Interactive priming of soil N transformations from combining biochar and urea inputs: A 15N isotope tracer study

Wood Mountain loam was wetted with water or (NH4)2SO4 solution to provide a factorial combination among three moisture and three NH4-N levels. Samples in polyethylene bags were incubated at 2.5-cm depths in fallow, and in an incubator that simulated the diurnal patterns of temperature fluctuation recorded in the field. During the growing season, treatments were sampled regularly for moisture, NO3− and exchangeable NH4-N. Similar determinations were made on in situ samples taken in fallow Wood Mountain loam. The incubator simulated the effects of growing season temperatures on soil N transformations satisfactorily. Pronounced increases or decreases in temperature led to flushes in N mineralization. However, in the 1972 growing season, temperature was suboptimal and temperature changes were generally small. Consequently, when a stepwise multiple regression technique was used to analyze the data, neither ammonification nor nitrification showed a quantitative relationship to temperature. Comparison of the nitrification occurring in laboratory-incubated soils with that occurring in situ led to the conclusion that 70 to 90% of the NO3-N produced in surface soil resulted from wetting and drying. Estimates of potentially ammonifiable soil N(No) and its rate of mineralization (k) were derived from cumulative ammonification by assuming that the laws of first-order kinetics were applicable. In the 10, 15, and 20% moisture treatments the average No was 27, 41, and 82 ppm, respectively. Under the conditions of this study, the time required to mineralize half of No was about 7 wk.

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Exploitation of a deep-water algal maximum by Daphnia: a stable-isotope tracer study

Aquatic Biodiversity ◽

10.1007/978-94-007-1084-9_6 ◽

2003 ◽

pp. 95-101

Author(s):

Winfried Lampert ◽

Jonathan Grey

Keyword(s):

Stable Isotope ◽

Deep Water ◽

Tracer Study ◽

Stable Isotope Tracer ◽

Isotope Tracer

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Distinct nitrogen cycling and steep chemical gradients in Trichodesmium colonies

The ISME Journal ◽

10.1038/s41396-019-0514-9 ◽

2019 ◽

Vol 14 (2) ◽

pp. 399-412 ◽

Cited By ~ 4

Author(s):

Isabell Klawonn ◽

Meri J. Eichner ◽

Samuel T. Wilson ◽

Nasrollah Moradi ◽

Bo Thamdrup ◽

...

Keyword(s):

Carbon Fixation ◽

Nitrate Concentration ◽

Concentration Gradients ◽

Ambient Seawater ◽

N Transformations ◽

Isotope Tracer ◽

Chemical Gradients ◽

Nitrate Consumption ◽

N Compounds ◽

Numeric Modelling

Abstract Trichodesmium is an important dinitrogen (N2)-fixing cyanobacterium in marine ecosystems. Recent nucleic acid analyses indicate that Trichodesmium colonies with their diverse epibionts support various nitrogen (N) transformations beyond N2 fixation. However, rates of these transformations and concentration gradients of N compounds in Trichodesmium colonies remain largely unresolved. We combined isotope-tracer incubations, micro-profiling and numeric modelling to explore carbon fixation, N cycling processes as well as oxygen, ammonium and nitrate concentration gradients in individual field-sampled Trichodesmium colonies. Colonies were net-autotrophic, with carbon and N2 fixation occurring mostly during the day. Ten percent of the fixed N was released as ammonium after 12-h incubations. Nitrification was not detectable but nitrate consumption was high when nitrate was added. The consumed nitrate was partly reduced to ammonium, while denitrification was insignificant. Thus, the potential N transformation network was characterised by fixed N gain and recycling processes rather than denitrification. Oxygen concentrations within colonies were ~60–200% air-saturation. Moreover, our modelling predicted steep concentration gradients, with up to 6-fold higher ammonium concentrations, and nitrate depletion in the colony centre compared to the ambient seawater. These gradients created a chemically heterogeneous microenvironment, presumably facilitating diverse microbial metabolisms in millimetre-sized Trichodesmium colonies.

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Sm-Nd Isotope Tracer Study of UHP Metamorphic Rocks: Implications for Continental Subduction and Collisional Tectonics

International Geology Review ◽

10.1080/00206819909465175 ◽

1999 ◽

Vol 41 (10) ◽

pp. 859-885 ◽

Cited By ~ 48

Author(s):

Bor-Ming Jahn

Keyword(s):

Metamorphic Rocks ◽

Tracer Study ◽

Nd Isotope ◽

Isotope Tracer ◽

Continental Subduction

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Evaluating the effect of liming on N2O fluxes from denitrification in an Andosol using the acetylene inhibition and 15N isotope tracer methods

Biology and Fertility of Soils ◽

10.1007/s00374-017-1239-4 ◽

2017 ◽

Vol 54 (1) ◽

pp. 71-81 ◽

Cited By ~ 14

Author(s):

Ikabongo Mukumbuta ◽

Yoshitaka Uchida ◽

Ryusuke Hatano

Keyword(s):

Acetylene Inhibition ◽

15N Isotope ◽

Isotope Tracer ◽

Tracer Methods ◽

N2o Fluxes

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Effect of reference plant on estimation of nitrogen fixation by subterranean clover using 15N methods

Australian Journal of Agricultural Research ◽

10.1071/ar9850663 ◽

1985 ◽

Vol 36 (5) ◽

pp. 663 ◽

Cited By ~ 21

Author(s):

SF Ledgard ◽

JR Simpson ◽

JR Freney ◽

FJ Bergersen

Keyword(s):

Isotope Dilution ◽

Subterranean Clover ◽

Trifolium Subterraneum ◽

15N Isotope Dilution ◽

Soil N ◽

15N Isotope ◽

Reference Plant ◽

Reconstituted Soil ◽

Isotope Technique ◽

Indigenous Plant

Subterranean clover (Trifolium subterraneum L.) was grown in separate associations with annual ryegrass (Lolium rigidum Gaud.) and with phalaris (Phalaris aguatica L.) in reconstituted soil profiles (0-400 mm depth), and N2 fixation was measured by 15N isotope dilution and 15N natural abundance methods. In all experiments, two values were determined, viz. P, the percentage of clover nitrogen (N) iixed from atmospheric N2, and R, the ratio of N assimilated from added 15N-labelled N to N assimilated from indigenous soil N. Estimates of P that were negative were obtained for the clover/phalaris association, using 15N isotope dilution, during the first 16 days after 15N addition. This was due to the R value being higher for clover than for phalaris, which in turn was due to differences in their temporal pattern of growth interacting with a declining ISN enrichment of the plant-available soil N. The R values for clover and ryegrass, when grown together, were similar throughout the experiment, and estimates of P by 15N isotope dilution and natural 15N abundance were similar. The activity of plant roots in different soil layers was examined by injecting a solution of 15N-labelled nitrate at 50, 150 and 300 mm depths. Uptake of 15N was similar at all depths for phalaris and clover, whereas ryegrass assimilated a greater amount at 150 and 300 mrn. However, since the amounts of roots and indigenous plant-available soil N were small in the 100-400 mm zone relative to the 0-100 mm zone, the greater activity of ryegrass roots at depth had no significant effect on the estimates of P. In both plant associations, the estimates of P, by both of the 15N methods, increased with time, and were higher in the clover/ryegrass association than with clover/phalaris. Since this was associated with lower levels of inorganic soil N in the clover/ryegrass association, it must be recognized that the reference plant can induce real changes in P by influencing the soil N status, in the association, as well as causing erroneous estimates of P by the 15N isotope technique.

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The simulated N deposition accelerates net N mineralization and nitrification in a tropical forest soil

Biogeosciences ◽

10.5194/bg-16-4277-2019 ◽

2019 ◽

Vol 16 (21) ◽

pp. 4277-4291

Author(s):

Yanxia Nie ◽

Xiaoge Han ◽

Jie Chen ◽

Mengcen Wang ◽

Weijun Shen

Keyword(s):

N Deposition ◽

Functional Genes ◽

Net N Mineralization ◽

Soil N ◽

Wet Season ◽

Inorganic N ◽

N Transformations ◽

N Transformation ◽

Soil N Transformation ◽

N Additions

Abstract. Elevated nitrogen (N) deposition affects soil N transformations in the N-rich soil of tropical forests. However, the change in soil functional microorganisms responsible for soil N cycling remains largely unknown. Here, we investigated the variation in soil inorganic N content, net N mineralization (Rm), net nitrification (Rn), inorganic N leaching (Rl), N2O efflux and N-related functional gene abundance in a tropical forest soil over a 2-year period with four levels of N addition. The responses of soil net N transformations (in situ Rm and Rn) and Rl to N additions were negligible during the first year of N inputs. The Rm, Rn, and Rl increased with the medium nitrogen (MN) and high nitrogen (HN) treatments relative to the control treatments in the second year of N additions. Furthermore, the Rm, Rn, and Rl were higher in the wet season than in the dry season. The Rm and Rn were mainly associated with the N addition-induced lower C:N ratio in the dry season but with higher microbial biomass in the wet season. Throughout the study period, high N additions increased the annual N2O emissions by 78 %. Overall, N additions significantly facilitated Rm, Rn, Rl and N2O emission. In addition, the MN and HN treatments increased the ammonia-oxidizing archaea (AOA) abundance by 17.3 % and 7.5 %, respectively. Meanwhile, the HN addition significantly increased the abundance of nirK denitrifiers but significantly decreased the abundance of ammonia-oxidizing bacteria (AOB) and nosZ-containing N2O reducers. To some extent, the variation in functional gene abundance was related to the corresponding N-transformation processes. Partial least squares path modelling (PLS-PM) indicated that inorganic N contents had significantly negative direct effects on the abundances of N-related functional genes in the wet season, implying that chronic N deposition would have a negative effect on the N-cycling-related microbes and the function of N transformation. Our results provide evidence that elevated N deposition may impose consistent stimulatory effects on soil N-transformation rates but differentiated impacts on related microbial functional genes. Long-term experimentation or observations are needed to decipher the interrelations between the rate of soil N-transformation processes and the abundance or expression of related functional genes.

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