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Doctoral Thesis
DOI
https://doi.org/10.11606/T.11.1983.tde-20210104-155402
Document
Author
Full name
Paulo Cesar Ocheuze Trivelin
E-mail
Institute/School/College
Knowledge Area
Date of Defense
Published
Piracicaba, 1982
Supervisor
Title in Portuguese
Medida da fixação simbiótica do nitrogênio marcando-se a atmosfera do solo com 15N2 a baixo enriquecimento isotópico
Keywords in Portuguese
ENRIQUECIMENTO ISOTÓPICO
FEIJÃO
FIXAÇÃO SIMBIÓTICA DE NITROGÊNIO
NITROGÊNIO-15
SOLOS
Abstract in Portuguese
Foi desenvolvida uma metodologia para medir diretamente a fixação simbiótica do nitrogênio, por todo o ciclo de leguminosas, marcando-se a atmosfera do solo com 15N2 a baixo enriquecimento isotópico. Nas determinações no campo e em casa de vegetação estabeleceu-se o confinamento do solo explorado pelo sistema radicular das plantas, utilizando respectivamente uma câmara e vasos vedados, a fim de manter a atmosfera do solo marcada com 15N2. A concentração média de 15N no ar do solo, necessária no cálculo de medida da fixação do de nitrogênio, foi obtida por integração de funções exponenciais de diluição do isótopo, verificadas nos experimentos, a partir de análises isotópicas do N2 da atmosfera do solo. O experimento no campo com atmosfera marcada desenvolveu- se do 22º ao 31º dia do ciclo da cultura do feijoeiro, e foi possível determinar a fixação de 5,5 mg de N por planta (24% do N-total/planta). Em experimentos com vasos foram feitas medidas integradas da fixação de N nas culturas do feijoeiro (do 19º ao 67º dia do plantio) e da soja (do 24º ao 70º dia do plantio), marcando-se a atmosfera do solo com 15N2. Para o feijoeiro foi obtida a fixação de 80 mg de N/planta (65% do N-total/planta), e 265 mg de N/planta (71% do N-total/planta) para a soja. No presente trabalho avaliou-se também a teoria básica do método de quantificação da fixação de N por diluição isotópica, proposto por FRIED e MIDDELBOE (1977), em experimentos com vasos. Medidas simultâneas da fixação de N na soja utilizando os métodos: diluição isotópica de Fried e Middelboe, variação natural das razões 15N/14N e por diferença no N-total foram realizadas, e evidenciaram os mesmos resultados para as condições de experimentação em vaso, com as colheitas realizadas no final do ciclo das plantas.
Title in English
Determination of symbiotic nitrogen fixation by labelling the soil atmosphere with 15N2 at low isotope enrichment
Keywords in English

Abstract in English
A direct method to determine the total symbiotic nitrogen fixation during the leguminous plants cycles has been developed, by labelling the soil atmosphere with 15N2 at low isotope enrichment, of about 1 atom % excess. The soil explored by the root system of leguminous plants was confined by means of a chamber in the field and by sealed pots in greenhouse experiments in order to montain the soil air labelled with 15N2. The average 15N concentration in the soil atmosphere, necessary to calculate dinitrogen fixation, was obtained by integration of the exponential functions of isotope dilution. Those functions were obtained by periodic sampling and analysis of the N2 in the soil atmosphere. The field experiment with labelled atmosphere was carried out from the 22nd to the 31st day of the bean crop cycle and 5.5 mg N/plant (24% of total plant N) was derived from fixation. In pot experiments, under greenhouse conditions, integrated determination of fixation was made in Phaseolus beans (from the 19th to the 67th day from planting) and in soybeans (from the 24th to the 70th day from planting). The soil atmosphere was labelled with 15N2 in both cases. Average fixation obtained for Phaseolus beans was 80 mg N/plant (65% of total plant N) and for soybeans 265 mg N/plant (71% of total plant N). Evaluation of the basic concept of the isotope dilution method to determine nitrogen fixation in pots experiments, as proposed by Fried and Middelboe (1977) has also been made in the present paper. Simultaneous determinations of fixation in soybeans, using the isotope dilution method of Fried and Middelboe, natural variation of the 15N/14N ratios, and total-N differences, indicated the same results for pot experiments, harvested at the end of the plant cycle.
 
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Publishing Date
2021-01-07
 
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