Diffusion,Boundary Layers And The Uptake Of Nutrients By Aquatic Macrophytes

271 Pages·2015·9.58 MB·English

Diffusion, Boundarv Lavers and the Uptake of
Nutrients bv Aquatic Macrophvtes
Jeffrey JuIius MacFarlane B.Sc. (Hons.
)
Botany Department
The University of Adelaiile.
Submitted for the Degree of
Doctor of Philosophy, June, 1985.
tlsl¡tt
flnrocbd
To my Father : Friend
and Master Teacher
CONTENTS
Summary vrt
Dec Iaration tx
Acknowl edgement s x
INTRODUCTION 1
I.The Kinetics of Heterogeneous Reactions 2
(i) Nernst's TheorY 2
ii ) Modifications of Nernst's Theory
( 6
(iii) Physical basis for kt
9
(iv) FIuid mechanical description of kT 13
(v)
Conclusions 20
II.Diffusion and Simultaneous Chemical Reaction 2I
(i) Equations for diffusion-reaction 2L
ii ) Determination of the extent of
(
internal diffusion limitations 25
III. Diffusion Boundary Layers and Nutrient
Uptake in Aquatic PIants 2'7
(i) Previous studies 2B
(ii) This work 35
MATERIALS AND METHODS 37
( i ) PIants 37
( ii ) solutions 3B
( iii ) ResPiration 40
( iv ) Photosynthesis 42
(v) Uptake of methylamine and phosphate 4B
(vi) Stirring gradient tower 49
(iíi)
MEMBRANE TRANSPORT 53
r . uptake of I l ac ] uethylamine by UIva qrgrqa 53
( i ) Results 53
(ii) Boundary layer Iimitations and V 54
(iii) The effect of stirring at high
methylamine concentrations 54
(iv) The saturation of influx with stirring 56
(v) Comparison of observed with predicted kinet¡cs 57
(vi) other ctnolyses 60
rr.uptake of l32plehosphate by ulva rrglda 62
r4c]uetrrylamine
rrr.uptake of 1,32p lPhosphate and I
by Vallisneria spiralis 7I
i ) Results 7l
(
( ii ) Discussion 72
RESPIRATION
I.Kinetics of OxYgen Reduction 75
II Respiration in Ulva rl-grqq
. BO
( i ) Results 80
( ii ) Discussion BI
III. Respiration of Vallisneria sPiralis 89
PHOTOSYNTHESIS 94
I.Photosynthesis of Ulva rfg-Lqq 94
( i ) Results 94
ii ) A note on the meaning of
( KM
for photosynthetic CO2 fixation 99
(iii) Photosynthesis at low 100
PH
(iv) Oxygen inhibition of photosynthesis 104
(iv¡
(v) Photosynthesis at higher PH's 107
(vi) Mechanisms of HCOã use II4
Il.Photosynthesis of Amphibol is antarctica
and Vallisneria spiralis r20
( i ) Results t20
( ii ) C supply for photosynthesis of
A. antarctica r23
( iii ) C supply for photosynthesis of
V. spiralis r26
CONCLUSIONS 133
Appendix I Fick's Laws I4I
Appendix II : Origin of the Quadratic Describing
an Enzyme-Catalysed Reaction in
Series with a Diffusion Resistance 143
Appendix III : The Meaning of the APParent Kt
for an Enzyme-Catalysed Reaction
in Series with a TransPort
Proce s s 145
Appendix IV : Relaxation of Diffusion to
a FIat Plate I47
Appendix V Diffusion and Reaction in
ParaI I e I r50
(i) The diffusion-reaction
equation ts0
(ii) First-order kinetics I52
( iii ) Zeroth-order kinetics I57
(v)

SUMMARY
Diffusion limitations on the influxes of tI4C]
methylamine and l32pl phosphate, and oî the respi ratory
uptake of o2r have been examined in the marine macroalga
Ulva rlgida and the freshwater angiospe rm Vallisneria
spiralis; photosynthetic 02 evolution (and fixation of
l4c-1abe11ed
inorganic carbon) has also been studied in
these two plants and in the marine angiosperm phibol is
Am
antarctica. In Ulva, the influx of methylamine and the
apparent "KM" of the process are greatly affected by the
rate of stirring of the bulk medium. The kinetics of
the influx are directly predicted by an equation of the
Michaelis-Menten form which includes a term for the rate
of transport of methylamine through the boundary layer
(the Briggs-MaskeIl equation). Transport coefficients
range f rom ,.U =-I in a barely-moving solution to
ft"
nearly 40 ¡rm s-1 in a well stirred one, with a
/
corresponding change in Ku f rom 20 to tO The
Æ.
equation is also directly applicable to the
photosynthesis of the alga at low pH provided that
O2
inhibition can be neglected. The equation is not
directly appticable to H2PO4 influx, respiratory O2
uptake or photosynthetic CO2 fixation at high pH. H2PO
4
')_
influx is complicated by the concomitant flux of HPoî
which effectively increases the concentration of
H2PO
4
at the plasmalemma. 02 uptake in dark respiration has a
complex relationship with the bulk concentration of o2,
(vii)
and the kinetics are not necessarily first-order
Michaelis-Menten; consequently the Briggs-MaskelI
equation is invalid. Rates of photosynthesis that are
observed at high pH could notbe attained if CO2 was the
only inorganic carbon species transporting carbon
through the unstirred Iayer. The alga probably uses
HCOJ ions directly from the bulk solution as a carbon
source and so again the Briggs-Maskell equation, in
terms of CO2 fixation, does not hold. The
photosynthesis of A[phibolis has a similar response to
CO2 and pH as that of UIva - again the Briggs-MaskeIl
equation is not directly applicable. Vallisneria leaves
have a cuticle which has such a high resistance to the
movement of solutes that boundary Iayer Iimitations are
negligible. The Ieaves also have a substantial supply
of endogenous COZ. Here the cuticle is a distinct
advantage because it increases the probabitity of a COZ
molecule being assimilated rather than escaping into the
bulk medium; this source of CO2 (originally derived from
the sediment? ) is probably much more important than the
COZ in the surrounding water.
(vii i )

ACKNOWLEDGEMENTS
This work was carried out under the supervision of
Dr. F.A. Smith, who was the ever-encouraging driving
force for this rather unsteady flux. I should also
I ike to thank others in the Botany Department - Drs.
J.T. Wiskich and G.G. Ganf for many varied and
stimulating discussions, Prof - H-8.S. Womersley, Dr R.
sinclair and B.c. Rowland for advice, Dr. E. Robertson
for culture room space, Ian Dry and Patrick Hone for
some good talks, and Jane Gibson and Anthony Fox for
company. Outwith the Botany Department, I acknowledge
the help given by B.C. van Wageningen in translating
some German scientific papers, the computer time allowed
by Prof. N.A. Wa1ker and the patience of Prof. J.A.
Raven. FinaIIy, to my wife, Carol, for typing the
manuscript, for numerous calculations, fot support and
for a sma1I portion of her indomitable spirit.
(x)