Most studies on soil N2O emissions have focused either on the quantifying of agricultural N2O fluxes or on the effect of environmental factors on N2O emissions. However, very limited information is ...available on how land-use will affect N2O production, and nitrifiers involved in N2O emissions in agricultural soil ecosystems. Therefore, this study aimed at evaluating the relative importance of nitrification and denitrification to N2O emissions from different land-use soils and identifying the potential underlying microbial mechanisms. A (15)N-tracing experiment was conducted under controlled laboratory conditions on four agricultural soils collected from different land-use. We measured N2O fluxes, nitrate (Formula: see text), and ammonium (Formula: see text) concentration and (15)N2O, (15)Formula: see text, and (15)Formula: see text enrichment during the incubation. Quantitative PCR was used to quantify ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB). Our results showed that nitrification was the main contributor to N2O production in soils from sugarcane, dairy pasture and cereal cropping systems, while denitrification played a major role in N2O production in the vegetable soil under the experimental conditions. Nitrification contributed to 96.7% of the N2O emissions in sugarcane soil followed by 71.3% in the cereal cropping soil and 70.9% in the dairy pasture soil, while only around 20.0% of N2O was produced from nitrification in vegetable soil. The proportion of nitrified nitrogen as N2O (PN2O-value) varied across different soils, with the highest PN2O-value (0.26‰) found in the cereal cropping soil, which was around 10 times higher than that in other three systems. AOA were the abundant ammonia oxidizers, and were significantly correlated to N2O emitted from nitrification in the sugarcane soil, while AOB were significantly correlated with N2O emitted from nitrification in the cereal cropping soil. Our findings suggested that soil type and land-use might have strongly affected the relative contribution of nitrification and denitrification to N2O production from agricultural soils.
In recent years, identification of the microbial sources responsible for soil N
2
O production has substantially advanced with the development of isotope enrichment techniques, selective inhibitors, ...mathematical models and the discoveries of specific N-cycling functional genes. However, little information is available to effectively quantify the N
2
O produced from different microbial pathways (e.g. nitrification and denitrification). Here, a
15
N-tracing incubation experiment was conducted under controlled laboratory conditions (50, 70 and 85% water-filled pore space (WFPS) at 25 and 35 °C). Nitrification was the main contributor to N
2
O production. At 50, 70 and 85% WFPS, nitrification contributed 87, 80 and 53% of total N
2
O production, respectively, at 25 °C, and 86, 74 and 33% at 35 °C. The proportion of nitrified N as N
2
O (
P
N2O
) increased with temperature and moisture, except for 85% WFPS, when
P
N2O
was lower at 35 °C than at 25 °C. Ammonia-oxidizing archaea (AOA) were the dominant ammonia oxidizers, but both AOA and ammonia-oxidizing bacteria (AOB) were related to N
2
O emitted from nitrification. AOA and AOB abundance was significantly influenced by soil moisture, more so than temperature, and decreased with increasing moisture content. These findings can be used to develop better models for simulating N
2
O from nitrification to inform soil management practises for improving N use efficiency.
Here we describe the potential for sediment microbial nitrogen-cycling gene (DNA) and activity (RNA) abundances to spatially resolve coastal areas impacted by seasonal variability in external ...nutrient inputs. Three sites were chosen within a nitrogen-limited embayment, Port Phillip Bay (PPB), Australia that reflect variability in both proximity to external nutrient inputs and the dominant form of available nitrogen. At three sediment depths (0–1; 1–5; 5–10 cm) across a 2 year study key genes involved in nitrification (archaeal amoA and bacterial β-amoA), nitrite reduction (clade I nirS and cluster I nirK, archaeal nirK-a), anaerobic oxidation of ammonium (anammox 16S rRNA phylogenetic marker) and nitrogen fixation (nifH) were quantified. Sediments impacted by a dominance of organic nitrogen inputs were characterised at all time-points and to sediment depths of 10 cm by the highest transcript abundances of archaeal amoA and archaeal nirk-a. Proximity to a dominance of external nitrate inputs was associated with the highest transcript abundances of nirS which temporally co-varied with seasonal changes in sediment nitrate. Sediments isolated from external inputs displayed the greatest depth-specific decrease in quantifiable transcript abundances. In these isolated sediments bacterial β-amoA transcripts were temporally associated with increased sediment ammonium levels. Across this nitrogen limited system variability in the abundance of bacterial β-amoA, archaeal amoA, archaeal nirk-a or nirS transcripts from the sediment surface (0–1 and 5 cm) demonstrated a capacity to improve our ability to monitor coastal zones impacted by anthropogenic nitrogen inputs. Specifically, the spatial detection sensitivity of bacterial β-amoA transcripts could be developed as a metric to determine spatiotemporal impacts of large external loading events. This temporal study demonstrates a capacity for microbial activity metrics to facilitate coastal management strategies through greater spatial resolution of areas impacted by external nutrient inputs.
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•Sediment microbial N-cycling profiles are shaped by dominant Nr.•Nitrifier transcripts are abundant in coastal sediments to depths of 10 cm.•Archaeal nirK-a and amoA can be applied to monitor archaeal nitrifiers in coastal sediments.
The soilborne fungus
anastomosis group (AG) 8 is a major pathogen of grain crops resulting in substantial production losses. In the absence of resistant cultivars of wheat or barley, a sustainable ...and enduring method for disease control may lie in the enhancement of biological disease suppression. Evidence of effective biological control of
AG8 through disease suppression has been well documented at our study site in Avon, South Australia. A comparative metatranscriptomic approach was applied to assess the taxonomic and functional characteristics of the rhizosphere microbiome of wheat plants grown in adjacent fields which are suppressive and non-suppressive to the plant pathogen
AG8. Analysis of 12 rhizosphere metatranscriptomes (six per field) was undertaken using two bioinformatic approaches involving unassembled and assembled reads. Differential expression analysis showed the dominant taxa in the rhizosphere based on mRNA annotation were
spp. and
spp. for non-suppressive samples and
spp. and
spp. for the suppressive samples. The assembled metatranscriptome analysis identified more differentially expressed genes than the unassembled analysis in the comparison of suppressive and non-suppressive samples. Suppressive samples showed greater expression of a polyketide cyclase, a terpenoid biosynthesis backbone gene (
) and many cold shock proteins (
). Non-suppressive samples were characterised by greater expression of antibiotic genes such as non-heme chloroperoxidase (
) which is involved in pyrrolnitrin synthesis, and phenazine biosynthesis family protein F (
and its transcriptional activator protein (
). A large number of genes involved in detoxifying reactive oxygen species (ROS) and superoxide radicals (
) were also expressed in the non-suppressive rhizosphere samples most likely in response to the infection of wheat roots by
AG8. Together these results provide new insight into microbial gene expression in the rhizosphere of wheat in soils suppressive and non-suppressive to
AG8. The approach taken and the genes involved in these functions provide direction for future studies to determine more precisely the molecular interplay of plant-microbe-pathogen interactions with the ultimate goal of the development of management options that promote beneficial rhizosphere microflora to reduce
AG8 infection of crops.
The role of organic amendments for natural degradation of aged persistent organic pollutants (POPs) in agricultural soils remains controversial. We hypothesised that organic amendments enhance ...bacterial activity and function at the community level, facilitating the degradation of aged POPs. An incubation study was conducted in a closed chamber over 12 months to assess the effects of selected organic amendments on extractable residues of aged dieldrin. The role of bacterial diversity and changes in community function was explored through sequenced marker genes. Linear mixed effect models indicated that, independent of amendment type, cumulative CO2 release was negatively associated with decreases in dieldrin concentration, by up to 7% per µmol CO2–C respired by microorganisms. The addition of poultry litter led to the highest daily carbon mineralisation, which was associated with low dieldrin dissipation after 9 months. In comparison, biochar resulted in significant decreases in extractable dieldrin residues over time, which coincided with shifts towards aerobic, oligotrophic, gram-negative bacteria, some with dehalogenation metabolism, and with increased potentials for biosynthesis of membrane components such as fatty acids and high redox quinones. The results supported an alternative theory that labile carbon promoted blooms of copiotrophic growth, which suppressed the required community-level traits and oligotrophic diversity to degrade chlorinated pollutants.
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•Biochar resulted in maximum decreases of aged dieldrin after 12-month incubation.•Biochar promoted the most phylogenetically diverse, oligotrophic community.•Copiotrophic growth limited the degradation of aged dieldrin.•Labile carbon amendments may slow down the degradation of persistent pollutants.
Understanding how nitrogen (N) fertilisation influences the priming effect (PE) in soils is imperative to predict the carbon loss and subsequent impact on climate. Three contrasting soil types with ...low mineral N, Vertosol, Calcarosol, and Chromosol, were treated for 4 weeks with the single supplement of N ranging from 0 to 300 mg kg
−1
and weekly addition of
13
C-glucose. Nitrogen addition did not affect the PE in the clay Vertosol. In contrast, the addition of N to the sandy loam Calcarosol above 10 mg N kg
−1
suppressed the PE by 14% in week 1, but increased by 20% at 120 mg N kg
−1
in week 4. In the silty loam Chromosol, the addition of 40 and 120 mg N kg
−1
increased the PE by 78% in week 4. Nitrogen addition increased the abundance of functional genes for decomposing chitin and recalcitrant phenolic compounds particularly in the Calcarosol which had a high proportion of recalcitrant soil C; the predicted pathways for the degradation of microbial necromass and recalcitrant compounds were also positively related to the PE in this soil. These functions concurred with an increase in the abundance of resource-acquisition strategists such as
Microbacteriaceae
,
Lysobacter
, and
Sphingomonadaceae
over time and under N addition. In the Chromosol rich in labile C, the PE was positively correlated with the predicted pathways for the microbial biosynthesis of diverse metabolites and compounds for growth and enzyme production, corresponding to the rise of
Micrococcaceae
(high-yield strategists) under N addition. In the Vertosol, although the abundances of C-relevant functional genes were stimulated by N addition, the greater clay content might protect the soil organic C from being further primed. Overall, N-induced alternation of PE is likely dependent of the microbial metabolisation on soil organic C sources which vary among soils, but this N effect may be defective under soil physical protection.
Objective: Information regarding the prevalence, nature, sources, and psychosocial correlates of teasing was obtained for overweight (OV) children (10 to 14 years of age) vs. non‐overweight (non‐OV) ...peers. It was hypothesized that weight‐related teasing would be negatively correlated with self‐esteem in specific domains and with enjoyment of physical/social activities and positively correlated with loneliness, bulimic behaviors, body dissatisfaction, and enjoyment of sedentary/isolative activities.
Research Methods and Procedures: Teasing experiences and psychosocial correlates were assessed among OV children from a fitness camp and a demographically similar school sample of non‐OV children.
Results: Among the OV children, appearance‐related teasing was more prevalent, frequent, and upsetting, involved disparaging nicknames focusing more on weight rather than less stigmatized aspects of appearance, and more often perpetrated by peers in general rather than a specific peer. Degree of teasing within the full sample was significantly associated with higher weight concerns, more loneliness, poorer self‐perception of one's physical appearance, higher preference for sedentary/isolative activities, and lower preference for active/social activities, all but the latter association holding up above and beyond actual weight status and demographics. Among OV children, teasing was associated with bulimic behaviors. Associations with type of teasing showed specificity, with weight‐related teasing predicting weight and appearance variables and competency‐related teasing related to social domain factors.
Discussion: When frequency, intensity, emotional impact, and stigmatized content are examined, findings indicate that teasing is more severe for OV children. Effective interventions are needed to help victims cope with and prevent further weight‐related teasing, which may improve peer functioning, enhance weight control efforts, and reduce risk for future eating disturbance.
Summary
The microbial community structure of bacteria, archaea and fungi is described in an Australian native grassland soil after more than 5 years exposure to different atmospheric CO2 ...concentrations (CO2) (ambient, + 550 ppm) and temperatures (ambient, + 2°C) under different plant functional types (C
3 and C
4 grasses) and at two soil depths (0–5 cm and 5–10 cm). Archaeal community diversity was influenced by elevated CO2, while under warming archaeal 16S rRNA gene copy numbers increased for C
4 plant Themeda triandra and decreased for the C
3 plant community (P < 0.05). Fungal community diversity resulted in three groups based upon elevated CO2, elevated CO2 plus warming and ambient CO2. Overall bacterial community diversity was influenced primarily by depth. Specific bacterial taxa changed in richness and relative abundance in response to climate change factors when assessed by a high‐resolution 16S rRNA microarray (PhyloChip). Operational taxonomic unit signal intensities increased under elevated CO2 for both Firmicutes and Bacteroidetes, and increased under warming for Actinobacteria and Alphaproteobacteria. For the interaction of elevated CO2 and warming there were 103 significant operational taxonomic units (P < 0.01) representing 15 phyla and 30 classes. The majority of these operational taxonomic units increased in abundance for elevated CO2 plus warming plots, while abundance declined in warmed or elevated CO2 plots. Bacterial abundance (16S rRNA gene copy number) was significantly different for the interaction of elevated CO2 and depth (P < 0.05) with decreased abundance under elevated CO2 at 5–10 cm, and for Firmicutes under elevated CO2 (P < 0.05). Bacteria, archaea and fungi in soil responded differently to elevated CO2, warming and their interaction. Taxa identified as significantly climate‐responsive could show differing trends in the direction of response (‘+’ or ‘−’) under elevated CO2 or warming, which could then not be used to predict their interactive effects supporting the need to investigate interactive effects for climate change. The approach of focusing on specific taxonomic groups provides greater potential for understanding complex microbial community changes in ecosystems under climate change.
To improve biodegradation strategies for chlorinated pollutants, the roles of soil organic matter and microbial function need to be clarified. It was hypothesised that microbial degradation of ...specific organic fractions in soils enhance community metabolic capability to degrade chlorinated pollutants. This field study used historic records of dieldrin concentrations since 1988 and established relationships between dieldrin dissipation and soil carbon fractions together with bacterial and fungal diversity in surface soils of Kurosol and Chromosol. Sparse partial least squares analysis linked dieldrin dissipation to metabolic activities associated with the highly decomposed carbon fraction. Dieldrin dissipation, after three decades of natural attenuation, was associated with increased bacterial species fitness for the decomposition of recalcitrant carbon substrates including synthetic chlorinated pollutants. These metabolic capabilities were linked to the decomposed carbon fraction, an important driver for the microbial community and function. Common bacterial traits among taxonomic groups enriched in samples with high dieldrin dissipation included their slow growth, large genome and complex metabolism which supported the notion that metabolic strategies for dieldrin degradation evolved in an energy-low soil environment. The findings provide new perspectives for bioremediation strategies and suggest that soil management should aim at stimulating metabolism at the decomposed, fine carbon fraction.
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•A resource-limiting soil favors dieldrin dissipation.•The persistent organic carbon pool is associated with great biodegradation potential.•Supply of labile carbon delays biodegradation of chlorinated pollutants.
Key message
Metabolic profiling of
Pratylenchus thornei
resistant and susceptible wheat genotypes indicates that fatty acid, glycerolipid and flavonoid classes of metabolites constitutively expressed ...in resistant wheat roots could reduce nematode reproduction.
The root-lesion nematode
Pratylenchus thornei
reduces wheat production in many parts of the world. In this study the metabolic profiles of two wheat genotypes ‘QT16258’ (moderately resistant) and ‘Janz’ (susceptible) were compared at 8 weeks post inoculation with or without
P. thornei
. We performed untargeted liquid chromatography mass spectrometry analysis (LC–MS) of the wheat root samples. A total of 11,704 MS features were identified, out of which 765 MS features were annotated using in-house chemical standards. Principal components analysis (PCA) and partial least square discriminant analysis (PLS-DA) indicated dissimilarity of the metabolome between
P. thornei
resistant and susceptible genotypes. Two-way analysis of variance indicated that metabolic differences were mainly constitutive rather than induced by inoculation with
P. thornei
. Eighty-four annotated metabolites were significantly (
p
≤ 0.01) higher in relative concentration in ‘QT16258’ than ‘Janz’ and belonged to the following classes of metabolites: flavonoids, fatty acids, glycerolipids, alkaloids, tannins, nucleotides, steroid glycosides and terpenoids. Eighty-five annotated metabolites were significantly (
p
≤ 0.01) higher in relative concentration in ‘Janz’ than ‘QT16258’ and belonged to the following classes of metabolites: amino acids, sugars, flavonoids and alkaloids. Several metabolites at higher concentration in ‘QT16258’, including quercetin-3,4'-O-di-beta-glucoside (flavonoid), linoleic acid (fatty acid), lysophosphatidylethanolamine (glycerolipid), hirsutine (alkaloid), 1-methylsulfinylbutenyl-isothiocyanate (glucosinolate), could potentially strengthen the root cell walls to inhibit nematode penetration and/or reduce nematode motility. Some metabolites at higher concentrations in susceptible ‘Janz’, including phenolics, coniferyl alcohol and indole acetic acid conjugates, could be nematode attractants as well as part of a hypersensitive browning reaction to nematode invasion.
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