Microbial nitrogen (N2) fixation supplies important nitrogen inputs to boreal peatlands, extremely oligotrophic ecosystems dominated by Sphagnum mosses. In this study, we coupled major and trace nutrient analyses and rate measurements to characterize interactions between N2 fixation and CH4 cycling at the S1 peat bog in Marcell Experimental Forest and the Zim bog (Minnesota, USA). Total dissolved inorganic nitrogen (NO3-+NO2-+NH4+) and phosphate were both consistently < 2 μM in the porewater of surface peat, indicating severe nutrient limitation. While dissolved Fe was fairly abundant (18-35 mM), Mo, V and Cu were scarce (2-40 nM), suggesting that alternative metalloenzymes containing Fe in place of other metals may be favored. Rates of diazotrophy measured by both 15N2 incorporation and the acetylene (C2H2) reduction assay (ARA) were 7-fold higher under anoxic vs. oxic incubations conducted at both 4°C and 25°C. No significant difference in N2 fixation rates measured by either method was observed with or without the amendment of 1% CH4 at 25 °C; however, a significant inhibitory effect by methane was seen at 4°C in material from the S1 bog hollows. Anoxic 15N2 incorporation was 3-4x higher in treatments lacking acetylene, suggesting that the ARA likely underestimates N2 fixation by inhibiting diazotrophs sensitive to C2H2. Aerobic methanotrophy was also inhibited by 1% C2H2 when incubated under oxic conditions. No observations for the production of ethane (C2H6) were detected during the ARA, a biomarker for alternative nitrogenase activity. Major differences in ARA rates were observed to vary locally within microhabitats and between two bogs. In June 2014, peat sampled from hollows incubated under anoxic conditions showed the highest ARA rates (94.9 ± 11.0 nmol C2H4 g-1 moss dry mass hr-1), while the lowest rates were observed in ix hummock samples incubated under oxic conditions (5.1 ± 0.8 nmol C2H4 g-1 moss dry mass hr-1) in the S1 bog (T3 site). Observed rates have the potential to be a function of oxygen concentrations and or water content. ARA rates in all microcosm treatments were significantly lower at Zim bog compared to the S1 bog. The developed conversion factor between the regression of 15N2 and ARA in this study was 3.9 and agrees with the theoretical conversion factor as well as previous studies of soils and forest mosses.

Zooplankton were sampled on a monthly basis at the Bermuda Atlantic Time-series Study (BATS) site from January 1995 to December 1999. Samples were collected using a 1-m², 200 µm mesh net. The net sampled the water column in an oblique manner from the surface to a mean depth of 200 m. One day and one night tow from each cruise was examined microscopically to determine the community structure of the non-calanoid copepods. In addition, a three year set of nighttime samples were examined taken by 0.5-m², 20 and 35 µm mesh nets (1995-1996 and 1997, respectively) towed obliquely to 150 m. The dominant orders in terms of overall abundance were the Cyclopoida and Poecilostomatoida. The cyclopoid genus, Oithona, was most abundant followed by the Poecilostomatoid family, Oncaeidae, and the genera Farranula and Corycaeus. Harpacticoids, although common, were about an order of magnitude less abundant and were dominated by Macrosetella gracilis. Representatives of the Mormonilloida and Siphonostomatoida also were frequently encountered, although in much lower numbers. Overall, pronounced seasonal signals were noted; highest abundances occurred during spring and lowest during winter. However, abundance of some groups peaked either in the fall or winter, with lowest abundance in spring or summer. Miraciid copepods are estimated to consume an overall average of 359 µg C m-2 d-1 and regenerate 55 µg N m-2 d-1 derived from Trichodesmium at BATS. Highest grazing and regeneration rates were found in late summer through fall and early winter and lowest in spring and early summer. The ecological consequences of miraciid copepod feeding on Trichodesmium are discussed. The 20-35 µm net samples revealed an astonishing abundance of non-copepod species, some totally missed and others woefully under-sampled by the 200 µm net. At least four species of oncaeid copepods and the harpacticoid copepod Microsetella norvegica were found in abundances that were more than an order of magnitude higher than the corresponding numbers of non-calanoid copepods sampled by the 200 µm net. The role of all non-calanoid copepods, from both net systems, in C and N dynamics at BATS is analyzed and discussed along with the sex-ratios of most identified species.

京都大学 / 0048 / 新制・課程博士 / 博士(農学) / 甲第21150号 / 農博第2276号 / 新制||農||1059(附属図書館) / 学位論文||H30||N5124(農学部図書室) / 京都大学大学院農学研究科地域環境科学専攻 / (主査)教授 北山 兼弘, 教授 小杉 緑子, 教授 本田 与一 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DGAM

The introduction of N2-fixing trees in mixed forest systems is a recent strategy that can reduce the use of external inputs and increase the Eucalyptus plantations sustainability. In these systems, there is a strong interconnection between the trees, which occurs through a complex network of interactions between microorganisms, above and belowground. These interactions result in innumerable biological functions and ecosystem services, which are essential for soil and plant health. Moreover, the result of the Eucalyptus-microbiome-Acacia interaction has been pointed out as essential in achieving higher Eucalyptus productivity indexes in mixed systems. Our aim was to explore the dynamics of microbiome related to nutrient cycling in pure and mixed Eucalyptus grandis and Acacia mangium plantations. Specifically, our efforts were focused on the microbiome benefits to the biological functions improvement in commercial Eucalyptus plantations driving by Acacia introduction in the system. We also give details regarding as the knowledge of the microbiome diversity, composition and functions can help us to understand their close relationship with carbon (C) and nitrogen (N) cycling in soil and litter layers. We believe that holistic approaches in which we can explore the biological interactions in systems using plants of high ecological value (Acacia) and high economic value (Eucalyptus) will be inevitable in the near future. If we learn how to manipulate important processes mediated by the microbiome involved in these interactions, we will take an important step to overcome the current resource constraints, combining increased productivity with the ecological intensification of forest plantations and the environmental sustainability. / A inserção de árvores fixadoras de nitrogênio (N2) em sistemas florestais mistos é uma estratégia recente que pode reduzir o uso de inputs externos e aumentar a sustentabilidade das plantações de Eucalipto. Nesses sistemas, existe uma forte interconexão entre as árvores, a qual ocorre por uma complexa rede de interações entre micro-organismos, acima e abaixo do solo. Essas interações resultam em inúmeros processos biológicos e serviços ecossistêmicos, os quais são essenciais para a saúde do solo e das plantas. Além do mais, o resultado da interação Eucalipto-microbioma-Acácia tem sido apontado como essencial no alcance de maiores índices de produtividade do Eucalipto em sistemas mistos. Nosso objetivo foi explorar a dinâmica do microbioma relacionado à ciclagem de nutrientes em plantações puras e mistas de Eucalyptus grandis e Acacia mangium. Especificamente, nossos esforços focaram nos benefícios do microbioma para a melhoria de funções biológicas, principalmente aquelas promovidas pela introdução da Acácia em plantações comerciais de Eucalipto. Por exemplo, abordamos detalhes como o conhecimento da diversidade, composição e funções desse microbioma pode nos ajudar a compreender sua íntima relação com a ciclagem de carbono (C) e nitrogênio (N) no solo e na serapilheira. Acreditamos que abordagens holísticas, com as quais possamos explorar as interações biológicas em sistemas com plantas de alto valor ecológico (Acácia) e alto valor econômico (Eucalipto) serão inevitáveis no futuro. Se aprendermos a manipular alguns processos mediados pelo microbioma envolvido nessas interações, daremos um passo importante para superar as atuais limitações de recursos, aliando o aumento da produtividade com a intensificação ecológica das plantações florestais e a sustentabilidade do meio ambiente.

The introduction of N2-fixing trees in mixed forest systems is a recent strategy that can reduce the use of external inputs and increase the Eucalyptus plantations sustainability. In these systems, there is a strong interconnection between the trees, which occurs through a complex network of interactions between microorganisms, above and belowground. These interactions result in innumerable biological functions and ecosystem services, which are essential for soil and plant health. Moreover, the result of the Eucalyptus-microbiome-Acacia interaction has been pointed out as essential in achieving higher Eucalyptus productivity indexes in mixed systems. Our aim was to explore the dynamics of microbiome related to nutrient cycling in pure and mixed Eucalyptus grandis and Acacia mangium plantations. Specifically, our efforts were focused on the microbiome benefits to the biological functions improvement in commercial Eucalyptus plantations driving by Acacia introduction in the system. We also give details regarding as the knowledge of the microbiome diversity, composition and functions can help us to understand their close relationship with carbon (C) and nitrogen (N) cycling in soil and litter layers. We believe that holistic approaches in which we can explore the biological interactions in systems using plants of high ecological value (Acacia) and high economic value (Eucalyptus) will be inevitable in the near future. If we learn how to manipulate important processes mediated by the microbiome involved in these interactions, we will take an important step to overcome the current resource constraints, combining increased productivity with the ecological intensification of forest plantations and the environmental sustainability. / A inserção de árvores fixadoras de nitrogênio (N2) em sistemas florestais mistos é uma estratégia recente que pode reduzir o uso de inputs externos e aumentar a sustentabilidade das plantações de Eucalipto. Nesses sistemas, existe uma forte interconexão entre as árvores, a qual ocorre por uma complexa rede de interações entre micro-organismos, acima e abaixo do solo. Essas interações resultam em inúmeros processos biológicos e serviços ecossistêmicos, os quais são essenciais para a saúde do solo e das plantas. Além do mais, o resultado da interação Eucalipto-microbioma-Acácia tem sido apontado como essencial no alcance de maiores índices de produtividade do Eucalipto em sistemas mistos. Nosso objetivo foi explorar a dinâmica do microbioma relacionado à ciclagem de nutrientes em plantações puras e mistas de Eucalyptus grandis e Acacia mangium. Especificamente, nossos esforços focaram nos benefícios do microbioma para a melhoria de funções biológicas, principalmente aquelas promovidas pela introdução da Acácia em plantações comerciais de Eucalipto. Por exemplo, abordamos detalhes como o conhecimento da diversidade, composição e funções desse microbioma pode nos ajudar a compreender sua íntima relação com a ciclagem de carbono (C) e nitrogênio (N) no solo e na serapilheira. Acreditamos que abordagens holísticas, com as quais possamos explorar as interações biológicas em sistemas com plantas de alto valor ecológico (Acácia) e alto valor econômico (Eucalipto) serão inevitáveis no futuro. Se aprendermos a manipular alguns processos mediados pelo microbioma envolvido nessas interações, daremos um passo importante para superar as atuais limitações de recursos, aliando o aumento da produtividade com a intensificação ecológica das plantações florestais e a sustentabilidade do meio ambiente.

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.

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