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¹⁵N discrimination as an indicator of nitrogen dynamics in Populus trichocarpa Buschhaus, Hannah Ariel Elizabeth
Abstract
The current understanding of nitrogen stable isotope ratios in plant tissues increasingly emphasizes the relationship between plant growth and nitrogen nutrition in determining plant δ15N. This demand relative to supply is thought to influence the plant's ability to discriminate against the heavier 15N. Discrimination (Dplant) is then linked to the ratio of efflux to influx. Factors which influence either of these thus affect Dplant- This thesis examines genotypic differences and physiological manipulations in Populus trichocarpa to further test the proposed efflux/influx model for Dplant. Substrate depletion experiments used ramets grown in hydroponic media containing 200µM NH4 + . Root pruning to reduce the plant's capacity to supply N correspondingly increased the rate of NH4 + uptake and decreased Dplant. Shoot pruning and genotypic variation did not appear to play a significant role in determining Dplant as assessed by this method. Substrate depletion experiments also allowed us to calculate the root NH4 + influx and efflux from the δ15N and the net uptake rate. This novel application of the efflux/influx model for discrimination generated efflux and influx values that corroborated existing radiolabelled 13N studies. The ability to accurately calculate efflux and influx using stable isotope methods at natural abundance levels provides a new, non-radioactive approach for further nutrient-uptake efficiency studies. In steady-state experiments, ramets were grown at either ambient (400ppm) or elevated (800ppm) atmospheric CO2 concentrations in either 200µM or 400µ.M NH4 + hydroponic media. Within the treatments, Dplant corresponded to the relative growth rate responses, signifying its dependence on physiological growth factors. Genotypic differences in the discrimination values of P. trichocarpa provenances could be manipulated by changing the supply/demand regimes. Plant tissue δ15N revealed an unexpected but distinct foliar enrichment. These data prompted the development of a revised efflux/influx model that accounts for translocation and subsequent assimilation of NH4 + in the leaves. This newest model now provides testable hypotheses for future NH4 + translocation and assimilation studies.
Item Metadata
Title |
¹⁵N discrimination as an indicator of nitrogen dynamics in Populus trichocarpa
|
Creator | |
Publisher |
University of British Columbia
|
Date Issued |
2007
|
Description |
The current understanding of nitrogen stable isotope ratios in plant tissues
increasingly emphasizes the relationship between plant growth and nitrogen nutrition in
determining plant δ15N. This demand relative to supply is thought to influence the
plant's ability to discriminate against the heavier 15N. Discrimination (Dplant) is then
linked to the ratio of efflux to influx. Factors which influence either of these thus affect
Dplant- This thesis examines genotypic differences and physiological manipulations in
Populus trichocarpa to further test the proposed efflux/influx model for Dplant.
Substrate depletion experiments used ramets grown in hydroponic media
containing 200µM NH4
+ . Root pruning to reduce the plant's capacity to supply N
correspondingly increased the rate of NH4
+ uptake and decreased Dplant. Shoot pruning
and genotypic variation did not appear to play a significant role in determining Dplant as
assessed by this method. Substrate depletion experiments also allowed us to calculate
the root NH4
+ influx and efflux from the δ15N and the net uptake rate. This novel
application of the efflux/influx model for discrimination generated efflux and influx
values that corroborated existing radiolabelled 13N studies. The ability to accurately
calculate efflux and influx using stable isotope methods at natural abundance levels
provides a new, non-radioactive approach for further nutrient-uptake efficiency studies.
In steady-state experiments, ramets were grown at either ambient (400ppm) or
elevated (800ppm) atmospheric CO2 concentrations in either 200µM or 400µ.M NH4
+
hydroponic media. Within the treatments, Dplant corresponded to the relative growth rate
responses, signifying its dependence on physiological growth factors. Genotypic
differences in the discrimination values of P. trichocarpa provenances could be
manipulated by changing the supply/demand regimes. Plant tissue δ15N revealed an
unexpected but distinct foliar enrichment. These data prompted the development of a
revised efflux/influx model that accounts for translocation and subsequent assimilation of
NH4
+ in the leaves. This newest model now provides testable hypotheses for future NH4
+
translocation and assimilation studies.
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Genre | |
Type | |
Language |
eng
|
Date Available |
2011-03-02
|
Provider |
Vancouver : University of British Columbia Library
|
Rights |
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.
|
DOI |
10.14288/1.0074934
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URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
|
Campus | |
Scholarly Level |
Graduate
|
Aggregated Source Repository |
DSpace
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Item Media
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Rights
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.