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76 results for “nitrogen enrichment”
Total and non-hydrolyzable soil carbon and nitrogen:BioCON : Biodiversity, Elevated CO2, and N Enrichment
BioCON (Biodiversity, CO2, and Nitrogen) is an ecological experiment started in 1997 at the University of Minnesota's Cedar Creek Ecosystem Science Reserve. BioCON's goal is to explore the ways in which plant communities will respond to three environmental changes that are known to be occurring on a global scale: increasing nitrogen deposition, increasing atmospheric CO2, and decreasing biodiversity. Why Biodiversity, CO2, and Nitrogen? While there are many uncertainties in global change biology, there are also some well documented facts. Some of these are: 1. The amount of carbon dioxide (CO2) in the atmosphere is rising. Since the industrial revolution, the CO2 concentration in the atmosphere has increased from approximately 275 parts per million (ppm) to about 378 ppm today. This has been largely the result of fossil fuel burning. It is expected that CO2 levels will continue to rise, and that by the year 2050 these levels will be approximately 550 ppm. CO2 is the raw material for photosynthesis and is known to affect plant growth and development. 2. The amount of nitrogen moving through terrestrial ecosystems has increased in the recent past. While natural "background" levels of nitrogen fixation have remained constant, human additions to the system through fertilizer production and fossil fuel use have increased dramatically. Nitrogen is a key nutrient for plant growth and plays a critical role in plant community structure and composition in many environments. 3. Biodiversity levels are falling. While the research and data are not as complete as they are for CO2 and nitrogen, data indicate that the number of species globally, is being reduced. Perhaps more important for ecosystem function, diversity levels on local to regional scales have fallen due to land use change, biotic invasion and many other drivers. While much is known about how each of these factors affects ecosystem functioning, many questions remain. There is also little data on how these issues affe
Photosynthesis Leaf Carbon and Nitrogen:BioCON : Biodiversity, Elevated CO2, and N Enrichment
BioCON (Biodiversity, CO2, and Nitrogen) is an ecological experiment started in 1997 at the University of Minnesota's Cedar Creek Ecosystem Science Reserve. BioCON's goal is to explore the ways in which plant communities will respond to three environmental changes that are known to be occurring on a global scale: increasing nitrogen deposition, increasing atmospheric CO2, and decreasing biodiversity. Why Biodiversity, CO2, and Nitrogen? While there are many uncertainties in global change biology, there are also some well documented facts. Some of these are: 1. The amount of carbon dioxide (CO2) in the atmosphere is rising. Since the industrial revolution, the CO2 concentration in the atmosphere has increased from approximately 275 parts per million (ppm) to about 378 ppm today. This has been largely the result of fossil fuel burning. It is expected that CO2 levels will continue to rise, and that by the year 2050 these levels will be approximately 550 ppm. CO2 is the raw material for photosynthesis and is known to affect plant growth and development. 2. The amount of nitrogen moving through terrestrial ecosystems has increased in the recent past. While natural "background" levels of nitrogen fixation have remained constant, human additions to the system through fertilizer production and fossil fuel use have increased dramatically. Nitrogen is a key nutrient for plant growth and plays a critical role in plant community structure and composition in many environments. 3. Biodiversity levels are falling. While the research and data are not as complete as they are for CO2 and nitrogen, data indicate that the number of species globally, is being reduced. Perhaps more important for ecosystem function, diversity levels on local to regional scales have fallen due to land use change, biotic invasion and many other drivers. While much is known about how each of these factors affects ecosystem functioning, many questions remain. There is also little data on how these issues affe
Data from: Synergistic effects of nitrogen and CO2 enrichment on alpine grassland biomass and community structure
<p>Global environmental change is altering Earth's ecosystems. However, much research has focused on ecosystem-level responses, and we know substantially less about community-level responses to global change stressors.<br> <br> Here we conducted a 6-year field experiment in a high-altitude (4600 m above sea level) alpine grassland on the Tibetan Plateau to explore the effects of nitrogen (N) addition and rising atmospheric CO2 concentration on plant communities.<br> <br> Our results showed that N and CO2 enrichment had synergistic effects on alpine grassland communities. Adding nitrogen or CO2 alone did not alter total community biomass, species diversity, or community composition, whereas adding both resources together increased community biomass, reduced species diversity, and altered community composition. The observed decline in species diversity under simultaneous N and CO2 enrichment was associated with greater community biomass and lower soil water content, and driven by the loss of species characterized simultaneously by tall stature and small specific leaf area.<br> <br> Our findings point to the co-limitation of alpine plant community biomass and structure by nitrogen and CO2, emphasizing the need for future studies to consider multiple aspects of global environmental change together to gain a more complete understanding of their ecological consequences.</p>
Processes at the soil-root interface determine the different responses of nutrient limitation and metal toxicity in forbs and grasses to nitrogen enrichment
<ol> <li>Nutrient limitation and metal toxicity have been implicated in changes of grassland communities by nitrogen (N) deposition. Belowground processes, especially those at the soil-root interface, play important roles in determining variation in nutrient concentrations in plants. However, few studies have specifically focused on the roles of these processes in mineral-element acquisition in grassland plants in response to N enrichment.</li> <li>Here we investigated the contributions of belowground processes at the soil-root interface to the differential acquisition of phosphorus (P), calcium (Ca) and manganese (Mn) by forbs and grasses of a temperate steppe in response to N addition by combining field and glasshouse experiments.</li> <li>Nitrogen addition increased the concentrations of both leaf P ([P]) and Mn ([Mn]) and decreased leaf [Ca] of forbs, while it had little effects on leaf concentrations of these elements in grasses. Nitrogen addition led to a higher activity of acid phosphatase in the rhizosphere of forb, and greater release of protons and carboxylates from forb roots than grass roots, contributing to the differential [P], [Ca] and [Mn] in leaves of forbs and grasses. Applying oxalate to soil to simulate the release of carboxylates by N enrichment enhanced [P] and [Mn], and decreased [Ca] in the soil solution. However, addition of hydrogen-ion increased [P], [Mn] and [Ca] in the soil solution. Lime addition mitigated the N addition-induced soil acidification, while it did not abolish the stimulatory effect of short-term N addition on leaf [P] and [Mn] of forbs. Therefore, we conclude that differences in the ecophysiological processes at the soil-root interface account for changes in leaf [P], [Ca] and [Mn] under short-term N addition, and that soil acidification aggravates the responses of these elements, especially [Ca] and [Mn], to long-term N enrichment.</li> <li><span>Synthesis: Our results highlight the contribution of belowground processes, especially those at the soil-root interface, to variation in plant element concentrations between dominant forbs and grasses in the temperate steppe. These findings greatly enhance our mechanistic understanding of the effects of N deposition on grassland communities.</span></li> </ol>
Nitrogen enrichment causes the thermal adaptation of soil microbial respiration
<p>As the climate warms, the feedback between soil carbon (C) and climate has the potential to decrease in magnitude over time due to the thermal adaptation of microbial respiration. However, the strength of microbial thermal adaptation (i.e., the degree to which microbial respiration adapts to temperature change) is uncertain, partly because the response of microbial respiration is regulated by multiple environmental factors acting simultaneously rather than by temperature alone; however, the combined effects of an environmental factor and warming on the thermal adaptation of microbial respiration have never been assessed. Using a 9-year two-way factorial experiment involving warming (daytime: 1.80℃; nighttime: 0.77℃) and nitrogen (N) enrichment (up to 15 g m<sup>-2</sup> y<sup>-1</sup>) treatments in an alpine permafrost on the Tibetan Plateau, we show that microbial respiration adapts to warming only under exogenous N enrichment and that the strength of thermal adaptation gradually increases as N enrichment increases. We identified two contrasting pathways by which N enrichment appears to affect the strength of thermal adaptation—via an increase caused by soil acidification and a decrease caused by the inhibition of soil C availability and stimulation of soil C-degrading enzymes—with a net positive effect of N enrichment on microbial thermal adaptation. Our findings emphasize the importance of considering multiple environmental change factors in shaping the strength of thermal adaptation when predicting future soil C-climate feedbacks.</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.
Intra-annual species gain overrides species loss in determining species richness in a typical steppe ecosystem after a decade of nitrogen enrichment
<p>Increasing deposition of atmospheric nitrogen (N) due to accelerated human activities is a threat to various ecosystems. However, there is a lack of long-term experimental evidence demonstrating the seasonal dynamics of plant species turnover that ultimately determine species richness in natural ecosystems under N enrichment. Moreover, the frequency of N addition also may affect species turnover in a community, but it is rarely studied.</p> <p>To assess the responses of a plant community to N addition, we manipulated the amounts (0-50 g N m<sup>-2</sup> year<sup>-1</sup>) and frequency (2 vs. 12 times year<sup>-1</sup>) of N addition in an Inner Mongolian typical steppe ecosystem in northern China for 12 consecutive years (2008-2020). We measured species richness and density of plant in the growing seasons (May-September) from 2018 to 2020, starting 10 years after the initial N addition treatment.</p> <p>Both species gain and species loss decreased with increasing amounts of N addition, resulting in a lower plant species turnover rate and greater similarity in the community between two adjacent months throughout the growing season. Species loss and species gain increased modestly under high N addition frequency. Species gain was more important than species loss in determining species richness after a decade of N application. In addition, plant density increased at high N amounts, mainly driven by enhanced clonal growth of the dominant species, <em>Leymus chinensis</em>.</p> <p><strong><em>Synthesis</em></strong>. Together, these results suggest that high levels of N deposition may suppress species richness due to aggravated soil chemical properties and may favor growth of a limited number of N-tolerant species compared to systems that experience low levels of N deposition. To conserve biodiversity and to facilitate restoration of degraded grassland ecosystems exposed to long-term N deposition, amelioration of the acidified soils induced by N deposition may be an important strategy to use.</p>
Trajectories and thresholds of multi-diversities and multi-functions in response to nitrogen enrichment
<p><span>An ecosystem is composed by multiple biota across several trophic levels, which interactively perform multiple ecosystem functions. </span><span>Anthropogenic reactive nitrogen</span><span> is expected to alter these ecosystem attributes including biota diversities and ecosystem functions. </span><span>Here, </span><span>we find that five biota diversities differ substantially in response trajectory and threshold with increasing nitrogen amount, and so do the four examined functions. </span><span>Our study provides a vivid picture of how multi-biota diversities and multiple functions concurrently respond to nitrogen enrichment and suggests that the attribute-specific response trajectories and thresholds should be taken into account in models predicting ecosystem feedbacks to nitrogen deposition.</span></p>
Nitrogen enrichment and foliar fungal pathogens affect the mechanisms of multispecies plant coexistence
<p>This is the data and code repository for the manuscript entitled "Nitrogen enrichment and foliar fungal pathogens affect the mechanisms of multispecies plant coexistence".</p> <p>DATA:</p> <p><strong>data.txt</strong></p> <p>Dataset collected in the PaNDiv experiment, a large field experiment in Münchenbuchsee (near Bern) which investigates the mechanisms by which nitrogen enrichment affects ecosystem functioning. The dataset is composed by the following elements:</p> <ul> <li><em>year </em>--- 2017 or 2018</li> <li><em>block </em>--- experimental block in the PaNDiv experiment (1, 2, 3 or 4)</li> <li><em>plot </em>--- experimental plot in the PaNDiv experiment (from 1 to 336)</li> <li><em>nitrogen </em>--- addition of nitrogen to the soil (0 = no, 1 = yes)</li> <li><em>fungicide </em>--- application of fungicide to the vegetation (0 = no, 1 = yes)</li> <li><em>treatment</em> --- control, nitrogen addition, fungicide application, and their combined effect</li> <li><em>number</em> --- replicate number of the focal species; numbers are repeated because it restarts with each target focal-neighbour species combination (not shown)</li> <li><em>focal_sp</em> --- 8 possible species: <ul> <li>tar_off = <em>Taraxacum officinale</em></li> <li>cre_bie = <em>Crepis biennis</em></li> <li>rum_ace = <em>Rumex acetosa</em></li> <li>dac_glo = <em>Dactylis glomerata</em></li> <li>ant_odo = <em>Anthoxanthum odoratum</em></li> <li>cen_jac = <em>Centaurea jacea</em></li> <li>sal_pra = <em>Salvia pratensis</em></li> <li>pla_med = <em>Plantago media</em></li> </ul> </li> <li><em>biomass_i </em>--- initial biomass of the focal plant (start of the growing season; February/March)</li> <li><em>biomass_f</em> --- final biomass of the focal plant (end of the growing season; June)</li> <li><em>tar_off</em> --- visually estimated cover for this species as a neighbour</li> <li><em>cre_bie</em> --- visually estimated cover for this species as a neighbour</li> <li><em>rum_ace</em> --- visually estimated cover for this species as a neighbour</li> <li><em>dac_glo</em> --- visually estimated cover for this species as a neighbour</li> <li><em>ant_odo</em> --- visually estimated cover for this species as a neighbour</li> <li><em>cen_jac</em> --- visually estimated cover for this species as a neighbour</li> <li><em>sal_pra</em> --- visually estimated cover for this species as a neighbour</li> <li><em>pla_med</em> --- visually estimated cover for this species as a neighbour</li> <li><em>herbs </em>--- visually estimated cover for non-target herb species in the PaNDiv experiment</li> <li><em>grasses </em>--- visually estimated cover for non-target grass species in the PaNDiv experiment</li> <li><em>legumes </em>--- visually estimated cover for non-target legume species in the PaNDiv experiment</li> </ul> <p> </p> <p>CODE:</p> <p><strong>001-optimx.R</strong></p> <p>Code that uses maximum likelihood to fit population models to the data. Produces several datasets with model coefficients and AIC values.</p> <p> </p> <p><strong>002-model_sel_coefs.R</strong></p> <p>Code to select the coefficients based on the best model and add the size effect of the focal plants when needed. Creates all interaction matrices and intrinsic growth rate vectors.</p> <p> </p> <p><strong>003-final_matrices.R</strong></p> <p>Code to adjust the matrices for coexistence computing.</p> <p> </p> <p><strong>004-coexistence.R</strong></p> <p>Computes structural coexistence outputs. Provides a clean dataset with structural niche differences, structural fitness differences, and other multispecies coexistence metrics.</p>
Enhanced foliar 15N enrichment with increasing nitrogen addition rates: Role of plant species and nitrogen compounds
<p>Determining the abundance of N isotope (δ15N) in natural environments is a simple but powerful method for providing integrated information on the N cycling dynamics and status in an ecosystem under exogenous N inputs. However, whether the input of different N compounds could differently impact plant growth and their 15N signatures remains unclear. Here, the response of δ15N signatures and growth of three dominant plants (Leymus chinensis, Carex duriuscula, and Thermopsis lanceolata) to the addition of three N compounds (NH4HCO3, urea, and NH4NO3) at multiple N addition rates were assessed in a meadow steppe in Inner Mongolia. The three plants showed different initial foliar δ15N values because of differences in their N acquisition strategies. Particularly, T. lanceolata (N2-fixing species) showed significantly lower 15N signatures than L. chinensis (associated with arbuscular mycorrhizal fungi, AMF) and C. duriuscula (associated with AMF). Moreover, the foliar δ15N of all three species increased with increasing N addition rates, with a sharp increase above an N addition rate of ~10 g N m-2yr-1. Foliar δ15N values were significantly higher when NH4HCO3 and urea were added than when NH4NO3 was added, suggesting that adding weakly acidifying N compounds could result in a more open N cycle. Overall, our results imply that assessing the N transformation processes in the context of increasing global N deposition necessitates the consideration of N deposition rates, forms of the deposited N compounds, and N utilization strategies of the co-existing plant species in the ecosystem.<span> </span></p>
Intra-annual species gain overrides species loss in determining species richness in a typical steppe ecosystem after a decade of nitrogen enrichment
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Data from: Phytoplankton responses to nitrogen enrichment in Pacific Northwest, USA mountain lakes
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Data from: Synergistic effects of nitrogen and CO2 enrichment on alpine grassland biomass and community structure
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Enhanced foliar 15N enrichment with increasing nitrogen addition rates: Role of plant species and nitrogen compounds
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Data from: Assessing the effects of iron enrichment across holobiont compartments reveals reduced microbial nitrogen fixation in the Red Sea coral Pocillopora verrucosa
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Data from: Mowing exacerbates the loss of ecosystem stability under nitrogen enrichment in a temperate grassland
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Processes at the soil-root interface determine the different responses of nutrient limitation and metal toxicity in forbs and grasses to nitrogen enrichment
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Data from: Foliar fungal pathogen inhibition increases ecosystem carbon sequestration independently of nitrogen enrichment in a Tibetan alpine meadow
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Data from: Trait identity and functional diversity co-drive response of ecosystem productivity to nitrogen enrichment
1. Exploring the mechanisms underlying the change in ecosystem productivity under anthropogenic nitrogen (N) inputs is of fundamental ecological interest. It has been proposed that functional traits, environmental factors, and species richness are central drivers linking ecosystem productivity with environmental change. However, few studies have considered the joint effects of functional traits, environmental factors, and species richness on ecosystem productivity under increasing N inputs. 2. We established a N-manipulation experiment in a Tibetan alpine steppe in 2013. Using structural equation models, we assessed the effects of N-induced changes in environmental factors, species richness, and trait metrics (the mean, variance, skewness and kurtosis of trait distribution) on gross ecosystem productivity as well as three resource use efficiencies (water, light, and phosphorus (P) use efficiencies), based on measurements during the peak growing season in 2016. 3. We found that both light and P use efficiencies decreased under N enrichment, largely due to the N-induced decline in functional diversity of leaf P concentration. However, both gross ecosystem productivity and water use efficiency exhibited initial increases and subsequent slight decreases with N addition. These nonlinear patterns were closely associated with both the increased morphological trait (i.e., mean-leaf area) and decreased diversity of leaf P concentration. 4. Synthesis. Our results illustrate how N-induced changes in functional traits may have dual effects on ecosystem productivity: the stimulating effects of the dominant trait identity via increasing canopy light interception vs. the inhibiting effect of decreasing trait diversity via declining resource use efficiencies. Our results highlight the importance of including functional traits in land surface models to improve predictions of the response of ecosystem function to N inputs.
Data from: Urine is an important nitrogen source for plants irrespective of vegetation composition in an Arctic tundra: insights from a 15N-enriched urea tracer experiment
1. Mammalian herbivores can strongly influence nitrogen (N) cycling and herbivore urine could be a central component of the N cycle in grazed ecosystems. Despite its potential role for ecosystem productivity and functioning, the fate of N derived from urine has rarely been investigated in grazed ecosystems. 2. This study explored the fate of <sup>15</sup>N-enriched urea in tundra sites that have been either lightly or intensively grazed by reindeer for more than 50 years. We followed the fate of the <sup>15</sup>N applied to the plant canopy, at 2 weeks and 1 year after tracer addition, in the different ecosystem N pools. 3. <sup>15</sup>N-urea was rapidly incorporated in cryptogams and in aboveground parts of vascular plants, while the soil microbial pool and plant roots sequestered only a marginal proportion. Further, the litter layer constituted a large sink for the <sup>15</sup>N-urea, at least in the short term, indicating a high biological activity in the litter layer and high immobilization in the first phases of organic matter decomposition. 4. Mosses and lichens still constituted the largest sink for the <sup>15</sup>N-urea 1 year after tracer addition at both levels of grazing intensity demonstrating their large ability to capture and retain N from urine. Despite large fundamental differences in their traits, deciduous and evergreen shrubs were just as efficient as graminoids in taking up the <sup>15</sup>N-urea. The total recovery of <sup>15</sup>N-urea was lower in the intensively grazed sites, suggesting that reindeer reduce ecosystem N retention. 5. <i>Synthesis</i> The rapid incorporation of the applied <sup>15</sup>N-urea indicates that arctic plants can take advantage of a pulse of incoming N from urine. In addition, δ <sup>15</sup>N values of all taxa in the heavily grazed sites converged towards the δ <sup>15</sup>N values for urine, bringing further evidence that urine is an important N source for plants in grazed tundra ecosystems.
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