scholarly journals More than stoichiometry: the molecular composition of inorganic and organic substrates controls ammonium regeneration by bacteria

2020 ◽  
Author(s):  
J. Guo ◽  
M. Cherif
Keyword(s):  
Experimental Data ◽  
Isotope Dilution ◽  
Inorganic Nitrogen ◽  
C:N Ratio ◽  
Molecular Composition ◽  
List Type ◽  
Organic Substrates ◽  
Mixed Substrates ◽  
C And N ◽  
Ammonium Regeneration

AbstractThe mineralization of nitrogen (N) and especially the regeneration of ammonium are critical processes performed by bacteria in aquatic ecosystems. Quantifying these processes is complicated because bacteria simultaneously consume and produce ammonium. Here we use experimental data on the effects of the molecular composition of the supplied substrates, combined with a classical stoichiometric model of ammonium regeneration, to demonstrate how the quantification of these processes can be improved. We manipulated a batch culture experiment with an isolated bacterial community by adding three different types of N substrates: dissolved inorganic nitrogen (DIN, nitrate), dissolved organic nitrogen (DON, amino acid) and a mixture of DIN and DON. With such experiment set-up, the ammonium regeneration per se could be easily tracked without using complicated methods (e.g. isotope dilution). We compared the experimental data with the predictions of Goldman et al’ model (1987) as well as with a revised version, using the measured consumption carbon:nitrogen ratio (C:N ratio), rather than an estimated consumption ratio. We found that, for all substrates, and in particular, mixed substrates where C and N are partially dissociated between different molecules, estimates of ammonium regeneration rates can be improved by measuring the actual consumption C: N ratio.ImportanceMeasuring bacterial ammonium regeneration in natural aquatic ecosystem is difficult because bacteria in the field simultaneously consume and produce ammonium. In our experimental design, we used nitrate as the inorganic nitrogen substrate. This way, we could measure separately the uptake and excretion of inorganic nitrogen by bacteria without incorporating cumbersome methods such as isotope dilution. Our experiment allowed us to evaluate the accuracy of various stoichiometric models for the estimation of net bacterial nitrogen regeneration. We found that:The exact distribution of C and N among the various molecules that make the bulk of DOM is a crucial factor to consider for bacterial net nitrogen regeneration.For all substrates, and in particular, mixed substrates where C and N are partially dissociated between different molecules, estimates of net nitrogen regeneration rates can be improved by measuring the actual C: N ratio of bacterial consumption.

Experimental Study on Critical Shear Stress of Cohesive Soils and Soil Mixtures

2021 ◽  
Vol 64 (2) ◽  
pp. 587-600
Author(s):  
Xiaojing Gao ◽  
Qiusheng Wang ◽  
Chongbang Xu ◽  
Ruilin Su
Keyword(s):  
Experimental Data ◽  
Shear Stress ◽  
Critical Shear Stress ◽  
Cohesive Soil ◽  
Future Research ◽  
Cohesive Soils ◽  
List Type ◽  
Soil Mixture ◽  
Linear Relationships ◽  
Soil Mixtures

HighlightsErosion tests were performed to study the critical shear stress of cohesive soils and soil mixtures.Linear relationships were observed between critical shear stress and cohesion of cohesive soils.Mixture critical shear stress relates to noncohesive particle size and cohesive soil erodibility.A formula for calculating the critical shear stress of soil mixtures is proposed and verified.Abstract. The incipient motion of soil is an important engineering property that impacts reservoir sedimentation, stable channel design, river bed degradation, and dam breach. Due to numerous factors influencing the erodibility parameters, the study of critical shear stress (tc) of cohesive soils and soil mixtures is still far from mature. In this study, erosion experiments were conducted to investigate the influence of soil properties on the tc of remolded cohesive soils and cohesive and noncohesive soil mixtures with mud contents varying from 0% to 100% using an erosion function apparatus (EFA). For cohesive soils, direct linear relationships were observed between tc and cohesion (c). The critical shear stress for soil mixture (tcm) erosion increased monotonically with an increase in mud content (pm). The median diameter of noncohesive soil (Ds), the void ratio (e), and the organic content of cohesive soil also influenced tcm. A formula for calculating tcm considering the effect of pm and the tc of noncohesive soil and pure mud was developed. The proposed formula was validated using experimental data from the present and previous research, and it can reproduce the variation of tcm for reconstituted soil mixtures. To use the proposed formula to predict the tcm for artificial engineering problems, experimental erosion tests should be performed. Future research should further test the proposed formula based on additional experimental data. Keywords: Cohesive and noncohesive soil mixture, Critical shear stress, Erodibility, Mud content, Soil property.

scholarly journals Changes in Denitrification Potentials and Riverbank Soil Bacterial Structures along Shibetsu River, Japan

2018 ◽  
Vol 2018 ◽  
pp. 1-9
Author(s):  
Yoshitaka Uchida ◽  
Hirosato Mogi ◽  
Toru Hamamoto ◽  
Miwako Nagane ◽  
Misato Toda ◽  
...  
Keyword(s):  
Bacterial Community ◽  
Inorganic Nitrogen ◽  
Anaerobic Incubation ◽  
Community Structures ◽  
Bacterial Response ◽  
Glucose Carbon ◽  
Soil Ecosystems ◽  
Increase Rate ◽  
Before And After ◽  
C And N

Riverbank soil ecosystems are important zones in terms of transforming inorganic nitrogen (N), particularly nitrate (NO3−-N), in soils to nitrous oxide (N2O) gases. Thus, the gasification of N in the riverbank soil ecosystems may produce a greenhouse gas, N2O, when the condition is favourable for N2O-producing microbes. One of the major N2O-producing pathways is denitrification. Thus, we investigated the denitrification potentials along Shibetsu River, Hokkaido, Japan. We sampled riverbank soils from eight sites along the Shibetsu River. Their denitrification potentials with added glucose-carbon (C) and NO3−-N varied from 4.73 to 181 μg·N·kg−1·h−1. The increase of the denitrification after the addition of C and N was negatively controlled by soil pH and positively controlled by soil NH4+-N levels. Then, we investigated the changes in 16S rRNA bacterial community structures before and after an anaerobic incubation with added C and N. We investigated the changes in bacterial community structures, aiming to identify specific microbial species related to high denitrification potentials. The genus Gammaproteobacteria AeromonadaceaeTolumonaswas markedly increased, from 0.0 ± 0.0% to 16 ± 17%, before and after the anaerobic incubation with the excess substrates, when averaged across all the sites. Although we could not find a significant interaction between the denitrification potential and the increase rate of G. AeromonadaceaeTolumonas, our study suggested that along the Shibetsu River, bacterial response to added excess substrates was similar at the genus level. Further studies are needed to investigate whether this is a universal phenomenon even in other rivers.

scholarly journals Elevation Gradient Altered Soil C, N, and P Stoichiometry of Pinus taiwanensis Forest on Daiyun Mountain

Forests ◽  
2019 ◽  
Vol 10 (12) ◽  
pp. 1089
Author(s):  
Lan Jiang ◽  
Zhongsheng He ◽  
Jinfu Liu ◽  
Cong Xing ◽  
Xinguang Gu ◽  
...  
Keyword(s):  
Elevation Gradient ◽  
C:N Ratio ◽  
Phosphate Fertilizer ◽  
High Elevation ◽  
Driving Factors ◽  
Slope Position ◽  
Elevation Gradients ◽  
Soil C ◽  
Soil P ◽  
C And N

Researches focused on soil carbon (C), nitrogen (N), and phosphorus (P) content and the stoichiometry characteristics along elevation gradients are important for effective management of forest ecosystems. Taking the soil of different elevations from 900 to 1700 m on Daiyun Mountain as the object, the elevation distribution of total C, N, and P in soil and their stoichiometry characteristics were studied. Also, the driving factors resulting in the spatial heterogeneity of soil stoichiometry are presented. The results show the following: (1) The average soil C and N content was 53.03 g·kg−1 and 3.82 g·kg−1, respectively. The content of C and N at high elevation was higher than that of at low elevation. Soil phosphorus fluctuated with elevation. (2) With increasing elevation, soil C:N ratio increased initially to 17.40 at elevation between 900–1000 m, and then decreased to 12.02 at elevation 1600 m. The changing trends of C:P and N:P were similar, and they all fluctuated with elevation. (3) Elevation, soil bulk density, and soil temperature were the main factors influencing the variation of soil C, N, and C:N. Soil pH and slope position were the driving factors for soil P, C:P, and N:P. The soil is rich in C and N, and has less total phosphorus on Daiyun Mountain. Raising the level of phosphate fertilizer appropriately can help to improve soil fertility and promote plant growth as well. In light of this information, in the near future, it will be necessary to conduct separation management of C, N, and P with regular monitoring systems to maintain favorable conditions for soil.

Mass loss and nitrogen dynamics of decaying litter of grasslands: the apparent low nitrogen immobilization potential of root detritus

1992 ◽  
Vol 70 (2) ◽  
pp. 384-391 ◽  
Author(s):  
T. R. Seastedt ◽  
W. J. Parton ◽  
D. S. Ojima
Keyword(s):  
Mass Loss ◽  
Nitrogen Availability ◽  
Inorganic Nitrogen ◽  
Nitrogen Concentration ◽  
C:N Ratio ◽  
Nitrogen Dynamics ◽  
Nitrogen Immobilization ◽  
Litter Bag ◽  
Root Litter ◽  
Low Nitrogen

Litter-bag studies and simulation modeling were used to examine the relationship between mass loss and nitrogen content of decaying prairie foliage and root litter. In contrast with forest studies, grassland roots were low in lignin and nitrogen, decayed more rapidly than foliage, and demonstrated very low nitrogen immobilization potentials. Our findings agree with reports indicating that buried substrates with high C:N ratios do not immobilize substantial amounts of nitrogen and that nitrogen-limited environments induce steeper slopes in the mass loss – nitrogen concentration relationship. However, results suggesting rapid nitrogen mineralization contradict our own studies demonstrating reduced inorganic nitrogen availability in soils of frequently burned prairie. Simulation of observed patterns using the CENTURY grassland model indicated that these results could not occur without creating soil organic matter with unrealistically high C:N ratios. Litter-bag studies of buried substrates therefore may provide an incomplete perspective on the mass loss and nitrogen dynamics of buried litter in grassland and agroecosystem soils. Key words: Andropogon gerardii, C:N ratio, decomposition, immobilization, mineralization, nitrogen.

The role of copepod-dominated meiofauna in the mineralization of organic matter in a cold marine mesocosm

1999 ◽  
Vol 56 (10) ◽  
pp. 1938-1948
Author(s):  
Serge Parent ◽  
Antoine Morin
Keyword(s):  
Particle Size ◽  
C:N Ratio ◽  
Organic Substrates ◽  
Mineralization Rate ◽  
Nutrient Regeneration ◽  
Sand Filters ◽  
Harpacticoid Copepods ◽  
Large Populations ◽  
Mineralization Of Organic Matter

Large populations of meiofauna are found in the sand filters of the St. Lawrence mesocosm at the Montreal Biodome. Three 30-day experiments were conducted in heterotrophic microcosms to quantify how populations of micro- and meio-faunal organisms affect mineralization using the apparent mineralization rate (AMR), i.e., nitrate production, as a proxy. Tryptone, mesocosm detritus, and fishmeal were used as organic substrates (C:N ratios 4-8). Harpacticoid copepods dominated the meiofauna in numbers (87%) and biomass (90%). AMR was inversely related to meiofaunal mass and not related to ciliate density. Through grazing, 1 g meiofaunal dry mass·m-2 reduced the AMR of tryptone by 42%, of detritus by 9.4%, and of fishmeal by 2.7%. Particle size affected the effect of meiofauna, whereas the C:N ratio affected the AMR. The scarcity of nematodes, which are known to stimulate mineralization, may explain these results. Copepod-dominated meiofauna decrease nutrient regeneration rates in heterotrophic habitats when C:N ratios are low.

Study on the Effect of Adding Substrates on the Quantitative Characteristics and Germination Dynamic of Soil Seed Banks

2015 ◽  
Vol 1092-1093 ◽  
pp. 1254-1258
Author(s):  
Lin Wei Han ◽  
Meng Xuan He ◽  
Gang Wu
Keyword(s):  
Rice Husk ◽  
Seed Banks ◽  
Community Diversity ◽  
Organic Substrates ◽  
Mixed Substrates ◽  
Promoting Effect ◽  
Soil Seed Banks ◽  
Germination Characteristics ◽  
Inorganic Substrates ◽  
Seeding Emergence

In order to study the effect of adding substrates on soil seed banks (SSBs) germination characteristics, vermiculite (inorganic substrates), rice husk char (organic substrates) and their mixed substrates were selected to be added to SSBs by different ratios. After the germination test, the results show that SSBs in different treatments present different germination characteristics. In this test, the nutrition of organic substrates is more important for promoting the rate of seeding emergence, while the inorganic substrates is better for greater density and seeding community diversity. T1(rice husk char: soil=1:9), T5(rice husk char: vermiculite: soil=2:1:7) and T4(vermiculite: soil=3:7) correspond the best promoting effect on these three aspects. Thus the substrates selection should be determined according to specific objectives during vegetation restoration. Mixed substrates combine the advantages of organic and inorganic substrates, which leads to comparative advantages in all aspects.

scholarly journals Are researchers following best storage practices for measuring soil biochemical properties?

SOIL ◽  
2021 ◽  
Vol 7 (1) ◽  
pp. 95-106
Author(s):  
Jennifer M. Rhymes ◽  
Irene Cordero ◽  
Mathilde Chomel ◽  
Jocelyn M. Lavallee ◽  
Angela L. Straathof ◽  
...  
Keyword(s):  
Soil Properties ◽  
Best Practice ◽  
Storage Temperature ◽  
Soil Depth ◽  
Inorganic Nitrogen ◽  
Biochemical Properties ◽  
Microbial Biomass C ◽  
Soil Extracts ◽  
Organic C ◽  
C And N

Abstract. It is widely accepted that the measurement of organic and inorganic forms of carbon (C) and nitrogen (N) in soils should be performed on fresh extracts taken from fresh soil samples. However, this is often not possible, and it is common practice to store samples (soils and/or extracts), despite a lack of guidance on best practice. We utilised a case study on a temperate grassland soil taken from different depths to demonstrate how differences in soil and/or soil extract storage temperature (4 or −20 ∘C) and duration can influence sample integrity for the quantification of soil-dissolved organic C and N (DOC and DON), extractable inorganic nitrogen (NH4+ and NO3-) and microbial biomass C and N (MBC and MBN). The appropriateness of different storage treatments varied between topsoils and subsoils, highlighting the need to consider appropriate storage methods based on soil depth and soil properties. In general, we found that storing soils and extracts by freezing at −20 ∘C was least effective at maintaining measured values of fresh material, whilst refrigerating (4 ∘C) soils for less than a week for DOC and DON and up to a year for MBC and MBN and refrigerating soil extracts for less than a week for NH4+ and NO3- did not jeopardise sample integrity. We discuss and provide the appropriate tools to ensure researchers consider best storage practice methods when designing and organising ecological research involving assessments of soil properties related to C and N cycling. We encourage researchers to use standardised methods where possible and to report their storage treatment (i.e. temperature, duration) when publishing findings on aspects of soil and ecosystem functioning. In the absence of published storage recommendations for a given soil type, we encourage researchers to conduct a pilot study and publish their findings.

Monitoring of the process of composting of kitchen waste in an institutional scale worm farm

2005 ◽  
Vol 51 (10) ◽  
pp. 171-177 ◽  
Author(s):  
R. Kristiana ◽  
J. Nair ◽  
M. Anda ◽  
K. Mathew
Keyword(s):  
Organic Waste ◽  
C:N Ratio ◽  
Cost Effective ◽  
Experimental Period ◽  
Lumbricus Rubellus ◽  
Organic Substrates ◽  
Cow Manure ◽  
Horse Manure ◽  
Significant Difference ◽  
Bedding Materials

Vermicomposting provides an alternative method of managing waste that is ecofriendly and cost-effective. The Environmental Technology Centre (ETC) at Murdoch University and St. John of God Hospital (SJOG) signed a Memorandum of Understanding (MOU) to install a vermiculture system in SJOG to treat some of the organic waste generated by the on site kitchen facility. This is an effort made by SJOG to reduce the amount of organic waste sent to landfill each year and to treat the waste on site as part of a recycling/reuse program. The study is aimed at scientifically monitoring vermicomposting process and to understand the optimum management requirements to improve the operation of an institutional scale worm farm. In addition, an experiment was conducted to investigate the suitability of bedding materials: horse manure, cow manure, peat coir, and natural bedding (vermicast). The species of earthworms used in this experiment were Red (Lumbricus rubellus), Tiger (Eisenia fetida), and Blue (Lumbricus excavatus). The pH, temperature, worm population and quality of castings were tested in different beds. Results indicated that vermicast was the best bedding for vermicomposting, and there were no significant difference between the performances of the other three beds. However, it can be concluded that the bedding material of horse manure, cow manure, and peat coir were successfully established well within the experimental period of eight weeks, and cow manure with the lowest C:N ratio produced the best quality bedding. As using vermicast for the initial bedding creates a very high capital cost these organic substrates provide cost-effective alternative. Therefore they would be quite appropriate to initiate an institutional scale worm farm.

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