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107 results for “Nitrogen fixation”
Effect of soil temperature on nitrogen fixation in Alnus
<p><span><span><span><span><span><span><span><span><span><span><span><i>Purpose:</i> The short growing season and cold climate of the boreal forest can restrict soil nitrogen availability, limiting plant growth and ecosystem productivity. Vascular nitrogen-fixing plants should have an advantage in low nitrogen environments. Yet, their abundance in the boreal forest is low. How nitrogen fixation is affected when temperature differences occur between the soil and air, especially in the spring when soil temperatures remain cool, has not been documented in actinorhizal shrubs.</span></span></span></span></span></span></span></span></span></span></span></p> <p><span><span><span><span><span><span><span><span><span><span><span><i>Methods:</i> A lab study was performed on <i>Alnus alnobetula</i> subsp. <i>crispa</i> (Aiton) Raus. For 13 weeks, soil was kept at either 10˚C, 14˚C or 16˚C, independently of shoot temperature, at 20˚C.</span></span></span></span></span></span></span></span></span></span></span></p> <p><span><span><span><span><span><span><span><span><span><span><span><i>Results:</i> Soils at 14˚C and 10˚C inhibited whole-plant nitrogen fixation (by 53% and 68%) and photosynthesis (by 43% and 39%), respectively, compared to soils at 16˚C. Reductions in photosynthetic rate were mainly attributed to a reduction in the fixed nitrogen supply and subsequent reduction in chlorophyll formation. Photosynthesis was not reduced immediately, suggesting some utilization of a nitrogen source not supplied from current fixation. Reduced amounts of fixed nitrogen and photosynthates resulted in diminished biomass production and relative growth rate.</span></span></span></span></span></span></span></span></span></span></span></p> <p><span><span><span><span><span><span><span><span><span><span><span><i>Conclusion:</i> The assumed advantages of being a nitrogen-fixing plant in a low nitrogen environment may be constrained by soil temperature to a larger extent than previously considered. This may restrict the abundance of nitrogen-fixing species in the boreal forest. </span></span></span></span></span></span></span></span></span></span></span></p>
Modeling cyanobacteria life cycle dynamics and historical nitrogen fixation in the Baltic Proper - Datasets
<p>Observational and model datasets used in: Modeling cyanobacteria life cycle dynamics and historical nitrogen fixation in the Baltic Proper.</p>
Data for: Tree symbioses sustain nitrogen fixation despite excess nitrogen supply
<p>Symbiotic nitrogen fixation (SNF) is a key ecological process whose impact depends on the strategy of SNF regulation – the degree to which rates of SNF change in response to limitation by N vs. other resources. SNF that is obligate or exhibits incomplete down-regulation can result in excess N fixation, whereas a facultative SNF strategy does not. We hypothesized that tree-based SNF strategies differed by latitude (tropical vs temperate) and symbiotic type (actinorhizal vs rhizobial). Specifically, we expected tropical rhizobial symbioses to display strongly facultative SNF as an explanation for their success in low-latitude forests. In this study, we used <sup>15</sup>N isotope dilution field experiments in New York, Oregon, and Hawaii to determine SNF strategies in six N-fixing tree symbioses. Nitrogen fertilization with +10 and +15 g N m<sup>-2</sup> y<sup>-1</sup> for 4-5 years alleviated N limitation in all taxa, paving the way to determine SNF strategies. Contrary to our hypothesis, all six of the symbioses we studied sustained SNF even at high N. <em>Robinia</em> <em>pseudoacacia</em> (temperate rhizobial) fixed 91% of its N (%N<sub>dfa</sub>) in controls, compared to 64% and 59% in the +10 and +15 g N m<sup>-2</sup> y<sup>-1</sup> treatments. For <em>Alnus</em> <em>rubra</em> (temperate actinorhizal), %N<sub>dfa</sub> was 95%, 70%, and 60%. For the tropical species, %N<sub>dfa</sub> was 86%, 80%, and 82% for <em>Gliricidia</em> <em>sepium</em> (rhizobial); 79%, 69%, and 67% for <em>Casuarina</em> <em>equisetifolia</em> (actinorhizal); 91%, 42%, and 67% for <em>Acacia</em> <em>koa</em> (rhizobial), and 60%, 51%, and 19% for <em>Morella</em> <em>faya</em> (actinorhizal). Fertilization with phosphorus did not stimulate tree growth or SNF. These results suggest that the latitudinal abundance distribution of N-fixing trees is not caused by a shift in SNF strategy. They also help explain the excess N in many forests where N-fixers are common. In addition to influencing community dynamics and rates of nutrient cycling, excess N accumulation and export from sustained SNF may exacerbate water pollution and greenhouse gas fluxes.</p>
Symbiotic nitrogen fixation does not stimulate soil phosphatase activity under temperate and tropical trees
<p>Symbiotic nitrogen (N)-fixing plants can enrich ecosystems with N, which can alter the cycling and demand for other nutrients. Researchers have hypothesized that fixed N could be used by plants and soil microbes to produce extracellular phosphatase enzymes, which release P from organic matter. Consistent with this speculation, the presence of N-fixing plants is often associated with high phosphatase activity, either in the soil or on root surfaces, although other studies have not found this association, and the connection between phosphatase and rates of N fixation—the mechanistic part of the argument—is tenuous. Here, we measured soil phosphatase activity under N-fixing trees and non-fixing trees transplanted and grown in tropical and temperate sites in the USA: two sites in Hawaii, and one each in New York and Oregon. This provides a rare example of phosphatase activity measured in a multi-site field experiment with rigorously quantified rates of N fixation. We found no difference in soil phosphatase activity under N-fixing vs. non-fixing trees nor across rates of N fixation, though we note that no sites were P limited and only one was N limited. Our results add to the literature showing no connection between N fixation rates and phosphatase activity.</p>
Nitrogen fixation in the Indian Ocean
<p>Dinitrogen (N2) fixation rates measured in the Indian Ocean, collected from previously published papers. The dataset contains 241 volumetric rates (units nmol N l-1 d-1), 89 depth-integrated rates (units µmol N l-1 d-1) and metadata (including temperature, salinity, inorganic nutrient and chlorophyll concentrations) when available in the original publications.</p> <p> </p> <p>Basin-scale N<sub>2</sub> fixation rates calculations were done as follows:</p> <ol> <li>Depth-integrated rates from the literature are listed and classified according to sub-basin and season</li> <li>The arithmetic mean, geometric mean and median are calculated for each sub-basin and season</li> <li>Means and median are extrapolated to the area of each sub-basin considering the duration (days) of each season</li> <li>Sub-basin seasonal rates are summed for each sub-basin to obtain sub-basin yearly rates</li> <li>Sub-basin yearly rates are summed to obtain basin-scale (i.e., all the Indian Ocean) rates</li> </ol>
Data from: Rapid nitrogen fixation by canopy microbiome in tropical forest determined by both phosphorus and molybdenum
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Data from: Nitrogen fixation and fertilization have similar effects on biomass allocation in nitrogen-fixing plants
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Data from: Disentangling the variability of symbiotic nitrogen fixation rate and the controlling factors
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Data for: Tree symbioses sustain nitrogen fixation despite excess nitrogen supply
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Phosphorus controls symbiotic nitrogen fixation in fire-dependent longleaf pine savannas
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Aphid infestation differently affects the defences of nitrate-fed and nitrogenfixing Medicago truncatula and alters symbiotic nitrogen fixation
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Data from: More diverse rhizobial communities can lead to higher symbiotic nitrogen fixation rates, even in nitrogen-rich soils
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Effect of soil temperature on nitrogen fixation in Alnus
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Symbiotic nitrogen fixation does not stimulate soil phosphatase activity under temperate and tropical trees
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Data from: Environmental change alters nitrogen fixation rates and microbial parameters in a subarctic biological crust
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Time series measurements of nitrogen fixation in the subtropical North Pacific
<p>Rates of N<sub>2</sub> fixation were measured using the <sup>15</sup>N<sub>2</sub> isotopic tracer technique. Sampling occurred during near-monthly Hawaii Ocean Time-series cruises. Whole seawater samples from six discrete depths (5, 25, 45, 75, 100, and 125 m) were subsampled into acid-washed 4.3 L polycarbonate bottles. Between June 2005 and May 2012, 3 mL of <sup>15</sup>N<sub>2</sub> gas was injected into each bottle. Beginning in August 2012, the <sup>15</sup>N<sub>2</sub> gas was first dissolved into seawater and 100 mL of the resulting <sup>15</sup>N<sub>2</sub>-enriched water was added to 4.3 L polycarbonate sampling bottles. The resulting atom % enrichment of stocks of <sup>15</sup>N<sub>2</sub>-enriched seawater was measured using a membrane inlet mass spectrometer. Incubation bottles amended with the <sup>15</sup>N<sub>2</sub> tracer were attached to a free-drifting array and incubated at the discrete depths from which samples had been collected. The array was deployed before dawn and samples were incubated at in situ light and temperature for 24 h. After recovery of the array, the entire volume from each bottle was filtered onto a pre-combusted glass microfiber filter (Whatman 25 mm GF/F) and filters were placed onto pre-combusted pieces of foil in Petri dishes and stored frozen at -20°C. Filters were dried for 24 h at 60°C, pelleted, and the total mass of N and its isotopic signature on each filter were analyzed on an elemental analyzer-isotope ratio mass spectrometer (Carlo-Erba EA NC2500 coupled with ThermoFinnigan Delta S). </p>
Data from: Drought and soil nutrients effects on symbiotic nitrogen fixation in seedlings from eight Neotropical legume species
<p>Symbiotic nitrogen fixation is a dominant source of nitrogen to many terrestrial ecosystems, and thus may influence their responses to global change. High legume species diversity and abundance are thought to lead to high rates of symbiotic nitrogen fixation in Neotropical forests. However, how changes in water and nutrient availability will affect symbiotic nitrogen fixation have only recently been explored, even as droughts begin to increase in severity and frequency in the Neotropics. To explore these effects, we grew eight species of Neotropical woody legume seedlings in a shadehouse for four months while manipulating soil water, phosphorus and molybdenum availability. Overall, drought reduced nodule biomass, nitrogenase activity (acetylene reduction g<sup>-1</sup> nodule), and acetylene reduction per seedling by 33%, 27%, and 41%, respectively, but reduced seedling biomass by only 18%. Species varied in the manifestation of drought effects. For example, drought reduced the probability that nodules formed in some species, but in others reduced the nitrogenase activity or acetylene reduction per seedling. In contrast, the effects of phosphorus and molybdenum availability were more species-specific. However, fertilization did affect (both positively and negatively) one or more symbiotic nitrogen fixation response variables in two of the eight species. Our results indicate drought reduces symbiotic nitrogen fixation in Neotropical legume seedlings, but the mechanism of response may be species-specific. Therefore, predicting the response of symbiotic nitrogen fixation in the Neotropics to a changing climate, with expected increases in drought frequency and severity, may require grappling with the diversity of responses among nitrogen-fixing legumes.</p>
Nitrogen economy of alpine plants on the north Tibetan Plateau: nitrogen conservation by resorption rather than open sources through biological symbiotic fixation
<p>Nitrogen (N) is one of the most important factors limiting plant productivity, and N fixation by legume species is an important source of N input into ecosystems. Meanwhile, N resorption from senescent plant tissues conserves nutrients taken up in the current season, which may alleviate ecosystem N limitation. N fixation was assessed by the <sup>15</sup>N dilution technique in four types of alpine grasslands along the precipitation and soil nutrient gradients. The N resorption efficiency (NRE) was also measured in these alpine grasslands. The aboveground biomass in the alpine meadow was 4–6 times higher than in the alpine meadow-steppe, alpine steppe, and alpine desert-steppe. However, the proportion of legume species to community biomass in the alpine steppe and the alpine desert steppe was significantly higher than the proportion in the alpine meadow. N fixation by the legume plants in the alpine meadow was 0.236 g N m<sup>-2</sup>, which was significantly higher than N fixation in other alpine grasslands (0.041 to 0.089 g N m<sup>-2</sup>). The NRE in the alpine meadows was lower than in the other three alpine grasslands. Both the aboveground biomass and N fixation of the legume plants showed decreasing trends with the decline of precipitation and soil N gradients from east to west, while the NRE of alpine plants showed increasing trends along the gradients, which indicates that alpine plants enhance the NRE to adapt to the increasing droughts and nutrient-poor environments. The opposite trends of N fixation and NRE along the precipitation and soil nutrient gradients indicate that alpine plants adapt to precipitation and soil nutrient limitation by promoting NRE (conservative nutrient use by alpine plants) rather than biological N fixation (open sources by legume plants) on the north Tibetan Plateau.</p>
Data from: Assessing the effects of iron enrichment across holobiont compartments reveals reduced microbial nitrogen fixation in the Red Sea coral Pocillopora verrucosa
The productivity of coral reefs in oligotrophic tropical waters is sustained by an efficient uptake and recycling of nutrients. In reef-building corals, the engineers of these ecosystems, this nutrient recycling is facilitated by a constant exchange of nutrients between the animal host and endosymbiotic photosynthetic dinoflagellates (zooxanthellae), bacteria, and other microbes. Due to the complex interactions in this so-called coral holobiont, it has proven difficult to understand the environmental limitations of productivity in corals. Among others, the micronutrient iron has been proposed to limit primary productivity due to its essential role in photosynthesis and bacterial processes. Here, we tested the effect of iron enrichment on the physiology of the coral Pocillopora verrucosa from the central Red Sea during a 12-day experiment. Contrary to previous reports, we did not see an increase in zooxanthellae population density or gross photosynthesis. Conversely, respiration rates were significantly increased, and microbial nitrogen fixation was significantly decreased. Taken together, our data suggest that iron is not a limiting factor of primary productivity in Red Sea corals. Rather, increased metabolic demands in response to iron enrichment, as evidenced by increased respiration rates, may reduce carbon (i.e., energy) availability in the coral holobiont, resulting in reduced microbial nitrogen fixation. This decrease in nitrogen supply in turn may exacerbate the limitation of other nutrients, creating a negative feedback loop. Thereby, our results highlight that the effects of iron enrichment appear to be strongly dependent on local environmental conditions and ultimately may depend on the availability of other nutrients.
Data from: Feedbacks between nitrogen fixation and soil organic matter increase ecosystem functions in diversified agroecosystems
Nitrogen (N) losses from intensified agriculture are a major cause of global change, due to nitrate (NO3-) export and the eutrophication of aquatic systems as well as emissions of nitrous oxide (N2O) into the atmosphere. Diversified agroecosystems with legume cover crops couple N and carbon (C) inputs to soil and reduce N pollution, but there is a need to identify controls on legume N2 fixation across ecosystems with variable soil conditions. Here, I tested the hypothesis that N mineralization from turnover of soil organic matter (SOM) regulates legume N2 fixation across 10 farms that spanned a gradient of SOM levels. I separated soil samples into two SOM fractions, based on size and density, which are indicators of soil nutrient cycling and N availability (free particulate organic matter and intra-aggregate particulate organic matter (POM)). This study indicates downregulation of legume N2 fixation in diversified agroecosystems with increasing N availability in intra-aggregate POM and increasing N mineralization. Intercropping the legume with a grass weakened the relationship between N in POM and N2 fixation due to N assimilation by the grass. Further, mean rates of N and C mineralization across sites increased with two seasons of a legume-grass cover crop mixture, which could enhance this stabilizing feedback between soil N availability and N2 fixation over time. These results suggest a potential mechanism for the diversity-ecosystem function relationships measured in long-term studies of agroecosystems, in which regular use of legume cover crops increases total soil organic C and N and reduces the environmental costs of crop production.
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Allen Brain Atlas
Allen Brain Atlas is an Allen Institute collection of brain map atlases, datasets, APIs, and analysis tools covering mouse, human, and non-human primate brain resources.
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DANDI Archive for NWB datasets
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International Brain Laboratory public data
The International Brain Laboratory public data releases expose standardized mouse decision-making experiments, including Neuropixels recordings, widefield calcium imaging, behavior, and session metadata accessed through the ONE API.
OpenNeuro
OpenNeuro is a free, open platform for sharing neuroimaging datasets, with public search, dataset pages, and download paths for web, S3, DataLad, and the OpenNeuro CLI.