| 1. |
- Aguetoni Cambui, Camila, et al.
(författare)
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Patterns of Plant Biomass Partitioning Depend on Nitrogen Source
- 2011
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Ingår i: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 6
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Tidskriftsartikel (refereegranskat)abstract
- Nitrogen (N) availability is a strong determinant of plant biomass partitioning, but the role of different N sources in this process is unknown. Plants inhabiting low productivity ecosystems typically partition a large share of total biomass to belowground structures. In these systems, organic N may often dominate plant available N. With increasing productivity, plant biomass partitioning shifts to aboveground structures, along with a shift in available N to inorganic forms of N. We tested the hypothesis that the form of N taken up by plants is an important determinant of plant biomass partitioning by cultivating Arabidopsis thaliana on different N source mixtures. Plants grown on different N mixtures were similar in size, but those supplied with organic N displayed a significantly greater root fraction. (15)N labelling suggested that, in this case, a larger share of absorbed organic N was retained in roots and split-root experiments suggested this may depend on a direct incorporation of absorbed amino acid N into roots. These results suggest the form of N acquired affects plant biomass partitioning and adds new information on the interaction between N and biomass partitioning in plants.
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| 2. |
- Blackburn, Meredith, et al.
(författare)
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Evaluating hillslope and riparian contributions to dissolved nitrogen (N) export from a boreal forest catchment
- 2017
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Ingår i: Journal of Geophysical Research: Biogeosciences. - : AMER GEOPHYSICAL UNION. - 2169-8953 .- 2169-8961. ; 122, s. 324-339
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Tidskriftsartikel (refereegranskat)abstract
- Catchment science has long held that the chemistry of small streams reflects the landscapes they drain. However, understanding the contribution of different landscape units to stream chemistry remains a challenge which frequently limits our understanding of export dynamics. For limiting nutrients such as nitrogen (N), an implicit assumption is that the most spatially extensive landscape units (e.g., uplands) act as the primary sources to surface waters, while near-stream zones function more often as sinks. These assumptions, based largely on studies in high-gradient systems or in regions with elevated inputs of anthropogenic N, may not apply to low-gradient, nutrient-poor, and peat-rich catchments characteristic of many northern ecosystems. We quantified patterns of N mobilization along a hillslope transect in a northern boreal catchment to assess the extent to which organic matter-rich riparian soils regulate the flux of N to streams. Contrary to the prevailing view of riparian functioning, we found that near-stream, organic soils supported concentrations and fluxes of ammonium (NH4+) and dissolved organic nitrogen that were much higher than the contributing upslope forest soils. These results suggest that stream N chemistry is connected to N mobilization and mineralization within the riparian zone rather than the wider landscape. Results further suggest that water table fluctuation in near-surface riparian soils may promote elevated rates of net N mineralization in these landscapes.
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| 3. |
- Boberg, Johanna, et al.
(författare)
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Nitrogen availability affects saprotrophic basidiomycetes decomposing pine needles in a long term laboratory study
- 2011
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Ingår i: Fungal Ecology. - : Elsevier BV. - 1754-5048 .- 1878-0083. ; 4, s. 408-416
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Tidskriftsartikel (refereegranskat)abstract
- Fungi, especially basidiomycetous litter decomposers, are pivotal to the turnover of soil organic matter in forest soils. Many litter decomposing fungi have a well-developed capacity to translocate resources in their mycelia, a feature that may significantly affect carbon (C) and nitrogen (N) dynamics in decomposing litter. In an eight-month long laboratory study we investigated how the external availability of N affected the decomposition of Scots pine needles, fungal biomass production, N retention and N-mineralization by two litter decomposing fungi - Marasmius androsaceus and Mycena epipterygia. Glycine additions had a general, positive effect on fungal biomass production and increased accumulated needle mass loss after 8 months, suggesting that low N availability may limit fungal growth and activity in decomposing pine litter. Changes in the needle N pool reflected the dynamics of the fungal mycelium. During late decomposition stages, redistribution of mycelium and N out from the decomposed needles was observed for M. epipterygia, suggesting autophagous self degradation. (C) 2011 Elsevier Ltd and The British Mycological Society. All rights reserved.
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| 4. |
- Bonner, Mark T. L., et al.
(författare)
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Why does nitrogen addition to forest soils inhibit decomposition?
- 2019
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Ingår i: Soil Biology and Biochemistry. - : Elsevier BV. - 0038-0717 .- 1879-3428. ; 137
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Tidskriftsartikel (refereegranskat)abstract
- Enrichment of forest soils with inorganic nitrogen (N) tends to inhibit oxidative enzyme expression by microbes and reduces plant litter and soil organic matter decomposition rates. Without further explanation than is currently presented in the scientific literature, we argue that upregulation of oxidative enzymes seems a more competitive response to prolonged N enrichment at high rates than the observed downregulation. Thus, as it stands, observed responses are inconsistent with predicted responses. In this article, we present a hypothesis that resolves this conflict. We suggest that high rates of N addition alter the competitive balance between enzymatic lignin mineralisation and non-enzymatic lignin oxidation. Using metatransciptomics and chemical assays to examine boreal forest soils, we found that N addition suppressed peroxidase activity, but not iron reduction activity (involved in non-enzymatic lignin oxidation). Our hypothesis seems positioned as a parsimonious and empirically consistent working model that warrants further testing.
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| 5. |
- Bonner, Mark TL., et al.
(författare)
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Those who can don't want to, and those who want to can't: An eco-evolutionary mechanism of soil carbon persistence
- 2022
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Ingår i: Soil Biology and Biochemistry. - : Elsevier. - 0038-0717 .- 1879-3428. ; 174
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Tidskriftsartikel (refereegranskat)abstract
- Reliable manipulation of soil organic matter (SOM) – a necessity for optimal land management – is constrained by our limited mechanistic understanding of SOM formation. Here we propose a novel mechanistic element that may contribute to SOM dynamics, supplementing existing frameworks, based on evolutionary-ecological rather than chemical or physical limitations to decomposition. We argue that decomposition of some substrates may be constrained by spatial competition from opportunists. We describe and test a mathematical model based on our framework, providing a proof-of-concept that substrate can, in principle, be spared decomposition and accumulate even when it is physically and chemically accessible. Our framework can help explain a variety of SOM dynamics, including priming and the suppression of decomposition by nitrogen addition, as well as the typical composition of SOM. An augmented mechanistic framework for understanding SOM dynamics can help guide targeted empirical study, which in turn can contribute to more optimised land management.
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| 6. |
- 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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| 7. |
- Buckley, Scott, et al.
(författare)
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Microdialysis as an in situ technique for sampling soil enzymes
- 2019
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Ingår i: Soil Biology and Biochemistry. - : Elsevier BV. - 0038-0717 .- 1879-3428. ; 135, s. 20-27
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Tidskriftsartikel (refereegranskat)abstract
- Soil extracellular enzyme activity (EEA) represents a critical bottleneck in the release of bioavailable nutrients from organic materials. However, quantifying spatial and temporal dynamics of EEA remains challenging. Techniques which measure the activity of, or directly sample free enzymes in situ may assist in understanding the short-term exoproteomic responses of microbes and roots to substrates, but few tools exist to explore EEA with minimal disturbance. We explore the potential of in situ microdialysis to directly sample soil enzymes, measuring their activity using a modified enzyme assay. We hypothesise that the technique's bias towards free solutes will also allow differentiation of free and stabilised enzyme pools. As little is known about the efficiency of micro dialysis to sample enzymes from soil, recovery of a protease standard was quantified from solution and soil, finding that enzyme recovery is hindered at lower soil moisture contents. We further measured the response of native protease activity after the addition of soybean litter to clay and sandy soils, finding microdialysis observed greater EEA in litter-amended treatments than controls in both soil types. In comparison, EEA as measured by conventional extraction-incubation methods was only greater in amended clay soils. In a final experiment, hydrolytic enzyme activity of free and stabilised clay soil fractions were estimated using microdialysis. Free enzymes contributed 9% of total hydrolytic activity in soil without litter, increasing to 46% in litter-amended soil, suggesting fresh litter promoted a transient increase in the production of free exoenzymes by soil microbes. In contrast, the addition of litter had no significant effect on stabilised EEA. In spite of the obvious challenges involved in applying microdialysis as a method for soil protein sampling, this method offers new possibilities for investigating challenging spatial and temporal aspects of enzyme dynamics and protein availability in soils.
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| 8. |
- Buckley, Scott, et al.
(författare)
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Microdialysis in soil environments: Current practice and future perspectives
- 2020
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Ingår i: Soil Biology and Biochemistry. - : Elsevier BV. - 0038-0717 .- 1879-3428. ; 143
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Tidskriftsartikel (refereegranskat)abstract
- Microdialysis is emerging as a sensitive tool in environmental sciences, allowing for in situ sampling of solutes with minimal disturbance to soil environments. This perspective presents the theoretical foundations and practical applications of the technique with a focus on its use in soil, microbial and plant sciences. Using small probes (usually 0.5 mm diameter) fitted with permeable membranes, soil solutes are sampled, so that solute flux (and potentially concentration) can be calculated at root-relevant scales. However, physical and biological characteristics of soil systems impose challenges to sampling efficiencies with microdialysis, particularly where solute concentrations are low. Experimental parameters such as perfusate flow rates, probe design and sampling times can also influence the findings, and reduce the comparability between studies. We explore how equipment setup and experimental conditions can be optimised for soil environments, and how standardisation and calibration techniques may improve cross-study comparability. We show that the technique's strength lies in the ability to integrate many soil factors into a biologically relevant measure of solute availability. Microdialysis has so far provided new insight regarding the bioavailability of soil nitrogen (N) and phosphorus (P), where fluxes have been related to mot uptake rates and gaseous fluxes from soil. The technique has also been used as a mot simulator, mimicking exudation of organic acids to mobilise soil P, and to measure the potential contribution of transpiration-induced mass flow on N availability at the root surface. With further development, and paired with sensitive analytical methods and equipment, microdialysis has much potential to explore fragile and dynamic soil processes in biologically-active zones such as the rhizosphere, and could contribute to solving challenges relating to under- and oversupply of nutrients to plants. We conclude that, with further advancements and critical evaluation, microdialysis could become an important instrument in the soil analysis toolkit.
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| 9. |
- Buckley, Scott, et al.
(författare)
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The influence of sucrose on soil nitrogen availability - A root exudate simulation using microdialysis
- 2022
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Ingår i: Geoderma. - : Elsevier BV. - 0016-7061 .- 1872-6259. ; 409
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Tidskriftsartikel (refereegranskat)abstract
- Root exudates are thought to promote nitrogen (N) availability via rhizosphere interactions, but empirical evidence is difficult to obtain given the scale and temporary nature of these processes. Microdialysis has potential to simulate root exudation patterns and quantify the effects on N availability simultaneously, but this has so far not been attempted. In a conceptual root exudation study, we used sucrose as a simple C source to investigate if microdialysis could detect the effects of continuous localised C supply on soil inorganic N fluxes. Through retrodialysis we released sucrose and simultaneously monitored diffusive soil N fluxes over one week, followed by a further seven days without sucrose. Based on current understanding of rhizosphere N dynamics, we hypothesised that N fluxes are inversely related to sucrose release, and upon ceasing release, N fluxes would increase. Using a 5 mM sucrose perfusate, C releases resulted in decreased N fluxes, but contrary to our hypothesis, N fluxes did not increase after ceasing sucrose release (c.f. control soil). Diffusive sucrose efflux from microdialysis probes increased in soils amended with N-rich litter suggesting that microbial activity and associated sucrose consumption altered sucrose concentration gradients. The fluxes of sucrose breakdown products glucose and fructose were greatest in litter treatments receiving sucrose, indicative of increased invertase activity in the presence of fresh organic matter. In the short term (days), sucrose release did not prompt an increase in inorganic N availability, possibly because of stimulated microbial growth and increased N demand under C-rich conditions. Our study confirms that microdialysis allows time-sensitive insight into the dynamic interactions of carbon and N in the rhizosphere.
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| 10. |
- Buckley, Scott, et al.
(författare)
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Using microdialysis with a deuterium oxide tracer to estimate water exchange, water content and active surface area of the probe
- 2023
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Ingår i: Geoderma. - 0016-7061 .- 1872-6259. ; 439
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Tidskriftsartikel (refereegranskat)abstract
- Microdialysis is a useful tool for measuring in situ fluxes of soil compounds with minimal disturbance of soil structure and function. Fluxes of sampled compounds are commonly calculated per unit of membrane surface area, assuming that the entire membrane surface is capable of exchange - which is unlikely given varying soil moisture and the occlusion of membrane pores by the soil solid phase. We present a method to quantify the degree of connectivity of the microdialysis probe membrane to the surrounding soil by means of water exchange between a microdialysis perfusate and soil solution using deuterium (2H2O; equilibrated to DHO) as an internal standard. We applied the method to a range of probe membrane surface areas and soil moisture conditions to generate empirical models that estimate membrane surface area active in exchange. Our results suggest that even in a saturated sandy soil, active membrane surface areas reach only 40.3% of the probe surface area, perhaps due to occlusion by soil particles. However, when accounting for volumetric water content of the soil, active surface areas approached 80-90% of the area likely in contact with water, indicating that sampling efficiency of waterfilled pores may still be high, particularly at slow flow rates. Furthermore, our method enables assessment of local soil water content around the probe. Models estimating soil water content were applied to field measurements of DHO exchange in three soil horizons (Organic, B1, B2) at two boreal sites, and in situ estimates were similar to those from conventional soil moisture methods when models were calibrated with the same soil type. We present DHO exchange as a powerful method for improving microdialysis flux interpretations in future studies, and for exploring small-scale water variability in relatively undisturbed soils.
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