Alan Richardson

Plant and microbial strategies to improve the phosphorus efficiency of agriculture

BackgroundAgricultural production is often limited by low phosphorus (P) availability. In developing countries, which have limited access to P fertiliser, there is a need to develop plants that are more efficient at low soil P. In fertilised and intensive systems, P-efficient plants are required to minimise inefficient use of P-inputs and to reduce potential for loss of P to the environment.ScopeThree strategies by which plants and microorganisms may improve P-use efficiency are outlined: (i) Root-foraging strategies that improve P acquisition by lowering the critical P requirement of plant growth and allowing agriculture to operate at lower levels of soil P; (ii) P-mining strategies to enhance the desorption, solubilisation or mineralisation of P from sparingly-available sources in soil using root exudates (organic anions, phosphatases), and (iii) improving internal P-utilisation efficiency through the use of plants that yield more per unit of P uptake.ConclusionsWe critically review evidence that more P-efficient plants can be developed by modifying root growth and architecture, through manipulation of root exudates or by managing plant-microbial associations such as arbuscular mycorrhizal fungi and microbial inoculants. Opportunities to develop P-efficient plants through breeding or genetic modification are described and issues that may limit success including potential trade-offs and trait interactions are discussed. Whilst demonstrable progress has been made by selecting plants for root morphological traits, the potential for manipulating root physiological traits or selecting plants for low internal P concentration has yet to be realised.

Soil microbial biomass and the fate of phosphorus during long-term ecosystem development

BackgroundSoil phosphorus availability declines during long-term ecosystem development on stable land surfaces due to a gradual loss of phosphorus in runoff and transformation of primary mineral phosphate into secondary minerals and organic compounds. These changes have been linked to a reduction in plant biomass as ecosystems age, but the implications for belowground organisms remain unknown.MethodsWe constructed a phosphorus budget for the well-studied 120,000xa0year temperate rainforest chronosequence at Franz Josef, New Zealand. The budget included the amounts of phosphorus in plant biomass, soil microbial biomass, and other soil pools.ResultsSoil microbes contained 68–78xa0% of the total biomass phosphorus (i.e. plant plus microbial) for the majority of the 120,000xa0year chronosequence. In contrast, plant phosphorus was a relatively small pool that occurred predominantly in wood. This points to the central role of the microbial biomass in determining phosphorus availability as ecosystems mature, yet also indicates the likelihood of strong competition between plants and saprotrophic microbes for soil phosphorus.ConclusionsThis novel perspective on terrestrial biogeochemistry challenges our understanding of phosphorus cycling by identifying soil microbes as the major biological phosphorus pool during long-term ecosystem development.

Direct measurement of roots in soil for single and mixed species using a quantitative DNA-based method

Molecular techniques present a new opportunity to study roots and their interactions in soil. Extraction and quantification of species-specific DNA directly from soil allows direct identification of roots in mixed swards reducing the need for labour-intensive methods to recover and identify individual roots. DNA was extracted directly from up to 0.5xa0kg of soil and the presence of individual species quantified using species-specific probes with quantitative real-time PCR. A range of plant and soil factors influenced the DNA content measured in roots and it was necessary to account for these influences when converting DNA amount to root mass. The utility of the method for quantitative root studies was demonstrated in an experiment to investigate the effect of lime on root growth of acid-soil resistant and sensitive perennial grasses grown together in an aluminium-toxic soil. The root mass of an acid-soil resistant species was unaffected by lime application, whereas that of an acid-soil sensitive species was restricted by soil acidity. Molecular techniques present a promising tool for quantification of root mass directly in soil and have applications for field studies involving mixed species of plants.

Root morphology, root-hair development and rhizosheath formation on perennial grass seedlings is influenced by soil acidity

Perennial pasture species are important for sustainable pasture systems; yet some species display poor persistence on acid soils. This work investigated the effect of soil acidity on primary root length and root-hair and rhizosheath development of five perennial grass genotypes varying in acid-soil resistance. Plants were grown in three low-P acid soils that were limed (CaCO3) to modify soil pH (0.01xa0M CaCl2 extractable) from <4.3 to >5.0 and Al3+ concentrations from ≥ 16 to <4xa0mgxa0kg−1 (0.01xa0M CaCl2 extractable). Root morphology of tall wheatgrass (Thinopyrum ponticum (Podp.) Z.-W. Liu & R.-C Wang), phalaris (Phalaris aquatica L.), cocksfoot (Dactylis glomerata L.) and weeping grass (Microlaena stipoides Labill. R. Br.) was assessed after 20–25xa0days growth. The root length of tall wheatgrass and phalaris cv Sirosa was sensitive to acidity, with lateral root length more sensitive to acidity than seminal root length. Lime increased the root-hair length and density of both acid-soil sensitive and resistant genotypes (cocksfoot and an acid-resistant line of phalaris) and root-hair length was positively correlated to an increase in rhizosheath size per unit root length. Restricted root length and poor root-soil contact of acid-soil sensitive genotypes may explain their low yield and relatively poor persistence on acid soils. The improvement to root-hair and rhizosheath development of genotypes that are acid-soil resistant in terms of root length demonstrates the benefit of using resistant genotypes in conjunction with liming to manage acid soils. Weeping grass was exceptional in its ability to maintain root length, root-hair and rhizosheath development in acid soil.

Effect of soil acidity, soil strength and macropores on root growth and morphology of perennial grass species differing in acid‐soil resistance

It is unclear whether roots of acid-soil resistant plants have significant advantages, compared with acid-soil sensitive genotypes, when growing in high-strength, acid soils or in acid soils where macropores may allow the effects of soil acidity and strength to be avoided. The responses of root growth and morphology to soil acidity, soil strength and macropores by seedlings of five perennial grass genotypes differing in acid-soil resistance were determined, and the interaction of soil acidity and strength for growth and morphology of roots was investigated. Soil acidity and strength altered root length and architecture, root hair development, and deformed the root tip, especially in acid-soil sensitive genotypes. Root length was restricted to some extent by soil acidity in all genotypes, but the adverse impact of soil acidity on root growth by acid-soil resistant genotypes was greater at high levels of soil strength. Roots reacted to soil acidity when growing in macropores, but elongation through high-strength soil was improved. Soil strength can confound the effect of acidity on root growth, with the sensitivity of acid-resistant genotypes being greater in high-strength soils. This highlights the need to select for genotypes that resist both acidity and high soil strength.

A Theory and a Method for the Psychological Study of Assimilation

A theory of assimilation is presented which specifies the characteristic sequence of psycho? logical changes through which an immigrant may pass. It is asserted that a minimal level of satisfaction with his new life constitutes the necessary prerequsite for the development of an identification or feeling of attachment to the new community. In its turn, a minimal level of identification is the typical prerequisite for a high level of acculturation to occur, in which the immigrant actually becomes more like rel? evant members of the host group. Support for this theory has been obtained from studies em? ploying cumulative scaling methods and from the finding that predictable relationships exist between each level of assimilation and variables selected on the basis of the theory. Dr. Richardsons theory is a very valuable tool of socio-psychological analysis, almost an indispensable step to be taken before any study of structural assimilation and it shows the need of approaching the problems of immigrants from their individual perspective as well as from the perspective of the societies of de? parture and arrival.**

Subjective Experience: Its Conceptual Status, Method of Investigation, and Psychological Significance

Abstract The aim of this article is to clarify the concept of subjective experience and, by illustrating some of the ways in which it has been successfully investigated, to encourage further research on specific experiential states and processes. Clarification has been undertaken by discussing the conceptual status of subjective experience, the methods available for its investigation, and its broader psychological significance.

Australian Attitudes Toward Immigrants: A Review of Social Survey Findings

Before the large scale immigration of European refugees began in 1949, the Australian population was almost entirely of English, Scottish and Irish origin. In 1947, 90 per cent of the population had been born in Australia and another eight per cent born in other British countries. Today only about 80 per cent of the total population were born in Aus? tralia and over 10 per cent were born in non-British countries. At the time when the immigration programme began in 1948, Aus? tralians as a whole were unfamiliar with non-British people and were opposed to their admission as immigrants, especially to those from Southern Europe, and from Asia and Africa. For example, in 1948, nearly 80 per cent of a Melbourne sample were opposed to the large scale

THE LONG RANGE EFFECT OF SLEEP ON RETENTION

A test is made of the hypothesis that a greater number of nonsense syllables will be retained after intervals of 24, 48 and 144 hours when learning is followed immediately by 8 hours sleep than when learning is followed by normal waking activities. The results for the 144-hour interval support the hypothesis at the p<.01 level of confidence but the differences at 48 and 24 hours are decreasing and insignificant. The possible roles of consolidation and interference are discussed and the need for further research into the critical period necessary for consolidation to occur is emphasized.

Field application of a DNA-based assay to the measurement of roots of perennial grasses

Background and aimsDNA-based methods present new opportunities for overcoming the difficulties of accurately identifying and quantifying roots of different plant species in field soils. In order to quantify species-specific root biomass from measurements of DNA, consideration needs to be given to replication and ability to recover roots for calibration purposes in order to account for spatial, temporal and inter- and intra-species variation in DNA content of roots and distribution of roots within the soil profile.MethodsThis paper develops the field application of a DNA-based technique for direct quantification of roots in soils. The method was applied to a field experiment to investigate differences in root growth of acid-soil resistant and sensitive genotypes of perennial pasture grasses in an acid soil. DNA was extracted directly from soil and species-specific DNA was quantified using quantitative real-time PCR prior to estimation of root biomass.ResultsRoot growth of the perennial grasses was quantified using the DNA-based technique, although separate calibration procedures were needed to convert DNA content to root mass for each species, soil layer and sampling date. Compared to acid-soil resistant genotypes, lesser root growth in acid soil layers and reduced above-ground dry matter production was observed for acid-soil sensitive genotypes.ConclusionsThe DNA-based method allowed genotypic differences in root growth to be assessed directly in soil and was advantageous for rapid processing of a large number of samples. However, high replication was still required to overcome spatial variability and separate calibrations were required for different species and soil depths across sampling times. The technique demonstrated greater root growth of acid-soil resistant perennial grasses which was beneficial for their establishment and persistence.