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Boreal peatlands play important roles in global C and nutrient cycling. Oligotrophic bogs are naturally nitrogen (N) limited, receiving nutrients only via atmospheric deposition. Increased nutrient deposition, particularly N will almost certainly change the microbiology, biogeochemistry, and C and nutrient balances in bogs. Both primary production and decomposition can be affected, but the net effects of N fertilization are complex and unclear. A three-year N fertilization experiment with 15N double labeled 15NH415NO3 as a tracer was designed to study the effects of increasing N deposition on various N pools (including microbial communities, moss, roots, litter, and aboveground vascular plants) and how these N pools process and retain applied N in four ombrogenous bogs in northern Alberta, Canada. Linear growth of Sphagnum mosses was highly variable. However, both capitulum and stem weight showed increase in weight with N addition, resulting in significant increase of capitulum and stem bulk density with N deposition. Total annual primary production, with both capitulum and stem growth accounted for, doubled from low N deposition plots to high N deposition plots. Microbial biomass N measured by chloroform fumigation-extraction only showed a decrease with N deposition in the first year of the experiment. Fungal biomass declined with N deposition as nutrients are readily available under high N loads, perhaps eliminating the need for help from symbiotic fungi for nutrient uptake. The growth of Sphagnum mosses and microbial communities may have been influenced by drier and warmer growing period during 2005 to 2007. These abnormal climatic events could have masked the effects of N deposition on surface Sphagnum moss and microbial communities. This 15N tracer experiment revealed high retention rates of 15N by moss layers as expected. However, retention efficiency of moss layers declined over time and with increasing N deposition, indicating a leakier system as N deposition exceeds the critical load of Sphagnum moss. Aboveground vascular plants overall benefited from N deposition, but different species responded differently based on the root morphology, rooting depths, and the mycorrhizae associations.

Natural abundance of 15N varies greatly and unpredictably within and between environments. The unpredictable nature of 15N limits the use of N isotope natural abundance (d15N) in tracing the flow and fate of N in environments. Recent investigations have, however, revealed consistent and repeatable patterns of 15N in some ecosystem components. These patterns suggest that d15N may yet provide a tool to investigate and illuminate ecosystem N cycling processes. Identifying and quantifying the sources of isotopic variation must precede any significant advance in the application of this technique, and to this end an assessment of isotopic variation associated with major ecosystem components has been carried out in this thesis. d15N patterns have been established, hypotheses proposed and tested, and conclusions about the application of the technique are presented. 15N patterns in surface and groundwater were measured in a variety of different land-use catchments in an attempt to identify distinct isotopic 'fingerprints'. High levels of 15N variation were measured in both stream and groundwaters, resulting in strongly overlapping land-use 'fingerprints'. Environmental 15N variation in streams and groundwaters was found to be too great to differentiate between land-uses based on d15N alone. In contrast, the artificially 15N enriched signature of effluent N was used to trace its flow and fate, following irrigation, in a forested catchment. The effluent d15N signature allowed it to be traced into the major ecosystem components, permitting a first order N budget to be determined for effluent N storage and loss. N sources with significantly different 15N signatures to that of 'background ecosystem N' can therefore be used to trace the flow and fate of N in ecosystems. During the course of this work a number of higher and lower order plants were observed to have highly depleted (lt; -8 ) d15N signatures. Epiphytes and lithophytes, strongly reliant on atmospheric N sources, were consistently depleted in 15N, with signatures as low as -24 , measured in a range of environments. A similar level of depletion was measured in a wide range of plants growing in early primary succession sites (as low as -22.3 ), which could not be accounted for by any abiotic or biotic factor or significantly depleted N source. The absence of any measurable driver of depletion suggested a universal fractionating mechanism which acts in a wide range of environments and vegetation types. Diffusive uptake of atmospheric NH3(g) and the proportional uptake of a supplied N source were two proposed mechanisms that could theoretically account for the level and universal nature of depletion. Diffusive uptake of atmospheric NH3(g) was tested as a primary fractionating mechanism in plants. Strongly N deficient plants were capable of utilising NH3(g) as a nutritional source, but the level of 15N depletion measured in these plants closely approximated that of the inherent NH3(g) d15N signature. No significant additional fractionation is associated with NH3(g) diffusive uptake. Diffusive uptake of atmospheric NH3(g) by plants cannot alone account for the level of depletion measured in early primary succession plant communities. Proportional uptake of a N source as a primary fractionating mechanism was tested by growing plants in various concentrations and rates of applied N. Fractionation attributed to the proportional uptake of a supplied N source, as a consequence of P limitation or rapid flow over roots, resulted in a significant level of 15N depletion in plants. The level of depletion attributed to this mechanism was, however, not sufficient to account for the level measured in early primary succession plant communities. Individual 15N fractionating mechanisms cannot alone explain the level of depletion observed in early primary succession plants, however a combination of fractionating mechanisms can. Fractionation attributed to the proportional uptake of an already depleted N source, i.e., wet deposited N, largely accounts for the level of depletion measured in early succession plant communities. This two-step fractionation model can act on both higher and lower plants, independent of ecosystem biotic and abiotic factors. Additional, and less dramatic fractionations attributed to atmospheric NH3(g) uptake, mycorrhizal associations, internal remobilisation, and taxon-specific N acquisition strategies, will contribute to the level of d15N depletion. This thesis presents the first extensive survey of highly depleted d15N signatures in terrestrial vegetation. Furthermore, thorough testing of theoretically plausible mechanisms has resulted in a full account of the highly depleted d15N signatures measured in a wide range of vegetation types and environments.

The solid product of pyrolysis, called \"biochar\" (BC) in the context of improving soil properties as part of agronomic or environmental management, also got into focus as a climate mitigation strategy. The researcher investigated the effects of BC on soil attributes, nitrogen (N) use and GHG emissions. In Chapter 1 the origin of BC was commented. In Chapter 2, BC from sugarcane straw was characterized, and its priming on native SC was evaluated with the treatments: (T1) Soil; (T2) BC; (T3) Soil + BC 10 Mg ha-1; (T4) Soil + BC 20 Mg ha-1; and (T5) Soil + BC 50 Mg ha-1. In Chapter 3, it was evaluated the combination of BC, filter cake (F) and vinasse (V), in relation to soil attributes and carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) emissions. The treatments were: (T1) Soil + FC + V; (T2) Soil + FC + V + BC 10 Mg ha-1; (T3) Soil + FC + V + BC 20 Mg ha-1; and (T4) Soil + FC + V + BC 50 Mg ha-1. In Chapter 4, the nitrogen (N) use efficiency was investigated in a pot trial under wheat using NH4[15N]O3 and rates of BC, with the treatments: (T1) Soil, with N, no BC; (T2) Soil, with N, BC 10 Mg ha-1; (T3) Soil, with N, BC 20 Mg ha-1; and (T4) Soil, with N, BC 50 Mg ha-1. BC had C and N contents higher compared to the feedstock. Total K, Mg and P also increased. The lowest CO2 fluxes were for BC, and CO2 from soil and soil + BC did not differ. The highest CO2 - C4 was in the first day, and there were no differences in the CO2 - C3. The BC presents characteristics to improve soil attributes. BC stability is an opportunity to reduce CO2 emissions. In Chapter 3, soil pH, P and base contents increased and Al3+ decreased with BC to sandy soil. Impacts of BC on the CEC were higher in sandy soil. Mineral N decreased with BC. Cumulative CO2 in T1 were higher in sandy and clayey soils than the control. T2 and T3 in sandy soil increased CO2 emissions, but T4 did not differ from T1. BC reduced N2O emissions from sandy and clayey soils relative to T1. BC with FC and V affected pH, CEC, P and base contents. However, those effects were higher in sandy soil. The BC supressed N2O from V and FC. In Chapter 4, BC decreased N2O from N fertilization compared to only N fertilizer. T4 had higher tillering and grain yield. Also, T2 to T4 had higher 100-grain weight and shoot. T3 and T4 had the highest N in grains. The application of BC to soil improves N availability and use efficiency, enhances grain yields and reduces N2O from N fertilization. This study opened encouraging perspectives to the evaluation of sugarcane straw BC to improve soil quality and mitigate GHG emissions. / O produto sólido da pirólise, denominado \"biochar\" (BC) no contexto da melhoria nos atributos do solo como parte do manejo agrícola e ambiental, também tem se destacado na mitigação das mudanças climáticas. O pesquisador investigou os efeitos do BC nos atributos do solo, uso do nitrogênio (N) e emissões de GEE. No Cap. 1 comentou-se a origem do BC. No Cap. 2, caracterizou-se o BC de palha de cana-de-açúcar e avaliou-se o potencial de decomposição do C do solo, com os tratamentos: (T1) Solo; (T2) BC; (T3) Solo + BC 10 Mg ha-1; (T4) Solo + BC 20 Mg ha-1 (T4); e (T5) Solo + BC 50 Mg ha-1. No Cap. 3, avaliou-se a combinação BC, torta de filtro (TF) e vinhaça (V) em atributos do solo e fluxos de dióxido de carbono (CO2), metano (CH4) e óxido nitroso (N2O) nos tratamentos: (T1) Solo + TF + V; (T2) Solo + TF + V + BC 10 Mg ha-1; (T3) Solo + TF + V + BC 20 Mg ha-1; e (T4) Solo + TF + V + BC 50 Mg ha-1. No Cap. 4 investigou-se a eficiência de uso do N num experimento em vasos com trigo usando NH4 [15N]O3 e doses de BC, com os tratamentos: (T1) Solo, com N, sem BC; (T2) Solo, com N, BC 10 Mg ha-1; (T3) Solo, com N, BC 20 Mg ha-1; e (T4) Solo, com N, BC 50 Mg ha-1. Os teores de C e N do BC foram maiores comparado à biomassa. K, Mg e P totais também aumentaram. Os menores fluxos de CO2 foram do BC. O CO2 do solo e solo + BC não diferiram. Observou-se maior CO2 - C4 no primeiro dia de incubação, porém sem diferenças no CO2 - C3. O BC apresenta características para melhorar atributos do solo e reduzir as emissões de CO2. No Cap. 3, pH, P e bases aumentaram e o Al3+ diminuíu com o BC. Os impactos do BC na CTC foram maiores em solo arenoso. O N mineral diminuíu com o BC. O CO2 acumulado no T1 foi maior nos solos arenoso e argiloso comparado ao controle. O T2 e T3 aumentaram o CO2 acumulado do arenoso relativo ao T1, enquanto T4 e T1 não diferiram. O BC reduziu as emissões de N2O pelos solos arenoso e argiloso comparado ao T1. O BC combinado à TF e V afetaram pH, CTC, P e bases do solo arenoso. O BC suprimiu o N2O de solos com V e TF. No Cap. 4, o BC diminuíu as emissões de N2O comparado ao fertilizante N apenas. T4 teve rendimento de grãos superior ao T1. T2 a T4 apresentaram maior peso de 100 grãos e biomassa aérea. T3 e T4 tiveram maior N em grãos. O BC melhora o uso do N, a produção de grãos e reduz o N2O de fertilizante N, abrindo perspectivas para a avaliação do BC de palha de cana-de-açúcar na melhoria da qualidade do solo e mitigar das emissões de GEE.

The solid product of pyrolysis, called \"biochar\" (BC) in the context of improving soil properties as part of agronomic or environmental management, also got into focus as a climate mitigation strategy. The researcher investigated the effects of BC on soil attributes, nitrogen (N) use and GHG emissions. In Chapter 1 the origin of BC was commented. In Chapter 2, BC from sugarcane straw was characterized, and its priming on native SC was evaluated with the treatments: (T1) Soil; (T2) BC; (T3) Soil + BC 10 Mg ha-1; (T4) Soil + BC 20 Mg ha-1; and (T5) Soil + BC 50 Mg ha-1. In Chapter 3, it was evaluated the combination of BC, filter cake (F) and vinasse (V), in relation to soil attributes and carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) emissions. The treatments were: (T1) Soil + FC + V; (T2) Soil + FC + V + BC 10 Mg ha-1; (T3) Soil + FC + V + BC 20 Mg ha-1; and (T4) Soil + FC + V + BC 50 Mg ha-1. In Chapter 4, the nitrogen (N) use efficiency was investigated in a pot trial under wheat using NH4[15N]O3 and rates of BC, with the treatments: (T1) Soil, with N, no BC; (T2) Soil, with N, BC 10 Mg ha-1; (T3) Soil, with N, BC 20 Mg ha-1; and (T4) Soil, with N, BC 50 Mg ha-1. BC had C and N contents higher compared to the feedstock. Total K, Mg and P also increased. The lowest CO2 fluxes were for BC, and CO2 from soil and soil + BC did not differ. The highest CO2 - C4 was in the first day, and there were no differences in the CO2 - C3. The BC presents characteristics to improve soil attributes. BC stability is an opportunity to reduce CO2 emissions. In Chapter 3, soil pH, P and base contents increased and Al3+ decreased with BC to sandy soil. Impacts of BC on the CEC were higher in sandy soil. Mineral N decreased with BC. Cumulative CO2 in T1 were higher in sandy and clayey soils than the control. T2 and T3 in sandy soil increased CO2 emissions, but T4 did not differ from T1. BC reduced N2O emissions from sandy and clayey soils relative to T1. BC with FC and V affected pH, CEC, P and base contents. However, those effects were higher in sandy soil. The BC supressed N2O from V and FC. In Chapter 4, BC decreased N2O from N fertilization compared to only N fertilizer. T4 had higher tillering and grain yield. Also, T2 to T4 had higher 100-grain weight and shoot. T3 and T4 had the highest N in grains. The application of BC to soil improves N availability and use efficiency, enhances grain yields and reduces N2O from N fertilization. This study opened encouraging perspectives to the evaluation of sugarcane straw BC to improve soil quality and mitigate GHG emissions. / O produto sólido da pirólise, denominado \"biochar\" (BC) no contexto da melhoria nos atributos do solo como parte do manejo agrícola e ambiental, também tem se destacado na mitigação das mudanças climáticas. O pesquisador investigou os efeitos do BC nos atributos do solo, uso do nitrogênio (N) e emissões de GEE. No Cap. 1 comentou-se a origem do BC. No Cap. 2, caracterizou-se o BC de palha de cana-de-açúcar e avaliou-se o potencial de decomposição do C do solo, com os tratamentos: (T1) Solo; (T2) BC; (T3) Solo + BC 10 Mg ha-1; (T4) Solo + BC 20 Mg ha-1 (T4); e (T5) Solo + BC 50 Mg ha-1. No Cap. 3, avaliou-se a combinação BC, torta de filtro (TF) e vinhaça (V) em atributos do solo e fluxos de dióxido de carbono (CO2), metano (CH4) e óxido nitroso (N2O) nos tratamentos: (T1) Solo + TF + V; (T2) Solo + TF + V + BC 10 Mg ha-1; (T3) Solo + TF + V + BC 20 Mg ha-1; e (T4) Solo + TF + V + BC 50 Mg ha-1. No Cap. 4 investigou-se a eficiência de uso do N num experimento em vasos com trigo usando NH4 [15N]O3 e doses de BC, com os tratamentos: (T1) Solo, com N, sem BC; (T2) Solo, com N, BC 10 Mg ha-1; (T3) Solo, com N, BC 20 Mg ha-1; e (T4) Solo, com N, BC 50 Mg ha-1. Os teores de C e N do BC foram maiores comparado à biomassa. K, Mg e P totais também aumentaram. Os menores fluxos de CO2 foram do BC. O CO2 do solo e solo + BC não diferiram. Observou-se maior CO2 - C4 no primeiro dia de incubação, porém sem diferenças no CO2 - C3. O BC apresenta características para melhorar atributos do solo e reduzir as emissões de CO2. No Cap. 3, pH, P e bases aumentaram e o Al3+ diminuíu com o BC. Os impactos do BC na CTC foram maiores em solo arenoso. O N mineral diminuíu com o BC. O CO2 acumulado no T1 foi maior nos solos arenoso e argiloso comparado ao controle. O T2 e T3 aumentaram o CO2 acumulado do arenoso relativo ao T1, enquanto T4 e T1 não diferiram. O BC reduziu as emissões de N2O pelos solos arenoso e argiloso comparado ao T1. O BC combinado à TF e V afetaram pH, CTC, P e bases do solo arenoso. O BC suprimiu o N2O de solos com V e TF. No Cap. 4, o BC diminuíu as emissões de N2O comparado ao fertilizante N apenas. T4 teve rendimento de grãos superior ao T1. T2 a T4 apresentaram maior peso de 100 grãos e biomassa aérea. T3 e T4 tiveram maior N em grãos. O BC melhora o uso do N, a produção de grãos e reduz o N2O de fertilizante N, abrindo perspectivas para a avaliação do BC de palha de cana-de-açúcar na melhoria da qualidade do solo e mitigar das emissões de GEE.

Mit zunehmender Meereshöhe werden die Wachstumsbedingungen in tropischen Bergregionen im Allgemeinen ungünstiger, was sich in einer sinkenden Nährstoffverfügbarkeit, sinkenden Temperaturen und sinkendem CO2-Partialdruck zeigt. In tropischen Bergregenwäldern führen verminderte Abbauraten in größeren Höhen einerseits zu dicken organische Auflageschichten und andererseits in Kombination mit verminderten Mineralisierungs- und Nitrifizierungsraten zu Veränderungen in der Verfügbarkeit der verschiedenen Stickstoffformen, und es gibt Nachweise einer Limitierung der Produktivität dieser Wälder durch Stickstoff. Auf welche Weise sich die Photosynthesekapazität (Amax) tropischer Bäume einerseits und die Stickstoffaufnahmekapazität und Präferenz für einzelne Stickstoffformen andererseits an die veränderten Umweltbedingungen entlang von Höhengradienten adaptieren ist nicht genau bekannt. Die vorliegende Untersuchung wurde in drei tropischen Bergregenwäldern durchgeführt, die entlang eines Höhengradienten auf 1000, 2000 und 3000 m ü. NN in Südequador liegen. Das Ziel war es, (1) die Photosynthesekapazität ausgewachsener tropischer Bäume entlang eines Höhengradienten mit Hilfe von Gaswechselmessungen zu bestimmen und die Effekte von Temperatur, CO2-Partialdruck und Nährstoffverfügbarkeit auf die Photosynthese zu quantifizieren und (2) Veränderungen in der Verwendung von Nitrat, Ammonium und organischen Stickstoffquellen durch tropische Waldbäume mit der Meereshöhe mittels einer Tracer-Untersuchung mit stabilen Isotopen an Jungpflanzen zu untersuchen. Mittelwerte der lichtgesättigten Photosyntheserate (Asat) auf Bestandeseben betrugen 8.8, 11.3 und 7.2 µmol CO2 m-2 s-1, die der Dunkelatmung (RD) 0.8, 0.6 und 0.7 µmol CO2 m-2 s-1 jeweils auf 1000, 2000 and 3000 m Meereshöhe, ohne einen signifikanten Höhentrend. Die Einordnung unserer Daten in den Kontext eines pantropischen Asat-Datensatzes von tropischen Bäumen (c. 170 Arten an 18 Standorten unterschiedlicher Meereshöhe) zeigte, dass das flächenbezogene Asat in tropischen Bergen im Mittel 1.3 µmol CO2 m-2 s-1 pro km Höhenzunahme abnimmt (bzw. 0.2 µmol CO2 m-2 s-1 pro K Temperaturabnahme). Die Abnahme von Asat trat auf, obwohl die Blattmasse je Fläche mit der Höhe zunahm. Eine verminderte Photosyntheserate und eine reduzierte Bestandesblattfläche bewirken gemeinsam eine Verringerung der Kohlenstoffaufnahme des Kronenraums mit der Meereshöhe in tropischen Bergregionen. Der Phosphorgehalt pro Blattmasse war der Faktor, der Amax entlang des Höhengradienten hauptsächlich beeinflusste, während die Effekte von Blattstickstoff, Temperatur und CO2-Partialdruck nicht signifikant waren. Amax erfuhr einen teilweisen und RD einen vollständigen homöostatischen Ausgleich als Reaktion auf die Verminderung von Temperatur und CO2-Partialdruck in größeren Höhen, was hauptsächlich durch eine stark reduzierte spezifische Blattfläche (SLA) und die daraus entstehende Zunahme von Blattstickstoff und -phosphor je Blattfläche bedingt war, während keine Zunahme der Karboxylierungseffizienz festgestellt wurde. Wir schlussfolgern, dass die Verminderung von SLA und Gesamtblattfläche mit der Meereshöhe die Kohlenstoffaufnahme von tropischen Wäldern in großen Meereshöhen deutlich stärker bestimmen als adaptive physiologische Modifizierungen des Photsyntheseapparates. Jungpflanzen von sechs Baumarten unterschieden sich hinsichtlich ihrer Präferenz für verschieden Stickstoffformen, allerdings schienen weder das Amonium- und Nitratvorkommen im Boden noch die Meereshöhe die Präferenz zu beeinflussen. Zwei Arten (jeweils die, mit den höchsten Wachstumsraten) bevorzugten Amonium gegenüber Nitrat, während die restlichen vier Arten Nitrat und Amonium mit ähnlichen Raten aufnahmen, wenn beide Stickstofformen verfügbar waren. Nach der Gabe von 15N13C-Glyzin zeigte sich bei drei Arten eine signifikante Akkumulierung von 13C in der Biomasse (zwei Arten mit arbuskulären Mykorrhiza und eine Art mit Ektomykorrhiza) zusätzlich zu einer signifikanten Akkumulierung von 15N, was darauf hindeutet, dass Bäume in tropischen Bergregenwäldern organische Stickstoffverbindungen unabhängig vom Typ ihrer Mykorrhizierung aufnehmen können.

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