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Some aspects of nitrogen nutrition of Boronia Megastigma Nees

Reddy, KS 1987 , 'Some aspects of nitrogen nutrition of Boronia Megastigma Nees', PhD thesis, University of Tasmania.

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Boronia is a native plant with potential as a new essential oil
crop. Various growth and metabolic responses of boronia to N were
investigated to improve N nutrition of boronia.
When N was supplied to boronia at 50 or 100 kg ha-1 , two fast release
N sources (ammonium sulfate and calcium nitrate) caused
toxicity while a slow-release N source (IBDU) did not cause
toxicity. When N was supplied in a single dose in October during
the active vegetative growth phase, highest flower yield was
obtained and when the same amount of N was supplied in split doses
at different phases of plant growth, the yield decreased.
Increasing N levels from 0 to 25 mM in the nutrient solution
increased the plant's production of nodes, lateral shoots from
these nodes and further nodes on these lateral shoots. With the
same level of N, production of nodes and lateral shoots was in the
order: NH4+ +NO3- > NH4+ > NO3. The increase in the number of nodes
subsequently translated into increased number of axils initiating
flower buds and then into fully developed flowers. However,
increasing N levels decreased the percentage of total flower buds
that developed to anthesis and the individual flower weight.
Increasing N levels increased the leaf N concentration, with the
concentration in the order: NH4+ +NO3- > NH4+ > NO3- . N form did not
affect the leaf tissue concentrations of P, K, Ca and Mg. At lower
N levels, the concentrations of these nutrients in the leaf tissue
were higher and may have reached toxic levels and caused the
toxicity symptoms on the leaves. At higher N levels, the concentrations of these nutrients were diluted due to increased
growth and no toxicity symptoms were produced.
At decontrolled as well as controlled pH (4.5 and 6.5) of the
nutrient solution, uptake of NH4+ -N by the plant was higher than
that of NO3- -N. With NH4+ nutrition, concentrations of amides
(namely, asparagine and glutamine) in plant tissues were higher
than with NO3- nutrition.
When a low NO3- level (15 mmol per plant) was given, NO 3- entering
the plant was reduced without any accumulation and without nitrate
reductase (NR) activity reaching its maximum capacity. When higher
NO3- levels (>-25 mmol per plant) were given, NR activity increased
to a maximum of only ca. 500 nmol NO2 - g-1 fresh weight h-1 both in
the roots and leaves irrespective of 6-fold difference in the NO3-
supply while NO3- continued to accumulate in proportion to the level
of NO3- supplied. Consequently, high levels of NO3- accumulated in
the plant tissue and at ca. 32 umol NO3- g-1 fresh weight, toxicity
symptoms appeared on the leaves. The low level of NR in boronia
was not due to limited NO3- or electron donor availability, but it
seems to be genetically tuned to slow growth in low NO3- producing
native soils.
These responses of boronia to N are discussed in terms of the
plant's adaptations to survive in native soils and their
manipulation in commercial cultivation of boronia.

Item Type: Thesis - PhD
Authors/Creators:Reddy, KS
Keywords: Rutaceae, Plants
Copyright Holders: The Author
Copyright Information:

Copyright 1987 the Author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s).

Additional Information:

Thesis (Ph.D.)--University of Tasmania, 1990. Bibliography: p. 196-208

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