| 1. |
- Brackin, Richard, et al.
(författare)
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Nitrogen fluxes at the root-soil interface show a mismatch of nitrogen fertilizer supply and sugarcane root uptake capacity
- 2015
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 5
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Tidskriftsartikel (refereegranskat)abstract
- Globally only approximate to 50% of applied nitrogen (N) fertilizer is captured by crops, and the remainder can cause pollution via runoff and gaseous emissions. Synchronizing soil N supply and crop demand will address this problem, however current soil analysis methods provide little insight into delivery and acquisition of N forms by roots. We used microdialysis, a novel technique for in situ quantification of soil nutrient fluxes, to measure N fluxes in sugarcane cropping soils receiving different fertilizer regimes, and compare these with N uptake capacities of sugarcane roots. We show that in fertilized sugarcane soils, fluxes of inorganic N exceed the uptake capacities of sugarcane roots by several orders of magnitude. Contrary, fluxes of organic N closely matched roots' uptake capacity. These results indicate root uptake capacity constrains plant acquisition of inorganic N. This mismatch between soil N supply and root N uptake capacity is a likely key driver for low N efficiency in the studied crop system. Our results also suggest that (i) the relative contribution of inorganic N for plant nutrition may be overestimated when relying on soil extracts as indicators for root-available N, and (ii) organic N may contribute more to crop N supply than is currently assumed.
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| 2. |
- Ganeteg, Ulrika, et al.
(författare)
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Amino acid transporter mutants of Arabidopsis provides evidence that a non-mycorrhizal plant acquires organic nitrogen from agricultural soil
- 2017
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Ingår i: Plant, Cell and Environment. - : Wiley. - 0140-7791 .- 1365-3040. ; 40, s. 413-423
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Tidskriftsartikel (refereegranskat)abstract
- Although organic nitrogen (N) compounds are ubiquitous in soil solutions, their potential role in plant N nutrition has been questioned. We performed a range of experiments on Arabidopsis thaliana genetically modified to enhance or reduce root uptake of amino acids. Plants lacking expression of the Lysine Histidine Transporter 1 (LHT1) displayed significantly lower contents of C-13 and N-15 label and of U-C-13(5),N-15(2) L-glutamine, as determined by liquid chromatography-mass spectrometry when growing in pots and supplied with dually labelled L-glutamine compared to wild type plants and LHT1-overexpressing plants. Slopes of regressions between accumulation of C-13-labelled carbon and N-15-labelled N were higher for LHT1-overexpressing plants than wild type plants, while plants lacking expression of LHT1 did not display a significant regression between the two isotopes. Uptake of labelled organic N from soil tallied with that of labelled ammonium for wild type plants and LHT1-overexpressing plants but was significantly lower for plants lacking expression of LHT1. When grown on agricultural soil plants lacking expression of LHT1 had the lowest, and plants overexpressing LHT1 the highest C/N ratios and natural N-15 abundance suggesting their dependence on different N pools. Our data show that LHT1 expression is crucial for plant uptake of organic N from soil.Brief Summary We studied the potential role of organic nitrogen (N) for plant N nutrition by feeding dual-labelled glutamine to soil-grown Arabidopsis thaliana mutants with enhanced or impeded expression of the amino-acid transporter LHT1. Significant differences between the genotypes in root contents of labelled glutamine and of N-15 and C-13 validate that it is the glutamine per se that is taken up by the root and not some product derived from it by microbial activity. Our results demonstrate that a non-mycorrhizal plant accesses organic N in competition with soil microbes and that expression of root organic N transporters is decisive for the efficacy of this process.
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| 3. |
- Hasselquist, Niles, et al.
(författare)
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Greater carbon allocation to mycorrhizal fungi reduces tree nitrogen uptake in a boreal forest
- 2016
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Ingår i: Ecology. - : Wiley. - 0012-9658 .- 1939-9170. ; 97:4, s. 1012-1022
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Tidskriftsartikel (refereegranskat)abstract
- The central role that ectomycorrhizal (EM) symbioses play in the structure and function of boreal forests pivots around the common assumption that carbon (C) and nitrogen (N) are exchanged at rates favorable for plant growth. However, this may not always be the case. It has been hypothesized that the benefits mycorrhizal fungi convey to their host plants strongly depends upon the availability of C and N, both of which are rapidly changing as a result of intensified human land use and climate change. Using large-scale shading and N addition treatments, we assessed the independent and interactive effects of changes in C and N supply on the transfer of N in intact EM associations with similar to 15 yr. old Scots pine trees. To assess the dynamics of N transfer in EM symbioses, we added trace amounts of highly enriched (NO3-)-N-15 label to the EM-dominated mor-layer and followed the fate of the N-15 label in tree foliage, fungal chitin on EM root tips, and EM sporocarps. Despite no change in leaf biomass, shading resulted in reduced tree C uptake, ca. 40% lower fungal biomass on EM root tips, and greater N-15 label in tree foliage compared to unshaded control plots, where more N-15 label was found in fungal biomass on EM colonized root tips. Short-term addition of N shifted the incorporation of N-15 label from EM fungi to tree foliage, despite no significant changes in below-ground tree C allocation to EM fungi. Contrary to the common assumption that C and N are exchanged at rates favorable for plant growth, our results show for the first time that under N-limited conditions greater C allocation to EM fungi in the field results in reduced, not increased, N transfer to host trees. Moreover, given the ubiquitous nature of mycorrhizal symbioses, our results stress the need to incorporate mycorrhizal dynamics into process-based ecosystem models to better predict forest C and N cycles in light of global climate change.
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| 4. |
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| 5. |
- Inselsbacher, Erich
(författare)
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A novel N-15 tracer model reveals: Plant nitrate uptake governs nitrogen transformation rates in agricultural soils
- 2013
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Ingår i: Soil Biology and Biochemistry. - : Elsevier BV. - 0038-0717 .- 1879-3428. ; 57, s. 301-310
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Tidskriftsartikel (refereegranskat)abstract
- One major challenge in agriculture is improving the nitrogen (N) use efficiency of crop plants and at the same time reducing the losses of fertilizer N to the environment. The use of N-15 tracer studies in combination with process-based models has been proven to be a powerful tool for increasing our understanding of the dynamic interactions between soil, microbes and plants. Here we present a novel approach that includes plant uptake of fertilizer NH4+ and NO3-. We developed, evaluated and applied an analytical model allowing the simultaneous estimation of 14 processes within the N cycle using results from a previously published N-15 tracer study (Inselsbacher, E., Hinko-Najera Umana, N., Stange, P.C., Gorfer, M., Schuller, E., Ripka, K., Zechmeister-Boltenstern, S., Flood-Novotny, R., Strauss, J., Wanek, W., 2010. Short-term competition between crop plants and soil microbes for inorganic N fertilizer. Soil Biology & Biochemistry 42, 360-372]. The model revealed that plant NO3- uptake governed the overall N cycle during the 8-days greenhouse study. Nitrification was the main fate of NH4+ but its kinetics differed significantly between soils. The model-based calculations proved to be a major advancement compared to the commonly used calculations based on the pool dilution technique, due to the number of estimated parameters, their respective kinetic shifts over prolonged time periods and their explanatory power. In future N-15 tracer studies this analytical tool will allow accounting for the effect of plant N uptake on soil N transformations. (C) 2012 Elsevier Ltd. All rights reserved.
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| 6. |
- Inselsbacher, Erich
(författare)
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Alternative Methods for Measuring Inorganic, Organic, and Total Dissolved Nitrogen in Soil
- 2010
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Ingår i: Soil Science Society of America Journal. - : Wiley. - 0361-5995 .- 1435-0661. ; 74, s. 1018-1027
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Tidskriftsartikel (refereegranskat)abstract
- There are numerous methods for measuring inorganic, dissolved organic, and microbial N in soils, although many of these are complex or require expensive equipment. We have modified methods for the measurement of NH(4)(+), NO(3)(-), total dissolved N (TDN), and soil microbial biomass N (SMBN) in soils. The methods are based on a microtiter plate format and are rapid and simple to perform. Ammonium is quantified by a colorimetric method based on the Berthelot reaction. Total dissolved N and SMBN (by CH(3)Cl fumigation-extraction) are quantified as NO(3)(-) after alkaline persulfate oxidation. Nitrate is estimated directly or after persulfate oxidation by reduction of NO(3)(-) to NO(2)(-) by VCl(3) and subsequent colorimetric determination of NO(2)(-) by acidic Griess reaction. The new suite of methods was compared with conventional methods such as high-performance anion-exchange chromatography for NO(3)(-) and high-temperature catalytic oxidation for TDN. Our methods produced comparable detection limits, linearities, and precisions compared with the conventional methods. Limits of quantification were 7 mu g NH(4)(+)-N L(-1), 55 mu g NO(3)(+)-N L(-1), and 0.275 mg TDN L(-1). The accuracy of the proposed methods was excellent, with recoveries of added NH(4)(+), NO(3)(-), and glycine ranging between 96 and 99%. Linearities of the respective calibrations were high (R(2) > 0.99), and precisions for NH(4)(+) (CV = 2.1%), NO(3)(-) (CV = 3.5%), and TDN (CV = 3.9%) were comparable to the reference methods. The simplicity, rapidity, and low cost of the proposed methods therefore allow an expansion of the scope and range of N cycle studies where sophisticated instrumentation is not available.
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| 7. |
- Inselsbacher, Erich, et al.
(författare)
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Early season dynamics of soil nitrogen fluxes in fertilized and unfertilized boreal forests
- 2014
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Ingår i: Soil Biology and Biochemistry. - : Elsevier BV. - 0038-0717 .- 1879-3428. ; 74, s. 167-176
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Tidskriftsartikel (refereegranskat)abstract
- The supply of soil nitrogen (N) for plant uptake largely controls plant growth and has a major impact on a wide range of biogeochemical processes in terrestrial ecosystems. The soil solution typically contains a large variety of N forms and recent evidence suggests that the share of amino acids to soil N fluxes dominates over inorganic N in boreal forest soils. In this study we applied a microdialysis technique to investigate in-situ induced diffusive fluxes across microdialysis membranes (F-MD) in fertilized and nonfertilized boreal forest sites in early spring, at the onset of plant growth. We studied temporal shifts of FmD at short (minutes to hours) and prolonged time-scales (hours to days). We also estimated N pools in soil water and KCl extracts and critically evaluated the significance of results depending on the method chosen. Our results indicate that F(MD)of boreal forest soil is dominated by amino acids in early spring and that growing roots should encounter the full range of organic and inorganic N forms in these soils. In contrast, soil water and KCl extracts were dominated by NH4+ Some amino acids displayed rapidly declining F-MD (<1 h) possibly due to the rapid formation of a depletion zone near the membrane surface but the F-MD of most amino acids remained high and unchanged over extended periods of dialysis indicating that these soils provide a continuous supply of amino acids for root uptake. Forest fertilization with NH4NO3 led to a significant increase in F-MD of NO3- and NH4+, with F-MD of NH4+ but not of NO3- remaining high for prolonged time. A separate trial with addition of NO3- showed a significantly slower decline of F-MD in soils of previously fertilized forests compared to unfertilized forests, suggesting biological immobilization being a major cause of rapid decline of nitrate fluxes. Our results corroborate earlier studies suggesting amino acids to be a significant fraction of plant available N in boreal forests. They also suggest that, besides inorganic N, roots may encounter a wide spectrum of amino acids after intercepting new soil microsites and that most, but not all, amino acids may be constantly replenished at the root surface. Further, from our results we conclude that detailed insights into in-situ N dynamics of soils can be gained through microdialysis. (C) 2014 Elsevier Ltd. All rights reserved.
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| 8. |
- Inselsbacher, Erich
(författare)
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Greenhouse gas fluxes respond to different N fertilizer types due to altered plant-soil-microbe interactions
- 2011
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Ingår i: Plant and Soil. - : Springer Science and Business Media LLC. - 0032-079X .- 1573-5036. ; 343, s. 17-35
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Tidskriftsartikel (refereegranskat)abstract
- The application of inorganic nitrogen (N) fertilizers strongly influences the contribution of agriculture to the greenhouse effect, especially by potentially increasing emissions of nitrous oxide (N(2)O), carbon dioxide (CO(2)) and methane (CH(4)) from soils. The present microcosm-study investigates the effect of different forms of inorganic N fertilizers on greenhouse gas (GHG) emissions from two different agricultural soils. The relationship between greenhouse gas emissions and soil microbial communities, N transformation rates and plant (Hordeum vulgare L. cv. Morex) growth were investigated. Repeated N fertilization led to increased N(2)O emissions. In a parallel survey of functional microbial population dynamics we observed a stimulation of bacterial and archaeal ammonia oxidisers accompanied with these N(2)O emissions. The ratio of archaeal to bacterial ammonium monooxygenase subunit A (amoA) gene copies (data obtained from Inselsbacher et al., 2010) correlated positively with N(2)O fluxes, which suggests a direct or indirect involvement of archaea in N(2)O fluxes. Repeated N fertilization also stimulated methane oxidation, which may also be related to a stimulation of ammonia oxidizers. The fertilizer effects differed between soil types: In the more organic Niederschleinz soil N-turnover rates increased more strongly after fertilization, while in the sandy Purkersdorf soil plant growth and soil respiration were accelerated depending on fertilizer N type. Compared to addition of NH (4) (+) and NO (3) (-) , addition of NH(4)NO(3) fertilizer resulted in the largest increase in global warming potential as a summary indicator of all GHG related effects. This effect resulted from the strongest increase of both N(2)O and CO(2) emission while plant growth was not equally stimulated, compared to e.g. KNO(3) fertilization. In order to decrease N losses from agricultural ecosystems and in order to minimize soil derived global warming potential, this study points to the need for interdisciplinary investigations of the highly complex interactions within plant-soil-microbe-atmosphere systems. By understanding the microbial processes underlying fertilizer effects on GHG emissions the N use efficiency of crops could be refined.
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| 9. |
- Inselsbacher, Erich
(författare)
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Recovery of individual soil nitrogen forms after sieving and extraction
- 2014
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Ingår i: Soil Biology and Biochemistry. - : Elsevier BV. - 0038-0717 .- 1879-3428. ; 71, s. 76-86
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Tidskriftsartikel (refereegranskat)abstract
- Plant biomass production and species composition is largely regulated by the availability of soil nitrogen (N). Detailed knowledge about the concentrations and composition of soil N pools are crucial for better understanding plant N nutrition. One commonly applied method to characterize soil N pools is the extraction of soil with water or salt solutions. The apparent problem with this sampling technique is the disruption of the soil matrix and the natural equilibrium of soil N pools during sampling and sample handling. Sieving and homogenizing soils as well as the extraction procedure itself are known to alter soil N composition through transformations, losses and contamination. Until now, however, information on the impact of soil extraction on individual N forms is scarce. This study therefore aimed at estimating the effect of sieving and extraction with water or KCl on NH4+, NO3- and individual amino acids. Nine different soils including boreal forest, agricultural and grassland soils were used for a series of experiments. In detail, after initial estimation of inorganic N and amino acid pools in extracts, in two separate experiments a small amount of standard solution containing NH4+, NO3- and amino acids was added either directly to the extractant or to the soils before sieving and extraction and, subsequently, the recovery of standard added was determined. I found that a significant proportion of amino acids were not recovered in any of the treatments and, conversely, there was a significant increase of inorganic N. Sieving and extracting generally led to a lower recovery of amino acids and a stronger increase of inorganic N than extraction only. The recovery of individual N forms strongly depended on soil type, extractant and N form, indicating that a comparison of results from soil extractions between different soils should be done with care. Still, soil extraction can provide valuable information on total plant-available N, as the sum of N added could largely be recovered in all soils and treatments. Future studies investigating the availability of individual N forms in soil for plant uptake should be aware of possible errors introduced during sample handling to avoid misinterpretation. (C) 2014 Elsevier Ltd. All rights reserved.
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| 10. |
- Inselsbacher, Erich, et al.
(författare)
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The below-ground perspective of forest plants: soil provides mainly organic nitrogen for plants and mycorrhizal fungi
- 2012
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Ingår i: New Phytologist. - : Wiley. - 0028-646X .- 1469-8137. ; 195, s. 329-334
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Tidskriftsartikel (refereegranskat)abstract
- Nitrogen (N) availability has a major impact on a wide range of biogeochemical processes in terrestrial ecosystems. Changes in N availability modify the capacity of plants to sequester carbon (C), but despite the crucial importance for our understanding of terrestrial ecosystems, the relative contribution of different N forms to plant N nutrition in the field is not known. Until now, reliably assessing the highly dynamic pool of plant-available N in soil microsites was virtually impossible, because of the lack of adequate sampling techniques. For the first time we have applied a novel microdialysis technique for disturbance-free monitoring of diffusive fluxes of inorganic and organic N in 15 contrasting boreal forest soils in situ. We found that amino acids accounted for 80% of the soil N supply, while ammonium and nitrate contributed only 10% each. In contrast to common soil extractions, microdialysis revealed that the majority of amino acids are available for plant and mycorrhizal uptake. Our results suggest that the N supply of boreal forest soils is dominated by organic N as a major component of plant-available N and thus as a regulator of growth and C sequestration.
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