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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.

The use of biochar as a soil amendment has substantial potential to enhance soil quality and carbon sequestration. However, the responses to the addition of biochar based on soil microbial residues are not well understood, particularly at the aggregate level. Herein, a two-year field experiment investigated the characteristics of distribution of microbial residues in calcareous fluvo-aquic soil aggregates (SA) in Henan Province, China. Four treatments were established as follows: no fertilizer (CK), chemical fertilizer (NPK), biochar (BC), and biochar combined with chemical fertilizer (NPK + BC). The results showed that the effects of particle size substantially impacted the microbial residues with 2–0.25 mm SA having the largest contents of amino sugars and microbial residual carbon (MRC), followed by >2 mm SA. Compared with the CK, the NPK treatment markedly enhanced the levels of glucosamine (GluN), galactosamine (GalN), muramic acid (MurA), total amino sugar (TAS), and MRC in the 2–0.25 mm SA by 26.69%, 24.0%, 23.62%, 25.11%, and 24.82%, respectively. The NPK + BC treatment significantly increased the contents of GluN, GalN, TAS, and MRC in the bulk soil and 0.25–0.053 mm SA compared with the NPK treatment. Bacterial biomass and the activity of N-acetyl-glucosaminidase in the bulk soil and SA markedly and positively affected the content of carbon in the amino sugars and microbial residues. Overall, the 2–0.25 mm SA were microenvironments with the largest accumulation of soil microbial residues, and the combined application of NPK + BC was more effective at increasing the accumulation of microbial residues in the SA, which provides an ideal fertilization strategy to improve the soil microenvironment and enhance soil quality.

Quantifying greenhouse gas intensity (GHGI) and soil carbon sequestration is a method to assess the mitigation potential of agricultural activities. However, the effects of different fertilizer amendments on soil carbon sequestration and net GHGI in a rice-wheat cropping system are poorly understood. Here, fertilizer treatments including PK (P and K fertilizers); NPK (N, P and K fertilizers), NPK + OM (NPK plus manure), NPK + SR (NPK plus straw returning), and NPK + CR (NPK plus controlled-release fertilizer) with equal N input were conducted to gain insight into the change of soil organic carbon (SOC) derived from the net ecosystem carbon budget (NECB), net global warming potential (GWP), and GHGI under rice-wheat rotation. Results showed that compared with NPK treatment, NPK + OM significantly increased wheat yield and NPK + SR caused significant increase in rice yield. Meanwhile, NPK + SR and NPK + CR treatments reduced net GWP by 30.80% and 21.83%, GHGI by 36.84% and 28.07%, respectively, which suggested that improved grain production could be achieved without sacrificing the environment. With the greatest C sequestration, lowest GHGI, the NPK plus straw returning practices (NPK + SR) might be the best strategy to mitigate net GWP and improve grain yield and NUE in the current rice-wheat rotation system.

Shifts in soil bacterial diversity and community composition are suggested to be induced by elevated input of nitrogen (N) fertilization with implications for soil quality, and consequently production. In this study, we evaluated the impacts of recommended fertilization (RF) and conventional fertilization (CF) on soil chemical properties, crop yield, bacterial diversity, and community composition from two long-term experiments conducted in fluvo-aquic soil and black soil of China. Each site comprised of four treatments, i.e., RF N−, RF N+, CF N−, CF N+. No N fertilization was indicated by N− and N fertilization was indicated by N+. Across both sites, N fertilization significantly increased crop yield compared with no N fertilization and RF successfully enhanced crop yield over CF. Interestingly, the RF maintained bacterial diversity, while CF depressed bacterial diversity in the two soils. Microbial taxa performing important ecological roles such as order Rhodospirillales and Bacillales were significantly enhanced in the RF approach, while Rhizobiales declined under CF. Furthermore, the results of partial least square path modeling revealed that soil available phosphorus (AP) negatively affected bacterial diversity while it positively affected bacterial community structure in fluvo-aquic soils. In contrast, soil pH was positively linked with both bacterial diversity and community structure in black soil. Overall, our study demonstrated that RF is an environmentally friendly approach which not only maintained above ground plant productivity, but also preserved belowground microbial populations and important soil variables regulating bacterial communities varied in different soil types.

Biochar (BC) addition to soil is a proposed strategy to enhance soil fertility and crop productivity. However, there is limited knowledge regarding responses of soil respiration and C-cycle enzyme activities to BC and nitrogen (N) additions in a calcareous soil. A 56-day incubation experiment was conducted to investigate the combined effects of BC addition rates (0, 0.5, 1.0, 2.5 and 5.0% by mass) and urea (U) application on soil nutrients, soil respiration and C-cycle enzyme activities in a calcareous soil in the North China Plain. Our results showed soil pH values in both U-only and U plus BC treatments significantly decreased within the first 14 days and then stabilized, and CO2emission rate in all U plus BC soils decreased exponentially, while there was no significant difference in the contents of soil total organic carbon (TOC), dissolved organic carbon (DOC), total nitrogen (TN), and C/N ratio in each treatment over time. At each incubation time, soil pH, electrical conductivity (EC), TOC, TN, C/N ratio, DOC and cumulative CO2 emission significantly increased with increasing BC addition rate, while soil potential activities of the four hydrolytic enzymes increased first and then decreased with increasing BC addition rate, with the largest values in the U + 1.0%BC treatment. However, phenol oxidase activity in all U plus BC soils showed a decreasing trend with the increase of BC addition rate. Our results suggest that U plus BC application at a rate of 1% promotes increases in hydrolytic enzymes, does not highly increase C/N and C mineralization, and can improve in soil fertility.