bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of aluminium on root elongation in two Australian perennial grasses
Authors: Crawford Simon A. , Wilkens Sabine
Published: August 2004

Inhibition of net root elongation and patterns of hematoxylin staining were
used to assess relative tolerance to phytotoxic Al in
Danthonia linkii Kunth and
Microlaena stipoides (Labill.) R.Br. According to net
root elongation, M. stipoides is significantly more
tolerant of phytotoxic Al than D. linkii. In nutrient
solutions with Al concentrations of 370 µM and higher, root elongation
is stopped in D. linkii after 24 h while in
M. stipoides root elongation is maintained at
60–70% of control rates over 72 h. After removal of Al-stress,
root growth in M. stipoides from all Al-treatments
recovered to be at or above control growth after 72 h. In
D. linkii, root elongation in plants exposed to Al
levels that caused a reduction in growth (<370 µM), but not complete
cessation, recovered after removal of Al stress. Greater intensities of
hematoxylin staining were seen in Al-stressed root tips of
D. linkii compared to
M. stipoides, suggesting that inhibition of root
elongation is associated with increased accumulation of Al in root tips. Roots
of M. stipoides seedlings exposed to all Al-treatments
showed a short band of intensely stained tissue, correlating with the position
of the root apex at the exact point of initial Al- exposure. New root growth
after this band did not stain with hematoxylin, indicating activation of a
mechanism of Al-exclusion in roots of M. stipoides.
The electrochromic signal, redox reactions in the cytochrome bf complex and photosystem functionality in photoinhibited tobacco leaf segments
Authors: Chow W. S. , Hope A. B.
Published: August 2004

Photosynthetic electron transport in vivo was
investigated in tobacco leaves pre-illuminated with strong light under
conditions where Photosystem (PS) II repair was inhibited by lincomycin.
Flash-induced redox changes of cytochrome
b563, cytochrome
f and plastocyanin, and the electrochromic (EC) signal
(caused by a carotenoid band-shift due to charge separation across thylakoid
membranes) from leaf segments were measured by deconvoluting absorbance
changes at 520, 554, 564 and 575 nm. The EC signal was composed of easily
separable fast and slow components. The fast EC signal decreased linearly with
the loss of functional PS II centres, but there was a residual fast EC phase
which was attributable to PS I centres alone. Inactivation of PS II centres by
photoinhibitory light was also well-correlated with the quenching of variable
fluorescence measured as the ratio of variable to maximum fluorescence,
Fv/Fm.
On complete photoinactivation of PS II centres, the slow rise of the
flash-induced EC signal became more prominent, suggesting enhanced
electrogenic charge transfer across the cytochrome bf
complex as part of a path of electron flow involving PS I. Thus, both PS I and
the cytochrome bf complex appeared to be fully
functional after treatment of tobacco leaves with photoinhibitory light at
room temperature. In totally photoinhibited leaf segments, the rate
coefficients of cyt fIII
re-reduction increased from 59 s-1 (+ lincomycin,
no photoinhibitory light) to 130 s-1, and that of
cytochrome b563 reduction also
increased, from 270 s-1 to 500
s-1, suggesting that the prevailing plastoquinol
concentration was higher after photoinhibitory light treatment. The source of
the electrons entering the pool under these conditions was probably a high
concentration of NADPH and reduced ferredoxin.
Localisation of aluminium in root apex cells of two Australian perennial grasses by X-ray microanalysis
Authors: Crawford Simon A. , Marshall Alan T. , Wilkens Sabine
Published: August 2004

To determine if an increased aluminium (Al) sensitivity is the result of
greater accumulation of Al in root apices, the quantity and distribution of Al
in root apex cells of Danthonia linkii Kunth and
Microlaena stipoides (Labill.) R.Br. was investigated by
X-ray microanalysis. Seedlings were grown in nutrient solution with 0, 185 and
370 µM total Al for 24 h after which the terminal 5 mm of the roots were
excised, rapidly frozen and embedded using freeze-substitution. Elemental
distribution maps of root apices showed that Al had accumulated in the nuclei
of root cap and meristematic cells in Al-stressed roots of
D. linkii but not in M. stipoides.
Al appeared to be co-localised with phosphorous (P) in the nuclei of these
cells. Quantitation of Al revealed that Al-stressed root apex cells of
D. linkiiaccumulated significantly more Al than
M. stipoides. Exposure of
D. linkii roots to Al resulted in substantial increases
in the P content of root apex cells, and a significant positive correlation
was found between Al and P in both root cap and meristematic cells. Analysis
of intracellular structures showed that the majority of Al had accumulated in
the nuclei of cells. A significant positive correlation was found between Al
and P in the nuclei, but not in the cytoplasm or cell walls. No positive
correlation was found between Al and P in root apex cells of
M. stipoides.
Photosynthesis is strongly reduced by antisense suppression of chloroplastic cytochrome bf complex in transgenic tobacco
Authors: Price G. Dean , Caemmerer Susanne von , Evans John R. , Siebke Katharina , Anderson Jan M. , Badger Murray R.
Published: August 2004

We have used transgenic tobacco (Nicotiana tabacum L.
cv. W38) plants expressing an antisense gene directed against the transcript
of the Rieske FeS protein of the chloroplast bf complex
to examine the effect a reduction in chloroplast Rieske FeS content on leaf
gas exchange and photosynthetic metabolite pools. Plants with chloroplast
Rieske FeS protein content ranging from 5 to 80% of wild-type were
analysed. CO2 assimilation rate declined linearly with
the reduction in Rieske FeS content when expressed on a leaf area basis. In
contrast to photosynthesis, there was no change in stomatal conductance except
for plants with less than 10% of wild-type Rieske FeS content. There
was a close correlation between Rieske FeS content and cytochrome
f content, showing that the reduction in Rieske FeS
content lead to a similar reduction in other components of the cytochrome
bf complex. While lower Rieske FeS content was
associated with declines in chlorophyll content, ATPδ subunit and
ribulosebisphosphate carboxylase–oxygenase (Rubisco) contents, these
declines were considerably smaller than the reduction in cytochrome
bf content. As Rieske FeS content was reduced, there was
a slight lowering of the chlorophyll a/b ratio. Lower
CO2 assimilation rates at ambient
CO2 and high light were associated with dramatic
reductions in ribulose bisphosphate (RuBP) and modest declines in 3-
phosphoglycerate (PGA). Rubisco carbamylation declined to 40–50%
in plants with Rieske FeS content lower than 20% of wild-type. We
conclude that, at high light, a reduction in chloroplast Rieske FeS protein
content leads to inhibition of CO2 assimilation rate via
reductions in the rate of RuBP regeneration caused by a restriction in
electron transport and via effects on in vivo Rubisco activity.
Inhibition of harpinPss-mediated hypersensitive response in tobacco and petunia by AP1, an amphipathic protein isolated from tomato leaves
Authors: Chen Ying , Lin Hao-Jan , Feng Teng-Yung , Liu Zin-Huang
Published: August 2004

HarpinPss, encoded by hrpZ in the
hrp gene cluster from
Pseudomonas syringae pv. syringae,
is a glycine-rich, cysteine-lacking protein. It acts as an hypersensitive
response (HR) elicitor in certain plants like tobacco, tomato and petunia. We
isolated a 20 kDa protein, AP1, from tomato leaves, that could inhibit the
activation of the HR by harpinPss. The interaction
between AP1 and harpinPss resulted in an increase in the
molecular weight of AP1.The inhibition of harpinPss
elicitor activity or interference may be due to the competition between these
two proteins for a putative receptor site in the plant cell plasma membrane.
The C-terminal portion of
harpinPss interacts more strongly with AP1 than the
N-terminal portion.
Interaction of stomatal responses to ABA and CO2 in Arabidopsis thaliana
Authors: Leymarie Juliette , Lascève Gérard , Vavasseur Alain
Published: August 2004

Stomatal responses to ABA and CO2 were investigated in
Arabidopsis thaliana (L.) Heynh. wild-type and ABA
insensitive mutants (abi1-1,
abi2-1,
abi1-1abi2-1) at the whole plant
and at the isolated epidermis levels. In wild-type plants, feeding roots with
ABA (1–50 µM) triggered a rapid drop in leaf conductance which
levelled off during the following photoperiods, and strongly inhibited the
increase in conductance induced by light. The rapid response was strongly
inhibited in abi1-1, abi2-1 and
abi1-1abi2-1 double mutants, but a
residual long-term decrease in leaf conductance was still observed. In
wild-type plants, exogenous ABA strongly enhanced the response to
CO2 removal. Conversely, in the absence of
CO2 the effect of ABA was drastically reduced in
epidermal strip experiments. These results reveal a strong interaction between
sensing of ABA and CO2 in stomata of
A. thaliana. Despite an initially wide stomatal aperture
in abi-1, abi-2 and double mutant
plants, their stomatal responses to light and CO2
removal were half those of wild-type plants. Moreover these responses were
totally independent of the presence of ABA, suggesting that ABI1 and ABI2 are
either directly involved in the interaction between the two signalling
pathways or, alternatively located upstream of this point of interaction.
Rate of leaf appearance in sugarcane, including a comparison of a range of varieties
Authors: Bonnett G. D.
Published: August 2004

Leaf appearance rate is a major determinant of canopy establishment, radiation
interception and therefore yield. The effect of genotype on leaf appearance
rate in sugarcane is largely unknown. Leaf appearance rate was recorded for
the mainstems of pot grown sugarcane plants of nine commercial varieties, over
10 months in Townsville, Australia. Bi-phasic linear, polynomial and power-law
models were fitted to data describing leaf appearance with thermal time. The
bi-phasic model (previously used for sugarcane) had a single large change in
phyllochron for which no biological explanation is apparent. Polynomials were
less likely to predict leaf appearance accurately outside the range of fitted
data. The power-law model gave a continuously increasing thermal time between
the appearance of successive leaves (phyllochron) and was used to compare the
varieties. An increasing phyllochron for the first 15 leaves could be
explained, in part, by the increasing length of lamina each successive leaf
had to grow through. However, an explanation for an increasing phyllochron
throughout ontogeny has yet to be found. The rate of leaf appearance was
significantly different between the varieties. After 5000˚Cd the number
of leaves predicted to have appeared ranged from 35 to 46. These variety
specific parameters make an important contribution to describing how different
varieties produce leaf area.
Temperature and leaf area expansion of sugarcane: integration of controlled-environment, field and model studies
Authors: Robertson Michael J. , Bonnett Graham D. , Hughes R. Michael , Muchow Russell C. , Campbell James A.
Published: August 2004

Canopy development is an important determinant of crop radiation interception,
and in the absence of stress is mainly driven by temperature. The responses to
temperature of the component processes of canopy dynamics in sugarcane: leaf
appearance, leaf size, tillering, and leaf senescence, were analysed for the
commercial Australian cultivar, Q117. Data were derived under optimal growth
conditions from controlled environments, and from irrigated field studies in
subtropical and tropical locations.
Regression of number of fully-expanded leaves in field-grown plants against
cumulative thermal time revealed that the thermal time between the appearance
of successive leaves increased as a function of leaf number, such that leaf 1
required 86˚Cd and leaf 40 required 160˚Cd. At any moment, on
average there were 3.7 leaves still expanding on the stalks. Functions
describing leaf appearance gave acceptable prediction of the time course of
leaf appearance taken from independent datasets of field-grown plant and
ratoon crops.
Leaf size increased with leaf position, with the largest leaves observed at
approximately leaf 17 and above. Combining functions describing leaf
appearance and leaf size as a function of leaf position allowed estimation of
leaf area index (LAI) of main stems in plant and ratoon crops in subtropical
and tropical environments. Tiller LAI, derived by difference, accounted for
60–90% of total LAI at the 5- leaf stage, declining to
20–50% at the 15-leaf stage. Plant and ratoon crops were similar
in terms of the amount and proportion of tiller LAI. Combining data from all
field studies indicated under potential growth conditions, leaf senescence was
closely related to leaf production.
The functions derived in this study give a basis for simulating canopy
dynamics under potential growth conditions in sugarcane, though the extent of
genotypic variation for the key parameters and their modification by stress
remains to be assessed.
Alleviation of aluminium phytotoxicity on soybean growth by organic anions in nutrient solutions
Authors: Ginting Sahta , Johnson Bruce B. , Wilkens Sabine
Published: August 2004

The effect of aluminium (Al) phytotoxicity on the growth of soybean
(Glycine max (L.) Merr.) cv. ‘Forrest’ in
nutrient solutions (pH 4.25) and its alleviation by organic anions has been
investigated. Both 100 and 500 µM Al caused significant reduction in
root and shoot lengths and root dry weights over 15 days. Citrate, oxalate,
tartrate, malate, malonate and lactate at 1000 µM and humic acid at 1 g
L-1 were used to alleviate phytotoxicity caused by the
presence of 500 µM Al. The effectiveness of the organic anions in
alleviating Al phytotoxicity, measured by the change in root length, was in
the order oxalate > citrate ≈ tartrate ≈ malate > malonate
>> lactate. Humic acid at 1 g L-1 proved almost as
effective as 1000 µM citrate. When the remaining fraction of phytotoxic
aluminium was measured by the aluminon method and the results combined with
calculated values obtained from stability constant data, the order of
effectiveness of complexation was citrate > oxalate > tartrate ≈
malate ≈ malonate >> lactate. It was concluded that benefits other
than from simple complexation of phytotoxic aluminium were provided by the
organic anions. Three of the anions were also used at different
concentrations; these were citrate and oxalate (at 250, 500 and 1000 µM)
and humic acid (at 0.01, 0.1 and 1.0 g L-1 ). For
citrate and oxalate, it was found that the concentration of the organic anion
must be at least that of the Al to reduce phytotoxicity significantly, and
twice as much oxalate as citrate was required to achieve the same reduction in
phytotoxicity.
Down-regulation of photosynthesis by drought under field conditions in grapevine leaves
Authors: Flexas J. , Escalona J. M. , Medrano H.
Published: August 2004

The importance of both stomatal closure and reduced carboxylation efficiency
on the photo- synthesis decline in response to long term water stress was
previously measured in field-grown grapevines. Here we address the question of
whether water stress affects the photochemical capacity of leaves, measuring
gas-exchange rates and chlorophyll fluorescence under drought and moderate
irrigat- ion at intervals through the summer season during three consecutive
years.
We conclude that usually water stress does not induce photoinhibition in
field-grown grapevines, even when stomatal conductance and photosynthesis are
reduced to very low values. Moreover, down-regulat- ion of photochemical
reactions is low, leading to a general pattern of photosynthetic response to
drought consistent in large reductions of stomatal conductance
(g), followed by a consistent decrease of
CO2 assimilation (A) but with a
much lower effect on electron transport rate (ETR). In consequence, the
intrinsic water-use efficiency (A/g) increased, as well
as the ratio ETR/A. It is suggested that increased
electron transport to alternative pathways, such as photorespiration,
prevented further down-regulation of ETR under drought conditions.
These results are in agreement with our previous reports for potted plants.
However it is clear that, under field conditions with a much more slowly
developed water stress, ETR reductions are more attenuated than in potted
plants, reducing their incidence in carbon assimilation, which seems to be
mainly regulated by stomatal closure.
Intraspecific variation in seed yield of soybean (Glycine max) in response to increased atmospheric carbon dioxide
Authors: Ziska Lewis H. , Bunce James A. , Caulfield Frances
Published: August 2004

The growth characteristics of six and the reproductive development of five
soybean [Glycine max (L.) Merr.] cultivars
were examined at 39 Pa (ambient) and 70 Pa (elevated)
CO2 partial pressures in temperature-controlled
glasshouses. Significant intraspecific variation for both growth and seed
yield in response to elevated CO2 was observed among the
cultivars. At elevated CO2, total biomass increased an
average of 42% at the end of the vegetative stage, while average seed
yield increased by only 28%. No changes in % protein or %
oil were observed for any cultivar at elevated CO2,
relative to ambient CO2. The relative enhancement of
either vegetative or reproductive growth at elevated CO2
was not correlated with changes in the absolute or relative increase in single
leaf photosynthetic rate among cultivars at elevated
CO2. For soybean, the greatest response of seed yield to
elevated CO2 was associated with increased production of
lateral branches, increased pod production or increased seed weight,
suggesting different strategies of carbon partitioning in a high
CO2 environment. Data from this experiment indicates
that differences in carbon partitioning among soybean cultivars may influence
reproductive capacity and fecundity as atmospheric CO2
increases, with subsequent consequences for future agricultural breeding
strategies.
Early signals in field grown wheat in response to shallow soil drying
Authors: Ali M. , Jensen C.R. , Mogensen V.O.
Published: August 2004

The aim of the present work was to test under field condition earlier climate
room findings that root-borne signals may control stomatal closure and leaf
extension rate during mild soil drying. Stomatal conductance
(g H2O) of flag leaves, leaf and
stem extension rates, leaf water relations, leaf ABA content and predawn xylem
[ABA] were measured daily in wheat grown in two soil types (sand and
loam) in lysimeters in the field during a period of soil drying with high and
low evaporative demands. At 3 days after withholding irrigation (DAI) on both
soil types, when soil water potential (Ψsoil) in the
upper soil profile of the droughted treatment had dropped to –70 kPa and
with the lower layers still at field capacity, predawn xylem [ABA]
increased. At 4 DAI the leaf extension rate decreased and midday leaf ABA
content increased. Stem extension rates decreased at 5 DAI in loam and 7 DAI
in sand. g H2O started to decrease
6 DAI in loam and 9 DAI in sand. These responses were observed before any
detectable decrease in the midday leaf water status of the droughted plants
had occurred relative to well- watered plants. The responses were closely
related to Ψsoil and independent of evaporative
demand. We conclude that, in wheat, root-borne signals probably control
stomatal conductance and leaf extension rate during mild soil drying in the
field.
Research Note: Calibration of micropipettes for pressure-probe studies
Authors: Murphy Ricardo , Ortega Joseph K.E.
Published: August 2004

In order to determine cell water-relation parameters with the pressure probe,
the ratio of inner to outer pipette diameters (α =
Di/Do)
must be estimated. Four different methods for estimating a were compared. I:
measurement of the volume of oil expelled from a pipette and the corresponding
movement of an oil/water meniscus within the pipette; II: measurement of
Di and
Do on fractured pipettes; III:
measurement of Di and
Do on intact pipettes; IV:
measurement of Di and
Do on capillary tubing. Methods I
and II gave mean values for α (± SE) that were in excellent
agreement [0.587 ± 0.004 (n = 12),
and 0.593 ± 0.003 (n = 14),
respectively]. Method III gave variable results for
Do < 80µm; for
Do > 80 µm a mean value
α = 0.624 ±0.007 (n = 4) was
obtained. Method IV gave a mean value α = 0.544 ± 0.001
(n = 5). It is suggested that any method for
calibrating micropipettes should be checked against an independent method
(e.g. Method I) that allows the determination of α for
Do < 100 µm. In the
present study, Method II gave the best combination of accuracy and
convenience.
Chloride uptake by oat coleoptile parenchyma described by combined influx and efflux transport systems
Authors: Babourina Olga K. , Knowles Andrew E. , Newman Ian A.
Published: August 2004

Chloride fluxes for oat coleoptile parenchyma were measured using the MIFE
system for non-invasive microelectrode ion flux measurement. The effects on
chloride fluxes of membrane potential, external chloride concentration, pH,
cation composition of the bathing solution, and the anion channel blocker
anthracene-9-carboxylic acid were studied.
From the experimental data we propose that the step-like appearance of the
chloride uptake curve at concentrations higher than 1 mM is due to combined
activity of influx and efflux systems. According to this hypothesis the uptake
of chloride ions is made by a pH sensitive active transport system with
Vmax = 4000 nmol
m-2 s-1,
Km = 7 mM
[Cl-]. Chloride ions are released from the
cell through channels with Gaussian type kinetics, the characteristics of
which are dependent upon the external bathing solution:
Vmax = –2300 nmol
m-2 s-1 at 25 mM
[Cl-] for CaCl2, and
Vmax = –2000 nmol
m-2 s-1 at 15 mM
[Cl-] for KCl; with both curves having the
same width of 17 mM [Cl-].
Key words: Cl- membrane transport,
flux kinetics, Avena sativa L.
Differential gene expression in desiccation-tolerant and desiccation-sensitive tissue of the resurrection grass, Sporobolus stapfianus
Authors: Blomstedt Cecilia K. , Gianello Robert D. , Gaff Donald F. , Hamill John D. , Neale Alan D.
Published: August 2004

The rare African grass Sporobolus stapfianus is capable
of surviving total air-dryness. Little is known about the genetic factors
associated with this remarkable trait. Several genes have been isolated from
drought-stressed leaf tissue of S. stapfianus, including
genes encoding a glycine-rich protein, another with similarity to a yeast
glyoxalase I gene and one cDNA which does not show any similarity with known
genes. Some of the genes have not previously been linked to desiccation
tolerance while some have previously been reported as being upregulated in
response to drought stress or expressed throughout all stages of desiccation
[Blomstedt, C., et al.,
Plant Growth Regulation 24,
219–228 (1998)]. To provide insight into changes in gene expression
which are important in drought resistance the transcript levels in both
desiccation-tolerant and desiccation-sensitive tissues, in response to varying
degrees of drought stress, have been analysed. Genes whose expression
decreases in leaf tissue in response to desiccation were also characterised,
such as those encoding chlorophyll a/b binding protein and catalase. This
study indicates the complexity of the drought stress response in the
resurrection grass, S. stapfianus, which involves
co-ordinated positive and negative regulation of several genes throughout the
dehydration process.
Effects of water stress on photosynthesis, chlorophyll fluorescence and photoinhibition in wheat plants
Authors: Lu Congming , Zhang Jianhua
Published: August 2004

Effects of water stress on photosynthesis, PS II photochemistry and
photoinhibition were investigated in wheat plants
(Tritium aestivum L.). To separate water stress effects
from photoinhibition, water stress was imposed at low irradiance (180
µmol m-2 s-1). When water
stress developed gradually, net CO2 assimilation rate
and leaf stomatal conductance decreased significantly. However, water stress
had no effects on the PS II photochemistry in dark-adapted leaves. There were
no significant changes in the maximal efficiency of PS II photochemistry and
no apparent damages in PS II reaction centre, its oxidising and acceptor
sides, or its antennae system. However, PS II photochemistry in light-adapted
leaves was modified in water-stressed plants. This was shown by the decrease
in the efficiency of excitation energy capture by open PS II reaction centres
and the quantum yield of PS II electron transport and a significant increase
in non-photochemical quenching.
In addition, water stress increased the susceptibility to photoinhibition. The
extent of photoinhibition became more pronounced as water stress increased. It
was found that water-stressed plants exhibited a much greater accumulation of
the QB-non-reducing PS II reaction
centres and a smaller increase in non- photochemical quenching during
photoinhibition. Such changes might be responsible for the increased
susceptibility to photoinhibition.
Soil erosion and nutrient loss. IV.
Authors: Palis R. G. , Rose C. W. , Saffigna P. G.
Published: August 2004

The effect of slope length on runoff and soil loss, and the loss and
enrichment ratio of nitrogen from steep slopes planted to pineapple, were
studied under natural field conditions over 3 sampling dates at Imbil, Gympie,
Queensland. The experiments were conducted on 3 sites, with each site having 3
slope lengths of 9, 15 and 23 m, each replicated twice. The mean slope
gradient was 32% with extreme variation from 24 to 37%. During
sampling for soil loss measurement, subsamples were also collected, air-dried,
weighed, and analysed for total nitrogen concentrations. Samples of the
original soil (uneroded) were also taken and analysed and the concentration of
total nitrogen in the original soil was used for enrichment ratio and nutrient
nitrogen loss determination.
The runoff per unit area was not significantly affected by slope length. Total
soil loss per unit area in each erosion event increased with increasing slope
length. The relationship between soil loss (Y ) and
slope (L) is well fitted by the function:

The measured sediment concentrations (in the case of site 3) for different
slope lengths were higher than those for the estimated sediment concentration
at the transport limit assuming either uniform overland flow, or furrow or
rill geometry. The estimated sediment concentration at the transport limit
provided evidence for the occurrence and importance of rilling which increased
soil loss per unit area. Furthermore, sediment concentration estimated at the
transport limit assuming rill or furrow geometry was higher than uniform
overland flow and increased as slope length increased from 9 to 23 m.
The enrichment ratio for total nitrogen decreased with increasing eroded
sediment. The eroded sediment was found to contain a nitrogen concentration
very similar to that of the original soil, resulting in the enrichment ratio,
in some cases, being close to or slightly below unity. Total nitrogen loss per
unit area showed a similar trend to total soil loss and it increased with
increasing slope length. The relationship between total soil loss in the event
(SL) and enrichment ratio (ER) for
total nitrogen for all slope lengths is represented by the logarithmic
function
Effect of crop duration and soil type on the ability of soil sulfur tests to predict plant response to sulfur
Authors: Chinoim Nanthana , Lefroy Rod D. B. , Blair Graeme J.
Published: August 2004

Soil testing for sulfur (S) is becoming increasingly important as soils become
more S-deficient due to lower S inputs in fertiliser and higher offtake in
product. Because of the differing rates of S supply required by a range of
crops, the relative importance of the soil sulfate and organic S pools could
be expected to vary between crops. A glasshouse experiment was conducted using
an Aquic Haplustalf of granitic origin and an Ultic Haplustalf of basaltic
origin collected from unfertilised pasture sites on the Northern Tablelands of
New South Wales from Uralla and Walcha, respectively. The soil was labelled
with 35S.
The experiment consisted of 2 rates of S fertiliser (0 and 17·7
mg/kg soil, equivalent to 0 and 30 kg S/ha), 3 crop species (radish,
corn, ryegrass), and 2 soils (granite and basalt). S was extracted using 2
extracts, mono-calcium phosphate (MCP) and 0·25 M KCl heated at
40°C (KCl-40), termed primary extracts, and the components of S in the
extracts were determined. The relationship between the amount of S removed
from the extract (S before planting – S after cropping) by the 2 test
extractants in the – S treatment and plant S uptake was also determined.
A higher S concentration was found in the KCl-40 extract than in the MCP
extract in the granite soil. Conversely, the MCP extract had a higher S
concentration in the basalt soil because of the relative size of the adsorbed
S and ester-S pools in this soil. More than 33% of the
35S was recovered in the extracted S pool, and
<11% from the organic S pool in both extractants and in both soils.
Data showed a lower specific activity (SA) of the S in the MCP extract as
measured by ICP than in KCl-40 in both soils and all crops. The specific
activity ratio of the extractants, as measured by ICP, was closest to
1·00 for the KCl-40 extract in both soils for each crop. The removal of
S from the MCP extractant during cropping was lower than plant uptake in all
treatments except ryegrass in the basalt soil. The KCl-40 extract tended to
underestimate S supply at low uptake and overestimate at higher uptake. The
results reported in this experiment showed that the KCl-40 extract generally
performed well for all 3 crops and on both soils. The data showed that the
KCl-40 extract removed S from pools similar to those reached by the crops.
The contribution of carbohydrate C and earthworm activity to the water-stable aggregation of a sandy soil
Authors: Degens B. P.
Published: August 2004

An incubation study was conducted to test the effects of decomposing clover
tops (added at 0, 6·2 or 12·5 mg organic matter/g soil) and
earthworm activity on the contribution of carbohydrate C to the stability of
aggregates in a sandy soil. Soils incubated with and without earthworms were
separated into surface-casts and bulk soil, and the amounts of water-stable
aggregates >1 mm surviving slow and rapid rewetting (when air-dry) in these
soil separates were determined. Organic C and acid- and water-extractable
carbohydrate C concentrations were determined in the aggregates and bulk soil.
The treatments of 6·2 and 12·5 mg organic matter/g soil
increased the >1 mm aggregation of the bulk soil by more than 2·2-
and 2·8-fold, respectively, compared with the non-amended soils. With
the addition of earthworms, there were increases from 1·7- to
1·8-fold only in aggregates surviving slow rewetting. The acid- and
water-extractable carbohydrate C contents of aggregates >1 mm in the bulk
and surface-cast soils were generally not greater than the carbohydrate C in
the bulk soil. Generally, the carbohydrate C fractions were also not increased
in the more stable aggregates (rapidly rewet) compared with the weaker
aggregates (slowly rewet). Carbohydrate C in bulk soil was generally
(P < 0·05) correlated with the amounts of
aggregates surviving each rewetting treatment (r >
0·71, P < 0·01). In contrast, greater
amounts of carbohydrate in aggregates surviving slow rewetting were not
correlated (r < -0·45, P
> 0·05), with a greater proportion of these aggregates resisting
disruption when the soils were rapidly rewet (except for acid-extractable
carbohydrate C; r = -0·84,
P < 0·05). These results cast doubt on the
usefulness of correlations in assessing the contribution of carbohydrate C to
aggregation. The amounts of carbohydrate materials in the soil appeared to
have little influence on aggregation, probably because the location of bonding
compounds in the soil pore matrix is more critical.
The interaction of a humic acid with heavy metals
Authors: Spark K. M. , Wells J. D. , Johnson B. B.
Published: August 2004

The solubility of a coal humic acid and the sorption of heavy metals
(Cu(II), Zn(II),
Co(II), and Cd(II)) in the absence
and presence of the humic acid were determined as a function of pH and
concentration of background electrolyte.
The solubility of the humic acid at low electrolyte concentration increases in
a 2-step process with increase in pH. About 80% dissolves in the pH
region 3–8·5, and the remainder in the region pH >8·5.
The sorption of metals occurs at pH values significantly lower than those
associated with the formation of insoluble metal hydroxides, with a maximum
occurring in the pH region 5·5–7·5, and involves the solid
state fraction of the humic acid. At the higher electrolyte concentration, the
solubility of the humic acid is again a 2-step process but the increase in
acid solution occurs over a relatively narrow pH range (5–6). At high
pH, the presence of the humic acid significantly reduces the precipitation of
the metals at both low and high salt concentration, probably due to the
formation of soluble metal–humate species. There is evidence to suggest
that the major functional group of the humic acid with which the metal cations
interact is the carboxyl group.
Characteristics of the sorption of humic acid by soil minerals
Authors: Spark K. M. , Wells J. D. , Johnson B. B.
Published: August 2004

The interaction of a humic acid with the minerals goethite, α-alumina,
kaolinite, and silica was studied with respect to the solubility of the humic
acid in the absence and presence of each of the minerals. The proton
consumption associated with the interaction process was also determined for
each mineral–humic acid system.
The sorption of humic acid was found to be related to the nature of charge on
the mineral surfaces, with positively charged surfaces sorbing the humic acid
to a greater extent than negatively charged surfaces.
The sorption process involving positively charged mineral surfaces was found
to be associated with a consumption of protons as a consequence of the
interaction, whereas that involving negatively charged mineral surfaces does
not consume protons. The interaction between α-alumina and humic acid appears
to involve aggregation of the mineral for the conditions used in this study.
The pH at which the aggregated particles are dispersed decreased with increase
in concentration of the background electrolyte.
Free aluminium and related parameters in soil solution from a South Island (New Zealand) high country site under contrasting S and P fertilisation
Authors: Powell H. K. J. , Hawke D. J. , Scott D.
Published: August 2004

Soil solution samples were taken from 7 plots of varying
Hieracium infestation at the AgResearch (NZ) Mt John
trial site, Lake Tekapo. The soils, which had been fertilised, oversown, and
grazed, were analysed for free (reactive) Al, total Al, pH, NOM (natural
organic matter), and phosphate. The plots had received annual fertiliser
combinations of 0–100 kg P and 0–20 kg S/ha·year. Soil
solution pH was in the range 4·33-5·76 and total Al
concentrations were in the range 13–68 µM. Free Al concentrations
were in the range 0·48–4·8 µM. The pH dependence of
log (free[Al]) (slope: –0·69±0·37)
indicated control of soluble Al by NOM rather than
Al(OH)3 solubility. Soil solution phosphate
concentrations depended strongly on P application rate, reaching over 100 mM.
At high P concentrations, the product
[Al3+][PO3-4]
indicated approximate saturation with respect to variscite. One comparison
indicated that effects on pH and NOM in the upper 5 cm were due to the
presence or absence of grazing.
The effect of crop type, crop rotation, and tillage practice on runoff and soil loss on a Vertisol in central Queensland
Authors: Carroll C. , Halpin M , Burger P. , Bell K. , Sallaway M. M. , Yule D. F.
Published: August 2004

In 1982, a long-term project was established in central Queensland to study
the effect of crop type, crop rotation, and tillage practice on runoff and
soil loss. Runoff and soil loss were measured at the outlet of 9 large contour
bay catchments (approximately 13 ha) where wheat, sorghum, and sunflower were
grown in 3 crop sequences. Each crop sequence consisted of zero, reduced, and
conventional tillage fallow practices. Monoculture cropping was practised from
1983 to 1985, then opportunity cropping from 1986 to 1993.
During the study, wheat cropping had lower average annual runoff and soil loss
(P < 0·01) than sorghum and sunflower. Zero
and reduced tillage retained more crop stubble (median >50%) and had
less soil loss (P < 0·05) than conventional
tillage. Zero tillage wheat had the lowest average annual runoff and soil
loss, and conventional sunflowers had the highest. The erosion risk associated
with sunflowers was reduced by a wheat–sunflower crop rotation,
particularly when zero-tilled. Monoculture sunflower must be avoided.
The region is susceptible to large episodic erosion when crops are not sown,
there are long fallows, and soil cover falls below levels critical to control
erosion (<30%). Opportunity cropping is the most appropriate system
to maximise the regions variable rainfall and reduce runoff and soil loss.
The UFA method for rapid, direct measurements of unsaturated transport properties in soil, sediment, and rock
Authors: Conca James L. , Wright Judith
Published: August 2004

These studies illustrate the efficacy of a newly developed
unsaturated/saturated flow apparatus (UFA) to decrease significantly the
time required to obtain direct measurements of transport parameters. The UFA
method can be applied to cores of soil, sediment, rock, concrete, or any other
porous media, especially highly unsaturated and relatively impermeable
materials. The UFA method is effective because it allows the operator to set
variables in Darcy"s Law and impose any desired steady-state hydraulic
conductivity. The UFA achieves hydraulic steady-state in hours by using an
adjustable body force (provided by a centrifugal acceleration in the rotating
frame of reference) to drive the fluid, coupled with precision fluid flow
through a rotating seal assembly. The normal operating range of unsaturated
hydraulic conductivity that can be imposed by the UFA is from the saturated
conductivity for that specimen [up to about 10-4
cm/s (10-1 darcy; 10-9
cm2)] down to about 10-11
cm/s (10-8 darcy; 10-16
cm2). For strictly saturated conditions, the UFA can
operate down to 10-14 cm/s. Temperatures can be
adjusted from -20° to 150°C, and constant flow can be imposed during
rotation down to 0·001 mL/h. Several comparisons are made among
K(θ) results, determined on splits of the same
samples using the UFA and other methods, to the van Genuchten/Mualem
estimations derived from water retention data using RETC. A case study is also
discussed involving subsurface hydrostratigraphic mapping and recharge
distribution at a mixed waste site. This study demonstrates the speed,
economy, and direct measurement capability of the UFA that make it optimal for
determining transport behaviour under unsaturated conditions.
Speciation of cadmium in soil solutions of saline/sodic soils and relationship with cadmium concentrations in potato tubers (Solanum tuberosum L.)
Authors: McLaughlin M. J. , Tiller K. G. , Smart M. K.
Published: August 2004

Fifty commercial potato crops and associated soils were sampled. Soil
solutions were extracted from rewetted soils by centrifugation, and solution
composition was related to Cd concentrations in tubers. Soils were also
extracted with 0·01 M
Ca(NO3)2 and 0·01 M
CaCl2 solutions, and Cd2+
activities in the extracts were calculated by difference using the stability
constants for formation of
CdCl2-nn species.
The soils had saline solutions (>4 dS/m), and Cl-
and SO2-4 in solution markedly
affected the speciation of Cd in soil solution, with chloro-complexes, in
particular, dominating. While low soil pH was associated with high (>25 nM)
concentrations of Cd in soil solution, chloro-complexation also led to high
concentrations of Cd in solution, even at neutral to alkaline soil pH values.
Tuber Cd concentrations were not related to activities of
Cd2+ in soil solution or to activities in dilute salt
extracts of soil. Tuber Cd concentrations were related to the degree of
chloro-complexation of Cd in solution. The relationship of tuber Cd
concentrations to chloro-complexation in soil solution suggests that Cd
species other than the free Cd2+ ion are involved in the
transport through soil and uptake of Cd by plants.
Carbonate chemistry, pH, and physical properties of an alkaline sodic soil as affected by various amendments
Authors: Chorom M. , Rengasamy P.
Published: August 2004

A greenhouse experiment evaluated the chemical and physical changes of a
Natrixeralf (with alkaline pH 9·4 and 5%
CaCO3), as influenced by the changes in carbonate
chemistry, pH, and particle charge following the application of gypsum, green
manure, and glucose.
Gypsum reduced the pH from 9·38 to 7·89, increased
Ca2+ in soil solution, and decreased the sodium
adsorption ratio (SAR1:5) from 11·6 to
1·2. Green manure, due to increased CO2
production, reduced the pH to 8·68 and SAR1:5 to
7·52. Green manure plus gypsum reduced pH to 7·67 and
SAR1:5 to 0·91. The interactive effect of gypsum
and green manure on all soil properties was highly significant as shown by
ANOVA analysis. Reduction of soil pH was also reflected in the levels of
carbonates in the soil solution.
Addition of glucose increased the microbial activity and produced fatty acids.
The drastic reduction in pH (<6·0) was related to the amount of
glucose added. The concentrations of Ca 2+ and
carbonates, and SAR1:5 values, were inversely related to
the soil pH after glucose addition. The data on soluble
Na2CO3 and
NaHCO3, zeta potential, mechanical dispersion, aggregate
stability, and saturated hydraulic conductivity confirm the effects of pH
reduction and carbonate solubility as influenced by the amendments in alkaline
sodic soil.
Phosphorus in runoff from a fertile dairy pasture
Authors: Nash David , Murdoch Craig
Published: August 2004

Losses of phosphorus (P) from grazed pastures in runoff can significantly
reduce the water quality in streams draining agricultural catchments. Many
preventative strategies depend for their success on the association of the P
with large soil particles (>0·45 mm). We investigated the forms of P
in runoff from a dairy pasture of high fertility.
A 3·6-ha paddock at Darnum in West Gippsland, Victoria, was set up to
measure runoff volume and rainfall, and to sample runoff water. Runoff from
the site was restricted to 3 months in late winter and spring. Total runoff
for 1994 of 660 m3 had an average total P concentration
of 5·2 mg/L. Runoff from a single storm system over 8 days in early
November accounted for 56% of the total runoff volume and 69% of
the P lost.
Of the total P in the runoff, 93% passed through a filter with
0·45-µm pores and 91% was reactive in an ascorbic
acid–molybdate medium, without digestion; 89% of the P was both
reactive in the ascorbic acid{molybdate medium and in the
<0·45-µm fraction. There was no apparent relationship
(P > 0·05) between P concentration and soil
cover.
In the Darnum catchment, the major runoff events occurred when the soil was
saturated. The low settling velocities of materials <0·45 µm
and the amount of P moving in larger storms would suggest that buffer strips
and riparian zones are unlikely to decrease P losses substantially from dairy
pastures in this area. Further, since erosion is unlikely to be the major
process by which P is lost, control measures which simply limit erosion will
be similarly ineffective at preventing P losses under the conditions that
prevailed in this study.
Phosphorus adsorption and desorption characteristics of constructed wetland gravels and steelworks by-products
Authors: Mann R. A.
Published: August 2004

Laboratory phosphorus (P) adsorption and desorption experiments were conducted
on 9 substrata to evaluate their potential to remove P from sewage effluent.
The substrata comprised 2 gravels used in constructed wetlands, Hawkesbury
sandstone, and 6 steelworks by-products: granulated blast furnace slag, blast
furnace slag, steel slag, fly ash, bottom ash, and coal wash. The studies
involved ion-exchange experiments and calculation of Langmuir and Freundlich
adsorption isotherms and column adsorption/desorption trials. The ability
to adsorb P was then correlated to the physico-chemical attributes including
X-ray fluorescence analyses of each substratum.
High P adsorption capacities (>380 mg/kg) were shown for granulated
blast furnace slag, blast furnace slag, and steel slag, as well as fly ash.
All steelworks by-products had adsorption capacities greater than the
constructed wetland gravels and Hawkesbury sandstone. The P adsorption
capacities of the substrata were significantly correlated with Ca
(r2 = 0 · 9206), Mg
(r2 = 0 · 8681), pH
(r2 = 0 · 7009), S
(r2 = 0 · 6696), and
Si (r2 = 0 · 6438)
when fly ash was omitted from the analyses.
Further research is recommended to evaluate the sustainability of using slags
for P removal (as well as other contaminants present in wastewater), using
full-scale constructed wetlands. Research should include an evaluation of any
likely environmental impacts using leachability and toxicity studies.