Explore the vast range of titles available.

Nitrification is a key process of the nitrogen (N) cycle in soil with major environmental implications. The recent discovery of ammonia-oxidizing archaea (AOA) questions the traditional assumption of the dominant role of ammonia-oxidizing bacteria (AOB) in nitrification. We investigated AOB and AOA growth and nitrification rate in two different layers of three grassland soils treated with animal urine substrate and a nitrification inhibitor [dicyandiamide (DCD)]. We show that AOB were more abundant in the topsoils than in the subsoils, whereas AOA were more abundant in one of the subsoils. AOB grew substantially when supplied with a high dose of urine substrate, whereas AOA only grew in the Controls without the urine-N substrate. AOB growth and the amoA gene transcription activity were significantly inhibited by DCD. Nitrification rates were much higher in the topsoils than in the subsoils and were significantly related to AOB abundance, but not to AOA abundance. These results suggest that AOB and AOA prefer different soil N conditions to grow: AOB under high ammonia (NH₃) substrate and AOA under low NH₃ substrate conditions.

Pasture-based livestock systems are often associated with losses of reactive forms of nitrogen (N) to the environment. Research has focused on losses to air and water due to the health, economic and environmental impacts of reactive N. Di-nitrogen (N 2 ) emissions are still poorly characterized, both in terms of the processes involved and their magnitude, due to financial and methodological constraints. Relatively few studies have focused on quantifying N 2 losses in vivo and fewer still have examined the relative contribution of the different N 2 emission processes, particularly in grazed pastures. We used a combination of a high 15 N isotopic enrichment of applied N with a high precision of determination of 15 N isotopic enrichment by isotope-ratio mass spectrometry to measure N 2 emissions in the field. We report that 55.8 g N m −2 (95%, CI 38 to 77 g m −2 ) was emitted as N 2 by the process of co-denitrification in pastoral soils over 123 days following urine deposition (100 g N m −2 ), compared to only 1.1 g N m −2 (0.4 to 2.8 g m −2 ) from denitrification. This study provides strong evidence for co-denitrification as a major N 2 production pathway, which has significant implications for understanding the N budgets of pastoral ecosystems.

Bacillus megaterium is well known as a plant growth-promoting rhizobacterium, but the relevant molecular mechanisms remain unclear. This study aimed to elucidate the effects of B. megaterium HT517 on the growth and development of and the control of disease in greenhouse tomato and its mechanism of action. A pot experiment was conducted to determine the effect of B. megaterium on tomato growth, and this experiment included the HT517 group (3.2 x 10⁸ cfu/pot) and the control group (inoculated with the same amount of sterilized suspension). An antagonistic experiment and a plate confrontation experiment were conducted to study the antagonistic effect of B. megaterium and Fusarium oxysporum f.sp. lycopersici. Liquid chromatography–mass spectrometry was used to determine the metabolite composition and metabolic pathway of HT517. PacBio+Illumina HiSeq sequencing was utilized for map sequencing of the samples. An in-depth analysis of the functional genes related to the secretion of these substances by functional bacteria was conducted. HT517 could secrete organic acids that solubilize phosphorus, promote root growth, secrete auxin, which that promotes early flowering and fruiting, and alkaloids, which control disease, and reduce the incidence of crown rot by 51.0%. The complete genome sequence indicated that the strain comprised one circular chromosome with a length of 5,510,339 bp (including four plasmids in the genome), and the GC content accounted for 37.95%. Seven genes (pyk, aceB, pyc, ackA, gltA, buk, and aroK) related to phosphate solubilization, five genes (trpA, trpB, trpS, TDO2, and idi) related to growth promotion, eight genes (hpaB, pheS, pheT, ileS, pepA, iucD, paaG, and kamA) related to disease control, and one gene cluster of synthetic surfactin were identified in this research. The identification of molecular biological mechanisms for extracellular secretion by the HT517 strain clarified that its organic acids solubilized phosphorus, that auxin promoted growth, and that alkaloids controlled tomato diseases.

Nitrate (NO ₃ - ) leaching and water contamination is a major environmental issue around the globe. In grazed grassland, most of the nitrate leaching occurs under the animal urine patch areas because of high nitrogen (N) loading rates. The aim of this study was to determine NO ₃ - -N leaching losses and pasture responses as affected by different animal urine-N loading rates and application of a nitrification inhibitor, dicyandiamide (DCD). Undisturbed monolith lysimeters (50 cm diameter by 70 cm deep) of a free-draining stony soil (Pallic orthic brown soil; Udic Haplustept loamy skeletal) with a mixture of perennial ryegrass (Lolium perenne) and white clover (Trifolium repens) were used for the study. Results showed that total NO ₃ - -N leaching losses increased significantly (P < 0.01) from 22.8 to 59.7, 188.1 and 254.9 kg NO ₃ - -N ha-¹, when urine N was applied at 0 (Control), 300, 700 and 1,000 kg N ha-¹, respectively, without DCD. The application of DCD to the corresponding treatments significantly (P < 0.01) reduced the total NO ₃ - -N leaching losses to 12.4, 9.9, 75.3 and 139.0 kg N ha-¹, respectively, resulting in an average reduction of 63%. Pasture yield increased linearly with increasing urine-N application rates and the application of DCD resulted in an average 25% increase in pasture dry matter production. The average N offtake was increased by 32% with the application of DCD, confirming the effectiveness of the inhibitor in improving the N cycle. These results indicate that the DCD nitrification inhibitor technology has the potential to be a valuable nitrogen management tool in different grazed pasture systems (e.g. sheep, beef cattle and dairy cattle) to mitigate NO ₃ - leaching and improve sustainable production.

AIMS: Identification of soil, environmental, or microbial properties linked with efficacy of the nitrification inhibitor dicyandiamide (DCD) in high and low-input pastoral farming system soils. METHODS: Soils were collected from under 25 pastures. Potential nitrification rate (PRN) was quantified in the presence and absence of DCD, and percentage efficacy of DCD in reducing PNR calculated. PNR and %DCD efficacy were statistically tested (REML analysis) for relationships to a suite of edaphic (33), environmental (5), and microbiological (8) variables. Microbiological properties included measurement of bacterial and archaeal ammonia monooxygenase genes (amoA qPCR) and soil DNA content. RESULTS: DCD reduced PRN by an average of 36 %. The percent DCD efficacy was not related to system intensity, soil type, nor PNR (all P > 0.05). However the numbers of bacterial amoA genes (r = 0.46; P < 0.05), and ratios of bacterial:archaeal amoA (r = −0.53; P < 0.05), were strongly correlated to %DCD efficacy. In both high and low input systems, models best explaining variance in %DCD efficacy fitted AOA: AOB g soil⁻¹ as the first varaible (P < 0.05). CONCLUSIONS: Characterisation of soils based on ammonia oxidising communities may increase the ability to predict the % efficacy of DCD between sites and provide for more targeted application of this nitrification inhibitor.

PurposeThe New Zealand Government requires gross emissions of biogenic methane (CH4) to be reduced to 10% below 2017 levels by 2030. However, the amount of CH4 emissions reported in the ‘Manure Management’ category of New Zealand’s Greenhouse Gas Inventory has increased by 123% since 1990. The purpose of this research was to determine the effect of treating farm dairy effluent (FDE) with polyferric sulphate (PFS) on CH4 emissions.MethodsThe effect of treating FDE with PFS on CH4 emissions was measured at four scales: (i) 1-L gas jars in the laboratory, (ii) 1.1-m-deep × 150-mm-diameter pipe microcosms in the laboratory, (iii) large 3.4-m-deep × 0.47-m-diameter pipes on-farm, and (iv) 2-m-deep × 8.4-m-diameter (100,000 L) commercial effluent storage tanks on a farm. Gas emissions were captured by repeated discrete sampling and CH4 concentrations were determined by gas chromatography.ResultsWe discovered that treating FDE with PFS at an average rate of 220 mg Fe L−1 of FDE reduced CH4 emissions by up to 99% and that this effect continued for an extended period of time (up to 2 months) after treatment. The PFS treatment also reduced CO2 emissions by approximately 50% and reduced hydrogen sulphide emissions. PFS treatment resulted in a small increase in nitrous oxide (N2O) emissions, but these emissions were very low and only represented < 3% of the total CO2-e greenhouse gas emissions from the treated FDE.ConclusionsA new method to reduce CH4 emissions from farm dairy effluent by up to 99% has been discovered.

Phenolic root exudates (PREs) secreted by wetland plants facilitate the accumulation of iron in the rhizosphere, potentially providing the essential active iron required for the generation of enzymes that degrade polycyclic aromatic hydrocarbon, thereby enhancing their biodegradation. However, the underlying mechanisms involved are yet to be elucidated. This study focuses on phenanthrene (PHE), a typical polycyclic aromatic hydrocarbon pollutant, utilizing representative PREs from wetland plants, including p -hydroxybenzoic, p -coumaric, caffeic, and ferulic acids. Using hydroponic experiments, 16S rRNA sequencing, and multiple characterization techniques, we aimed to elucidate the interaction mechanism between the accelerated degradation of PHE and the formation of rhizosphere biofilm/iron plaque influenced by PREs. Although all four types of PREs altered the biofilm composition and promoted the formation of iron plaque on the root surface, only caffeic acid, possessing a similar structure to the intermediate metabolite of PHE (catechol), could accelerate the PHE degradation rate. Caffeic acid, notable for its catechol structure, plays a significant role in enhancing PHE degradation through two main mechanisms: (a) it directly boosts PHE co-metabolism by fostering the growth of PHE-degrading bacteria, specifically Burkholderiaceae, and by facilitating the production of the key metabolic enzyme catechol 1,2-dioxygenase (C12O) and (b) it indirectly supports PHE biodegradation by promoting iron plaque formation on root surfaces, thereby enriching free iron for efficient microbial synthesis of C12O, a crucial factor in PHE decomposition.

PurposePhosphorus (P) and potassium (K) are two important essential nutrient elements for plant growth and development but their availability is often limited in calcareous soils. The objective of this study was to determine the effects of applying microbial inoculants (MI, containing effective strains of Bacillus megaterium and Bacillus mucilaginous) on the availability of P and K, plant growth, and the bacterial community in calcareous soil.Materials and methodsA greenhouse experiment was conducted to explore the effects of the addition of MI (control: without MI addition; treatment: with MI addition at the rate of 60 L ha−1) on the concentrations of P and K in soil and plant, soil bacterial community diversity and composition, and chili pepper (Capsicum annuum L.) growth.Results and discussionThe results showed that MI inoculation significantly increased the fruit yields by 28.5% (p < 0.01), available P and K in the rhizosphere soil by 32.1% and 28.1% (p < 0.05), and P and K accumulation in the whole plants by 40.9% and 40.2%, respectively (p < 0.05). Moreover, high-throughput sequencing revealed that Proteobacteria, Acidobacteria, Bacteroidetes, Chloroflexi, and Gemmatimonadetes were the dominant phyla of soil bacteria. MI application did not significantly impact the diversity and composition of soil bacterial communities, but increased relative abundances of bacterial genera Flavobacterium responsible for promoting root development across growing stages (p < 0.05), and changed the soil bacterial community structure associated closely with soil properties of available P, K, and pH in soil.ConclusionsThe application of MI improved the bioavailability of P and K and plant growth due to its impact on the soil bacterial community structure.

PurposeLand application of farm dairy effluent (FDE) can cause phosphorus contamination of freshwater due to its high nutrient content especially phosphorus (P) in the animal dung. A novel FDE treatment technology has been developed that uses poly-ferric sulphate (PFS) to treat the FDE and recycle water for washing farmyard and reduce the risk of water pollution from P leaching from through the soil. It is important that the application of PFS-treated FDE (TE) does not cause any adverse impacts on soil fertility or plant growth when the TE is applied to the soil.Materials and methodsA multi-year field plot study was conducted to determine the effect of repeat applications of FDE and PFS-treated FDE (TE) on soil P availability, P fractionations, plant yield and nutrient uptake. Eight applications of untreated FDE, TE and water as control were applied to replicated soil plots over the period of 4 years. The soil samples were collected on 1 December 2020, and nine pasture samples were harvested during the 2021–2022 dairy milking season. Measurements included soil chemical properties, soil phosphorous fractionations, plant biomass and plant phosphorus and nitrogen uptake.Results and discussionThe results indicated that the majority of soil fertility indices and soil P fractions had no significant difference between the FDE and TE applications, with the exception of labile P which was significantly higher in the TE (122.7 mg kg−1) than in the FDE treatments (103.0 mg kg−1) at 0–10-cm soil depth and was also significantly higher in the TE (114.6 mg kg−1) than in the FDE treatments (74.0 mg kg−1) at 10–20-cm soil depth. Similarly, plant P uptakes and dry matter yields were also the same between the TE and FDE treatments with the average of being 54.4 kg P ha−1 and 12.8 t ha−1, respectively.ConclusionsRepeated applications of PFS-treated FDE had no adverse effect on soil P availability or plant growth when compared to untreated FDE application and had the potential to benefit soil fertility compared to control.

Biological nitrogen fixation plays an important role in nitrogen cycling by transferring atmospheric N2 to plant-available N in the soil. However, the diazotrophic activity and distribution in different types of soils remain to be further explored. In this study, 152 upland soils were sampled to examine the diazotrophic abundance, nitrogenase activity, diversity and community composition by quantitative polymerase chain reaction, acetylene reduction assay and the MiSeq sequencing of nifH genes, respectively. The results showed that diazotrophic abundance and nitrogenase activity varied among the three soil types. The diazotrophic community was mainly dominated by Bradyrhizobium, Azospirillum, Myxobacter, Desulfovibrio and Methylobacterium. The symbiotic diazotroph Bradyrhizobium was widely distributed among soils, while the distribution of free-living diazotrophs showed large variation and was greatly affected by multiple factors. Crop type and soil properties directly affected the diazotrophic ɑ-diversity, while soil properties, climatic factors and spatial distance together influenced the diazotrophic community. Network structures were completely different among all three types of soils, with most complex interactions observed in the Red soil. These findings suggest that diazotrophs have various activities and distributions in the three soil types, which played different roles in nitrogen input in agricultural soil in China, being driven by multiple environmental factors.