Alan E Richardson

• The Commonwealth Scientific and Industrial Research Organisation

Microbial community structure and function were assessed in the organic and upper mineral soil across a ~4000‐year dune‐based chronosequence at Big Bay, New Zealand, where total P declined and the proportional contribution of organic soil in the profile increased with time. We hypothesized that the organic and mineral soils would show divergent com...

Changes in carbon (C) and nitrogen (N) associated with fine fraction (FF) soil organic matter (SOM) were determined to a depth of 1.80 m at a field site that was managed with supplementary nutrients (2007–2012) to sequester soil C from crop residues. Soil C and N stocks were monitored for a further 3 years (to 2015) with supplementary nutrients mai...

Changes in carbon (C) and nitrogen (N) associated with fine fraction (FF) soil were determined to a depth of 180 cm at a field site that was managed with supplementary nutrients (2007–2012) to sequester soil C from crop residues. Soil C and N stocks were monitored for a further 3 years (to 2015) with supplementary nutrients maintained, and then for...

The global phosphate rock reserves that underpin phosphorus (P) fertiliser production are finite. Recovery of P from waste streams (e.g., by producing fertiliser products from sewage sludge) is an important way to conserve scarce P resources. This study evaluated the P fertiliser and soil pH amendment values of a municipal sewage sludge ash (SA) fo...

Purpose Organic anions commonly released from plant roots and microorganisms are widely reported to mobilize soil phosphorus (P). We characterized soil organic P that was mobilized by organic anions and assessed its amenability to hydrolysis by phosphatase enzymes. Methods Six soils differing in organic P concentration were extracted with citrate,...

Purpose Organic anions commonly released from plant roots are widely reported to mobilize soil phosphorus (P). We characterized soil organic P that was mobilized by organic anions and assessed its amenability to hydrolysis by phosphatase enzymes. Methods Six soils differing in organic P content were extracted with citrate, malate or oxalate soluti...

Context Gravel is a common constituent in soil and is routinely excluded when estimating soil carbon (C) and nitrogen (N) stocks. Aims We investigated the contribution that the gravel fraction (>2 mm) makes to C and N stocks in an agricultural soil. Methods The amount of gravel and the C and N content of gravel-associated organic matter (OM) was...

Microbial communities are the main catalysts of ecosystem carbon dynamics. The contribution of sub-soil microorganisms to relatively stable fine-fraction carbon content may be critical for soil carbon sequestration. Here we assessed bacterial, fungal and archaeal communities at three different soil depths (over 90 cm) in a 25-year old crop-tillage...

Certain soil microorganisms can improve plant growth, and practices that encourage their proliferation around the roots can boost production and reduce reliance on agrochemicals. The beneficial effects of the microbial inoculants currently used in agriculture are inconsistent or short-lived because their persistence in soil and on roots is often po...

Differences in root morphology and acclimation to low‐phosphorus (P) soil were examined among eight legume species from the Trifolium Section Tricocephalum to understand how these root attributes determine P acquisition. Ornithopus sativus was included as a highly P‐efficient benchmark species. Plants were grown as microswards in pots with five rat...

Fertilizer phosphorus (P) is a finite resource, necessitating the development of innovative solutions for P fertilizer efficiency in agricultural systems. Myo-inositol hexakisphosphate (phytate) constitutes the majority of identified organic P in many soil types and is poorly available to plants. Incorporating phytase-producing biofertilizers into...

Phosphorus (P) is an essential element to all living beings but also a finite resource. P-related problems center around broken P cycles from local to global scales. This paper presents outcomes from the 9th International Phosphorus Workshop (IPW9) held 2019 on how to move towards a sustainable P management. It is based on two sequential discussion...

There is increasing interest in understanding how the microbial communities on roots can be manipulated to improve plant productivity. Root systems are not homogeneous organs but are comprised of different root types of various ages and anatomies that perform different functions. Relatively little is known about how this variation influences the di...

The Haast chronosequence in New Zealand is a ∼6500-year dune formation series, characterized by rapid podzol development, phosphorus (P) depletion, and a decline in aboveground biomass. We examined bacterial and fungal community composition within mineral soil fractions using amplicon-based high-throughput sequencing (Illumina MiSeq). We targeted b...

Plant root–biota associations involve complex networks between micro- and macroorganisms that interact across diverse temporal and spatial scales and in response to a wide range of climatic and environmental variables. The root–microbiome has a major impact on plant health through interactions on growth and development, facilitation of nutrient upt...

Acacia and Eucalyptus species are commonly used for revegetation in Australia and other parts of the world, yet little is known regarding how their litter might differentially impact decomposition rates and extracellular enzyme activities. To investigate this, a litter decomposition experiment was established using a reciprocal design (litter type...

Microbial detritus contributes substantially to the soil organic matter (SOM). Analysis of global literature indicated that microbial detritus carbon (C) contributed 59 and 64% of total soil C in arable agricultural and grassland systems respectively, with a 2.5% greater contribution of bacterial-derived detritus in grasslands and with no differenc...

A substantial proportion of soil carbon (C) is commonly lost following cultivation of soil and in the transition of pastures to crops. Incorporation of plant residues with nutrient addition (nitrogen, phosphorus and sulphur) may reduce these losses. We investigated the impact of initial soil fertility and supplementary nutrient addition on breakdow...

Soil organic matter (SOM) in agricultural soils is generally lower in cultivated and intensively managed cropping soils than in pasture soils. Cultivation during the transition from pasture to crop leads to a loss of SOM, which may affect soil functionality and subsequent agricultural productivity. However, it is unclear how management practices in...

Historically, the chemical nature of organic phosphorus (P) in soil has largely been considered to comprise of recognizable biomolecules that predominantly include inositol phosphates, nucleic acids and phospholipids. However, these forms alone do not explain the existence of, or account for the processes responsible for, a larger pool of “unresolv...

Different fertiliser products are commonly promoted for use on pastures in order to improve pasture productivity and support a more ‘healthy’ soil microbial environment. However, minimal field research has been conducted to validate such claims. A 6-year study (2009–14) was conducted on phosphorus (P)-deficient soils at three sites near Yass, New S...

It is important to understand the stability of soil organic matter (SOM) sequestered through land management changes. In this study we assessed differences in carbon (C) stability of pasture soils that had high and low C content (2.35% vs 1.73% whole soil C in the 0–10 cm layer) resulting from long-term phosphorus fertilisation. We used soil size f...

The impact of phosphorus (P) fertilizer application on the sequestration of soil organic carbon (C) was investigated in an acidic permanent pasture soil grazed by sheep. Data were collected after 20 years of P fertilization (average 19 kg P ha⁻¹ year⁻¹) compared to a non-P fertilized control, on a P deficient soil. The high P treatment had higher p...

Background Plant roots release a variety of organic compounds into the soil which alter the physical, chemical and biological properties of the rhizosphere. Root exudates are technically challenging to measure in soil because roots are difficult to access and exudates can be bound by minerals or consumed by microorganisms. Exudates are easier to me...

Ecotones between distinct ecosystems have been the focus of many studies as they offer valuable insights into key drivers of community structure and ecological processes that underpin function. While previous studies have examined a wide range of above‐ground parameters in ecotones, soil microbial communities have received little attention. Here we...

European earthworms have colonised many parts of Australia, although their impact on soil microbial communities remains largely uncharacterised. An experiment was conducted to contrast the responses to Aporrectodea trapezoides introduction between soils from sites with established (Talmo, 64 A. trapezoides m⁻²) and rare (Glenrock, 0.6 A. trapezoide...

Citrate and phytase root exudates contribute to improved phosphorus (P) acquisition efficiency in Nicotiana tabacum (tobacco) when both exudates are produced in a P deficient soil. To test the importance of root intermingling in the interaction of citrate and phytase exudates, Nicotiana tabacum plant-lines with constitutive expression of heterologo...

Grazing systems are a major producer of food and fibre across the world. These systems often require the addition of fertiliser phosphorus (P) for maximum pasture growth, and it is now estimated that a four-fold increase in the use of P fertiliser in grasslands is needed to meet increased food demand by the year 2050. However, the recovery of P fro...

Aims Rytidosperma species are native Australian grasses which have different growth rates and phosphorus (P) requirements. This study examined the role of root morphology traits in response to P supply. Methods Nine Rytidosperma species ranging from slow- to fast-growth were examined along with Lolium perenne and Bromus hordeaceus. Plants were grow...

Background and Aims Plant acquisition of endogenous forms of soil phosphorus (P) could reduce external P requirements in agricultural systems. This study investigated the interaction of citrate and phytase exudation in controlling the accumulation of P and depletion of soil organic P by transgenic Nicotiana tabacum plants. Methods N. tabacum plant...

Root exudation of phytase could improve the ability of plants to access organic forms of soil phosphorus (P), thereby minimizing fertilizer requirements and improving P use efficiency in agroecosystems. After 75 days growth in a high available P soil, shoot biomass and P accumulation, soil pH, and rhizosphere P depletion were investigated in Nicoti...

Inefficiency of fertilizer phosphorus (P) use in grazing systems is often associated with the accumulation of inorganic and organic P in fertilized soil. However, the chemical nature of the accumulated organic P remains poorly understood. The aim of this study was to use solution 31P nuclear magnetic resonance (NMR) spectroscopy on sodium hydroxide...

Background The structure and function of plant roots and their interactions with soil are exciting scientific frontiers that will ultimately reveal much about our natural systems, global water and mineral and carbon cycles, and help secure food supplies into the future. This Special Issue presents a collection of papers that address topics at the f...

Research suggests that relatively stable, fine fraction soil organic matter ( FF‐SOM ) has almost constant concentrations of nitrogen, phosphorus and sulphur ( NPS ) per unit of carbon ( C ), although there are considerable differences in the datasets used. Such differences could, in agricultural situations in particular (where inorganic nutrients...

Removing carbon dioxide (CO2) from the atmosphere and storing the carbon (C) in resistant soil organic matter (SOM) is a global priority to restore soil fertility and help mitigate climate change. Although it is widely assumed that retaining rather than removing or burning crop residues will increase SOM levels, many studies have failed to demonstr...

Rytidosperma species are perennial grasses found in cool temperate grasslands of Australia. The species differ in their intrinsic growth rates, response to phosphorus (P) fertiliser application and critical external P requirements (P required for 90% maximum growth). The present study examined whether internal P-utilisation efficiency (PUE) by Ryti...

Rhizosheaths comprise soil bound to roots, and in wheat (Triticum aestivum L.) rhizosheath size correlates with root hair length. The aims of this study were to determine the effect that a large rhizosheath has on the phosphorus (P) acquisition by wheat and to investigate the genetic control of rhizosheath size in wheat grown on acid soil. Near-iso...

Archaea are ubiquitous and highly abundant in Arctic soils. Because of their oligotrophic nature, archaea play an important role in biogeochemical processes in nutrient-limited Arctic soils. With the existing knowledge of high archaeal abundance and functional potential in Arctic soils, this study employed terminal restriction fragment length polym...

Phosphorus (P) is an essential element for life, an innate constituent of soil organic matter, and a major anthropogenic input to terrestrial ecosystems. The supply of P to living organisms is strongly dependent on the dynamics of soil organic P. However, fluxes of P through soil organic matter remain unclear because only a minority (typically < 30...

Introduction For many plant species the exudation of organic anions and phosphatases by roots represents an important mechanism for the acquisition of soil phosphorus (P) (Richardson et al. 2011). However, the benefits of citrate and phytase exudation have been shown to be limited in soils due to interactions with soil (George et al. 2005) or the d...

Background and aims Single superphosphate (SSP) is a major source of phosphorus (P) used in grazing systems to improve pasture production. The aim of this experiment was to determine the fate of fertiliser P in clover pastures under field conditions. Methods A procedure was developed to radiolabel SSP granules with a 33P radiotracer, which was then...

Land-use change is one of the most important factors influencing soil microbial communities, which play a pivotal role in most biogeochemical and ecological processes. Using agroforestry systems as a model, this study examined the effects of land-uses and edaphic properties on bacterial communities in three agroforestry types covering a 270 km soil...

Phosphorus fertilizer use efficiency of pastures is often low because P accumulates in soils as sparingly-available forms of inorganic and organic P. The aim of this study was to use sequential chemical fractionation to identify which forms of P have accumulated in soil under permanent pasture from a medium-term (13 y) field experiment. Treatments...

Abstract Cellulose accounts for approximately half of photosynthesis fixed carbon, however the ecology of its degradation in soil is still relatively poorly understood. The role of actinobacteria in cellulose degradation has not been extensively investigated, despite their abundance in soil and known cellulose degradation capability. Here, the dive...

Solution phosphorus (P) nuclear magnetic resonance (NMR) spectroscopy following extraction with sodium hydroxide–ethylenediaminetetraacetic acid (NaOH–EDTA) is the most powerful and widely used technique for characterising soil organic P. However, poor spectral sensitivity (related to the signal to noise ratio) can limit its applicability for soils...

Data on the distribution of phosphorus (P) species in soils with differing land uses and properties are essential to understanding environmental P availability and how fertiliser inputs, cropping and grazing affect accumulation of soil inorganic P (Pi) and organic P (Po) forms. We examined thirty-two temperate soils (with soil organic C concentrati...

“ Inorganic nutrients are a hidden cost for sequestering carbon in soil organic matter. ”

Network and multivariate statistical analyses were performed to determine interactions between bacterial and fungal community T-RFLPs as well as soil properties in paired woodland and pasture sites. Canonical correspondence analysis (CCA) revealed that shifts in woodland community composition correlated with soil dissolved organic carbon, while cha...

Organic phosphorus (P) in grazed pastures/grasslands could sustain production systems that historically relied on inorganic P fertiliser. Interactions between inorganic P, plants and soils have been studied extensively. However, less is known about the transformation of organic P to inorganic orthophosphate. This paper investigates what is known ab...

Rhizoctonia solani AG-8 is a major root pathogen in wheat (Triticum aestivum L.) systems worldwide and while natural disease suppression can develop under continuous cropping, this is not always the case. The main aim of our work was to elucidate the rhizosphere microbial community underlying a Rhizoctonia suppressive soil (Avon, South Australia) a...

The gap between current average global wheat yields and that achievable through agronomic management and crop genetics is large. This is notable in intensive wheat rotations which are widely used. Expectations are that this gap can be reduced through soil processes, especially those that involve microbial ecology. Cross-year analysis of the soil mi...

Soils are the largest reservoir of global terrestrial carbon (C). Conversion from natural to agricultural ecosystems has generally resulted in a significant loss of soil organic-C (SOC, up to 50% or ~30-40tha-1) and 'restoring' this lost C is a significant global challenge. The most stable component of soil organic matter (SOM), hereafter referred...

Phosphorus deficiency in some plant species triggers the release of organic anions such as citrate and malate from roots. These anions are widely suggested to enhance the availability of phosphate for plant uptake by mobilizing sparingly-soluble forms in the soil. Carazinho is an old wheat (Triticum aestivum) cultivar from Brazil that secretes citr...

The manuscript by Ulrich et al. (2013) describes and discusses key large scale international policy and communication issues associated with the development of appropriate responses to improving the utilisation of global phosphorus (P) resources. In particular the paper outlines the need for an integrated and holistic-multidisciplinary approach to...

The more stable fine fraction pool of soil organic matter (FF-SOM; <0.4 mm) has more nitrogen, phosphorus and sulphur (N, P, S) per unit of carbon (C) than the plant material from which it originates and has near constant ratios of C:N:P:S. Consequently, we hypothesised that the sequestration of C-rich crop residue material into the FF-SOM pool cou...

Background Soil 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 implica...

Root exudates provide carbon for rhizosphere microbial communities and thus potentially play an important role in regulation of community composition and activity. The rhizosphere is an extremely complex environment with simultaneous spatial and temporal interactions between soil, plants, and microorganisms. There are significant technical challeng...

Microbial denitrification plays a key role in determining the availability of soil nitrogen (N) to plants. However, factors influencing the structure and function of denitrifier communities in the rhizosphere remain unclear. Waterlogging can result in root anoxia and increased denitrification, leading to significant N loss from soil and potential n...

The TaMATE1B gene from wheat was isolated and shown to encode a citrate transporter that is located on the plasma membrane. TaMATE1B expression in roots was induced by iron deficiency but not by phosphorus deficiency or aluminium treatment. Comparison of genomic sequences indicated that the TaMATE1B coding region was identical in a genotype showing...

Despite their large areas and potential importance as methane sinks, the role of methane-oxidizing bacteria (MOB) in native woodland soils is poorly understood. These environments are increasingly being altered by anthropogenic disturbances, which potentially alter ecosystem service provision. Dryland salinity is one such disturbance and is becomin...

Background Agricultural 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 reduc...

Microbial community diversity and structure, which underpin soil function, can in turn be impacted by land-use practices. In this study an agricultural site with consistent long term (+20 years) treatments and a non-agricultural site (grassland) were investigated to determine land-use effects on soil microbial community structure and function. We u...

Sequestering soil carbon (C) relies upon the availability of stabilising elements, nitrogen (N), phosphorus (P) and sulphur (S) which are known to be essential components of the stable organic C pool (Himes, 1998; Lal, 2008). The C:N:P:S ratios were investigated for a series of soils to test the hypothesis that the stable portion of the soil organi...

Low-molecular-weight organic compounds in root exudates play a key role in plant-microorganism interactions by influencing the structure and function of soil microbial communities. Model exudate solutions, based on organic acids (OAs) (quinic, lactic, maleic acids) and sugars (glucose, sucrose, fructose), previously identified in the rhizosphere of...

Update Article - No Abstract Provided.

Phosphorus (P)-deficiency is a significant challenge for agricultural productivity on many highly P-sorbing weathered and tropical soils throughout the world. On these soils it can be necessary to apply up to five-fold more P as fertiliser than is exported in products. Given the finite nature of global P resources, it is important that such ineffic...

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....

Background and aims DNA-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 calibr...

To determine the influence of pooling strategies on detected soil bacterial communities, we sampled 45 soil cores each from a eucalypt woodland, a sown pasture and a revegetated site in an Australian landscape. We assessed the spatial variation within each land-use plot, including the influence of sampling distance, soil chemical characteristics an...

Collection of root exudates is always a challenge because of difficulties accessing the rhizosphere without damaging plant roots. This paper describes a novel technique for repeated in situ collection of low molecular weight organic anions from plant roots grown in large-scale rhizotrons under controlled environmental conditions. Anion exchange mem...

HvALMT1 from barley (Hordeum vulgare L.) encodes a protein capable of facilitating the transport of malate and other organic anions when expressed in Xenopus oocytes. The HvALMT1 gene is primarily expressed in guard cells of stomata, in regions behind the root apex and at lateral root junctions. We investigated the function of HvALMT1 in planta by...

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 a...

The extent to which the distribution of soil bacteria is controlled by local environment vs. spatial factors (e.g. dispersal, colonization limitation, evolutionary events) is poorly understood and widely debated. Our understanding of biogeographic controls in microbial communities is likely hampered by the enormous environmental variability encount...

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...