bluuebunny/crossref_metadata_2025 huggingface dataset:
Sources and Sinks of Atmospheric CO2
Authors: Taylor JA , Lloyd J
Published: December 2005

The biosphere plays an important role in determining the sources, sinks, levels and rates of change of atmospheric CO2 concentrations. Significant uncertainties remain in estimates of the fluxes of CO2 from biomass burning and deforestation, and uptake and storage of CO2 by the biosphere arising from increased atmospheric CO2 concentrations. Calculation of probable rates of carbon sequestration for the major ecosystem complexes and global 3-D tracer transport model runs indicate the possibility that a significant net CO2 uptake (> 1 Pg C yr-1), a CO2 'fertilisation effect', may be occurring in tropical rainforests, effectively accounting for much of the 'missing sink'. This sink may currently balance much of the CO2 added to the atmosphere from deforestation and biomass burning. Interestingly, CO2 released from biomass burning may itself be playing an important role in enhanced carbon storage by tropical rainforests. This has important implications for predicting future CO2 concentrations. If tropical rainforest destruction continues then much of the CO2 stored as a result of the CO2 'fertilisation effect' will be rereleased to the atmosphere and much of the 'missing sink' will disappear. These effects have not been considered in the IPCC (Intergovernmental Panel on Climate Change) projections of future atmospheric CO2 concentrations. Predictions which take account of the combined effects of deforestation, the return of carbon previously stored through the CO2 'fertilisation effect' and the loss of a large proportion of the 'missing sink' as a result of deforestation, would result in much higher predicted concentrations and rates of increase of atmospheric CO2 and, as a consequence, accelerated rates of climate change.
Rubisco: Maladapted or Misunderstood
Authors: Morell MK , Paul K , Kane HJ , Andrews TJ
Published: December 2005

Life depends on a single enzyme, D-ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco), for the acquisition of essentially all of its carbon. Applying Darwinian principles, one would expect this enzyme to have been rigorously selected for speed and accuracy, and it is a surprise to discover that, even in its most highly developed forms, it is both slow and confused. This review looks for clues about the causes of Rubisco's slow evolutionary refinement in its complex catalytic chemistry and in its tendency to catalyse abortive side reactions. We assess the possibilities for improving Rubisco artificially, either by random mutagenesis or by rational design, and imagine the consequences of an improved Rubisco for plant productivity and the global ecosystem.
Influence of Elevated Atmospheric CO2 Concentrations on Plant Nutrition
Authors: Conroy JP
Published: December 2005

The rising levels of atmospheric CO2 are likely to increase biomass production of C3 species in both natural and managed ecosystems because photosynthetic rates will be higher. The greatest absolute increase in productivity will occur when nitrogen and phosphorus availability in the soil is high. Low nitrogen does not preclude a growth response to high CO2, whereas some C3 species fail to respond to high CO2 when phosphorus is low, possibly because insufficient phosphorus is available to maintain maximum photosynthetic activity at high CO2. C3 plants response to high CO2 because the flux of carbon through the photoreductive cycle is increased and photorespiration is suppressed. This change in metabolism appears to alter the foliar nutrient concentration required to promote maximum productivity (critical concentration). Higher phosphorus concentrations are needed at elevated CO2, whereas the nitrogen requirement is reduced by CO2 enrichment. Since critical concentrations are used to evaluate nutrient status of crop and forest species and to manage fertiliser programs, they will need reassessing as the atmospheric CO2 concentration rises. Another consequence of the altered nutrient requirement at high CO2 is that the nitrogen concentrations of foliage, roots and grain are consistently lower in plants grown at elevated CO2, irrespective of availability of nitrogen in the soil. In natural ecosystems, the lower nitrogen to carbon ratio of the litter may alter rates of nutrient cycling. For farmers, the rising CO2 concentrations could cause reductions in grain nitrogen, and therefore protein content. This could have important implications for baking quality of hard wheats as well as affecting the nutrient value of grain such as rice.
Plant Responses to Temperature Under Conditions of Elevated CO2
Authors: Rawson HM
Published: December 2005

A literature survey of the interactive effects of CO2 enrichment and temperature on plant development
and growth, indicated that the responses cannot be interpreted within a simple framework. For example,
although plant development is generally accelerated by increased temperature, CO2enrichment can
accelerate it even further in some instances, or CO2 enrichment may have neutral or even retarding
effects in other cases. Where the temperature and CO2 effects are additive, it is argued that CO2 is
operating in the same way as radiation to reduce a carbon limitation. If this were true, CO2 enrichment
would be most likely to accelerate development in tropical regions during the low-radiation monsoon
season.
Similarly, while it would be expected that CO2-enrichment would have increasingly enhancing effects
with increasing temperature on phytomass growth, this is not invariably the case. In extreme examples
which followed the expected trend, plants grown in twice-normal CO2-enriched atmospheres performed
progressively better than those grown at current levels of CO2 by 8.7% for every 1°C rise in temperature.
However, the difference between the two CO2 treatments more commonly increased by only around
2% for every °C rise in temperature. Of examples examined, both sunflower and nodulated cowpea
showed the reverse response to temperature, while non-nodulated cowpea, supplied with luxuriant levels
of nutrition, showed no interaction with temperature but a strong interaction between CO2 and radiation.
Other aspects of the environment such as nutrition and radiation strongly modify the responses to
temperature. It is also clear that plant factors such as stage of development can alter the response
to CO2. Long-term studies with several species are required which will take into account many environmental
variables within a realistic envelope. One methodology for doing this is presented.
There was no evidence among species that responses to CO2 arise through any consistent change
in morphology such as via increased branching or increased leaf number. Plant plasticity is such that
responses can be expressed in a variety of ways determined by other environmental variables.
Will Plant Performance on Soils Prone to Drought or With High Mechanical Impedance to Root Penetration Be Improved Under Elevated Atmospheric CO2 Concentration
Authors: Masle J
Published: December 2005

Plants growing on dry soils or on soils with high mechanical resistance to root penetration grow more
slowly and exhibit lower stomatal conductance than those growing on moist and loose soils. In most
situations in nature where edaphic stresses develop rather slowly (compared to stresses imposed in most
pot experiments conducted under controlled conditions), photosynthesis is mainly reduced via stomatal
effects rather than via changes in mesophyll capacity for photosynthesis. Elevated CO2 will induce an
increase in the internal partial pressure of CO2, despite stomatal conductance being lowered even
further. Photosynthesis will therefore be improved, and leaf turgor will be increased.
It is widely thought that growth on dry or hard soils is not carbon limited because levels of soluble
carbohydrates in the leaves and root cells are increased. It is shown in this paper that growth on soil
with high mechanical resistance does respond to elevated CO2. However, this response is smaller than
expected from the increase of carbon assimilation rate because: (a) carbon partitioning is altered so that
supplementary carbohydrates are preferentially allocated to the roots; (b) leaf growth sensitivity to
internal availability of sugars is lower than in plants growing on loose soils. These alterations of 'sink
activity' and carbon partitioning are mediated by unknown signalling factor(s) induced in the roots. It
is not known whether the root factors acting in droughted plants are of the same nature. In both
droughted and impeded plants the interacting effects of these factors and of ambient CO2 levels are
likely to result in improved transpiration efficiency. More experiments are needed in this area, however,
especially to ascertain the relative contribution of changes in growth patterns versus changes in the
patterns of water use. In conclusion, the importance of identifying the nature of the sink limitations
induced by root signals is emphasised. It is a fundamental area of research to be developed not only for
assessing growth responses to rising CO2 under edaphic stress, but likely also for reconciling
conflicting responses of field-grown and pot-grown plants.
A Quantitative-Analysis of Dark Respiration and Carbon Content as Factors in the Growth-Response of Plants to Elevated CO2
Authors: Poorter H , Gifford RM , Kriedemann PE , Wong SC
Published: December 2005

An analysis of elevated CO2 effects (2-4 times ambient) on dark respiration rate and carbon content was undertaken for a wide range of plant species, using both published reports and new data. On average, leaf respiration per unit leaf area was slightly higher for plants grown at high CO2 (16%), whereas a small decrease was found when respiration was expressed on a leaf weight basis (14%). For the few data on root respiration, no significant change due to high CO2 could be detected. Carbon content of leaves and stem showed a small increase (1.2 and 1.7% respectively), whereas C-content of roots was not significantly affected. In both data sets direction of responses was variable. A sensitivity analysis of carbon budgets under elevated CO2 identified changes in respiration rate, and to a lesser extent carbon content, as important factors affecting the growth response to elevated CO2 in quite a number of cases. Any comprehensive analysis of growth responses to increased CO2 should therefore include measurements of these two variables.
Plant Responses to Salinity Under Elevated Atmospheric Concentrations of CO2
Authors: Ball MC , Munns R
Published: December 2005

This review explores effects of elevated CO2 concentrations on growth in relation to water use and salt balance of halophytic and non-halophytic species. Under saline conditions, the uptake and distribution of sodium and chloride must be regulated to protect sensitive metabolic sites from salt toxicity. Salt-tolerant species exclude most of the salt from the transpiration stream, but the salt flux from a highly saline soil is still considerable. To maintain internal ion concentrations within physiologically acceptable levels, the salt influx to leaves must match the capacities of leaves for salt storage and/or salt export by either retranslocation or secretion from glands. Hence the balance between carbon gain and the expenditure of water in association with salt uptake is critical to leaf longevity under saline conditions. Indeed, one of the striking features of halophytic vegetation, such as mangroves, is the maintenance of high water use efficiencies coupled with relatively low rates of water loss and growth. These low evaporation rates are further reduced under elevated CO2 conditions. This, with increased growth, leads to even higher water use efficiency. Leaves of plants grown under elevated CO2 conditions might be expected to contain lower salt concentrations than those grown under ambient CO2 if salt uptake is coupled with water uptake. However, salt concentrations in shoot tissues are similar in plants grown under ambient and elevated CO2 conditions despite major differences in water use efficiency. This phenomenon occurs in C3 halophytes and in both C3 and C2 non-halophytes. These results imply shoot/root communication in regulation of the salt balance to adjust to environmental factors affecting the availability of water and ions at the roots (salinity) and those affecting carbon gain in relation to water loss at the leaves (atmospheric concentrations of water vapour and carbon dioxide).
Implications of the Globally Increasing Atmospheric CO2 Concentration and Temperature for the Australian Terrestrial Carbon Budget: Integration Using a Simple-Model
Authors: Gifford RM
Published: December 2005

A simple continentally aggregated model of the Australian terrestrial carbon budget (CQUESTA) integrates information on CO2 and temperature effects and is applied to evaluating whether vegetation is absorbing anthropogenic CO2. Information from the literature is used to parameterise CQUESTA. A standard set of parameters is adopted for exploratory purposes. Historical information is used to describe the average CO2 concentration and temperature over the southern hemisphere from 1750 AD to the present. From the present to 2050 AD the 'business-as-usual' scenario described by the Intergovernmental Panel on Climate Change (IPCC) is applied. The standard parameterisation of the model suggests that the changing CO2 concentration and temperature regime since 1750 AD has been causing continuous net sequestration of carbon into Australian live vegetation and soils. The present modelled rate of net sequestration is of a similar magnitude to CO2 emissions from continental fossil fuel burning and land clearing combined. The rate of sequestration is predicted to continue to increase until 2050 AD and beyond if atmospheric CO2 concentration and temperature continue to increase. However, there remains considerable experimental uncertainty about the correct parameterisation of the model. The findings have implications for policies on greenhouse effect gas emissions.
Plant Plant Interactions in Elevated CO2 Environments
Authors: Bazzaz FA , McConnaughay KDM
Published: December 2005

Increasing atmospheric carbon dioxide concentrations present a novel resource condition for plant communities. In order to understand and predict how plant community structure and function may be altered in a high CO2world, we need to understand how interactions among neighbouring plants within a community will alter the growth and reproduction of component species. Because CO2 is readily diffusible, plants have little influence on the CO2 acquisition of their neighbours, except within particularly dense canopies. Thus, plants seldom compete directly for CO2. Rather, CO2 availability is likely to alter plant-plant interactions indirectly through its effects on plant growth and competition for other resources. As a consequence, competitive outcome under elevated CO2 atmospheres within even simple systems is not easy to predict. For example, under some conditions, C4 species in competitive assemblages have improved competitive ability relative to C3 competitors as a result of CO2 enrichment, contrary to expectations based on their photosynthetic pathways. It is now clear that individually grown plants can differ substantially from those within mono- or multispecific stands in response to CO2 enrichment. At present, our understanding of how stands of interacting plants modify the availability of CO2 and other resources is incomplete. We urgently need information about how elevated CO2 atmospheres influence stand formation and population dynamics, specifically with regard to the identities, numbers, sizes and reproductive fitnesses of individuals within single and multiple species stands, if we are to make multi-generational predictions concerning the fate of populations and communities in an elevated CO2 world.
A Field-Study of the Effects of Elevated CO2 on Ecosystem Processes in a Chesapeake Bay Wetland
Authors: Drake BG
Published: December 2005

Open top chambers are being used in a long-term project to determine the effects of elevated CO2 on ecosystem processes on a Chesapeake Bay wetland. Three communities are studied: mono-specific stands of the C3 sedge, Scirpus olneyi, and the C4 grass, Spartina patens, and a mixed community of these two species and the C4 grass, Distichlis spicata. Treatment began in the spring of 1987 and will continue through the 1994 growing season. During the first 4 years of exposure, elevated CO2 had the following effects on mono-specific stands of the C3 sedge, Scirpus olneyi: increased quantum yield and photosynthetic capacity, reduced dark respiration, increased numbers of shoots, roots and rhizomes, reduced nitrogen concentration of all tissues, increased nitrogen fixation and increased ecosystem carbon accumulation. In a mixed community of the sedge and C4 grass species, Spartina patens and Distichlis spicata, biomass of the C3 component increased over 100% and this was accompanied by decreased biomass in the C4 component of the community. Elevated CO2 reduced water loss, increased water potential and delayed senescence in all three species. Many factors contributed to CO2 stimulated carbon accumulation in the plant community dominated by the C3 sedge, Scirpus olneyi, including: sustained high photosynthetic capacity, decreased respiration, delayed senescence, and allocation of the additional carbon to roots and rhizomes. The complex interaction of these diverse responses suggests that the rising atmospheric CO2 may have a significant impact on ecosystem processes.
Seed and Seedling Biology in Relation to Modelling Vegetation Dynamics Under Global Climate Change
Authors: Leishman MR , Hughes L , French K , Armstrong D , Westoby M
Published: December 2005

The distribution of many plant species will change with global climate change, depending on their ability to disperse into, and establish in, new communities. Past migrations of species under climate change have been an order of magnitude slower than the rate of predicted climate change for the next century. The limited evidence available suggests that chance long distance dispersal events will be critically important in determining migration rates. The JABOWA-derived gap replacement models and vital attributes/FATE models were examined, and the dispersal and establishment processes necessary to make improved projections of vegetation dynamics under climate change using these models were investigated. The minimum modifications of these models required to incorporate directional migration of species are described. To predict establishment success of species, it was suggested that a more fundamental understanding is needed of how establishment ability under different conditions relates to seed and seedling attributes and how this may be affected by elevated CO2. Finally, an examination was carried out of whether plant functional types based on vegetative attributes (used to model the response of adult plants) are correlated with functional types based on seed and seedling attributes. Available evidence suggests that the two sets of attributes are not strongly correlated; consequently, models of vegetation dynamics will need to incorporate seed biology explicitly.
Estimates of Carbon Storage in the Aboveground Biomass of Victorias Forests
Authors: Grierson PF , Adams MA , Attiwill PM
Published: December 2005

The pool of carbon in the world's forests is of similar magnitude to that in the atmosphere, yet little attention has been given to improving measures of carbon in terrestrial biomass. Much of the critical data for forest biomass on which models of global carbon cycling rely is, in fact, based on the accurate sampling of less than 100 ha of forest. Uncertainties in biomass estimation at the local and regional level may be responsible for much of the current speculation as to unidentified sinks for carbon. We have used a forest inventory (i.e. records of forest volume obtained for harvesting purposes) approach to quantify the biomass of forests in Victoria, Australia. Forests were analysed by type, age and region. Regression equations were developed for the accumulation of biomass with age across all productivity classes for each forest type. The mean carbon density for above-ground components of Victorian native forests is 157 tonnes ha-1 (t ha-1), although forest types range in mean carbon density from 250 to 18 t ha-1. Pinus radiata D. Don plantations in Victoria have a mean carbon density of 91 t ha-1 in the above-ground components. Total carbon stored in above-ground biomass is estimated to be 1.2 X 109 t. Rates of carbon fixation vary with forest age, species and site. Mountain ash (Eucalyptus regnans F. Muell.) forests fix around 9 t of carbon ha-1 annually during the first few years of growth, decreasing to 6 t ha-1 by age 10. Rates of carbon accumulation by other forests are generally less than this and, at the lower end of the range, box-ironbark forests, mallee and woodlands accumulate between 0.5 and 2 t ha-1 year-1. P. radiata plantations in Victoria will accumulate around 7 t carbon ha-1 year-1.
Modifying Existing Forest Growth Models to Take Account of Effects of Elevated CO2
Authors: McMurtrie RE , Comins HN , Kirschbaum MUF , Wang YP
Published: December 2005

Most published process models of the growth of forest stands are concerned predominantly with either
tree physiology or nutrient cycling, concentrating respectively on photosynthetic carbon gain and
allocation, or on decomposition and nutrient uptake processes. Mechanistic formulations of direct CO2
effects on photosynthesis have been incorporated in some physiology-based models, whereas
modifications incorporating direct CO2 effects in nutrient-driven models have usually been more
empirical. Physiology-based models predict considerable CO2-fertiliser effects, while nutrient driven
models tend to be less sensitive to elevated ambient CO2 concentration (Ca). This paper describes how
effects of elevated Ca can be incorporated in these various types of forest growth models.
The magnitude of the simulated response to elevated Ca varies markedly depending on a particular
model's spatial and temporal resolution and on which processes are incorporated. Two physiology-
based models of forest canopy processes (MAESTRO and BIOMASS) and a plant-soil model (G'DAY)
are considered here. MAESTRO and BIOMASS incorporate mechanistic descriptions of the
biochemical basis of photosynthesis by C3 plants, while G'DAY contains a simplified formulation but
includes soil processes. All three models are used to simulate the response to an instantaneous doubling
of Ca. Simulations of MAESTRO and BIOMASS show that on a clear day total canopy photsynthesis
is temperature-dependent with increases of approximately 10, 45 and 70% at 10. 25 and 40°C
respectively. A simulation for a stand of Pinus radiata growing with abundant water and nutrients and
mean annual day-time temperature of 14.8°C shows an increase of 25% in annual canopy
photosynthesis. On nutrient-limited sites plant responses to elevated Ca are constrained by feedbacks
associated with rates of decomposition and nutrient cycling. According to the G'DAY model, which
incorporates these feedbacks, an instantaneous doubling of Ca leads to a 27% initial productivity
increase lasting less than a decade and a more modest increase of 8% sustained in the long term.
Simulations of Hydroecological Responses to Elevated CO2 at the Catchment Scale
Authors: Hatton TJ , Walker J , Dawes WR , Dunin FX
Published: December 2005

A spatially explicit hydroecological landscape model of water, carbon and energy balances (Topog-
IRM) is described. The landscape is envisaged as a catchment forested with a single stratum comprising
Eucalyptus maculata trees. The model was used to simulate the direct effects of a 2× elevation in
atmospheric carbon dioxide at two levels of nitrogen on catchment water yield, soil moisture status
and tree growth. Experimental results used to parameterise the model are detailed. Key features of
the model are (1) an ability to scale hydrological processes at the catchment scale in three dimensions,
and (2) a means to integrate multiple factors/ stresses on plant growth.
The effects of CO2 on catchment hydrology (water yield or soil moisture content) and forest growth
(expressed as leaf area index, LAI) were modelled for a 2.-year period, and contrasted with the effects
of added nitrogen. Results were expressed as totals for the catchment or spatially distributed across
the catchment. For the total catchment, water yield increased in the order: high CO2 with low N,
high CO2 with high N, ambient CO2 with low N, ambient Co2 with high N. LAI increased from
3.3 to 5.7 in the order: ambient CO2 with low N, ambient CO2 with high N, high CO2 with low
N, high Co2 with high N. These results agree with previous data. New findings are:
(1) with elevated CO2 a new equilibrium in transpiration is established in which leaf area increases
offset decreases in stomatal conductance;
(2) the addition of nitrogen increases transpiration without any indication of a new equilibrium
being reached during the simulated period;
(3) the spatial distribution of soil moisture changes, presenting a new resource base for spatial changes
to species composition and growth rates.
The major hydroecological responses to elevated CO2 are seen as increased maximum upper canopy
leaf area, increased litter inputs, especially at times of drought (hence changed fire regimes), changes
in the composition of the understorey (hence litter composition, soil microfauna, and the spatial expression
of biological diversity) and a slight increase in water yield.
Cereal Callus Cultures: Control of Headspace Gases Can Optimise the Conditions for Callus Proliferation
Authors: Adkins SW
Published: December 2005

The protective conditions under which callus cultures are grown to prevent microbial contamination
and to reduce tissue desiccation cause the accumulation of volatiles in the vessel headspace and reduce
the availability of oxygen for respiration. To demonstrate the importance of the gaseous atmosphere
to culture growth a study was undertaken on non-morphogenic rice and wheat callus incubated under
a number of environmental conditions.
Changes in the gaseous atmosphere above rice (Oryza sativa L.) callus during routine culture in
a petri dish suppressed growth and promoted necrosis. Incubating callus under a continuous flow of
gas mixtures of known composition suggested that the inhibition of growth was caused by the accumulation
of high levels of ethylene and to the rapid depletion of oxygen. In order to evaluate the importance
of ethylene accumulation aminoethoxyvinyl glycine (AVG), I-aminocyclopropane-I-carboxylic acid
(ACC) and silver nitrate (AgNO3) were added to the nutrient medium and ethylene was measured
during callus culture. Ethylene restricted callus growth particularly under high (35°C) compared with
moderate (25°C) incubation temperatures and under illuminated compared with dark incubation. Under
illuminated incubation at 25°C, AVG ( 5 μM ) and AgNO3 (50 μM) improved rice callus growth by 69
and 54% respectively while ACC (100 μM) decreased growth by 15%. Furthermore, rice callus growth
was better in large compared with small culture vessels since ethylene accumulation was reduced.
In contrast, wheat (Triticum aestivum L.) callus grew well in the petri dish system and released
very little ethylene into the culture vessel headspace. Growth was better under illuminated than darkened
conditions and under moderate (25°C) compared with high (35°C) incubation temperatures. Furthermore,
wheat callus growth was only marginally better in large compared with small culture vessels. Ethylene
was not a restrictive factor of wheat callus growth since only low levels were detected in all conditions
of incubation.
Better control of ethylene and increased oxygen availability could be a way of increasing cell and
tissue production for genetic engineering studies of otherwise recalcitrant species such as rice, and may
be a way of improving manipulation of wheat.
In vitro Approaches to Extending the Host-Range of Agrobacterium for Plant Transformation
Authors: Godwin ID , Fordlloyd BV , Newbury HJ
Published: December 2005

Since the first report of successful gene transfer in 1983, engineered Agrobacterium vectors have been the most widely used means of stable plant transformation. There are host-range limitations to the utility of this approach, however, with most success in dicotyledonous species. Recent evidence has indicated that the host-range is dependent on the protocol used to infect plant tissues with Agrobacterium. Modifications of co-cultivation conditions can lead to successful gene transfer to species once thought beyond the host-range of Agrobacterium, including a number of monocots. Hence, when defining the host-range of Agrobacterium, distinction must be made between host-range for pathogenicity (oncogenicity) and host-range for transformation. Important factors in determining the ability of Agrobacterium to transfer DNA to the plant genome include genetic, physiological and physical components of the bacterium × plant interaction. Simple, empirical experiments with oncogenic strains can yield useful information regarding the importance of co-cultivation conditions. The applications of these to extending the host-range of Agrobacterium for transformation are discussed.
Genetic-Improvement of Floricultural Crops Using Biotechnology
Authors: Hutchinson JF , Kaul V , Maheswaran G , Moran JR , Graham MW , Richards D
Published: December 2005

Floricultural crops are an ideal target for improvement using biotechnology. While a range of techniques such as somaclonal variation, embryo and haploid culture has been successfully used, they have yet to result in the release of a new cultivar that has a major impact on the industry. Genetic engineering, more than any other technique, offers the most potential because it is possible to transfer a new gene, conferring a single trait, to an existing cultivar. Recent advances in the regeneration of adventitious shoots and somatic embryos, and Agrobacterium-mediated transformation of the major flower crops (carnation, chrysanthemum, rose and gerbera) are reviewed. To date, all four species can be regenerated and transformed but with varying degrees of success. Notable advances have been made with carnation and chrysanthemum, where genes of potential importance have been transferred and expressed.
A Paedomorphocline in Eucalyptus. II. Variation in Seedling Morphology in the E. risdonii/E. tenuiramis Complex
Authors: Wiltshire RJE , Potts BM , Reid JB
Published: December 2005

Previous studies of phenotypic variation among natural populations in the Eucalyptus risdonii/E. tenuiramis cindicated that the two taxa are linked by a cline in the retention of the juvenile leaf
form (paedomorphocline) and that division into the two taxa, E. risdonii and E. tenuiramis, on the basis
of these ontogenetic differences obscures the phenetic relationships within and between the taxa. This
study attempts to remove the environmental and ontogenetic variation to reveal the genetically based
variation by examining seedling morphology. The results suggest that genetic variation between
geographically contiguous populations of E. risdonii and E. tenuiramis is relatively small and
continuous, and classification into either taxon on the basis of seedling phenotype is not possible for
populations in this transitional area. The major dichotomy between phenetic clusters is not between
forms that can be assigned to E. risdonii and E. tenuiramis on the basis of ontogenetic differences, but
between geographically isolated forms of E. tenuiramis. The ambiguous variation in the adult
phenotype is clarified by the marked difference in seedling morphology between the two East Coast
populations and the other E. tenuiramis populations which, on present data, appear to be separated by a
geographical disjunction. When viewed in terms of the phenetic distance between populations of the
two closest species (E. coccifera and E. nitida), the magnitude of the difference between the East Coast
E. tenuiramis and the other phenetic groups in the E. risdonii/E. tenuiramis complex is emphasised.
The relationship and origin of populations intermediate between E. tenuiramis and E. coccifera are also
discussed.
Utilisation of Microspore Culture in Wheat and Barley Improvement
Authors: Luckett DJ , Darvey NL
Published: December 2005

This review examines some of the recent developments in microspore tissue culture in wheat and
barley, and the application of this technology to practical plant breeding. Several new techniques are
described as well as areas where additional research is required.
The Relationship Between Dysploidy and Reproductive Capacity in Myrtaceae
Authors: Rye BL , James SH
Published: December 2005

Australian Myrtaceae show a positive correlation between base chromosome number and reproductive capacity. There is some evidence of a similar trend in other Australian plant families. Reduced chromosome numbers in the Myrtaceae arose in lineages with critically reduced reproductive capacities, occurring mainly in small shrub species with four or fewer ovules per flower and one seed per fruit or per fruit loculus. Dysploid reduction serves the short-term advantage of ensuring greater genetic uniformity through reduced recombination, therefore resulting in less seed wastage. However, lineages with reduced chromosome numbers (x=5-10) have reduced evolutionary flexibility, as evidenced by their failure to fully penetrate the arid zones, in contrast to the species with the primitive chromosome number or above (x=11 or 12). Trends for decreased ovule and seed numbers have apparently resulted partly from the selection for larger seed size. Among species with more than one ovule per flower but normally only one seed per fruit, there is evidence of physiological and genetic selection systems determining which of the fertilised ovules becomes the seed.
Factors Affecting Protoplast Isolation and the Regeneration of Shoot-Like Structures From Protoplast-Derived Callus of Sugarcane (Saccharum spp Hybrids)
Authors: Taylor PWJ , Ko HL , Adkins SW
Published: December 2005

High yields of protoplasts were isolated from non-regenerable, homogeneous cell suspension cultures of sugarcane, compared with regenerable, heterogeneous cell suspension cultures after incubation in an enzyme composition containing Cellulase RS, Pectinase, Macerozyme and Driselase. Higher yields of protoplasts were released from heterogeneous cell suspension cultures after the addition of 10 mg L-1 silver nitrate to the culture medium; however, ethylene production was not involved in protoplast isolation. Use of 0-05-2% Pectolyase Y23 pectinase rather than other pectinases resulted in higher yields of protoplasts from heterogeneous cell suspension cultures. These results suggest that there are differences in the cell walls between cells from heterogeneous and homogeneous cell suspension cultures which affect the isolation of protoplasts. Protoplasts isolated from heterogeneous cell suspension cultures failed to develop beyond the cell division stage. Protoplasts isolated from homogeneous cell suspension cultures and cultured in agarose droplets bathed in modified 8p medium, reformed cell walls, divided and developed into microcallus. Microcallus transferred to solid modified MS medium containing 1 mg -1 .2,4-D developed into callus. Protoplast-derived callus from one cultivar formed compact nodular callus when subcultured onto the same medium containing 1% activated charcoal. Incubation of this callus on MS medium containing BAP at 0.5 mg L-1, then a combination of BAP and fluridone each at 0.5 mg L-1, resulted in the regeneration of small, chlorophyll-containing shoot-like structures. As yet no intact plants have developed from these shoot-like structures.
Anther and Ovule Development in Tasmannia (Winteraceae)
Authors: Prakash N , Lim AL , Sampson FB
Published: December 2005

Three species of Tasmannia R.Br. ex DC., T. glaucifolia, T. insipida and T. stipitata are studied. The
anther is tetrasporangiate and its waU development conforms to the Basic type. The tapetum follows the
secretory type of development. Cytokinesis in the microspore mother cells is simultaneous but an
evanescent cell plate is present at telophase I and anaphase I1 during meiosis. Pollen tetrads are
permanent and tetrahedral. The mature pollen is anaulcerate, reticulate and 2-celled.
The ovule. is anatropous, bitegmic and crassinucellate. The micropyle in T. stipitata and T.
Glaucifolia is formed by the inner integument only whereas in T. insipida it is formed by both the
integuments and is zigzag in outline. Meiosis in the single megaspore mother cell produces a linear or
T-shaped megaspore tetrad in T. stipitata and T. glaucifolia but only a linear tetrad in T. insipida.
Female gametophyte development is of the monosporic Polygonum type. Fertilisation is porogamous;
triple fusion and syngamy occur simultaneously.
In vitro Induction of Banana Autotetraploids by Colchicine Treatment of Micropropagated Diploids
Authors: Hamill SD , Smith MK , Dodd WA
Published: December 2005

Alternative breeding strategies, based on colchicine-induced autotetraploids, have been proposed as a means of introducing disease resistance into banana breeding programs. This paper describes techniques for the in vitro induction of banana autotetraploids by the use of colchicine on cultured explants. The technique can be readily applied and large numbers of autotetraploids produced. The optimum treatment involved immersing shoot tips in a 0-5% w/v colchicine solution for 2 h under aseptic conditions. Dimethyl sulfoxide (DMSO) was applied with the colchicine treatments to increase cell permeability and so absorption of colchicine, resulting in the optimum treatment unchanged at 0-5% colchicine, but including the addition of 2% v/v DMSO. Of the shoot tips treated over 30% were induced to the autotetraploid level. Methods for in vitro selection of induced tetraploids from treated diploid plantlets were also developed. Tetraploid plants were more robust with thicker pseudostems, roots and broader leaves than diploids and they could be selected on these morphological characteristics. Mean stomatal lengths of diploid banana plants growing in vitro were significantly smaller (16-0 mum) than the tetraploids (26.9 mum) and were used as a more reliable indicator of ploidy than morphological criteria alone. A root tip squash technique using carbol fuchsin was developed for positive confirmation of ploidy change by chromosome counts- Although chimerism and reversion to the diploid form occurred, it was not considered a problem because of the large number of autotetraploids induced. Stable autotetraploids were recovered and established in the field and were characterised by their large, drooping leaves and thick pseudostems. They have retained these characteristics for more than 3 years in the field.
Canopy-Stored Seed Banks of Allocasuarina distyla and A. nana in Relation to Time Since Fire
Authors: Pannell JR , Myerscough PJ
Published: December 2005

Aspects of the serotinous seed banks of Allocasuarina distyla (Vent.) L. Johnson and A. nana (Sieb. ex Spreng.) L. Johnson are presented in relation to fire. A. distyla is single-stemmed and fire-sensitive; A. nana resprouts multiple stems from a lignotuber following fire. Vegetative above-ground plant growth correlates with seed bank size in A. distyla better than in A. nana. There is approximately 10 times the canopy-stored seed in A. nana 8 years after fire than in A. distyla 9 years after fire. The critical period to initial seed set in A. distyla is between about 7 and 9 years. In A. nana, this period is typically longer but appears to depend on the age of the seed-producing genets. The age structure of the seed banks in both species remains more or less constant in time, with most seed being young. Seed viability declines in A. distyla from an initial 60% to less than 10% within about 12 years after seed set. A similar pattern appears likely for A. nana, although initial seed viability is about 40%. Attrition in seed viability is attributed to seed predation by insects, fungal attack and seed senescence. The dynamics of seed production and survivorship appear to be similar to those in serotinous proteaceous species studied to date.
Breeding Systems of Disjunct Populations of Christmas Bells (Blandfordia grandiflora R.Br., Liliaceae): Variation in Self-Fertility and an Ovular Mechanism Regulating Self-Fertilisation
Authors: Ramsey M , Prakash N , Cairns S
Published: December 2005

The breeding systems of disjunct tableland and coastal populations of Christmas bells were determined
using hand-pollination experiments. In both populations, 90% or more of self-pollinated plants
produced seeds. Tableland plants were significantly more self-fertile than coastal plants (ratio of self
seed set to cross seed set: tableland, 0.55 ± 0.03; coast, 0.08 ± 0.02). Significant variation among plants
for self-fertility was found in both populations. Autofertility was 1.6% or less in both populations
indicating that pollen vectors are necessary for seed set. Seed set by agamospermy in both populations
was less than 0.1%. Percentage seed abortion was greater in self-pollinated plants than cross-pollinated
plants in both populations. In both self- and cross-pollinated plants, seed abortion was twice as great in
the coastal population than in the tableland population. No evidence was found for stigmatic or stylar
self-incompatibility. Self and cross pollen adhered to and germinated equally well on stigmas in both
populations (72 - 77% germination). Similarly, there were no differences between pollination
treatments or populations in the percentage of ovules penetrated by pollen tubes (82 - 89% penetration).
When self-pollination preceded cross-pollination by 24 h or longer seed set was significantly reduced
compared to flowers that were cross-pollinated only, suggesting ovules were pre-empted by self pollen
tubes. Collectively these results strongly suggest that self seed set was reduced by a mechanism
operating at the ovule level, such as early-acting inbreeding depression due to recessive seed-aborting
genes, although incomplete late-acting self-incompatibility cannot be ruled out. For coastal plants, this
ovular mechanism largely prevents selfing, indicating plants were predominantly outcrossing although
most produced some self seed. For tableland plants, substantial seed set by selfing may occur under
natural conditions.
Patterns of Abundance in Grassy Vegetation of the New-England Tablelands; Identifying Regional Rarity in a Threatened Vegetation Type
Authors: Mcintyre S , Huang Z , Smith AP
Published: December 2005

A survey of understorey species in grassy vegetation was conducted at 120 sites on the New England Tablelands (part of the northern tablelands of New South Wales), and the frequency of 371 taxa is presented. Very few species were common and the majority were recorded at < 5% of the sites. Similar patterns of abundance were also observed within the quadrats. Only 16% of taxa achieved dominance (i.e. > 10% canopy cover ) in any of the sampled quadrats, and while the average richness was 28 species (per 30 m²), the average number of dominant species per quadrat was only 1.6. The main dominants were perennial gasses. Of the native grasses thought to dominate this vegetation type at the time of European settlement, it would seem that Poa sieberiana has not declined. In contrast, Sorghum leiocladum and to a lesser extent Themeda australis appear to have declined. Although some native dicot species were very frequent, they rarely achieved dominance in the vegetation. These observations support the notion that sparseness may be a more common form of rarity than has been previously recognised.
Genetic Diversity of Natural-Populations of Acacia auriculiformis
Authors: Wickneswari R , Norwati M
Published: December 2005

Seeds from 18 populations of Acacia auriculiformis A. Cunn. ex Benth. from natural riverine and coastal forests in Australia and Papua New Guinea were electrophoretically analysed at 22 isozyme loci representing 17 enzyme systems. Genetic variability measures were determined using 12 isozyme loci. On average, 39.8% of the loci were polymorphic (0.99 criterion). Average and effective numbers of alleles per locus were 1.5 and 1.1 respectively. Mean expected heterozygosity was 0.081 with values ranging from 0.002 (South Alligator River, Northern Territory) to 0.180 (North Mibini, Papua New Guinea). The genetic differentiation between populations was high (GST = 0.270), indicating that about 73% of the isozyme variation was among progenies within populations. Hence, both intra- and inter-population genetic variations are important in initial selections in A. auriculiformis improvement programs. Nei's unbiased genetic distance between populations ranged from 0.000 to 0.120, with populations from the Northern Territory, Australia, generally being very closely related to each other. UPGMA cluster analysis using Nei's unbiased genetic distance revealed three distinct clusters of populations corresponding to the geographic distribution of the species in the Northern Territory and Queensland, Australia, and Papua New Guinea. Populations from Queensland were closely related to populations from Papua New Guinea rather than to populations from the Northern Territory, which is in the same land mass.
Factors Influencing the Germination of Six Perennial Grasses of Central New South Wales
Authors: Maze KM , Koen TB , Watt LA
Published: December 2005

The effect of light, storage time, temperature regimes and water potential were examined on the germination of five native grasses of central New South Wales (Enteropogon ramosus, Bothriochloa macra, Elymus scabrus, Chloris truncata and Danthonia caespitosa), and one introduced grass (Eragrostis curvula). Caryopses of E. ramosus, B. macra and E. curvula reached maximum germination soon after harvest. The remaining species reached maximum germination after 6-10 months storage. For all species, except E. scabrus, the effect of light on germination changed with duration of storage and with the presence of the lemma and palea. The viability of naked caryopses was reduced more rapidly than the viability of caryopses stored with the lemma and palea intact, for all tested species; E. scabrus and E. curvula were not tested. E. scabrus, C. truncata, D. caespitosa and E. curvula had greater than 50% germination over a range of alternating temperatures. E. ramosus had the narrowest temperature range for good germination, exceeding 50% germination only at temperatures above 30/20*#176 (day/night). E. ramosus and E. curvula germinated over a wider range of water potential than the other species. The germination of D. caespitosa, B. macra and C. truncata fell significantly at a water potential of -0.1 MPa. It is concluded that temperature is likely to impede the germination of most of these grasses only in mid winter, and that soil water potential will probably have an overriding influence on the season of germination.