Biology and Fertility of Soils最新文献

Organic farming can enhance biodiversity and soil health and is a sustainable alternative to conventional farming. Yet, soil protists especially protistan predators, have received inadequate attention, and their contributions to the sustainability of organic farming remained underexplored. In this study, we examined soil microbial communities from 379 samples, including both organic and chemically fertilized soils from China. Our findings revealed higher bacterial diversity and increases in plant-beneficial bacteria in organically farmed soils. Notably, organic farming systems facilitated dynamic predator-prey interactions, which may be disrupted by the application of chemical fertilizers. Additionally, organic farming enriched protistan predators, enhancing the relative abundance of functional PGPR, thus improving soil health. We further conducted a case study highlighting the critical role of organic matter in sustaining protistan predator populations and their interactions with bacteria. We propose the crucial contributions of organic inputs for supporting protistan predators and the interplay of predator-prey, ultimately enhancing soil functions and promoting agricultural sustainability.

Legume/cereal intercropping is an example of classic nitrogen-efficient planting that can effectively improve crop yield and nutrient-utilization efficiency. However, the interaction between rhizosphere microorganisms and rhizodeposition and the related ecological mechanisms remain unclear. We conducted a pot experiment using ¹³CO₂ continuous labeling, DNA stable isotope probe technology, high-throughput sequencing, and the carbon-nitrogen-phosphorus functional gene chip to effectively track rhizosphere-deposited C and compare the microorganisms that utilize this C pool in the rhizosphere of a soybean/maize intercropping system at 21 days after labeling. The relative abundance of Caldalkalibacillus and Nesterenkonia that use rhizosphere-deposited C was significantly higher in the soybean/maize intercropping system than in monocropped soybean, but there were no significant differences between intercropped and monocropped maize. The soybean/maize intercropping system altered the composition of the microbial community that utilizes rhizosphere-deposited C and reduced the community richness. Moreover, intercropping improved the expression of functional genes associated with carbon fixation (acsH and exg) and nitrous oxide reduction (nosZ1). Overall, by tracking the flow of C from plant photosynthetic products to root exudates, our research provides new insights into identifying the microbial communities that assimilate and deposit carbon in soil.

It is unknown whether soil microbiota and soil bacteria isolated from the rhizosphere of selenium hyperaccumulator plants can affect selenium absorption by selenium non-hyperaccumulator plants. Here, we used pot experiments and split root experiments to investigate the role of soil microbiota and isolated rhizosphere bacteria from a selenium hyperaccumulator plant (Cardamine violifolia) in affecting selenium absorption by a selenium non-hyperaccumulator plant (Brassica napus), combining root metabolism analysis, microbiome profiling, strain isolation and its selenium absorption functional validation. We found that soil microbiota of Cardamine violifolia significantly increased the root selenium content by 31.8% and regulated root exudation by Brassica napus. Additionally, the application of upregulated long-chain organic acids + amino acids, long-chain organic acids + short-chain organic acids, ethanolamine, and 2-ketobutyric acid increased the selenium contents in the roots of Brassica napus by 69.6%, 38.4%, 81.2%, and 48.8%, respectively. Further investigation revealed that dominant bacteria were significantly enriched in the rhizosphere of C. violifolia compared to B. napus. After that, we isolated the rhizosphere bacteria of Cardamine violifolia and observed that Bacillus sp.-2, Chryseobacterium sp., and Pseudomonas sp., as well as their combined communities, significantly improved selenium absorption in Brassica napus. Moreover, the combined bacterial communities significantly regulated specific-root metabolism, enhanced rhizosphere soil available selenium content, promoted root development, increased expression levels of genes encoding selenium transporter in root. These findings provide insights into utilizing rhizosphere bacteria of selenium hyperaccumulator plants to increase selenium absorption by non-hyperaccumulator plants.

Graphical Abstract

Cereals zinc (Zn) biofortification represents an effective strategy for alleviating human Zn malnutrition. However, understanding how to enhance Zn uptake in shoots by optimizing the soil–root interface, particularly considering Zn availability, microbiome interactions, and plant physiology, remains poorly understood, especially in high-pH soils. In this study, we investigated Zn rhizomobilization, plant Zn uptake, and the composition of bacterial and fungal communities in the rhizosphere and roots of ten high-yielding wheat cultivars with consistently contrasting grain Zn concentrations, within calcareous fields. We found that a range of beneficial bacteria, fungi/mycorrhizas, and their interactions play crucial roles in Zn rhizomobilization and wheat Zn uptake. Zn-solubilizing rhizobacteria demonstrated the ability to enhance Zn rhizomobilization, leading to a 35.4% increase in available Zn concentration and a 0.11 units reduction of soil pH. Increased colonization by arbuscular mycorrhizal fungi, along with reduced the presence of fungal pathogens, significantly promoted Zn uptake, ranging from 22 to 132% per unit of root biomass. Additionally, the enriched bacteria relevant with nitrogen cycle and plant growth-promotion not only optimized soil mineral-N/available-P supply but also potentially suppressed fungal pathogens in root and rhizosphere. Optimizing the microbiome to enhance soil nutrient supply and root health emerges as a promising strategy for improving Zn-efficient wheat cultivars’ ability to uptake Zn in shoots. Combining Zn-efficient cultivars with specific soil bacteria and fungi in the rhizosphere holds potential for realizing Zn biofortification in wheat.

The use of natural plant growth regulators (PGRs) as ecofriendly agrochemicals is gaining much attention, but the fate of these compounds once they enter the soil environment is poorly understood. In this work, we compared the plant growth inhibitory activity of the phytohormone S-abscisic acid (S-ABA) in the presence of three soils with that observed in soilless (Petri dish) conditions and related the differences in activity to the sorption and dissipation processes of the phytohormone in the soils. In Petri dishes, S-ABA inhibited the germination of Eruca sativa, Allium porrum, Lactuca sativa, and Hordeum vulgare with mean inhibitory concentration values (IC₅₀) in the range of 0.5–8.2 mg/L. Eruca sativa was selected for subsequent studies based on its high sensitivity to S-ABA (IC₅₀ = 0.5 mg/L). The inhibition of germination of E. sativa by S-ABA was fully reversible at a low phytohormone concentration (5 mg/L) and partially reversible at a higher phytohormone concentration (60 mg/L). S-ABA also inhibited the growth of pre-germinated seedlings of E. sativa, albeit at higher concentrations than those at which it inhibited germination. The three soils used in the study weakened the inhibitory activity of S-ABA by soil factors in the range of 0.008–0.380. As S-ABA displayed low or even negative sorption in the soils tested, the decrease in the activity of S-ABA was attributed to its biodegradation in the soils, rather than to a decrease in its bioavailability due to sorption. Despite the reduction in the activity of S-ABA observed in the presence of the soils, the phytohormone still expressed its activity at quite low soil concentrations (0.3–20 mg/kg), showing higher activity in soils where the compound degraded more slowly.

The study aimed to measure soil-atmosphere N₂O fluxes and their controlling factors, as well as NH₃ emissions and yields for two soils (silt loam and clay loam) in three management systems over two years under subsequent wheat and maize cultivation. The management systems were characterized as follows: (1) cash crop (C) with mineral fertilizer and conventional tillage; (2) livestock (L) with biogas residue fertilization and its incorporation prior to sowing in maize and reduced tillage; and (3) climate optimized (O) with minimum tillage, 8-year crop rotation, with biogas residue fertilization, in maize without incorporation in clay loam soil or incorporation by strip-tillage prior to seeding in silt loam soil. Stable isotope ratios of N₂O and mineral N were determined to identify N₂O processes. Within the organically fertilized maize treatments, cumulative N₂O fluxes were highest in the O-system treatments of both sites (4.0 to 9.4 kg N ha^− 1 a^− 1), i.e. more than twice as high as in the L-system (1.5 to 3.1 kg N ha^− 1 a^− 1). Below root-strip till fertilizer application did not enhance N₂O fluxes. Fluxes with mineral fertilization of wheat (1.1 to 3.1 kg N ha^− 1 a^− 1) were not different from those with organic fertilization. Isotopic values of emitted N₂O revealed that bacterial denitrification dominated most of the peak flux events, while the N₂O/(N₂ + N₂O) ratio of denitrification was mostly between 0.1 and 0.5. It can be concluded that, contrary to the intention to lower greenhouse gas fluxes by the O-system management, the highest N₂O fluxes occurred in the O-system without biogas digestate incorporation in maize. With respect to NH₃ fluxes, we could confirm that the application of digestate application in growing crops without incorporation or late incorporation in fertilization before sowing induces high fluxes. The beneficial aspects of the O-system including more stable soil structure and resource conservation, are thus potentially counteracted by increased N₂O and NH₃ emissions.

Understanding the plant–soil feedbacks (PSFs) of dominant species of alpine meadow under different degradation status could provide insights into sustainable restoration. The direction, strength, and influencing factors of dominant species’ PSFs in nondegraded (Intact), moderately degraded (MD), and severely degraded (SD) alpine meadows were examined in a two-phase PSFs experiment. Species of Intact exhibited neutral conspecific PSFs, whereas those of MD and SD exhibited negative conspecific PSFs. The species of MD demonstrated neutral heterospecific PSFs to those of Intact, whereas that of SD negatively feedbacked to those of Intact and MD. The NO₃⁻-N and NH₄⁺-N of soil conditioned by the species of Intact were 66% and 58% higher than the control (mixture soil conditioned by all species); but they were 37% and 32% lower in soil conditioned by the dominant species of SD. The relative abundance of soil fungal pathotrophs was 57% and 74% higher in soil conditioned by the dominant species of MD and SD than in Intact soil. The conspecific and heterospecific PSFs of all species positively correlated with the plant conditioning and degradation induced changes of difference in NO₃⁻-N and NH₄⁺-N and negatively correlated with the difference in relative abundance of pathotrophs. Soil microorganisms and nutrients explained most of the variation in conspecific (43%) and heterospecific PSFs (60%). Our results indicated that the N addition would facilitate the sustainable restoration of degraded alpine meadows because the addition of available N could drive the heterospecific PSFs toward more positive.

Inoculation of cyanobacteria has been studied as a valuable approach to promote soil stabilization and fertilization and counteract the erosion of marginal soils. One of the results of the inoculation of cyanobacteria is the formation of biological soil crusts, or biocrusts, which are complex soil communities playing a pivotal role in providing essential ecosystem services in drylands. While numerous studies have addressed the effects of different biocrust attributes on ecosystem functions, few studies have focused on the distribution of biocrust successional stages in the soil and their link with soil fertility properties. In this work, we investigated how the distribution of biocrust types (cyano-crust; cyano/moss crust, and moss crust) is related to soil nutrient status. We evaluated phototrophic abundance, exopolysaccharide production, and nutrient content in distinct biocrust types in an experimental area in the Hopq Desert, China, where their occurrence had been induced by cyanobacteria inoculation. In addition, we investigated the correlation between these variables. Photosynthetic pigment content, total carbohydrates, exopolysaccharides, organic C, and total N increased during the biocrust maturation stages. We found significant correlations between the levels of organic C, total carbohydrates, and total N with the abundance of diazotrophic cyanobacteria. Organic N was greater in the cyano/moss crust, while available P accumulated mainly in the cyano-crust. The three biocrust types are essential to each other as each represents a stage in which distinct nutrients are stored. This study complements previous studies by offering a more comprehensive view of how phototrophic variability in the distribution of biocrusts dominated by cyanobacteria or by mosses is closely interconnected with nutrient content and biocrust development.

Biodegradable plastics applied to soil stimulate the production of greenhouse gases and inhibit plant growth under aerobic conditions. This study aimed to examine the effects of biodegradable plastics on paddy rice growth and greenhouse gas emission under flooding conditions in pot experiments and also on greenhouse gas production under flooding conditions in an incubation experiment. Two series of pot experiments were conducted with rice (Oryza sativa). First series as immediate flooded and 2nd series as 2 weeks nonflooding before flooded, and both kept flooded until harvest. The following four kinds of materials were added to the sandy paddy soil, (1) nonwoven fabric sheets made of polylactic acid and polybutylene-succinate, (2) laminate sheets made of polybutylene adipate terephthalate and pulp, (3) cellulose filter paper, and (4) rice straw. Only soil was used as control. Methane (CH₄) emission, measured by chamber method followed by gas chromatography, was significantly larger only in the cellulose treatment than the laminate treatment in the immediate flooded series, indicating that biodegradable plastics had no significant impact on CH₄ emission from paddy rice soil. Rice growth and yield did not show significant difference among treatments in both series. Incubation experiment showed the largest CH₄ production in cellulose-amended soil, followed by straw-amended and laminate amended soils, and least in fabric-amended soil, while CO₂ did not show significant differences among treatments. We need further examination with different biodegradable plastics for a longer period that test used in this study.

The mechanism by which residual straw incorporation affects nitrous oxide (N₂O) and carbon dioxide equivalent (CO₂-eq) emissions throughout the rice season under upland-paddy rotation systems is currently unknown. We aimed to elucidate its effect using a four-year experiment and meta-analysis in southwest China. In garlic–rice (GR) and wheat–rice (WR) systems, residual straw incorporation significantly decreased N₂O emissions (43.6% and 73.5%, respectively) and NO₃⁻-N concentrations, relative abundance of denitrifying bacteria (Anaeromyxobacter, Bacillus and Hyphomicrobium), and copy numbers of the norB and nosZ genes. Ultimately, the soil denitrification rate was reduced during rice tillering and full heading periods, but the soil organic nitrogen accumulation level was increased. The reduction in N₂O also resulted in an average reduction in the total CO₂-eq of the GR (23.4%) and WR (32.9%) systems in 2021–2022. In addition, the meta-analysis results showed that straw incorporation had a generally positive effect on soil N₂O emissions, but this effect was negative during the rice season in upland-paddy rotation systems, which supports the main results of our study. The path analysis results indicated that dry season residual straw incorporation slowed N₂O emissions during the rice season by increasing the soil C/N ratio and downregulating denitrifying microorganisms, thereby inhibiting the denitrification rate. Our findings challenge the understanding that straw incorporation increases greenhouse gas emissions during the rice season and suggest that future estimates of straw incorporation on methane (CH₄) emissions during the rice season should consider the offsetting effect of N₂O.