查看更多>>摘要：? 2022 Elsevier B.V.Micro-sized pyrogenic carbon (PyC) is expected to interact more efficiently with soil biota such as earthworms than coarse pyrogenic carbon. Little is known about whether the micro-sized PyC poses a threat to earthworms. We investigated the effects of hydrophilic micro-sized PyC on earthworm mortality in two contrasting soil substrates from young and old reclaimed soils of a successional chronosequence. These two soil substrates had different hydraulic properties, total organic carbon, pH, and nutrient status. Lower earthworm survival rates were observed in both soil substrates receiving dry micro-sized soil particles and the micro-sized PyC. Specifically, the addition of micro-sized PyC resulted in the lowest survival rate compared to the addition of micro-sized soil particles and the control from day 8 to 11. The decreased earthworm survival rate due to micro-sized PyC was more pronounced in the old soil substrate than in the young substrate. Fully moistened soil substrates containing micro-sized PyC or dry micro-sized soil substrate particles did not result in decreased earthworm survival. Micro-sized PyC turned from hydrophilic to hydrophobic when mixed with rhamnolipids, possibly hindering the uptake of dissolved oxygen by earthworm skins. Our results thus provide a new explanation for the negative effects of micro-sized PyC on earthworms and demonstrate the importance of assessing the hydraulic properties of both the micro-sized PyC and soil prior to PyC's application to soils.
查看更多>>摘要：? 2022In the present study the chemical structure of the non-toxic metabolite of a fungicide difenoconazole produced by a difenoconazole-degrading bacterium, Sphingomonas histidinilytica C8–2, was identified and it was found that strain C8–2 detoxifies difenoconazole by segregating the chlorobenzene group and attaching a hydroxyl group to the cleavage site. And then it was investigated whether strain C8–2 can restore earthworm reproduction and microbial community structure disturbed by the fungicide. Difenoconazole (4 mg kg?1 soil) did not affect the number or bodyweight of adult earthworms in soil, but it reduced the average number of newly hatched juveniles (by 71.9%) and cocoons (by 30.0%) when compared to uncontaminated soils. Difenoconazole (20 mg kg?1 soil) did not affect bacterial and archaeal activities in soil after 27 days of incubation, but reduced fungal activity to 4% of uncontaminated soil. It also reduced the relative activities of the bacterial genus Arthrobacter (8.2% to 6.7%) and the fungal genus Humicola (32.4% to 0.0%). The application of strain C8–2 to difenoconazole-contaminated soil prevented the decline in the reproductivity of earthworms, fungal activity, and the relative activities of Arthrobacter and Humicola, by degrading the fungicide. These results showed that the metabolite of difenoconazole produced by strain C8–2 had no toxic effects on these important soil organisms, suggesting that the presence or intentional application of pesticide-detoxifying microorganisms can restore soil ecosystems disturbed by pesticides.
查看更多>>摘要：? 2022 Elsevier B.V.Crop residue return can improve soil fertility and crop yield, but it may also increase the risk of soil borne disease. Here, we investigated cotton biomass, Verticillium wilt incidence, root exudates, soil Verticillium dahliae abundance, soil available potassium (K) concentrations, and leaf K concentrations in two 8-year residue management experiments under wheat-cotton rotation in Nanjing and Dafeng of China. Six treatments were compared based on uniform rates of nitrogen and phosphate fertilizers: three residue return treatments without K fertilizer (wheat residue, WR; cotton residue, CR; wheat residue plus cotton residue, WR + CR), two K fertilizer treatments (150 kg K2O ha?1, K150 and 300 kg K2O ha?1, K300), and CK treatment without residue or K fertilizer. Our results showed that the incidence and disease index of Verticillium wilt were the lowest in K300, followed by K150, WR + CR, WR or CR, and the highest in CK at both sites. The responses of cotton biomass, leaf K concentrations and soil available K concentrations to different treatments were generally opposite to that of the disease severity. The disease index was significantly negatively correlated with the concentration of K in soil or cotton leaf, while it had significant correlations with root exudates but not soil microbe abundances. Structural equation modeling indicated that K nutrition affected cotton Verticillium wilt disease index by affecting alanine, glutamate and total phenol in cotton root exudates. These findings suggested that K nutrition status was the key factor affecting the occurrence of cotton Verticillium wilt, and residue retention could increase cotton resistance to Verticillium dahliae by improving soil K availability and subsequently regulating specific root exudates.
查看更多>>摘要：? 2022Long-term nitrogen fertilization imparts significant effects on the soil environment and soil microbial communities relevant to nutrient cycling. Understanding the complex interactions between soil biology, management practices, and the soil environment is an important step toward improving soil health. The Crop Residue study of the Long-Term Plots at Pendleton, Oregon USA demonstrate declines in soil quality with acidification and reduced soil carbon under a wheat-fallow cropping system. Soil enzyme activity (β-glucosidase, β-glucosaminidase, acid and alkaline phosphatase, arylsulfatase, and arylamidase) and ammonia oxidation was measured in plots managed with three different fertilizer treatments (no fertilization, urea-ammonium nitrate, and manure) at two stages of crop growth. The fertilizer treatments had a strong impact on total carbon and nitrogen and produced a broad range of soil pH from 4.8 (urea-ammonium nitrate) to 5.7 (no fertilizer) and 6.7 (manure). Overall, potential nutrient cycling activity (hydrolytic enzymes and ammonia oxidation) was enhanced in manure-fertilized soils except for acid phosphatase which was greater in the low pH soil. Treatment trends in the proportional geometric mean (an index of soil nutrient cycling capacity) were generally consistent over a 32-year transect excluding acid phosphatase. All activities were highly correlated to total carbon, nitrogen, and sulfur. Except for β-glucosaminidase, all enzymes were also highly correlated to pH. The only enzyme to vary by crop phase was β-glucosidase which was greater at boot than tillering. Soils remaining after the analyses were oven-dried at 40 °C and stored in a non-climate-controlled warehouse for archiving. After 2-years of storage, the oven-dried soils were re-assessed for hydrolytic enzyme activity to determine whether the ability to distinguish treatment differences is retained in archived soils. The oven-dried archived samples showed similar contrasts as the soils analyzed moist between manure and the other fertilizer treatments, although the level of activity was significantly reduced. Overall, long-term fertilization with manure slowed the decline in soil acidity and enhanced soil function relevant to nutrient cycling and organic matter dynamics in the wheat-fallow cropping system.
查看更多>>摘要：? 2022 Elsevier B.V.Arbuscular mycorrhizal fungi (AMF) are soil microorganisms symbiotic with plants and play critical roles in the growth and survival of their hosts. However, the influence of shrub encroachment on AMF remains unclear. We analysed the soil microbial biomass of fungi, especially AMF, under interspace grass patches and shrub patches during the process of shrub encroachment using phospholipid fatty acid (PLFA) analysis. The results illustrated that the soil microbial biomass of AMF gradually increased under the shrub patches and gradually decreased under the interspace grass patches during the process of shrub encroachment. The most obvious change in the soil microbial biomass of AMF was found from moderately disturbed grassland to severely disturbed grassland under interspace grass patches and shrub patches. Soil nutrients, especially soil organic carbon (SOC), were found in greater amounts under the shrub patches than under the interspace grass patches. Shrub encroachment positively affected the microbial biomass of AMF by increasing the SOC content, and the increase in the microbial biomass of AMF increased the soil available phosphorus (AP) content and further promoted the development of shrub encroachment. There was a positive feedback relationship between shrub encroachment and AMF. This feedback mechanism was only applicable to AMF and was not found for other fungi. Our results highlight that there is a linkage between shrub encroachment and the microbial biomass of AMF, which explains the potential irreversibility of the transition from grass dominance to shrub dominance in the case of shrub encroachment.
查看更多>>摘要：? 2022 Elsevier B.V.Ecological restoration using native mangrove species (i.e., Kandelia obovata) is a practical approach for controlling Spartina alterniflora invasion in the coastal wetlands. Diazotrophs play a critical role in enhancing productivity of both S. alterniflora and mangrove plant, via providing new nitrogen to the coastal wetlands ecosystems. However, response of the diazotrophic community to S. alterniflora invasion and subsequent mangrove restoration remains unclear. The present study monitored sediment physicochemical properties and diazotrophic communities across a chronosequence of restored mangrove wetland (bare mudflat, invasive S. alterniflora stands, 3-year and 10-year K. obovata restoration areas, and mature K. obovata forests over 30 years). The results showed an orderly succession in the sediment properties and diazotrophic community composition after S. alterniflora invasion and along mangrove restoration chronosequences. Almost all sediment nutrient contents (e.g., TC, TN, and C/N) were significantly (P < 0.05) increased by S. alterniflora invasion, then they decreased sharply in the newly restored mangrove and increased gradually with restoration ages, with the highest values in the mature mangrove. The diazotrophs demonstrated distinct community structure in different seasons. Diazotrophic alpha diversity increased with S. alterniflora invasion and mangrove restoration age in winter. Sulfate-reducing bacteria (SRB) was the dominant diazotrophic group, especially Desulfuromonadales. Moreover, network analyses revealed that SRB groups were the major keystone taxa. The relative abundance of Desulfuromonadales decreased, while the abundance of Chromatiales increased gradually with the S. alterniflora invasion and mangrove restoration age. Redundancy analysis revealed that TC, TN, and TS were the significant (P < 0.05) environmental factors in altering sediment diazotrophic communities in both seasons. These findings expand the current understanding of succession patterns of diazotrophic communities in mangrove restoration and provide new perspectives on the sustainable management of mangrove ecosystems.
查看更多>>摘要：? 2022 Elsevier B.V.The impact of micro- and nanoplastics (M/NPs) on terrestrial ecosystems has been a hot topic in recent years since the soil has been recognized as an important sink for M/NPs. In the current study, a CiteSpace-based scientometric analysis of 506 papers was performed to show the intellectual background, research performance, and state of art knowledge structure of M/NPs in the terrestrial environment over the past six years (2016 - January 2022). The most prolific publications, journals, authors, and countries involved in the flourishment of this field were identified. Additionally, visualization methods were employed to determine the highly productive keywords, hotspots, and research frontiers in the field of M/NPs in terrestrial environments. Furthermore, cluster analysis was performed to provide an accurate summary of this field by exploring the sub-domains of this field. China has proven to be the most prominent country among others in terms of publications and funding. This study can help researchers identify new research fronts and distinguish the most critical sub-domains of M/NPs in the terrestrial environment research.
查看更多>>摘要：? 2022 Elsevier B.V.Nitrite (NO2?) oxidation is the second step in nitrification, following ammonia (NH3) oxidation, and catalyzed by nitrite oxidizing bacteria (NOB). Their activity is critical in preventing toxic accumulation of NO2?. The two major NOB genera in soil are Nitrobacter and Nitrospira. This study investigated how N fertilization and tillage management influenced these two NOB communities in long-term (>40 years) maize (Zea mays L.) cropping. To evaluate NOB community changes we used PCR and denaturing gradient gel electrophoresis (DGGE) to analyze Nitrobacter and Nitrospira NO2? oxidoreductase genes (nxr). Season, fertilizer rate, and tillage all influenced Nitrobacter and Nitrospira communities, but differentially for the two genera. Nitrobacter was more diverse in summer, whereas Nitrospira was more diverse in winter. Nitrobacter was more diverse in N-fertilized samples, whereas Nitrospira diversity decreased with increasing fertilizer rate in winter but not summer. Nitrobacter diversity was not significantly influenced by tillage, whereas no-tillage samples had more diverse Nitrospira, compared to plow tillage samples. In addition to providing evidence for better understanding the relationship between soil management and NOB communities, this study also helped to suggest linkages between ammonia oxidizing bacteria and Nitrobacter and between ammonia oxidizing archaea and Nitrospira that may facilitate future studies concerning ammonia-oxidizing nitrifiers and NOB.
查看更多>>摘要：? 2022 Elsevier B.V.Nematodes, with functional groups at all trophic levels, play a key role in soil food webs. Their community structure allows to assign food web conditions and soil health, e.g. to address management impact on arable land. A field experiment was set up near Potsdam (Brandenburg, north-east Germany) to investigate the effects of different fertilization and irrigation regimes on the nematode fauna and the micro-food web in a sandy soil. At an arable site cropped with potatoes the following treatments were established in a randomized plot design: surface, drip and no irrigation, combined with/without fertilization. Additionally, fertigated plots (simultaneous application of fertilizer in dissolved drip irrigation water) with/without crops were investigated. Soil samples were collected during one vegetation period in June, July and August. The nematode community structure was determined and a faunal analysis performed resulting in: Maturity Index (MI), Plant Parasite Index (PPI), Channel Index (CI), Enrichment Index (EI), Structure Index (SI) and metabolic footprints (F). In addition, phospholipid fatty acids were determined to identify microbial community structure and biomass. In August, surface irrigation resulted in a higher MI (i.e. lower disturbance) at unfertilized compared to fertilized plots. Furthermore, the fertigated plots showed a higher MI with crops than without. The PPI increased over time, while the CI indicated higher fungal decomposition at dryer conditions in August. The EI points to moderately enriched nutrient conditions, which was underlined by a high metabolic footprint of bacterial feeders. The structure and enrichment footprint showed that the stability of the micro-food web increased with time, indicating a positive influence of crop growth. In sum, effects of irrigation practice on the nematode community were apparent, while no response to the different fertilizer treatments was detected.
查看更多>>摘要：? 2022 Elsevier B.V.Soil bacterial communities are critical for stability and function of terrestrial ecosystems. Viruses are ubiquitous in soils and have significant impacts on the structure and functions of bacterial host communities. However, little is known concerning the impact of various land use management practices on bacterial and viral communities. This study aimed to estimate variations of composition and structure of bacterial and viral communities under long term management practices including inorganic N fertilization, cover cropping, and tillage treatments in a long-term conservation management experimental site in western Tennessee USA. We evaluated bacterial and DNA viral diversity using 16s rRNA sequencing and RAPD-PCR, respectively, and enumerated viral and bacterial abundance via epifluorescence microscopy. Structural equation modeling was applied on the dataset to reveal relationships among viruses, bacteria and soil properties. No significant differences in bacterial alpha-diversity were identified among inorganic N fertilization (ammonia nitrate), cover cropping, and tillage treatments. However, community structure (beta-diversity) differed significantly. Higher soil pH and water content favored greater bacterial abundances. Cover cropping, soil water content, and bacterial abundances were the main factors explaining the variation of viral abundances and community structure in soil. Structural equation modeling suggested that bacterial abundances positively influenced viral abundances, and in turn virus abundances and bacterial alpha diversity affected the level of extractable dissolved organic C, which exerted a feedback effect on the structure of bacterial communities. This feedback loop suggests that bacterial lysates resulting from viral infection might significantly contribute to the reshaping of bacterial community structure while indirectly influencing bacterial alpha diversity. This supports the theory of the “viral shunt” in soil ecosystems. This study suggests that the structure of soil bacteria and viruses can be reshaped by long-term management practices. Viruses may indirectly involve in C cycling through positively influencing microbial dissolved organic C under long-term conservation management practices.
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