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Plant biostimulants (PBs) are a potential strategy to improve crop growth and grain quality. In the present study, 100 mg/L trehalose, chitosan, humic acid and gamma-aminobutyric acid treatments were applied to analyze the effects of maize production and reproductive characteristics. The contents of nitrogen, phosphorus and potassium and grain quality were significantly affected by the PBs, but not yield. The seed germination rate of all PB treatments was significantly reduced, but the drought resistance of progeny seedlings was significantly improved, with humic acid having the strongest effect. Liquid chromatography mass spectrometry analysis indicated that the disruption of the tricarboxylic acid cycle, probably due to the blockage of intermediate anabolism, reduced the supply of energy and nutrients in the early stages of germination, thus inhibiting seed germination, while the increased resistance of the offspring seedlings may be due to the up-regulation of the synthesis of unsaturated fatty acids and alkaloids by humic acid treatment. This study revealed the similarity and heterogeneity of the effects of different PBs on nutrient accumulation, yield characteristics and grain quality of maize, providing guidance for the application of PBs in intensive and sustainable agricultural production.

Although soil microorganism is an active area of research, we are still in the early stages of understanding how living microorganisms influence the accumulations of soil microbial residues under different agricultural practices. Based on a 39-year fertilization experiment, we characterized the soil microbiota and correlated their compositions to soil microbial residues, which are indicated by amino sugars under a rice-wheat rotation. In the present study, fertilization regimes and crop season all exerted significant impacts on the compositions of soil microbial communities and their residues, although no significant difference in the microbial residues was found between soil depth (0–10 cm vs. 10–20 cm). Compared within fertilization regimes, the long-term fertilization, especially the application of organic manure, stimulated the accumulations of carbon (C) and nitrogen in soils and microbial residues. Upland soils in wheat season accumulated more microbial residues, particularly in fungal residues, than paddy soils in rice season. Our results suggested that the long-term application of organic manure favored the growth of soil microbial communities, and then increased the contents of microbial residues, particularly in fungal residues, leading to an enlargement of soil C pools. The keystone taxa Pseudaleuria identified by network analysis showed a significantly positive potential in soil C sequestration by increasing the accumulation of fungal residues. Thus, this study revealed the strong and close connections between microbial communities and their residues, and provided evidence about the critical role of keystone taxa in regulating C sequestration.

Soil aggregates provide different ecological niches for microorganisms, and in turn, the microbial interactions affect soil aggregation process. The response of the microbial community in bulk soil to different fertilization regimes has been well studied; however, the co-occurrence patterns of bacteria and fungi in different aggregates under various fertilization regimes remain unclear. Based on the long-term field experiment, we found that fertilization regimes contributed more to fungal than to bacterial community composition. Long-term fertilization decreased microbial interactions in large macroaggregates (LM), macroaggregates (MA) and silt and clay (SC) fractions, but increased in microaggregates (MI). The application of manure with inorganic fertilizers (NPKM) significantly increased the intensive cooperation between bacteria and fungi in LM and MA. Microbial communities in LM and MA were well separated and showed strong competition against microbes in MI and SC; hence, we concluded that the microbial habitat could be divided into two groups, large fractions (LM and MA) and small fractions (MI and SC). The bacterial genera Anaerolinea, Nocardioides, Ohtaekwangia, Geoalkalibacter, Lysobacter, Pedomicrobium, and Flavisolibacter were keystone taxa in inorganic fertilization, and Roseiflexus, Nitrospira, and Blastocatella were keystone taxa in NPKM, which were all sensitive to soil aggregation. In this study, we demonstrated that the NPKM decreased the microbial interactions within and between kingdoms in LM, MA, and SC, but enhanced nutrient availability and microbial interactions in MI, leading to the formation of biofilms and the strengthening of stress tolerance, which finally stimulated the formation and stabilization of soil aggregates. Thus, this study revealed how soil microbial competition or cooperation responded to different fertilization regimes at aggregate scales, and provided evidence for the stimulation of soil stability.