Browsing by Subject "nitrogen"

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Agronomic and storage factors affecting acrylamide formation in processed potatoes
(2017-07) Sun, Na
Acrylamide has been classified as a probable human carcinogen with neurological and reproductive effects. The compound is formed from reducing sugars and asparagine in the Maillard reaction during high-temperature processing, such as frying, baking and roasting. Among all foods containing acrylamide, fried potato products have been shown to be the highest contributors. Therefore, lowering acrylamide concentration in French fries and chips is a priority for the potato industry. The overall objective of this research is to determine effects of nitrogen (N) rate on tuber yield, tuber quality and acrylamide formation of recently developed potato cultivars, relative to the standard cultivars during the growing season and storage. The first experiment determined the effect of N rate on tuber yield and tuber quality at harvest, and on tuber glucose concentrations and acrylamide concentrations in French fries and chips during storage at 7.2 ºC. New cultivars Alpine Russet, Dakota Trailblazer and Ivory Crisp were compared to conventional cultivars Russet Burbank and Snowden over two years. The new cultivars had similar or higher marketable yields than standard cultivars, which quadratically increased with greater N rate and optimized at 231 kg ha-1 in 2011 and 319 kg ha-1 in 2012. Critical petiole nitrate-N concentrations 50 and 70 days after planting for all cultivars were greater in 2012 than in 2011, suggesting that interpretation of critical values can be affected by growing conditions. Alpine Russet and Ivory Crisp had specific gravities suitable for commercial processing and low hollow heart incidence at all N rates. Dakota Trailblazer had high hollow heart incidence (greater than 10 % at N rates above 125 kg ha-1), and excessively high specific gravity, making it undesirable for processing but with potential to be a parent in a breeding program. In chip cultivars, glucose and acrylamide concentrations linearly decreased in 2011, and quadratically increased then decreased with greater N rates in 2012. The effect of N rate on French fry glucose concentrations varied with cultivar. Russet Burbank and Alpine Russet glucose concentrations decreased with increasing N rate, while they were not affected by N rate in Dakota Trailblazer. Glucose and acrylamide concentrations of chip cultivars generally increased during storage, while they were not changed, increased or decreased depending on year in the French fry cultivars. While N supply and storage time can affect acrylamide concentrations in fried potato products, the direction of response will depend upon cultivar and growing conditions, which often precludes the ability to predict effects on acrylamide formation. The second experiment determined the effects of N rate on tuber yield, tuber quality, reducing sugars and asparagine concentrations during the growing season, glucose and acrylamide concentration during storage, and the relationships between acrylamide and its precursors for Dakota Russet and Easton compared to standard cultivar Russet Burbank over two years. Highest yield was produced by Easton, followed by Russet Burbank and then Dakota Russet in both years. New cultivars had less hollow heart tubers than Russet Burbank when environmental conditions were favorable for hollow heart formation. Dakota Russet and Easton had lower stem end reducing sugars than Russet Burbank at harvest under contrasting environmental conditions. Easton had lower asparagine concentrations at the stem and bud ends than Dakota Russet and Russet Burbank at harvest. Nitrogen rate effects were significant for yield, specific gravity and asparagine concentration, but these parameters were sometimes influenced by sampling times and environmental conditions. The effect of storage time on glucose concentrations was significant, but differed by cultivar and year. When the potato crop experienced cold stress before harvest in 2014, higher stem end glucose concentration accumulated and then decreased during storage for all cultivars. However, in a growing season with minimal stress, stem end glucose concentrations either increased or did not significantly change after 32 weeks of storage depending on cultivar, while bud end glucose stayed at the same level for all cultivars. At 16 weeks of storage at 7.8 °C, acrylamide concentration linearly increased with increasing N rate. French fries produced from Dakota Russet and Easton contained significantly lower acrylamide concentrations than those produced from Russet Burbank both years. Glucose concentrations were positively correlated with acrylamide concentration with an R2 = 0.61. Asparagine concentrations measured in tubers at harvest were also correlated with acrylamide concentration (R2 = 0.37), when the ratio of asparagine/glucose was less than 1.06. These relationships suggest that in addition to tuber glucose and asparagine, other factors are involved with acrylamide formation in fried potato products.
Amino Acid Pool Sizes, Turnover, and Kinetics in Spirodela polyrhyza Grown Under Photoautotrophic, Mixotrophic, and Heterotrophic Conditions
(2018-05) Evans, Erin
In this study I describe a [15N] stable isotopic labeling study of amino acids in Spirodela polyrhiza (common duckweed) grown under three light and carbon input conditions to mimic photoautotrophic, mixotrophic, and heterotrophic metabolic inputs. Labeling patterns, pool sizes, and kinetics/turnover rates were estimated for fifteen of the proteinogenic amino acids. Estimates of these parameters followed several trends. First, most amino acids showed plateaus in labeling patterns of less than 100% labeling. Second, total pool sizes appear largest in the heterotrophic condition, whereas active pool sizes appear to be largest in the mixotrophic growth condition. In contrast turnover measurements based on pool size were highest overall in the mixotrophic experiment. K-means clustering analysis also revealed more rapid turnover in the auto/mixotrophic. Emerging insights from other research were also supported, such as the prevalence of alternate pathways for serine metabolism in non-photosynthetic cells. These data provide extensive novel information on amino acid pool size and kinetics in S. polyrhiza and can serve as groundwork for future metabolic studies.
Are shade tolerance, survival, and growth linked? Low light and nitrogen effects on hardwood seedlings
(1996) Walters, Michael B; Reich, Peter B
Variation in shade tolerance is a primary mechanism driving succession in northern deciduous forests. However, little is known about interspecific differences in the traits responsible for shade tolerance. Is shade tolerance due to the ability to grow or survive in deep shade, or both? How do plant morphology and photosynthesis relate to growth in shade? Is low light the sole critical stress determining differences in "shade tolerance" or do below ground resources interact with low light to affect growth and survival? In this study we address these questions for seedlings of Betula papyrifera Marsh., Betula alleghaniensis Britton, Ostrya virginiana (Mill.) K. Koch, Acer saccharum Marsh., and Quercus rubra L. grown for 2 yr in outdoor shade houses in a complete factorial of low light (2 and 8% open sky) and nitrogen (forest soil and forest soil plus 200 kg N.ha-'.yr-'). For these seedlings we examined effects of light and nitrogen on the interrelationships among survival, growth, and shade tolerance and explored the physiological bases of shade tolerance by examining the relationship of plant morphology and photosynthesis to growth. Nitrogen amendments did not have a significant effect on any plant trait at either light level. In 8% light, growth and survival were highest for shade-intolerant Betula papyrifera and mid-tolerant Betula alleghaniensis, lower for shade-tolerant Ostrya and Acer, and lowest for disturbance-adapted Quercus. In 2% light, species rankings reversed as Ostrya and Acer had higher growth and survival than the other species. Second-year survival was strongly related to 1st-yr growth (P < 0.001), whereas relationships with 1st-yr plant mass and 1styr absolute growth rates were weak. Therefore, survival of shade-tolerant species at 2% light was related to their maintenance of positive growth, whereas intolerant species had growth near zero and high rates of mortality. In both 2 and 8% light photosynthetic rates on mass (but not area) bases and the proportion of the plant in leaves (leaf area ratio and leaf mass ratio) were positively related to growth. Greater rates of growth and survival for shade-tolerant species in very low light, and for intolerant species in higher light, suggest that there is a species-based trade-off between maximizing growth in high light and minimizing the light compensation point for growth. This trade-off may be an important mechanism driving forest community dynamics in northern hardwood forests.
Biogeochemical Interactions And Ecological Consequences Of Sulfur In Stands Of Wild Rice
(2020-05) LaFond-Hudson, Sophia
Wild rice is an ecologically and culturally important plant that typically grows in lakes and rivers in Minnesota that have low sulfate concentrations. Previous work demonstrated that elevated sulfate concentrations contribute to the decline in wild rice populations when conditions allow for the reaction of sulfate to sulfide. This dissertation investigates the fate of sulfate in the rooting zone of wild rice, mechanisms and consequences of sulfide exposure to plants, and the long-term effects of sulfide exposure on population dynamics. Key findings include 1) iron plaques on root surfaces transition from iron oxide to iron sulfide during reproduction if sulfate is elevated; 2) in elevated sulfate, seed production is delayed and shortened and plants produce fewer, smaller seeds with less nitrogen; and 3) populations of wild rice grown in low sulfate have stable biomass oscillations with a period of approximately 4 years, but elevated sulfate destabilizes these cycles and drives the population toward extinction.
Characterization of streams and rivers in the Minnesota River Basin Critical Observatory: water chemistry and biological field collections, 2013-2016
(2017-09-06) Dolph, Christine, L.; Hansen, Amy, T.; Kemmitt, Katie, L.; Janke, Ben; Rorer, Michelle; Winikoff, Sarah; Baker, Anna; Boardman, Evelyn; Finlay, Jacques, C.; dolph008@umn.edu; Dolph, Christine, L.
This dataset was collected to inform the Water, Sustainability and Climate Minnesota River Basin Observatory, and was supported by the National Science Foundation under Grant No. 1209402 Water, Sustainability and Climate (WSC) – Category 2, Collaborative: Climate and human dynamics as amplifiers of natural change: a framework for vulnerability assessment and mitigation planning. The dataset contains point locations, watershed areas and water quality information for 231 ditch, stream, river and wetland sites located in the Le Sueur River, Chippewa River, Cottonwood River, Cannon River, Wantonwan River and Blue Earth River basins of Minnesota. Study sites ranged in size from 1st order ditches and streams to an 8th order river. Each of these sites was sampled at least once between 2013-2016 (most sites were sampled multiple times) for one or more of the following parameters: 1) water chemistry (total dissolved nitrogen, nitrate-N, nitrite-N, ammonium-N, particulate nitrogen, soluble reactive phosphorus, total dissolved phosphorus, particulate phosphorus, total phosphorus, dissolved organic carbon, dissolved inorganic carbon, particulate carbon, chlorophyll a, total suspended solids, volatile suspended solids, delta-H-2 and delta-O-18 stable isotopes of site water, specific UV absorbance (SUVA) of site water, fluorescence index (FI) of site water); 2) stable isotopes (delta-C-13, delta-N-15, delta-H-2) of invertebrate consumers, particulate carbon and potential food sources; 3) denitrification rates and characteristics of benthic sediment in agricultural drainage ditches; and 4) stream discharge. This dataset also includes spatial data files containing study site locations and watershed areas delineated for each site.
Consequences of nutrient enrichment for soil organic matter cycling in grasslands
(2015-07) Riggs, Charlotte
Human activities have increased the availability of nutrients, such as nitrogen (N), phosphorus (P), and potassium (K), worldwide. Since alterations to nutrient cycles influence carbon (C) fixation and decomposition processes, nutrient enrichment affects global C stocks -- such as soil C. Carbon in soil organic matter (SOM) far outweighs vegetative C in the majority of biomes, especially grasslands. Consequently, either positive or negative changes to grassland soil C sequestration could feed back to influence the global C cycle. Unfortunately, the effects of nutrient enrichment on SOM cycling remain uncertain. In my dissertation, I examined the effects of nutrient addition on SOM cycling at participatory sites of the Nutrient Network -- a coordinated, global network of nutrient addition experiments that follow standard protocols for sampling and analysis. I found that the total soil C stock at experimental grasslands worldwide increased in response to the addition of N, P, and K. Furthermore, in a regional study in the US Central Great Plains, I found that N addition decreased microbial decomposition of SOM and tended to increase soil aggregation. Finally, in a laboratory study I found that decreased microbial biomass likely explains the decreased microbial decomposition of SOM in response to N addition. Overall, my results suggest that nutrient enrichment will lead to increased sequestration of soil C in some grassland soils.
Cyanobacteria phenology and toxicity across six Minnesota temperate lakes
(2022-10) Egan, Leah
Cyanobacteria harmful algal blooms (cHABs) represent both chronic and emerging water quality threats in lakes globally and are the consequence of complex, interacting stressors. While we know that water temperature, nutrient loading and availability, and water column mixing conditions are important drivers of cHABs, the combination of abiotic conditions leading to bloom development, maintenance, and toxicity remain poorly understood across different lake types. To better understand relationships among cyanobacteria abundances and composition, toxin concentrations, and nutrient conditions, we monitored six temperate Minnesota lakes with differing watershed land uses and lake morphometric characteristics across a latitudinal gradient. This project combined limnological approaches, comprehensive phytoplankton community analyses using taxonomic approaches, and advanced analytical characterization of toxin molecules to determine mechanisms leading to bloom formation and toxicity. Findings show that our study lakes had differing bloom phenologies influenced by different community assemblages and nutrient limitation states. The southern lakes had contrastingly different watershed land uses, such that Peltier Lake was predominantly urbanized, and Carrie Like was highly agricultural, which led differing nutrient growth conditions. Peltier (low N:P) experienced chronic surface blooms, whereas Carrie (extremely high N:P) did not. In Peltier Lake, the dominant cyanobacteria taxa present switched midsummer from nitrogen fixers (Dolichospermum spp.) to non-nitrogen fixers (Microcystis spp.) which tracked with decreasing nitrogen to phosphorus ratios. This community shift was counterintuitive based on changes in nutrient deficient growth conditions, suggesting that other drivers were likely impacting the shift in dominant cyanobacteria genera. Random Forest Models predicted major drivers of cyanotoxins in the bloom dominated lake, Peltier, to be in-lake growth conditions including dissolved organic carbon, soluble reactive phosphorus, and total phosphorus concentrations. Cyanotoxins were surprisingly detected in all lakes, including our least productive systems such as a northernly located lake, White Iron, and we observed a gradient of microcystin congeners present among our sample lakes. Cyanotoxin production can vary at the species (strain) level, therefore, it is essential to determine abiotic drivers of cHABs for various strains in differing lake types to properly inform management and mitigation of future system specific HABs.
Decomposition of the finest root branching orders: Linking belowground dynamics to fine-root function and structure
(2011) Goebel, Marc; Hobbie, Sarah E; Bulaj, Bartosz; Zadworny, Marcin; Archibald, Douglas D; Oleksyn, Jacek; Reich, Peter B; Eissenstat, David M
Root turnover is fastest in the finest roots of the root system (first root order). Additionally, tissue chemistry varies among even the finest root orders and between white roots and older, pigmented roots. Yet the effects of pigmentation and order on root decomposition have rarely been examined. We separated the first four root orders (all <1 mm) of four temperate tree species into three classes: white first- and second-order roots; pigmented first- and second-order roots; and pigmented third- and fourth-order roots. Roots were enclosed in litterbags and buried under their own and under a common species canopy in a 34-year-old common garden in Poland. When comparing decomposition of different root orders over 36 months, pigmented third- and fourth-order roots with a higher C:N ratio decomposed more rapidly, losing 20–40% of their mass, than pigmented first- and second-order roots, which lost no more than 20%. When comparing decomposition of roots of different levels of pigmentation within the same root order over 14 months, pigmented (older) first- and second-order roots lost ∼10% of their mass, while white (younger) first- and second-order roots lost ∼30%. In contrast to root mass loss, root N content declined more rapidly in the first- and second-order roots than in third- and fourth-order roots. In higher-order roots, N increased in the first 10 months from ∼110% to nearly 150% of initial N content, depending on species; by the end of the study N content had returned to initial levels. These findings suggest that, in plant communities where root mortality is primarily of pigmented first- and second-order roots, microbial decomposition may be slower than estimates derived from bulk fine-root litterbag experiments, which typically contain at least four root orders. Thus, a more mechanistic understanding of root decomposition and its contribution to ecosystem carbon and nutrient dynamics requires a fundamental shift in experimental methods that stratifies root samples for decomposition along more functionally based criteria such as root order and pigmentation, which parallel the markedly different longevities of these different root classes.
Determining optimal nitrogen fertility rates for reduced-input fine fescue putting greens
(2018-11) Petrella, Dominic; Bauer, Sam; Horgan, Brian; Watkins, Eric
The use of nitrogen fertilizers on golf courses is scrutinized worldwide. Identifying alternatives to creeping bentgrass Agrostis stolonifera L for putting greens may help decrease nitrogen use while maintaining turfgrass quality. Fine fescue turfgrasses are known for lower nitrogen requirements and reduced input management. Fine fescues are used for putting greens in northern Europe, Ireland, the UK, and other European countries, but have received limited attention in the U.S. Our objective was to determine the optimum annual nitrogen fertilizer rate for maintaining a reduced input fine fescue putting green in Minnesota.
Development of a Mathematical Model to Predict the Role of Surface Runoff and Groundwater Flow in Overfertilization of Surface Waters
(Water Resources Research Center, University of Minnesota, 1971-06) Johnson, Jack D.; Straub, Conrad P.
A nutrient enrichment accounting mathematical model was devised for the New Prague watershed in Minnesota. The New Prague watershed is 23.3 square miles in area and is predominately a rural watershed. Model input data was collected over a 2 1/2 year period from a stream gauging station and two automatic sampling stations. Over 800 water samples were analyzed. Extensive effort was placed on better understanding the nitrogen and phosphorus cycles. It is evident that the spring runoff process and accumulative winter fertilizer applications constitute the major portion of diffuse sources of nutrients in the watershed. Point sources from feedlots and municipal and industrial effluents contribute only 11 percent of the annual EN (total nitrogen, four components) and 7 percent TP (total phosphorus). Disperse sources accounted for 89 percent of EN and 93 percent of TP, with spring runoff in the two months of March and April accounting for 79 percent of the annual EN and 64 percent of the TP. The nutrient output from the watershed could be decreased by increasing penetration of the large amounts of EN and TP in snowpacks into the soil through land terracing to restart rapid spring runoffs and sub-surface drains to allow rapid drainage during the crop season.
Evaluating nitrogen losses, soil physical properties, and biological indicators in artificially drained fields in Northwest Minnesota
(2022-06) Frankl, Aaron
Subsurface drainage is a common practice to improve agricultural production in fields with poorly drained soils. This practice is becoming increasingly common in the Upper Midwest and NW Minnesota, where changing precipitation patterns are generating an increased need for artificial drainage systems. These systems increase yields, and over time, can reshape the soil ecosystem. By changing soil moisture throughout the profile, drainage can alter microbial activity and soil physical properties. In the first chapter of this study, we examined how drainage installation altered N cycling, which is largely mediated by soil microbes. In the two years following subsurface drainage installation, we observed several differences between the drained and undrained treatments: soil nitrate concentrations (NO3-), nitrous oxide (N2O) emissions, N mineralization, and edge of field losses. In the second chapter, we examined the longer-term changes facilitated by drainage to physical and soil health properties by sampling six sites. Three of these sites had their most recent drainage system installation before 2005; the remaining three had installations since 2015. The fields with older drainage systems had increased saturated hydraulic conductivity (Kfs) rates and increased biological activity (potentially mineralizable carbon, water-extractable organic carbon, and water-extractable organic nitrogen). Together, both studies identify the importance of understanding how drainage systems alter the soil ecosystem and demonstrate the importance of understanding drainage as an on-farm management decision. Additionally, they point to a need for more long-term drainage studies which focus on a wider range of soil properties.
Evaluating relationships between plant traits and nitrogen use to help predict species' responses to climate change
(2020-08) King, Rachel
In many ecosystems, nitrogen (N) is the predominant nutrient limiting plant growth. Plants have therefore developed diverse strategies to compete for and partition soil N resources to ensure an adequate N supply. Differences in how plants acquire N may be important for predicting plant responses to different global changes. In particular, how species respond to climate change may depend on their N use strategy since climate change will likely alter the forms of N available to plants as well as total N availability. However, there remain key gaps in our understanding of plant N acquisition that impede our ability to project the impacts of climate change on plant communities. My research focuses on one of these gaps, the variation in plant use of different chemical forms of N, and examines how that variation can influence plant responses to climate change. Specifically, my research aims to increase our understanding of N acquisition in trees by examining whether plant traits can improve our ability to identify and explain differences in the use of different N forms. My first three chapters explore (1) the relationship between N uptake rates and root morphology for different N forms; (2) whether plant traits can help explain how species vary in their growth on different N forms; and (3) whether warming and drought alter patterns of N use in a regenerating forest. I then examine (4) how plant nutrient acquisition strategies and traits influence links between ecosystem carbon (C) and N cycling. Together, my research highlights that plants differ in their capacity to use different forms of N, which are in some cases associated with their traits. I also show that plants differ in how they partition N resources in the field, especially between mycorrhizal types. Finally, I show that both species’ mycorrhizal type and phylogeny contribute to differences in C and N cycling in ecosystems where they dominate. Overall, my research adds to our knowledge of how plants acquire N and shows that these strategies are an important influence on species and ecosystem responses to global change.
Evaluating the Sustainability of Double-Cropping Rotations with Pennycress (Thlaspi arvense)
(2019-12) Moore, Sarah
Pennycress (Thlaspi arvense L.) is an emerging winter annual cash cover crop that can help address environmental concerns with summer annual cropping systems while also providing additional income as an industrial feedstock. Cropping systems research has mainly focused on incorporating pennycress into the corn – soybean rotation that dominates the upper Midwest. However, research into double-cropping systems with specialty crops is lacking. The purpose of this thesis is to assess the environmental and economic feasibility of a variety of specialty crops following pennycress; determine the effects of sweetcorn nitrogen fertilization on following pennycress yields; and quantify the ability of pennycress to reduce residual inorganic soil nitrogen.
Generality of leaf traits relationships: a test across six biomes
(Ecological Society of America, 1999) Reich, Peter B; Ellsworth, David S; Walters, Michael B; Vose, James M; Gresham, Charles; Volin, John C; Bowman, William D
Convergence in interspecific leaf trait relationships across diverse taxonomic groups and biomes would have important evolutionary and ecological implications. Such convergence has been hypothesized to result from trade-offs that limit the combination of plant traits for any species. Here we address this issue by testing for biome differences in the slope and intercept of interspecific relationships among leaf traits: longevity, net photosynthetic capacity (Amax), leaf diffusive conductance (Gs), specific leaf area (SLA), and nitrogen (N) status, for more than 100 species in six distinct biomes of the Americas. The six biomes were: alpine tundra–subalpine forest ecotone, cold temperate forest–prairie ecotone, montane cool temperate forest, desert shrubland, subtropical forest, and tropical rain forest. Despite large differences in climate and evolutionary history, in all biomes mass-based leaf N (Nmass), SLA, Gs, and Amax were positively related to one another and decreased with increasing leaf life span. The relationships between pairs of leaf traits exhibited similar slopes among biomes, suggesting a predictable set of scaling relationships among key leaf morphological, chemical, and metabolic traits that are replicated globally among terrestrial ecosystems regardless of biome or vegetation type. However, the intercept (i.e., the overall elevation of regression lines) of relationships between pairs of leaf traits usually differed among biomes. With increasing aridity across sites, species had greater Amax for a given level of Gs and lower SLA for any given leaf life span. Using principal components analysis, most variation among species was explained by an axis related to mass-based leaf traits (Amax, N, and SLA) while a second axis reflected climate, Gs, and other area-based leaf traits.
Global effects of soil and climate on leaf photosynthetic traits and rates
(Wiley, 2015) Maire, Vincent; Wright, Ian J; Prentice, I. Colin; Batjes, Niels H; Bhaskar, Radika; Bodegom, Peter M; Cornwell, Will K; Ellsworth, David; Niinemets, Ülo; Ordonez, Alejandro; Reich, Peter B; Santiago, Louis S
Aim The influence of soil properties on photosynthetic traits in higher plants is poorly quantified in comparison with that of climate. We address this situation by quantifying the unique and joint contributions to global leaf-trait variation from soils and climate. Location Terrestrial ecosystems world-wide. Methods Using a trait dataset comprising 1509 species from 288 sites, with climate and soil data derived from global datasets, we quantified the effects of 20 soil and 26 climate variables on light-saturated photosynthetic rate (Aarea), stomatal conductance (gs), leaf nitrogen and phosphorus (Narea and Parea) and specific leaf area (SLA) using mixed regression models and multivariate analyses. Results Soil variables were stronger predictors of leaf traits than climatic variables, except for SLA. On average, Narea, Parea and Aarea increased and SLA decreased with increasing soil pH and with increasing site aridity. gs declined and Parea increased with soil available P (Pavail). Narea was unrelated to total soil N. Joint effects of soil and climate dominated over their unique effects on Narea and Parea, while unique effects of soils dominated for Aarea and gs. Path analysis indicated that variation in Aarea reflected the combined independent influences of Narea and gs, the former promoted by high pH and aridity and the latter by low Pavail. Main conclusions Three environmental variables were key for explaining variation in leaf traits: soil pH and Pavail, and the climatic moisture index (the ratio of precipitation to potential evapotranspiration). Although the reliability of global soil datasets lags behind that of climate datasets, our results nonetheless provide compelling evidence that both can be jointly used in broad-scale analyses, and that effects uniquely attributable to soil properties are important determinants of leaf photosynthetic traits and rates. A significant future challenge is to better disentangle the covarying physiological, ecological and evolutionary mechanisms that underpin trait–environment relationships.
Global nitrogen deposition (2°×2.5° grid resolution) simulated with GEOS-Chem for 1984-1986, 1994-1996, 2004-2006, and 2014-2016
(2018-05-31) Ackerman, Daniel E; Chen, Xin; Millet, Dylan B; dackerma@umn.edu; Ackerman, Daniel E; Ecology, Evolution, and Behavior Department, University of Minnesota
Atmospheric deposition of inorganic nitrogen is critical to the function of ecosystems and elemental cycles. During the industrial period, humans have doubled the amount of inorganic nitrogen in the biosphere and radically altered rates of atmospheric nitrogen deposition. Despite this rapid change, estimates of global nitrogen deposition patterns generally have low, centennial-scale temporal resolution. Lack of information on annual- to decadal-scale changes in global nitrogen deposition makes it difficult for scientists researching questions on these finer timescales to contextualize their work within the global nitrogen cycle. Here we use the GEOS-Chem Chemical Transport Model to estimate wet and dry deposition of inorganic nitrogen globally at a spatial resolution of 2°×2.5° for 12 individual years in the period from 1984 to 2016. During this time, we found an 8% increase in global inorganic nitrogen deposition from 86.6 TgN yr-1 to 93.6 TgN yr-1, a trend that comprised a balance of variable regional patterns. For example, inorganic nitrogen deposition increased in areas including east Asia and Southern Brazil, while inorganic nitrogen deposition declined in areas including Europe. Further, we found a global increase in the percentage of inorganic nitrogen deposited in chemically reduced forms from 30% to 35%, and this trend was largely driven by strong regional increases in the proportion of chemically reduced nitrogen deposited over the United States. This study provides spatially explicit estimates of inorganic nitrogen deposition over the last four decades and improves our understanding of short-term human impacts on the global nitrogen cycle. We provide all output from these GEOS-Chem simulations related to atmospheric deposition. We provide all output from these GEOS-Chem simulations related to atmospheric deposition.
Historical plant and fungal nitrogen isotopes and concentrations from Minnesota, USA, 1871–2016
(2023-11-06) Michaud, Talia J; micha938@umn.edu; Michaud, Talia J; University of Minnesota Kennedy Lab
Historical declines in plant tissue nitrogen concentrations and d15N have been interpreted as evidence of declining terrestrial ecosystem nitrogen status. To test whether plant mycorrhizal type influences trajectories of plant nitrogen status, and whether fungi also exhibit declining nitrogen status, we analyzed herbarium collections made in MN, USA, from 1871–2016.
Host Diet and Pathogen Diversity: How Soil Nutrients Affect Plant Virus Interactions
(2017-12) Kendig, Amy
Human activities and management choices can impact the spread and intensity of diseases in plant and animal populations. For example, high nutrient inputs to terrestrial and aquatic systems may enhance pathogen success or aid hosts in resisting and tolerating disease. Because nutrient supply rates and ratios mediate interactions among free-living species, they may also influence interactions between hosts and pathogens. Further, it is increasingly clear that infections involve multiple different kinds of pathogens, and their interactions may also be mediated by environmental nutrients. The goal of my dissertation research was to understand how soil nutrients affect interactions among plant viruses and the consequences of these interactions for disease dynamics. We used field-collected data to determine how nutrients, among other factors, affected spatial patterns of viruses in grasslands. We found that virus pairs frequently co-occurred, and phosphorus (P) addition promoted the aggregation of one pair. Then, we performed growth chamber experiments to evaluate how nitrogen (N) and P mediated within-host interactions between two viruses, disease severity, and transmission to new hosts. We found that pathogens coexisted within hosts and occasionally benefitted from increased N. Disease severity was not strongly influenced by soil nutrients, but modeling results indicated that this outcome depended on the mechanism behind virulence. Finally, we found that the viruses were likely to coexist at the host population scale, despite inhibition that occurred during transmission. These results indicate that soil N and P influence some aspects of the system, but are not the main drivers behind virus diversity. This research contributes to a growing body of knowledge about the mechanisms linking environmental nutrients to disease across systems.
Impacts of global changes on leaf-level physiology of plant functional groups and ecosystem carbon storage
(2020-08) Pastore, Melissa
A key uncertainty in ecology is how concurrent global change factors will interact to affect terrestrial ecosystems. Humans have altered Earth’s carbon dioxide (CO2) concentrations, climate, nutrient levels, and biodiversity, all of which affect plant communities and ecosystem function. Yet, few multi-factor field studies exist to examine interactive effects of global changes on plants and ecosystems. I characterized the physiological responses of perennial grassland species from four plant functional groups (C3 grasses, C4 grasses, nitrogen-fixing leguminous forbs, and non-leguminous forbs) to single and interactive global changes including elevated carbon dioxide, increased soil nitrogen supply, reduced rainfall, and climate warming. I also determined how elevated CO2, increased soil nitrogen supply, and planted species richness affected total ecosystem carbon (C) storage over 19 years. These studies took place in the open-air, global change grassland ecosystem experiment, BioCON (Biodiversity x CO2 x Nitrogen), located at the Cedar Creek Ecosystem Science Reserve in Minnesota, USA. I present evidence that (1) the ability of plants to capture additional C as atmospheric CO2 rises via photosynthesis may be more limited than traditionally believed; (2) substantial, sustained declines in stomatal conductance and increases in water-use efficiency under elevated CO2 occur widely among grassland species; (3) global change factors interact in complex ways to affect photosynthesis, and how factors interact varies among grassland species; and (4) declines in biodiversity may influence ecosystem C storage more than a 50% increase in CO2 or high rates of nitrogen deposition in perennial grassland systems. These findings show that simple predictions of plant physiological responses to global changes based on theoretical expectations of isolated effects and on functional classifications of species are not sufficient – global changes and other environmental factors interact in complex ways to impact responses of species. These results also highlight the importance of biodiversity in promoting ecosystem function and call into question whether elevated CO2 will increase the C sink in grassland ecosystems and help to slow climate change.
Improving the sustainability of pork production by assessing the nutritional value of corn co-products and environmental impacts of swine feeding strategies
(2022-08) Yang, Zhaohui
The animal agriculture sector has developed and modernized rapidly because of the growing demand for high quality protein driven by population growth and greater purchasing power globally. However, livestock supply chains are important contributors to environmental issues including climate change, eutrophication, acidification, and land and water use. Among all processes involved in livestock production, feed production, processing, and transportation have been shown to cause the largest fraction of greenhouse gases emissions and human-induced nitrogen emissions. Furthermore, the efficiency of nitrogen and phosphorus utilization in pigs to produce lean pork for human consumption is relatively poor, which causes significant nitrogen and phosphorus wastage. As a result, practices to improve nutrient efficiency and reduce nutrient waste through feeding are needed. The objectives of this dissertation were to assess the nutritional value of corn co-products for precision diet formulation and quantity environmental impacts of different swine feeding strategies. The first study used an in vitro digestion model to evaluate novel corn co-products and showed that new processing technologies improved nutritional values of corn co-products for swine. The second study determined the accurate energy and digestible amino acid content of emerging corn co-products for precision swine diet formulation. The third study explored new analytical methods to dynamically assess digestible amino acid concentrations in corn co-products and showed the potential of estimating digestible lysine content using front-face fluorescent spectroscopy. The fourth study used a systems approach to evaluate the effectiveness of using precision feed formulation in swine diets to improve productivity, nitrogen utilization efficiency and environmental impact of pork production. Main findings from this dissertation suggested that several practices can be adopted to improve the overall sustainability of pork production including recycling novel corn co-products into swine diets, using precision diet formulation with accurate nutritional values, and incorporating life cycle assessment of environmental impacts into diet evaluation.

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