Living (biotic) and non-living (abiotic) factors drive the function of ecosystems across a variety of scales from the root-soil interface to the watershed. Biotic and abiotic global change pressures such as increasing temperature and invasive species are shifting how ecosystems function. Thus, exploring and understanding how these factors shape function across the landscape is an important research area. For example, climate change both directly and indirectly affects soil microbial functions – such as carbon mineralization and nitrogen transformations – through increasing activity under warming and altering inputs to the soil through species composition changes. Mountains provide a useful tool for studying relationships among biotic and abiotic factors because climate and species diversity shift along gradients. Here, I measured carbon and nitrogen soil processes as well as microbial extracellular enzyme activity along an elevational gradient to explore how changes in climate, edaphic properties, and biotic composition affects ecosystem function. As expected, climate and species composition varied in predictable ways along the gradient – actual evapotranspiration declined, and conifer dominance increased. Soil functions also shifted along the gradient. Potential carbon mineralization increased with elevation and with conifer dominance. Potential nitrogen mineralization rates increased with elevation and with conifer dominance. Surprisingly, there were few predictors for potential soil nitrification, which increased only with soil functional diversity. While temperature and moisture availability drive ecosystem function at broad scales and biotic factors typically drive function at the regional scale, we saw that function of soils at the mountain watershed scale was best explained by a combination of both abiotic and biotic factors.

Ongoing climate change has emerged as a major scientific challenge in the current century. Grassland ecosystems are considered net carbon (C) sinks to mitigate climate change. However, they are in turn, influenced by climate change and management practices, providing feedback to climate change via soil microbial community and biogeochemical fluxes. In this thesis, I examined the impact of warming, altered precipitation, and defoliation on soil microbial composition and function, C and N dynamics, and fluxes in soil respiration (CO2), nitrous oxide (N2O) and methane (CH4), together with other belowground ecosystem functions, within two ecosites in a northern native temperate grassland in central Alberta, Canada, over a two-year period. Fungi-to-bacteria ratio was not affected by climatic parameters or defoliation, indicating a high degree of resistance in the below ground community to the treatments imposed. However, C substrate utilization was influenced by warming and defoliation, as was soil microbial biomass. In contrast, soil respiration (or C loss) was not. Soil respiration acclimatized rather quickly to warming, and N2O and CH4 effluxes showed minor responses to warming at both ecosites, regardless of defoliation. These results suggest warming is unlikely to lead to positive climate change feedback due to soil-based responses, regardless of ongoing land use. However, altered precipitation ( 50%) demonstrated greater impacts on C and N fluxes relative to warming and defoliation. Increased precipitation stimulated soil C loss to the atmosphere, potentially generating positive feedback for climatic warming in this northern temperate grassland. / Soil Science

Increasing soil degradation and its consequences on overall ecosystem services urge for restoration strategies. Construction of Technosols through assemblage of treated soil and industrial wastes is an innovative technology for the restoration of polluted land and re-use of industrial by-products. Recent studies have evidenced that Technosols could support ecosystemic services such as primary production but the knowledge about other soil functions, such as biogeochemical cycling, is limited. Due to the significant contribution of microbial communities to soil functioning, this PhD work was carried out to study the effect of the type of Technosol on microbial communities with a focus on functional guilds involved in N cycling. For this purpose, the abundance and diversity of the total bacterial community and the abundance of crenarchaeal community together with the abundance and activities of the nitrifying and denitrifying communities were investigated in two types of Technosols. Results demonstrated that diversity and composition of the bacterial community were similar to 'natural soils' and were not significantly different between the two Technosols with Proteobacteria being the dominant phylum (50-80%). The bacterial ammonia oxidizers were greater in number than crenarchaeal ammonia oxidizers but also correlated to the potential nitrification activity suggesting that bacteria are the dominant ammonia oxidizers in Technosols. The abundance of both the ammonia oxidizers and the denitrifiers were in the same range than that observed in other soil systems. Analyses of the vertical distribution of the activity and abundance of N-cycling communities in the Technosols showed a significant depth-effect, which was more important than the Technosol type-effect. Technosols physicochemical properties and the abundance of the bacterial ammonia oxidizers were the main drivers of the nitrification activity whereas the denitrification activity was controlled mainly by the Technosols physicochemical properties and, to a minor extent, by the abundances of the nirS denitrifiers. The estimation of the functional stability of the denitrification process against the heat-drought stresses revealed that Technosol exhibited the high resistance and resilience in comparison to the thermally treated soil. This work highlighted the potential of constructed Technosols to ensure the N cycling ecosystem services, along with a high capacity to resist and recover from environmental stresses, suggesting that construction of Technosols is a promising technology and a solution for the restoration of industrial wastelands and waste recycling

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Magistro darbe tiriama azotinių medžiagų dinamikos dėsningumai skirtingo amžiaus ir priežiūros sąlygų golfo laukų dirvožemiuose. Darbo objektas – seniai naudojamo ir naujai įrengto golfo laukų dirvožemiai. 2009-2010 m. laikotarpyje senojo golfo lauko (16 ha) dirvožemiams tręšti sunaudota 3303,2 kg ha-1, o naujojo golfo lauko (140 ha) dirvožemiams – 5006 kg ha-1 trąšų, t.y. 1,5 karto daugiau. Darbo rezultatai. Atlikus tyrimą nustatyta, kad vidutiniai suminiai (Nb) ir mineralinio azoto (Nmin) kiekiai tirtuose senojo ir naujojo golfo laukų dirvožemiuose buvo 2-2,6 karto didesni nei vidutiniškai Lietuvos dirvožemiuose ir kito nuo 0,11 % naujojo iki 0,19 % senojo golfo laukų dirvožemiuose. Nmin senojo golfo lauko dirvožemyje vidutiniškai sudarė 17,98 mg kg-1 arba 0,94 % bendrojo N kiekio (Nb+Nmin), o naujojo golfo lauko dirvožemyje – 13,58 mg kg-1 arba 1,22 % Nb+Nmin. Amonio azoto (NH4-N) senojo golfo lauko dirvožemyje nustatyta vidutiniškai 1,69 ± 0,91 mg kg-1 arba 9,4 % Nmin. Naujojo golfo lauko dirvožemyje NH4-N sudarė 8,5 % Nmin ir buvo statistiškai reikšmingai (p<0,05) mažiau negu senojo golfo lauko. Nitritų azotas (NO2-N) sudarė 1,91 % Nmin naujojo golfo lauko dirvožemyje ir 2,11 % senojo golfo lauko dirvožemyje (skirtumai nereikšmingi, p>0,05). Nitratų azoto (NO3-N) senojo golfo lauko dirvožemyje nustatyta 88,5 % Nmin, o naujojo golfo lauko dirvožemyje – 89,6 % Nmin , tačiau DLK (130 mg kg-1 pagal NO) neviršijo. Priklausomai nuo vegetacijos sezoniškumo senojo golfo lauko... [toliau žr. visą tekstą] / Dynamics of nitrogen substances in soil of golf courses of various age and management conditions are investigated in the Master’s Thesis. Object of the work – soils of long-used and newly installed golf courses. In the year 2009-2010 3303.2 kg ha-1 of fertilizers were used to fertilize the soils of the old golf course (16 ha) and 5006 kg ha-1 of fertilizers were used for the soils of the new golf course (140 ha). Results of the work. The research disclosed that total (Nb) and mineral nitrogen (Nmin) contents in the soils of investigated old and new golf courses were 2-2,6 times more than mean Lithuanian soil Nb contents and varied in the range 0.11-0.19% . The Nmin content in the soil of the old golf course was 17.98 mg kg-1 or 0.94% of the total amount of N (Nb + Nmin), while the amount in the soil of the new golf course was 13.58 mg kg-1 or 1.22% Nb+Nmin. The mean amount of ammonium nitrogen (NH4-N) in the soil of the old golf course was 1.69 ± 0.91 mg kg-1 or 9.4%. NH4-N constituted 8.5% of the Nmin in the new golf course, and it was significantly less (p<0.05) than in the old one. The amount of nitrite nitrogen (NO2-N) constituted 1.91% of Nmin in the soil of the new golf course and 2.11% in the old golf course, but difference insignificant (p>0.05). Amount of nitrate nitrogen (NO3-N) in the soil of the old golf course constituted 88.5% of Nmin, and in the new golf course – 89.6%of Nmin, but it did not exceed the MPC (130 mg kg-1 according to NO) (HN 60:2004)... [to full text]

The increased use of synthetic nitrogen fertilizers since the early 1900s has resulted in greater food production but also problems with nitrogen pollution in freshwaters. Nitrate (NO3-) is a common pollutant in rivers and groundwater in agricultural watersheds; the drinking water limit in Canada is 10 mg N/L. Microbial processing of NO3- and ammonium (NH4+) can produce nitrous oxide (N2O), a potent greenhouse gas responsible for about 5% of the greenhouse effect. Rivers provide a complex environment, where a variety of redox conditions, available substrates and microbial populations can co-exist on small spatial and temporal scales. Therefore, many questions remain about N cycling in river environments. N2O is produced during anoxic microbial NO3- or NO2- reduction to N2 (denitrification) and oxic microbial NH4+ oxidation to NO3- (nitrification). A significant portion (~25%) of global anthropogenic N2O is produced in rivers and estuaries, but mechanisms are not clear and predictability is poor. The United Nations Intergovernmental Panel on Climate Change (IPCC) provides default equations for calculating N2O emission estimates, in which annual NO3- loading to rivers is positively linearly related to N2O emissions. However, it is unclear how sound these linear relationships are and if measured N2O emissions are similar to IPCC estimates. The Grand River watershed is the largest in southern Ontario. Nutrient discharge to the Grand River is high due to extensive agriculture and high urban populations. The river often has a hypoxic water column due to high community respiration in summer. However, although nitrogen pollution is significant, N cycling is not well understood in the river. This thesis shows that NO3- and NH4+ do not typically change on the diel scale, with the exception of two sites downstream of wastewater treatment plants (WWTPs). However, N2O concentration changes dramatically. N2O concentrations are higher at night and lower during the day for most sites, but are reversed at very low-nutrient sites. N2O is therefore a sensitive indicator of changes in N cycling that may not be evident from NO3- and NH4+ concentrations or stable isotope ratios. Additionally, this work shows the importance of having a sampling design that captures diel variability in N2O. Previous work in rivers and streams worldwide focused on the appropriate N2O:NO3- ratio used to predict N2O emissions. In contrast, this thesis shows that there is a significant but very weak relationship between instantaneous N2O emissions and NO3- concentrations. However, there is a much stronger negative exponential relationship between DO and N2O. Annual N2O emissions tripled between 2006 and 2007 but NO3- masses in the river were only 10% higher, likely because river levels were lower and anoxia more prevalent in 2007. This research suggests that the IPCC needs a new conceptual model for N2O-NO3- relationships in rivers. N2O is produced in rivers, partially due to microbial processing of NO3- and NH4+ from WWTP effluent. However, WWTP effluent may also include dissolved N2O and CH4 but this previously had not been directly quantified. It was also unclear if stable isotopic ratios of NH4+, NO3-, N2O and CH4 in WWTP effluent were distinct from river sources and could be used for effluent tracing. N2O emissions from three WWTPs in the Grand River Watershed were measured over 24 hours in summer and winter. N2O emissions were similar to direct emissions from WWTPs but CH4 emissions were about an order of magnitude lower than direct WWTP emissions. This is a previously-ignored source of N2O and CH4 to the atmosphere. While stable isotopic ranges of NO3- and NH4+ were not always distinct from river sources, ??15N-N2O, ??18O-N2O and ??13C-CH4 were distinct, making them potentially useful tracers of WWTP effluent in rivers. N2O isotopic signatures may help determine production and removal processes in rivers, but isotopic effects of the major production pathway, denitrification, have not been characterized for river sediments. This was addressed by preparing anoxic laboratory incubations of river sediment from two sites (non-urban and urban) in the Grand River and measuring stable isotopic effects of N2O production via denitrification. Stable isotopic fractionations were similar to published values but, surprisingly, strongly negatively correlated to production rate, even though NO3- substrate was plentiful. This novel finding suggests that N2O reduction resulting in isotopic effects is more prevalent in high-substrate systems than previously thought, and that N2O reduction may be inhibited by high NO3- or NO2- or by lags in N2O reductase activity in high N2O-production incubations. This could explain why N2O emissions from the Grand River are lower than predicted by IPCC equations, which assume that N2O:(N2O+N2) ratios produced by denitrification are constant. Concern about NO3- export to freshwater lakes and to oceans is growing, but the role of large, eutrophic rivers in removing watershed NO3- loading via denitrification and biotic assimilation is not clear. To understand how much NO3- the Grand River receives, and how much it removes annually, a NO3- isotope mass balance for the Grand River was created. The river denitrified between 0.5% and 17% of incoming NO3-, less than the 50% suggested by the IPCC. This is surprising, as the river is well mixed, has moderate to high NO3- concentrations, experiences hypoxia (promoting denitrification), and has extensive biomass (biofilm and macrophytes) that assimilate N. However, the river???s short residence time (~3 days not counting reservoirs), organic carbon-poor sediment and mineralization of organic matter could contribute to low denitrification rates. These findings suggest that denitrification rates in rivers worldwide could be lower than previously estimated. Although error was high, most ??15N-NO3- values for losses were in the expected range for denitrification and most ??15N-NO3- values for gains were within ranges from tributaries, WWTP effluent and groundwater measured in the watershed. The model suggests that 68% to 83% of N loads to the watershed are lost before entering the Grand River, and 13% is exported to Lake Erie, leaving 5 to 19% lost in the Grand River from a combination of denitrification, assimilation and storage. These findings suggest that large rivers are much less efficient in denitrification than other locations in watersheds such as small streams, ponds, groundwater and riparian zones. They also indicate that agricultural NO3- loading is much higher than WWTP effluent, suggesting that N management strategies should focus on agricultural runoff and groundwater. Given that N2O:NO3- relationships are weak and non-linear in the Grand River, a new conceptual model for N2O:NO3- relationships is presented. First, the Grand River dataset was supplemented with data from high-oxygen streams in southern Ontario. Regression tree analysis shows a weak relationship between NO3- and N2O in these streams with no other factors (temperature, DO, NH4+, TP, DOC, etc.) improving fit. A conceptual model was then created, which posits that N2O emission variability (between and within sites) increases with NO3- concentration when NO3- concentrations are above the threshold for NO3- limitation. The global dataset does not dispute this model, though a NO3- threshold was not clear. The lack of sites with both high NO3- and high N2O may indicate a paucity of research on eutrophic sites. Alternatively, high NO3- may indicate oxic conditions (i.e. little to no denitrification to remove it) which are incompatible with very high N2O emissions. In this case, the conceptual model can be modified such that N2O variability decreases when NO3- > ~ 4 mg N/L. The work also shows that low DO consistently results in high N2O emissions but high temperatures result in a very large range of N2O emissions. This approach allows N2O emissions, which have very high variability and are difficult to predict, to be constrained to likely ranges.

Marine nitrogen (N) is an essential nutrient for all oceanic organisms. The cycling of N between biologically available and unavailable forms occurs through numerous reactions. Because of the vast number of reactions and chemical species involved, the N cycle is still not well understood. This dissertation focuses on understanding some of the reactions involved in the cycling of marine N, as well as improving techniques used to measure dissolved N2 gas. The largest loss term for global marine N is a reaction called denitrification. In this work, denitrification was measured in the sandy sediments of the Georgia continental shelf, an area where this reaction was thought to be unlikely because of the physical properties of the sediments. Nitrogen fixation, which is a reaction that produces biologically available N, was detected in Georgia estuarine sediments. N fixation was measured concurrently with denitrification in these sediments, resulting in a much smaller net loss of marine N than previously thought. Lastly, membrane inlet mass spectrometry (MIMS) is a technique that measures dissolved N2, the end product of denitrification and a reactant in N fixation reactions. This study suggests that N2 measurements by MIMS are influenced by O2 concentrations due to pressure differences inside of the ion source of the mass spectrometer. These findings seek to improve denitrification measurements using MIMS on samples with varying O2 concentrations. In conclusion, this dissertation suggests that the marine N cycle is more dynamic than has been suggested, due to the recognition of input and loss reactions in a wider range of marine and estuarine environments. However, improvements in the understanding of MIMS will help with direct measurements with reactions involved in the global marine N cycle.

A expansão agrícola tem provocado modificações expressivas na dinâmica de nitrogênio (N) em sistemas tropicais. No Brasil, a expansão dos cultivos de soja é uma realidade e, portanto, investigações a cerca dos processos que controlam o ciclo de nitrogênio nestes sistemas são fundamentais. A fixação biológica de nitrogênio (FBN) por leguminosas pode promover aportes significativos de N nos sistemas agrícolas em solos tropicais, no entanto, o destino destes aportes e o balanço entre entradas e saídas de N não é completamente entendido. Este trabalho teve como objetivo investigar comparativamente a dinâmica de nitrogênio em cultivos de soja e floresta no estado de Mato Grosso, sudeste da Amazônia. Foram determinados o \'delta\'15N e %N do solo e da vegetação, estoques de N e C, N-NO3-, N-NH4+, bem como outras propriedades químicas e físicas do solo em áreas de floresta e em áreas submetidas a cultivos de soja ao longo de uma cronosequência (1, 2, 5 e 6 anos de cultivo). Foram realizadas estimativas de FBN (Fixação Biológica de Nitrogênio) em cultivos de soja utilizando a abundância natural de 15N sob condições de campo. A conversão das áreas de cultivo partiu de pastagem, sendo esta área utilizada como referência inicial quanto aos estoques de N e ao \'delta\'15N do solo. Foi observado um aumento significativo nos estoques de nitrogênio do solo (0 a 10cm) ao longo dos anos de cultivo de soja, estes no entanto, foram menores que os estoques encontrados na floresta. Os estoques de N no solo (0-10cm) variaram de 1230 kg N ha-1 na pastagem a 1370 kg N ha-1 nos cultivos mais antigos. O acúmulo anual de N pela soja foi de 158,6 kg N ha-1 nos cultivos mais antigos, do qual 79% foi derivado da FBN. Não foram encontradas diferenças significativas nas taxas de mineralização e nitrificação líquida entre as áreas, no entanto, altos valores de N-NO3- foram encontrados nas camadas mais profundas de solo em cultivos de soja. Apesar de não serem observadas diferenças significativas no \'delta\'15N do solo entre os cultivos, estes, no entanto, apresentaram valores de \'delta\'15N intermediários entre a pastagem e a floresta. Os resultados indicaram um padrão de acúmulo de nitrogênio ao longo da cronosequência de cultivos de soja, indicando um possível retorno gradual dos estoques de N e do sinal isotópico do solo que ocorriam na floresta antes da conversão para pastagem e cultivo de soja, este retorno, no entanto, não parece acontecer a médio-prazo / Agricultural expansion has greatly changed the nitrogen (N) dynamics in tropical systems. The expanding soybean frontier in Brazil is a reality, and investigations of the processes driving N dynamics in these systems are needed to minimize environmental impacts and to promote the sustainability of agricultural systems. Biological nitrogen fixation (BNF) by legumes can provide significant N inputs to crop systems on highly weathered tropical soils, although the fate of these inputs in the environment and the balance between inputs and outputs of N in these systems is poorly understood. This work investigated N dynamics in a chronosequence of soybean fields (1, 2, 5 and 6 years of cultivation) and mature forest in the Brazilian state of Mato Grosso, which is at the southern limit of the Amazon forest. We measured soil N and C stocks, N-NO3-, N-NH4+ concentration and soil \'delta\'15N as well as biological nitrogen fixation (BNF) inputs by soybean, which were assessed using the 15N natural abundance technique under field conditions. Additional measurements of physical and chemical properties of soils were also provided. The land-use-conversion started from pasture, so this site was used as an initial reference for soil N stocks and soil \'delta\'15N. Mature forest stands on the ranch were also used as an additional reference. Soil N stocks (top 10cm) ranged from 1230 kg N ha-1 in the pasture to 1370 kg N ha-1 in the oldest soybean fields. The trend of increasing N stocks with field age was statistically significant. The annual N accumulation by soybean plant biomass was 158,6 kg N ha-1 in the oldest soy fields, of which 79% was estimated to be derived by BNF, based on the natural abundance technique. There was no statistically significant trend in the mineralization and nitrification rates among the areas. However, extracts of soil profiles showed significant increases in deep soil nitrate concentrations in soybean soils compared to forest soils. There was no statistically significant trend in the soil \'delta\'15N within the chronosequence of soybean fields, although the values were intermediate between the soil \'delta\'15N values found in the pasture and the forest. These results showed a pattern of nitrogen accumulation in the soil along the chronosequence of soybean fields, indicating a possible gradual return to soil N stocks and isotopic signatures occurring in the forest soil before the conversion to pasture and soybean, although this may not happen in the near future

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