Showing papers by "Commonwealth Scientific and Industrial Research Organisation published in 1985"

Number of kernels in wheat crops and the influence of solar radiation and temperature

Abstract: The number of kernels per m2 (K) in well managed and watered wheat crops was studied using results of experiments in Mexico and Australia in which short spring wheat cultivars were subjected to independent variation in radiation, largely via artificial shading, and in temperature. Also crops subjected to differences in weather (year), sowing date and location within Mexico, revealed responses to the natural and simultaneous variation which occurs in radiation and temperature. Responses in K were interpreted in terms of spike dry weight at anthesis (g/m2) and number of kernels per unit of spike weight.K was linearly and most closely related to incident solar radiation in the 30 days or so preceding anthesis, herein termed the spike growth period; for the cultivar Yecora 70 with full ground cover the slope was 19 kernels/MJ. This response seemed largely due to a linear response of crop growth rate to intercepted solar radiation. The proportion of dry weight increase partitioned to the spike increased somewhat with reduced radiation. Also increasing temperature in the range 14–22 °C during this period reduced K (slope approximately 4% per CC at 15 °C). The cause appeared to be lower spike dry weight due to accelerated development. The number of kernels per unit spike weight at anthesis was little affected by radiation or temperature, and averaged 78±2/g for the cultivar Yecora 70.With natural variation in radiation and temperature, K was closely and linearly correlated with the ratio of mean daily incident or intercepted radiation to mean temperature above 4·5 °C in the 30 days preceding anthesis. As this ratio, termed the photothermal quotient, increased from 0·5 to 2·0 MJ/m2/day/degree, K increased from 70 to 196 × 102/m2. These responses of K to weather, sowing date and location were closely associated with variation in spike dry weight.It was concluded that the ratio of solar radiation to temperature could be very useful for estimating K in wheat crop models. Also the analysis of K determination in terms of spike dry weight appeared promising, and suggests that wheat physiologists should place greater emphasis on the growth period immediately before anthesis.

On the Three-Dimensional Propagation of Stationary Waves

Abstract: A locally applicable (nonzonally-averaged) conservation relation is derived for quasi-geostrophic stationary waves on a zonal flow, a generalization of the Eliassen-Palm relation. The flux which appears in this relation constitutes, it is argued, a useful diagnostic of the three-dimensional propagation of stationary wave activity. This is illustrated by application to a simple theoretical model of a forced Rossby wave train and to a Northern Hemisphere winter climatology. Results of the latter procedure suggest that the major forcing of the stationary wave field derives from the orographic effects of the Tibetan plateau and from nonorographic effects (diabatic heating and/or interaction with transient eddies) in the western North Atlantic and North Pacific Oceans and Siberia. No evidence is found in the data for wave trains of tropical origin; forcing by the orographic effects of the Rocky mountains seems to be of secondary importance.

A Kernel Method for Smoothing Point Process Data

Abstract: A method for estimating the local intensity of a one‐dimensional point process is described. The estimator uses an adaptation of Rosenblatt's kernel method of non‐parametric probability density estimation, with a correction for end‐effects. An expression for the mean squared error is derived on the assumption that the underlying process is a stationary Cox process, and this result is used to suggest a practical method for choosing the value of the smoothing constant. The performance of the estimator is illustrated using simulated data. An application to data on the locations of joints along a coal seam is described. The extension to two‐dimensional point processes is noted.

The responses of stomata and leaf gas exchange to vapour pressure deficits and soil water content : II. In the mesophytic herbaceous species Helianthus annuus

Abstract: The responses of leaf water potential, leaf conductance, transpiration rate and net photosynthetic rate to vapour pressure deficits varying from 10 to 30 Pa kPa-1 were followed in Helianthus annuus as the extractable soil water decreased. With a vapour pressure deficit of 25 Pa kPa-1 around the entire plant as the soil water content decreased, the leaf conductance and transpiration rate showed a strong closing response to leaf water potential at a value of-0.65 MPa, whereas with a vapour pressure deficit of 10 Pa kPa-1 around the entire plant, the rate of transpiration and leaf conductance decreased almost linearly as the leaf water potential decreased from-0.4 to-1.0 MPa. Increasing the vapour pressure deficit from 10 to 30 Pa kPa-1 in 5 Pa kPa-1 steps decreased the leaf conductance by a similar proportion at all extractable soil water contents. At high soil water contents, the decrease in conductance with leaf water potential was greater when the vapour pressure deficit was increased than when it was not, indicating a direct influence of vapour pressure deficit on the stomata. The rate of net photosynthesis decreased to a smaller degree than the leaf conductance when the vapour pressure deficit around the leaf was varied. Overall, the net photosynthetic rate decreased almost linearly from 20 to 25 μmol m-2 s-1 at-0.3 MPa to 5 μmol m-2 s-1 at-1.2 MPa. As the soil water decreased, the internal carbon dioxide partial pressure was maintained between 14 and 25 Pa.No unique relationship between leaf conductance, transpiration rate or photosynthetic rate and leaf water potential was observed, but in all experiments leaf conductance and the rate of net photosynthesis decreased when about two-thirds of the extractable water in the solid had been utilized irrespective of the leaf water potential. We conclude that soil water status, not leaf water status, affects the stomatal behaviour and photosynthesis of H. annuus.

Flux-Gradient Relationships in a Forest Canopy

Abstract: Relationships between the flux densities of sensible heat, water vapor and C02 and the appropriate gradients were examined systematically above and within a pine forest, 16–20 m high. Above the forest, the stability functions for heat and water vapor appeared to be identical, but different from those pertaining to smoother surfaces. Consequently, aerodynamic methods for calculating the flux densities of those scalars, which require exact knowledge of the stability functions, were unsuccessful, but the energy balance approach, which requires only that the functions be identical, still proved reliable. However, all gradient-diffusion schemes failed completely within the canopy, where counter-gradient or zero-gradient fluxes were observed for all three scalars. The failure of conventional flux-gradient relationships in that space is due in part to the sporadic penetration of transporting eddies into the canopy and their large scale.

The galactic population of pulsars

Abstract: Afin d'etablir des conclusions statistiques sur la population globale des pulsars dans la Galaxie, on analyse un echantillon de 316 pulsars detectes

Sensitivity of stomata and water use efficiency to high CO2

Abstract: The observed responses of stomata to carbon dioxide are reviewed, and the interaction of other known factors on the sensitivity to CO2 are summarized. The role of stomatal response to CO2 is discussed, and it is argued that while the effect of the CO2 response in normal daily stomatal behaviour is presently poorly understood the stomatal response to CO2 will have major impact in improving water use efficiency in future CO2 atmospheres. However, the attenuation of this increase is emphasized so that increases at the crop level will probably be much smaller than those observed at the single leaf assimilation level.

Smoothing noisy data with spline functions

Abstract: A procedure for calculating the trace of the influence matrix associated with a polynomial smoothing spline of degree2m?1 fitted ton distinct, not necessarily equally spaced or uniformly weighted, data points is presented. The procedure requires orderm 2 n operations and therefore permits efficient orderm 2 n calculation of statistics associated with a polynomial smoothing spline, including the generalized cross validation. The method is a significant improvement over an existing method which requires ordern 3 operations.

Rainfall in the wet‐dry tropics: Extreme events at Darwin and similarities between years during the period 1870–1983 inclusive

Abstract: This paper supplements the existing climatic analyses for Darwin and the surrounding region, by providing a classification of years in terms of amount and distribution of rainfall, and highlighting the extreme, episodic rainfall events that have occurred in the period 1870 to 1983 inclusive. Approximately 77% of years have had significant departures from the two most frequent rainfall patterns and these are described. Much of the variation between years or groups of years lies in the dry and dry-wet transition periods. While the reliability of rainfall in the wet-dry tropics has been emphasized, rainfall variability over both the dry and wet seasons would seem to be an equally important characteristic, at least for the biota. In an environment such as the wet-dry tropics, where moisture is the primary limiting factor, rainfall variability has important implications for the design and interpretation of faunal and floristic surveys, monitoring programs and field experiments.

The density and pressure of helium in bubbles in implanted metals: A critical review

Abstract: A review is presented of experiments and calculations which have yielded information on the state of helium in small bubbles in implanted metals. Recent findings which indicate extremely high densities and pressures are discussed in the light of the mechanical properties of the metal substrate. A short review of research on high pressure helium is also presented in order to establish an equation of state relevant to small room temperature helium bubbles.

Effects of suspensoids (turbidity) on penetration of solar radiation in aquatic ecosystems

Abstract: In mainland Australia and in southern Africa the aridity of the climate and sparse vegetative cover increase the susceptibility of the soils to erosion, and as a consequence surface waters are usually turbid. The inanimate suspensoids in such waters, the ‘tripton’ fraction of the limnologist,are responsible for virtually all the light scattering, and also, by virtue of the yellow-brown humic materials adsorbed on their surface, for a substantial part of the light absorption. Spectral absorption data for suspensoids in terms of their in situ absorption coefficient values, and the contribution of suspensoids to absorption of photosynthetically available radiation (PAR) are given for certain. Australian water bodies.

Specific expression of a foreign β-globin gene in erythroid cells of transgenic mice

Abstract: The globin gene family represents an attractive system for the study of gene regulation during mammalian development, as its expression is subject to both tissue-specific and temporal regulation. While many aspects of globin gene structure and expression have been described extensively1, relatively little is known about the cis-acting DNA sequences involved in the developmental regulation of globin gene expression. To begin to experimentally define these regulatory sequences, we have taken the approach of introducing cloned globin genes into the mouse germ line and examining their expression in the resulting transgenic animals2,3. Here we describe a series of transgenic mice carrying a hybrid mouse/human adult β-globin gene, several of which express the gene exclusively or predominantly in erythroid tissues. These studies demonstrate that regulatory sequences closely linked to the β-globin gene are sufficient to specify a correct pattern of tissue-specific expression in a developing mouse, when the gene is integrated at a subset of foreign chromosomal positions.

High temperature and chemical effects on wood stability

Abstract: A study was made of the softening curves of wood in different growth rings taken from young radiata pine trees. The curves were determined from the rate of twist of a strip of wood under constant torque when heated at a steadily increasing temperature. The softening points of about 80° and 100°C are attributed to hemicelluloses and lignins respectively and were indistinct in sapwood taken from the 3rd and 4th growth rings from the pith but became increasingly distinct in growth rings further from the pith. Heartwood in the juvenile wood zone had two distinct softening points. Differences in the softening curves are attributed to differences in the chemistry of the hemicelluloses.

Control of transcription of α -amylase and rRNA genes in barley aleurone protoplasts by gibberellin and abscisic acid

Abstract: Gibberellin A3 (GA3) promotes and abscisic acid (ABA) inhibits the production of α-amylase in aleurone layers of barley (Hordeum vulgare L.); this sytem has been used extensively to study the mechanisms of action of these hormones1. Cell-free messenger RNA translation studies have shown that the GA3-promoted increase in α-amylase synthesis and its inhibition by ABA are associated with corresponding changes in the levels of translatable α-amylase mRNA2–5. Subsequent studies using hybridization of an α-amylase complementary DNA-rich probe6 and of clonedα-amylase cDNA probe6 to aleurone RNA7–9 have shown that the abundance of α-amylase mRNA increases in response to GA3, and that this increase is inhibited by ABA. The increased abundance of mRNA could result from an increased rate of transcription, increased stability of mRNA, or both, as in some animal cells10–12. By using methods for studying gene transcription in isolated plant nuclei13–15, we present here evidence that GA3 and ABA regulate the transcription of both α-amylase and ribosomal RNA (rRNA) genes

Turbulent Transport in Flexible Plant Canopies

Abstract: The inapplicability of flux-gradient models of turbulent transport in plant canopies is demonstrated through formal manipulation of the rate equations for eddy flux and consideration of the nature of the diffusivity that describes release from point sources in homogeneous turbulence. A new set of scalar conservation and flux equations is derived by volume averaging the primitive equations which hold exactly in the air spaces between the plants. Source terms and extra waving terms arise because of the noncommutivity of differentiation and volume averaging in the multiply-connected canopy air space. The implicatons of the equation set are worked out for three cases. In the first, they are used to show the exact relationship between leaf transfer resistances and the averaged canopy resistances of the Penman-Monteith single leaf model. Second, we explore the relationship between the eddy flux produced by the action of the turbulent wind on the mean concentration field and the flux produced by the interaction of scalar concentration on foliage surfaces with the drag force and its consequences for canopy models. Third, the importance of the production of eddy flux by buoyant plumes generated at the foliage surface is deduced by a consideration of flux and buoyancy equations in the free convection limit.

The joint use of coincident loop transient electromagnetic and Schlumberger sounding to resolve layered structures

Abstract: One-dimensional earth models consisting of uniform horizontal layers are useful both as actual representations of earth structures and as host models for more complex structures. However, there are often inherent difficulties in establishing layer thicknesses and resistivities from one type of measurement alone. For example, the dc resistivity method is sensitive to both conductive and resistive layers, but as these layers become thin, nonuniqueness becomes a severe problem. Electromagnetic (EM) methods are good for establishing the parameters of conductive layers, but they are quite insensitive to resistive layers.The use of both coincident loop transient EM (TEM) and Schlumberger methods, together with a joint inverse computer program, can vastly improve interpretation of layered-earth parameters. The final model is less dependent upon starting guesses, error bounds are much improved, and nonuniqueness is much less of a problem. These advantages are illustrated by interpretation of real field data as well as by a theoretical study of four different types of earth models.

Determination of ethanol, volatile fatty acids, lactic and succinic acids in fermentation liquids by gas chromatography

Abstract: A rapid and simple quantitative method was developed to determine, by gas chromatography, the concentrations in fermentation liquids of ethanol, the C2-C6 volatile fatty acids, and lactic and succinic acids. Aqueous samples were acidified with 250μlml−1 metaphosphoric acid (5:1 ratio), centrifuged, and injected directly on to a column containing a porous aromatic polymer (Chromosorb 101) maintained at 200°C in a gas chromatograph fitted with a flame ionisation detector. It was unnecessary to purify samples further before injection, although distillation and ion-exchange methods were examined. Derivatisation of lactic and succinic acids before injection was not necessary, but the lowest level of detection of these two relatively non-volatile acids was about four times greater than that for the volatile fatty acids. The method described was suitable for the analysis of rumen fluid, methane digester fluid, silage extracts and other anaerobic fermentation fluids. The relative retention times are given for 23 organic acids and six other fermentation end-products.

Equivalent-circuit formulas for metal grid reflectors at a dielectric boundary.

Abstract: This paper points out a number of errors that have appeared in the literature concerning transmission-line models for metal grid reflectors (strip gratings and meshes) especially in regard to the design of laser mirrors and filter elements for use at submillimeter wavelengths. General formulas are given for the transmittance of lossy grids and for the equivalent circuit impedances to be used in these formulas for strip gratings and meshes at a plane boundary between two lossless dielectrics. The results apply for normal incidence and for wavelengths in both dielectrics greater than the grid period. Limitations of the transmission-line models for meshes at dielectric boundaries are discussed.

Hydrogen-isotope composition of leaf water in C3 and C4 plants: its relationship to the hydrogen-isotope composition of dry matter

Abstract: The natural abundance hydrogen-isotope composition of leaf water (\(\delta _{\text{D}}^{{\text{H}}_{\text{2}} {\text{O}}} \)) and leaf organic matter (δDorg) was measured in leaves of C3 and C4 dicotyledons and monocotyledons. The \(\delta _{\text{D}}^{{\text{H}}_{\text{2}} {\text{O}}} \) value of leaf water showed a marked diurnal variation, greatest enrichment being observed about midday. However, this variation was greater in the more slowly transpiring C4 plants than in C3 plants under comparable environmental conditions. A model based on analogies with a constant feed pan of evaporating water was developed and the difference between C3 and C4 plants expressed in terms of either differences in kinetic enrichment or different leaf morphology. Microclimatic and morphological features of the leaves which may be associated with this factor are discussed. There was no daily excursion in the δDorg value in leaves of either C3 or C4 plants. When δDorg values were referenced to the mean \(\delta _{\text{D}}^{{\text{H}}_{\text{2}} {\text{O}}} \) values during the period of active photosynthesis, the discrimination against deuterium during photosynthetic metabolism (ΔD) was greater in C3 plants (-117 to -121‰) than in C4 plants (-86 to -109‰).

Physiological influences on carbon isotope discrimination in huon pine (Lagarostrobos franklinii).

Abstract: Measurements of the light environment and stomatal and photosynthetic behaviour are reported for Huon Pine (Lagarostrobos franklinii, family Podocarpaceae) in western Tasmanian rainforest. For a variety of microenvironments, these are used in an analysis of stable carbon isotope measurements in the air, and in branch and leaf material, using a model for carbon isotope fractionation in leaves (Farquhar et al. 1982).