Biology and Fertility of Soils最新文献

¹⁵N tracing was carried out on sandy loam soil amended with (i) mineral nitrogen-phosphorus-potassium fertilizer (NPK) alone, (ii) half mineral N and half N from chicken manure (HFC), or (iii) half mineral N and half N from cattle manure (HCM), for 8 years. Cumulative N₂O emissions during incubation were 30.2 µg N kg^− 1 in the NPK treatment, which increased to 37.8 and 51.3 µg N kg^− 1 in the HFC and HCM treatments, respectively. The majority of N₂O emissions in all the treatments were attributed to nitrification (81.0% in the NPK treatment, 83.0% in the HFC treatment, and 85.1% in the HCM treatment). Compared with NPK, HCM treatment caused a significant increase in the gross rate of nitrification, while HFC treatment slightly enhanced the rate of dissimilatory NO₃⁻ reduction to NH₄⁺. Additionally, HFC treatment achieved higher gross rates of organic N mineralization, and both HFC and HCM treatments had higher NH₄⁺ mineralization-immobilization turnover (MI_AT) rates than NPK treatment. The results suggest that application of cattle or chicken manure increased soil NH₄⁺ availability. The gross rate of NO₃⁻ adsorption in the HCM treatment was greater than that in the NPK treatment, while the release of adsorbed NO₃⁻ in the HFC treatment was slower than that in the NPK treatment, indicating that application of cattle or chicken manure lowered the potential for NO₃⁻ leaching in soil. Overall, combining cattle or chicken manure with mineral fertilizer decreased NO₃⁻ availability but increased NH₄⁺ availability, leading to higher N₂O emissions through nitrification. Our results suggest that organic manures should be applied with nitrification inhibitors in sandy loam soil containing low organic carbon to increase soil fertility and mitigate N₂O emissions.

It remains unclear whether microbial carbon limitation exists in the rhizosphere, a microbial hotspot characterized by intensive labile carbon input. Here, we collected rhizosphere soils attached to absorptive and transport roots and bulk soils in three alpine coniferous forests and evaluated the limiting resources of microbes based on the responses of microbial growth (¹⁸O incorporation into DNA) and respiration to full-factorial amendments of carbon, nitrogen, and phosphorus. The results showed that adding carbon enhanced microbial growth and respiration rates in the rhizosphere soils by 1.2- and 10.3-fold, respectively, indicating the existence of carbon limitation for both anabolic and catabolic processes. In contrast, the promoting effects of nutrient addition were weak or manifested only after the alleviation of carbon limitation, suggesting that nutrients were co-limiting or secondarily limiting resources. Moreover, the category and extent of microbial resource limitations were comparable between the rhizosphere of absorptive and transport roots, and between the rhizosphere and bulk soils. Overall, our findings offer direct evidence for the presence of microbial carbon limitation in the rhizosphere.

We investigated the potential of earthworm casts to emit N₂O, hypothesizing that emission levels are influenced by the species of earthworm and their ecological category. This study examined casts a broad taxonomic and ecological coverage of tropical earthworms, i.e., 16 different species across four ecological categories. We quantified the potential nitrification, N₂O production and consumption as well as the abundance of N-related microbial functional groups, including ammonia-oxidizers, nitrite-reducers, and distinct clades of N₂O-reducers, along with casts chemical properties to determine cast organic matter quality and substrate availability. Earthworm casts exhibited significantly higher concentrations of carbon, nitrogen, and nitrate compared to control soil, while humification index were lower. A negative correlation between humification index and potential N₂O production suggests that more labile substrates in the casts promote higher N₂O flux. Net potential N₂O emissions were higher in the casts of 7 out of 16 species compared to control soil, and all species’ casts showed higher gross potential N₂O production, with substantial interspecific variability. The abundance of nitrite and N₂O reducers was significantly higher in the casts and positively correlated with potential N₂O emissions. Casts from epigeic and mixed categories displayed higher carbon and nitrogen content, abundance of nitrite and N₂O reducers, ammonia-oxidizing bacteria, and potential N₂O production compared to anecic and endogeic categories, which exhibited higher values of humification index. Structural equation modeling indicated that gross potential N₂O production was primarily explained by the abundance of nitrite reducers and substrate availability indicators such as humification index and nitrate concentration. Our study demonstrates significant interspecific variability in N₂O potential emissions from a broad range of tropical earthworm casts, influenced by species feeding behavior, microbial communities, and substrate availability.

Soil microbial necromass carbon (C) is a crucial component of the soil organic C pool. The impact of both straw mulching treatments and years on the soil microbial necromass C accumulation remains unclear. We investigated factors driving soil microbial necromass C accumulation and its role in improving yield by analyzing the dynamic response of microbial necromass C, total organic C (TOC) and available nutrients, genes encoding carbohydrate-degrading enzymes and fruit yield of citrus under different straw types of mulching (wheat, rice, oilseed rape, no mulch) from 2019 to 2022. Annual rainfall was the main factor affecting the soil bacterial necromass C (BNC) accumulation. Straw mulching treatments were the main factor affecting the soil fungal necromass C (FNC) accumulation. Increased annual rainfall and high soil moisture levels hindered the soil microbial necromass C accumulation, especially BNC. No correlation was found between BNC and the relative abundance of genes encoding peptidoglycan (bacteria-derived biomass) degrading enzymes. Decreased relative abundance of genes encoding chitin (fungal-derived biomass) degrading enzymes, particularly GH18, favored the accumulation of FNC. Actinomycetes were the most significant contributors of the GH18 gene among microbial phyla. Moreover, oilseed rape and rice mulching treatments reduced the relative abundance of genes encoding enzymes degrading chitin. Microbial necromass C, especially BNC, was key for sustaining TOC, supplying nutrients, and enhancing citrus fruit yield. Our results provide new information for optimizing straw mulch type and application time in citrus orchards to improve soil microbial necromass accumulation.

Litter decomposition has historically been attributed to soil microbial community at local scale, but which fundamental process directly contributes to carbon release from decomposing litter remains not fully understood. Here we used in situ microcosms to assess the temporal changes in soil microbial biomass, taxonomic composition, alpha and beta diversity, network complexity and carbon-degrading functional genes during litter decomposition of a subtropical dominant species (Castanopsis carlesii) in an older (45-years) and a younger (9-years) evergreen broadleaved forests. The soil phospholipid fatty acids, bacterial and fungal community composition, α-diversity indexes and network topological properties were not changed significantly after short-term litter input when litter was decomposed by approximately 70%. However, the absolute abundance of functional genes involved in the decomposition of starch, pectin, hemicellulose, cellulose, chitin and lignin were up-regulated, and these variations were associated with soil α-1.4-glucosidase, β-glucosidase and cellobiohydrolase activities in contributing to litter carbon release during decomposition. These results suggest that the upregulation of functional genes rather than microbial community composition and diversity controls local-scale litter decomposition by encoding and secreting enzymes in these subtropical forests.

Organic carbon based amendments can improve soil structure and fertility, as well as increase composition and diversity of soil microbial community. One of the major functions of improving soil fertility is to achieve effective nitrogen (N) management and mineralization. In this study, 746 paired observations were pooled from 20 long-term field experiments to verify the hypothesis that compared to synthetic only fertilization, long-term application of organic fertilization alone or in combination with synthetic fertilization could strengthen multiple internal pathways for soil N supply under various climatic conditions. We found that long-term application of synthetic N fertilizers alone or in combination with phosphorus (P) and potassium (K) led to an increase only in the recalcitrant organic N mineralization rate (M_Nrec) by 210% and 263%, respectively. However, long-term application of organic fertilizers alone or in combination with synthetic N fertilizers increased M_Nrec, labile organic N mineralization rate (M_Nlab) and release of adsorbed ammonium from cation exchange sites (R_NH4a) by 160% and 200%, 153% and 353%, and 1025% and 541%, respectively. This indicates that organic fertilization can strengthen multiple internal pathways for mineral N production. The long-term co-application of organic and synthetic fertilizers stimulated M_Nlab (197%), M_Nrec (151%) and R_NH4a (563%) in subtropical regions, but it had no effect on heterotrophic nitrification (O_Nrec). In contrast, it stimulated M_Nrec (505%), R_NH4a (633%) and O_Nrec (184%) in temperate regions, with no observed effect on M_Nlab. These data confirm that if one N supply source is shut-off under specific climatic conditions the other pathways continue to provide N. The meta-analysis advances our understanding of agroecosystems and as such help to improve frameworks for enhancing soil health.

The complexity of the opaque soil matrix is a major obstacle to studying the organisms that inhabit it. Fast technological progress now offers new possibilities for the monitoring of soil biodiversity and root growth, such as in situ soil imaging. This study presents the potential of soil imaging devices to investigate the temporal dynamics and spatial distribution of soil biological activity and their interactions. The soil imaging devices were buried in a truffle field located in the south of France and set up to capture images automatically every 6 h at 1200 dpi. For the first time, root growth, mycorrhizal colonization and invertebrate occurrences – for 16 taxa – were studied simultaneously on the images captured over 3 months (between May and July 2019). The peak in root growth occurred at the end of May and beginning of June, followed by a peak in ectomycorrhizal colonization in mid-June. For invertebrates, specific dynamics of activity were observed for each taxon, reflecting contrasting phenologies. The constructed network of co-occurrences between invertebrates shows a change in its structure over the period, with a reduction of connectance. At a fine scale, oak fine roots revealed temporally variable growth rates with higher values at night. This window on the opaque soil matrix addresses many methodological challenges by allowing the monitoring of soil biological activity in an integrative, dynamic and non-destructive way. This innovative in situ imaging tool opens new questions and new ways of answering long-standing questions in soil ecology.

Currently, little is understood about the role of different anaerobic oxidation of methane (AOM) pathways and their relative contributions in reducing CH₄ emissions from rice fields. The potential rates of AOM caused by nitrate-, iron-, and sulfate-reduction, as well as the anaerobic methanotrophic (ANME-2d) archaeal absolute abundance and community composition were investigated across varying rice growth periods (tillering, jointing, flowering, and maturing) and soil layers (0–10, 10–20, 20–30, and 30–40 cm). The average potential rate of nitrate-AOM (2.73 nmol ¹³CO₂ g^-1 d^-1) was significantly higher than those of iron- (1.15 nmol ¹³CO₂ g^-1 d^-1) and sulfate-AOM (0.42 nmol ¹³CO₂ g^-1 d^-1) across growth periods and soil layers. The AOM rates in surface soils (0–20 cm) and earlier periods (tillering and jointing) were significantly higher than those in deep soils (20–40 cm) and later periods (flowering and maturing), respectively. Differently, ANME-2d archaeal absolute abundance and community compositions were only significantly affected by soil layers, with the highest absolute abundance in the 10–20 cm layer. The organic carbon content and availability of electron acceptor were the primary factors governing the rates of different AOM pathways and community of ANME-2d archaea. Overall, this study provided the variation in AOM rates driven via multiple electron acceptors and ANME-2d archaeal community across rice growth periods and soil layers, and provided an important scientific basis for precise quantification of AOM as a potential CH₄ sink in rice fields.

While it is established that dominant plant species of alpine meadows showed differential preference for N forms (ammonia, nitrate, and amino acids) under various degradation stages, the perseverance of the N-uptake preference and its affecting factors remains unknown. This is an important consideration because it determines efficacy of nutrient additions for restoration of degraded alpine meadows. An indoor pot experiment was conducted to investigate the plasticity and determinants of different plant species’ N-uptake preference using ¹⁵N-labeled inorganic N (¹⁵NH₄⁺ and ¹⁵NO₃⁻) and one of dual-labeled (¹³C-¹⁵N) amino acid (glycine). In the experiment, dominant species of alpine meadow from specific degradation status were planted in soils of alpine meadows with three different degradation status. Most species preferred to uptake nitrate in all soils, except the Kobresia humilis, Carex moorcroftii, and Aster flaccidus planted in the soil of severely degraded alpine meadow (SD-soil) that take up more ammonia. The relative abundance of different available N forms directly affects the N-uptake preferences of all species. The partial correlations between percentage uptake and availability of various N forms were different with the zero-order correlations when either soil moisture or pH was controlled. Differences in soil moisture and pH among the three alpine meadows affects the N uptake preference of the nine species through their impacts on the relative abundance of different available N forms. In conclusion, the differences in soil moisture and pH among soils of alpine meadows under different degradation statuses influence the relative abundance of various available N forms, thereby affecting the plant N uptake.

Soil suppressiveness can reduce the damage by plant parasitic nematodes (PPN) in agricultural soils and is conveyed by the activity of soil microorganisms. While natural suppressiveness has been reported, it is still poorly understood if soil suppressiveness can be elicited by manipulating the soil microbial community. In the present study we assessed the number of the Pratylenchus penetrans (Pp) and the bacterial and fungal community composition over 7 years in a long-term soil health experiment. The field experiment consisted of an organic and conventional agricultural land management system and three soil health treatments (SHT): an untreated control (CT), anaerobic disinfestation (AD) and a combination of marigold cover cropping, compost and chitin amendment (CB). The land management systems were kept continuously, while the soil health treatments were applied only twice in seven years. The microbial community significantly differed between the organic and conventional system, but there was no significant difference in Pp numbers between the two systems. However, both the CB treatment and to a lesser extent the AD treatment reduced Pp numbers and increased yield with the effect being the strongest in the years immediately after the treatment. Accordingly, both the bacterial and fungal community differed significantly between the treatments, the differences being largest in the years after the treatments. Notably, the CB treatment elicited both long-term changes in the microbial community and a reduction of Pp numbers lasting for at least three years. These results indicated that a combination of treatments can lead to an altered soil microbial community in combination with persisting suppressiveness of Pp.