long fertilization experiment in northeast China, this study examined the impact of long-term manure input on soil organic carbon (SOC), total and easily extractable GRSP (GRSP_t and GRSP_e) and their respective allocations in four soil aggregates (>2000 μm; 2000–250 μm; 250–53 μm; and <53 μm). The treatments include no fertilization (CK), low and high manure amendment (M1, M2), chemical nitrogen, phosphorus and potassium fertilizers (NPK) and combined manure and chemical fertilizers (NPKM1, NPKM2). Though SOC, GRSP_e and GRSP_t in soil and SOC in each aggregate generally increased with increasing manure input, GRSP_t and GRSP_e in each aggregate showed varying changes with manure input. Both GRSP in macroaggregates (2000–250 μm) were significantly higher under low manure input, a pattern consistent with changes in soil aggregate stability. Constituting 38~49% of soil mass, macroaggregates likely contributed to the nonlinear changes of aggregate stability under manure amendments. The regulatory process of GRSP allocations in soil aggregates has important implications for manure management under intensive agriculture.

Polycyclic aromatic hydrocarbons (PAHs), especially high molecular weight PAHs, are carcinogenic and mutagenic organic compounds that are difficult to degrade. Microbial remediation is a popular method for the PAH removal in diverse environments and yet it is limited by the lack of electron acceptors. An emerging solution is to use the microbial electrochemical system, in which the solid anode is used as an inexhaustible electron acceptor and the microbial activity is stimulated by biocurrent in situ to ensure the PAH removal and avoid the defects of bioremediation. Based on the extensive investigation of recent literatures, this paper summarizes and comments on the research progress of PAH removal by the microbial electrochemical system of diversified design, enhanced measures and functional microorganisms. First, the bioelectrochemical degradation of PAHs is reviewed in separate and mixed PAH degradation, and the removal performance of PAHs in different system configurations is compared with the anode modification, the enhancement of substrate and electron transfer, the addition of chemical reagents, and the combination with phytoremediation. Second, the key functional microbiota including PAH degrading microbes and exoelectrogens are overviewed as well as the reduced microbes without competitive advantage. Finally, the typical representations of electrochemical activity especially the internal resistance, power density and current density of systems and influence factors are reviewed with the correlation analysis between PAH removal and energy generation. Presently, most studies focused on the anode modification in the bioelectrochemical degradation of PAHs and actually more attentions need to be paid to enhance the mass transfer and thus larger remediation radius, and other smart designs are also proposed, especially that the combined use of phytoremediation could be an eco-friendly and sustainable approach. Additionally, exoelectrogens and PAH degraders are partially overlapping, but the exact functional mechanisms of interaction network are still elusive, which could be revealed with the aid of advanced bioinformatics technology. In order to optimize the efficacy of functional community, more advanced techniques such as omics technology, photoelectrocatalysis and nanotechnology should be considered in the future research to improve the energy generation and PAH biodegradation rate simultaneously.

Soil moisture is the major factor influencing microbial properties and nitrous oxide (N₂O) production. Agricultural soils can be probed under wetting, wet/dry alternating, and constant moisture conditions to evaluate the combined effects of early (previous) and immediate (current) moisture on N₂O emission and nitrification/denitrification. In view of the water history of upland black soil, five moisture regimes comprising different antecedent and present water holding capacity (WHC) levels were set up in the microcosm study. The 20% WHC was adopted as the initial legacy moisture, while three immediate water statuses include constant WHC, dry-wet cycle, and incremental moisture. Quantitative PCR and 16S rRNA amplicon sequencing were used to assess the impact of current and previous moisture on the bacterial community composition and abundance of nitrification/denitrification genes (amoA, nirS, and nosZ); the soil physicochemical properties, and N₂O emission were monitored. The N₂O production and nitrifying-denitrifying microbial communities were influenced by the antecedent moisture and pattern of the dry-wet cycle. The nitrifying-denitrifying microbial communities, especially members of β-/γ-Proteobacteria, Bacteroidetes and Gemmatimonadetes, in black soil were important in explaining the variation of N₂O production. The key taxonomic groups in response to the moisture alteration, e.g., Acidobacteria, Sphingobacteriia, Deltaproteobacteria, Methylobacterium, Gemmatimonas and Pseudarthrobacter, etc., were also highlighted. The soil nitrate, ammonium nitrogen, N₂O emission, nitrification/denitrification and mineralization were profoundly impacted by water regimes and showed statistically significant correlation with specific bacterial genera; the nitrite/nitrate reduction to ammonium could be boosted by high moisture. Both nitrifier denitrification and heterotrophic denitrification could be enhanced substantially when the black soil moisture was increased to above 60% WHC. These findings help evaluate the effects of the water mode on the N₂O emission from black soil, as well as the associated impacts on both soil fertility and the global environment.

To understand the contribution of key microbial processes to nitrous oxide (N₂O) emission in intensively cultivated black soil, laboratory incubation were conducted at 70% water-holding capacity (WHC) and 25 °C, using different gases (air, oxygen, or argon) within the headspace of the incubation chambers to evaluate gas inhibition effects. Arable black soil was sampled from an experimental field that has received urea since October 1979. Nitrification contributed to 57% of total N₂O emission, of which as much as 67% resulted from heterotrophic nitrification. These data strongly suggest that high soil organic carbon concentrations and low pH values are more favorable to N₂O production through heterotrophic, rather than autotrophic, nitrification. Nitrous oxide produced by denitrification accounted for 28% of the total N₂O emission, and the nitrifier denitrification accounted for 15% of the N₂O emitted from the tested soil. These findings indicate that heterotrophic nitrification was the primary N₂O production process in the tested soil.

Diverse microbes in arable black soil participate in the biogeochemical cycling of nitrogen, which profoundly impact on the fertility and greenhouse gas (GHG) emission. However, the effects of environmental factors on the structure and functions of microbial communities have not been thoroughly elucidated. We performed the indoor microcosm study to collect the soil samples under six moisture (constant and wetting)/gas (air, 10% acetylene, oxygen and argon) regimes and investigated the alterations of bacterial community composition, nitrification/denitrification gene abundance and nitrogen metabolic functions under different conditions by high-throughput sequencing, quantitative PCR, physicochemical analyses and bioinformatics. It was found that the N₂O/CO₂ emission under six moisture/gas regimes were significantly different (p < 0.001), the processing time also dramatically influenced the GHG emission, and there were considerable interactions between moisture/gas regime and processing time. The impact of moisture/gas regimes, processing time and interaction item on \({\text{NH}}_{4}^{ + }\)-N and \({\text{NO}}_{3}^{ - }\)-N was also conspicuous. The moisture/gas regime significantly affected the community diversity rather than community richness. The key responsive bacterial classes under different gas conditions were Gammaproteobacteria, Bacteroidia and Alphaproteobacteria, in contrast to Actinobacteria, Alphaproteobacteria and Thermoleophilia under different moisture regimes. The abundance of Piscinibacter, Chujaibacter, Symbiobacteraceae and Acidobacteriales species was positively correlated with moisture and N₂O emission, and denitrification, nitrate reduction to ammonium, nitrification, nitrogen mineralization/fixation were the dominant processes of nitrogen cycle in black soil, which were supported by co-occurring network analyses and Spearman correlation heatmap. The hub nodes and connection mode of microbial nitrogen-cycling network differ under six moisture/gas regimes, and the same species could be active in multiple major nitrogen turnover processes simultaneously. These findings shed light on the prevention and control of soil fertility decline and global warming.