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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 heterologous citrate (Cit) or fungal phytase (Phy) exudation traits were grown under two root treatments (roots separated or intermingled) and in two soils with contrasting soil P availability. Complementarity of plant mixtures varying in citrate efflux rate and mobility of the expressed phytase in soil was determined based on plant biomass and P accumulation. Soil P composition was evaluated using solution (31) P NMR spectroscopy. In the soil with limited available P, positive complementarity occurred in Cit+Phy mixtures with roots intermingled. Root separation eliminated positive interactions in mixtures expressing the less mobile phytase (Aspergillus niger PhyA) whereas positive complementarity persisted in mixtures that expressed the more mobile phytase (Peniophora lycii PhyA). Soils from Cit+Phy mixtures contained less inorganic P and more organic P compared to monocultures. Exudate-specific strategies for the acquisition of soil P were most effective in P-limited soil and depended on citrate efflux rate and the relative mobility of the expressed phytase in soil. Plant growth and soil P utilization in plant systems with complementary exudation strategies are expected to be greatest where exudates persist in soil and are expressed synchronously in space and time.

Zymographic methods for the 2D distribution of phosphatase activity in soils have markedly advanced our understanding of root-soil-microbiota interactions. Robust quantitative approaches for 2D assays, which use 4-methylubelliferyl phosphate (4-MUP), are needed to advance a mechanistic understanding of enzyme behaviour and distribution in soils. We present improvements to the method for phosphatase zymography in rhizobox studies, involving (1) a systematic evaluation of 4-methylumbelliferone (4-MU) based calibration functions in relation to image exposure time and (2) the development of advanced image analysis tools for lateral and longitudinal distributions of phosphatase activity along barley roots (Hordeum vulgare L., cv Optic). Exposure time (

Aims Intercropping can improve plant yields and soil phosphorus (P) use efficiency. This study compares inter- and intra-species intercropping, and determines whether P uptake and shoot biomass accumulation in intercrops are affected by soil P availability. Methods Four barley cultivars (Hordeum vulgare L.) and three legume species (Trifolium subterreneum, Ornithopus sativus and Medicago truncatula) were selected on the basis of their contrasting root exudation and morphological responses to P deficiency. Monocultures and barley-barley and barley-legume intercrops were grown for 6 weeks in a pot trial at very limiting, slightly limiting and excess available soil P. Above-ground biomass and shoot P were measured. Results Barley-legume intercrops had 10–70% greater P accumulation and 0–40% greater biomass than monocultures, with the greatest gains occurring at or below the sub-critical P requirement for barley. No benefit of barley-barley intercropping was observed. The plant combination had no significant effect on biomass and P uptake observed in intercropped treatments. Conclusions Barley-legume intercropping shows promise for sustainable production systems, especially at low soil P. Gains in biomass and P uptake come from inter- rather than intra-species intercropping, indicating that plant diversity resulted in decreased competition between plants for P. Electronic supplementary material The online version of this article (doi:10.1007/s11104-017-3365-z) contains supplementary material, which is available to authorized users.

Phosphorus (P) and nitrogen (N) use efficiency may be improved through increased biodiversity in agroecosystems. Phenotypic variation in plants’ response to nutrient deficiency may influence positive complementarity in intercropping systems. A multicomponent screening approach was used to assess the influence of P supply and N source on the phenotypic plasticity of nutrient foraging traits in barley (H. vulgare L.) and legume species. Root morphology and exudation were determined in six plant nutrient treatments. A clear divergence in the response of barley and legumes to the nutrient treatments was observed. Root morphology varied most among legumes, whereas exudate citrate and phytase activity were most variable in barley. Changes in root morphology were minimized in plants provided with ammonium in comparison to nitrate but increased under P deficiency. Exudate phytase activity and pH varied with legume species, whereas citrate efflux, specific root length, and root diameter lengths were more variable among barley cultivars. Three legume species and four barley cultivars were identified as the most responsive to P deficiency and the most contrasting of the cultivars and species tested. Phenotypic response to nutrient availability may be a promising approach for the selection of plant combinations for minimal input cropping systems.

The buffering of phosphorus concentrations in soil solution by the soilsolid phase is an important process for providing plant root access to nutrients. Accordingly, the size of labile solid phase-bound phosphorus pool and the rate at which it can resupply phosphorous into the dissolved phase can be important variables in determining when the plant availability of the nutrient may be limited. The phosphorus labile pool (Plabile) and its desorption kinetics were simultaneously evaluated in 10 agricultural UK soils using the diffusive gradients in thin-films (DGT) technique. The DGT-induced fluxes in the soil and sediments model (DIFS) was fitted to the time series of DGT deployments (1−240 h), which allowed the estimation of Plabile, and the system response time (Tc). The Plabile concentration was then compared to that obtained by several soil P extracts including Olsen P, FeO-P, and water extractable P, in order to assess if the data from these analytical procedures can be used to represent the labile P across different soils. The Olsen P concentration, commonly used as a representation of the soil labile P pool, overestimated the desorbable P concentration by 6-fold. The use of this approach for the quantification of soil P desorption kinetic parameters found a wide range of equally valid solutions for Tc. Additionally, the performance of different DIFS model versions working in different dimensions (1D, 2D, and 3D) was compared. Although all models could provide a good fit to the experimental DGT time series data, the fitted parameters showed a poor agreement between different model versions. The limitations of the DIFS model family are associated with the assumptions taken in the modeling approach and the three-dimensional (3D) version is here considered to be the most precise among them.

The article “Organic phosphorus in the terrestrial environment: a perspective on the state of the art and future priorities”, written by Timothy S George et al., was originally published with incorrect affiliation information for one of the co-authors, E. Klumpp.

Made available in DSpace on 2018-12-11T16:49:52Z (GMT). No. of bitstreams: 0 Previous issue date: 2018-06-01 Biotechnology and Biological Sciences Research Council Background: The dynamics of phosphorus (P) in the environment is important for regulating nutrient cycles in natural and managed ecosystems and an integral part in assessing biological resilience against environmental change. Organic P (Po) compounds play key roles in biological and ecosystems function in the terrestrial environment being critical to cell function, growth and reproduction. Scope: We asked a group of experts to consider the global issues associated with Po in the terrestrial environment, methodological strengths and weaknesses, benefits to be gained from understanding the Po cycle, and to set priorities for Po research. Conclusions: We identified seven key opportunities for Po research including: the need for integrated, quality controlled and functionally based methodologies; assessment of stoichiometry with other elements in organic matter; understanding the dynamics of Po in natural and managed systems; the role of microorganisms in controlling Po cycles; the implications of nanoparticles in the environment and the need for better modelling and communication of the research. Each priority is discussed and a statement of intent for the Po research community is made that highlights there are key contributions to be made toward understanding biogeochemical cycles, dynamics and function of natural ecosystems and the management of agricultural systems. The James Hutton Institute Lancaster Environment Centre Lancaster University Lincoln University, Lincoln Universidade Estadual do Norte Fluminense Darcy Ribeiro (UENF - Laboratório de Solos), Av. Alberto Lamego 2000 Plant and Soil Sciences University of Delaware, 160 Townsend Hall Faculty of Environment and Natural Resources Chair of Soil Ecology University of Freiburg, Bertoldstraße 17 Rothamsted Research West Common Harpenden Rothamsted Research West Common Harpenden, North Wyke College of Agricultural Sciences Department of Crop Science Sao Paulo State University (UNESP), 1780, Jose Barbosa de Barros st Institute of Bio- and Geosciences IBG-3: Agrosphere Forschungszentrum Jülich GmbH Oak Ridge National Laboratory, P.O.Box 2008 DISAFA Soil Biogeochemistry University of Turin, largo Braccini 2 University of Minnesota-, Cities, 1479 Gortner Ave. Saint Paul China Agricultural University Le Laboratoire des Sciences du Climat et de l’Environnement IPSL-LSCE CEA/CNRS/UVSQ Saclay Institute of Soil Science University of Hohenheim, Emil Wolff Str. 27 INRA UMR ECO&SOLS Evolutionary Biology Centre EBC, Kåbovägen 4, house 7 Centre for Agri-environmental Research School of Agriculture Policy and Development University of Reading, Whiteknights, PO Box 237 Climate Impacts Research Centre Dep. of Ecology and Environmental Science Umeå University CSIRO Agriculture & Food D-USYS ETH Zurich, Tannenstrasse 1 Department of Environmental Sciences Norwegian University of Life Sciences, Post Box 5003 University of Guelph, 50 Stone Road East National Institute of Agricultural Research of Uruguay Department of Chemical & Biological Engineering The University of Sheffield, Mappin Street, S1 3JD School of Biological Sciences University of East Anglia, Norwich Research Park, Norwich International Plant Nutrition Institute, 18 Maplewood Drive Centro Interdipartimentale di Ricerca sulla Risonanza Magnetica Nucleare per l’Ambiente l’Agro-Alimentare ed i Nuovi Materiali (CERMANU) Università di Napoli Federico II, Via Università 100 Universidad de La Frontera School of Environment and Life Sciences University of Salford School of the Environment Natural Resources and Geography Bangor University School of Biological Sciences and Institute for Global Food Security The Queen’s University of Belfast, Medical Biology Centre, 97 Lisburn Road CENA University of Sao Paulo, Avenida Centenario, 303 Teagasc Environmental Research Centre, Johnstown Castle Centre for Ecology & Hydrology, Library Avenue, Bailrigg Department of Soil Biogeochemistry Bayreuth Center of Ecology and Environmental Research (BayCEER) University Bayreuth, Dr.-Hans-Frisch-Str. 1-3 Guangdong Provincial Key Laboratory of Applied Botany South China Botanical Garden Chinese Academy of Sciences, 723 Xingke Road, Tianhe District School of Geographical Sciences & School of Chemistry University of Bristol, University Road Soil Science and Soil Protection Martin Luther University Halle-Wittenberg, von-Seckendorff-Platz 3 Centre for Ice and Climate Niels Bohr Institute University of Copenhagen NERC Isotope Geosciences Facility British Geological Survey Department of Microbiology and Ecosystem Science University of Vienna, Althanstrasse 14 University of Northern British Columbia, 3333 University Way Brigham Young University Centre for Environmental Sciences Hasselt University Building D, Agoralaan Yamagata University Department of Biology Lund University, Biology Building Sölvegatan 35 Assessment of Microbial Environment Graduate School of Biosphere Science Hiroshima University College of Agricultural Sciences Department of Crop Science Sao Paulo State University (UNESP), 1780, Jose Barbosa de Barros st Biotechnology and Biological Sciences Research Council: BB/K018167/1 Biotechnology and Biological Sciences Research Council: BB/L025671/2

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 Nicotiana tabacum wild-type and transgenic plant-lines expressing and exuding Aspergillus niger phytase (ex::phyA), or a null-vector control. Solution 31P NMR analysis revealed a 7% to 11% increase in orthophosphate and a comparable depletion of undefined monoester P compounds (-13 to -18%) in the rhizosphere of tobacco plants relative to the unplanted soil control. Wild-type plants had the greatest impact on the composition of rhizosphere P based on the depletion of other monoester P, polyphosphate, and phosphonate species. The depletion of phytase-labile P by ex::phyA plants was associated with decreased proportions of other monoester P, rather than myo-InsP6 as expected. Rhizosphere pH increased from 6.0 to 6.5–6.7 in transgenic plant soils, beyond the pH optimum for A. niger phyA activity (pH=5), and may explain the limited specificity of ex::phyA plants for phytate in this soil. The efficacy of single exudation traits (e.g., phytase) therefore appear to be limited in P-replete soil conditions and may be improved where soil pH matches the functional requirements of the enzyme or trait of interest.

By use of a multi-site surface complexation model, Duputel et al. (2013) showed that citrate can decrease the solubility of phosphorus in soils, in contrast to what is commonly expected. We have identified several major errors in their model, which put the conclusions in doubt. We argue that major re-evaluation of their modelling approach is needed. (c) 2014 Elsevier Ltd. All rights reserved.

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 lines including wild-type, vector controls, transgenic plants with single-trait expression of a citrate transporter (A. thaliana frd3) or fungal phytases (phyA: A. niger, P. lycii) and crossed plant lines expressing both traits, were characterized for citrate efflux and phytase exudation. Monocultures and intercropped combinations of single-trait plants were grown in a low available P soil (12 weeks). Plant biomass, shoot P accumulation, rhizosphere soil pH and citrate-extractable-P fractions were determined. Land Equivalent Ratio and complementarity effect was determined in intercropped treatments and multiple-linear-regression was used to predict shoot P accumulation based on plant exudation and soil P depletion. Results Crossed plant lines with co-expression of citrate and phytase accumulated more shoot P than single-trait and intercropped plant treatments. Shoot P accumulation was predicted based on phytase-labile soil P, citrate efflux, and phytase activity (Rsq=0.58, P < .0001). Positive complementarity occurred between intercropped citrate- and phytase-exuding plants, with the greatest gains in shoot P occurring in plant treatments with A. niger phyA expression. Conclusions We show for the first time that trait synergism associated with the exudation of citrate and phytase by tobacco can be linked to the improved acquisition of P and the depletion of soil organic P.

Moorland carbon reserves in organo-mineral soils may be crucial to predicting landscape-scale variability in soil carbon losses, an important component of which is dissolved organic carbon (DOC). Surface water DOC trends are subject to a range of scaling, transport and biotic processes that disconnect them from signals in the catchment's soils. Long-term soil datasets are vital to identify changes in DOC release at source and soil C depletion. Here we show, that moorland soil solution DOC concentrations at three key UK Environmental Change Network sites increased between 1993–2007 in both surface- and sub- soil of a freely-draining Podzol (48 % and 215 % increases in O and Bs horizons, respectively), declined in a gleyed Podzol and showed no change in a Peat. Our principal findings were that: (1) considerable heterogeneity in DOC response appears to exist between different soils that is not apparent from the more consistent observed trends for streamwaters, and (2) freely-draining organo-mineral Podzol showed increasing DOC concentrations, countering the current scientific focus on soil C destabilization in peats. We discuss how the key solubility controls on DOC associated with coupled physico-chemical factors of ionic strength, acid deposition recovery, soil hydrology and temperature cannot readily be separated. Yet, despite evidence that all sites are recovering from acidification the soil-specific responses to environmental change have caused divergence in soil DOC concentration trends. The study shows that the properties of soils govern their specific response to an approximately common set of broad environmental drivers. Key soil properties are indicated to be drainage, sulphate and DOC sorption capacity. Soil properties need representation in process-models to understand and predict the role of soils in catchment to global C budgets. Catchment hydrological (i.e. transport) controls may, at present, be governing the more ubiquitous rises in river DOC concentration trends, but soil (i.e. source) controls provide the key to prediction of future C loss to waters and the atmosphere.

Rapid organic matter turnover is driven by advective transport processes in sandy permeable sediments, allowing them to act as biocatalytic filters. This filtering capacity is largely defined by the permeability of the sediment, which describes the flow of water through a porous medium. However, little is known about the temporal variability of sandflat permeability under natural conditions. Therefore, the changes in sediment permeability in an intertidal sandflat were measured over a year. The results demonstrated temporal variation in permeability related to the sediment water content and concentration of extracellular polymeric substances (EPS) in the pore space. The refractory bound fraction of EPS was one of the main contributors to this variation. Proteins associated with the bound EPS fraction appeared to covary with the effect of EPS on permeability. Levels of EPS proteins were as high (415 to 2170 μg g−1 bovine serum albumin equivalents) as carbohydrate levels (560 to 1400 μg g−1 D-glucose equivalents) in this sediment. Elevated levels of EPS were observed in the summer corresponding to low permeability, which also corresponded with microphytobenthic blooms and resulting production of exudates. A powerful storm event during the experiment with associated wind-generated waves resulted in a reworking of the sediment. This cleared pore spaces, resuspended material and reduced sediment compaction, effecting an overall change in permeability from 3.6 × 10−11 to 4.8 × 10−11 m2. The hypotheses that sandy sediment permeability varies with time and is influenced by EPS production were supported, and the effect of an episodic storm event was recorded.

The retention of Cd by an organic soil was investigated as a function of pH and ionic strength. The adsorption of Cd at pH values from 2 to 11 at two ionic strengths (0.053 M and 0.017 M LiNO3) wer...

Chromium concentrations of up to 91 mg l(-1) were found by ICP-OES for ground water from nine boreholes at four landfill sites in an area of S.E. Glasgow/S. Lanarkshire where high-lime chromite ore processing residue (COPR) from a local chemical works had been deposited from 1830 to 1968. Surface water concentrations of up to 6.7 mg l(-1) in a local tributary stream fell to 0.11 mg l(-1) in the River Clyde. Two independent techniques of complexation/colorimetry and speciated isotope dilution mass spectrometry (SIDMS) showed that Cr was predominantly (90%) in hexavalent form (CrVI) as CrO4(2-), as anticipated at the high pH (7.5-12.5) of the sites. Some differences between the implied and directly determined concentrations of dissolved CrIII, however, appeared related to the total organic carbon (TOC) content. This was most significant for the ground water from one borehole that had the highest TOC concentration of 300 mg l(-1) and at which3% of Cr was in the form of CrVI. Subsequent ultrafiltration produced significant decreases in Cr concentration with decreasing size fractions, e.g.0.45 microm,100 kDa,30 kDa and1 kDa by the tangential-flow method. As this appeared related more to concentrations of humic substances than of TOC per se, horizontal bed gel electrophoresis of freeze-dried ultrafilter retentates was carried out to further characterise the CrIII-organic complex. This showed for the main Cr-containing fraction, 100 kDa-0.45 microm, that the Cr was associated with a dark brown band characteristic of organic (humic) matter. Comparison of gel electrophoresis and FTIR results for ultrafilter retentates of ground water from this borehole with those for a borehole at another site where CrVI predominated suggested the influence of carboxylate groups, both in reducing CrVI and in forming soluble CrIII-humic complexes. The implications of this for remediation strategies (especially those based on the addition of organic matter) designed to reduce highly mobile and carcinogenic Cr(VI)O4(2-) to the much less harmful CrIII as insoluble Cr(OH)3 are discussed.

The hypothesis, that metal toxicity is dominated by free ion activity, was tested by comparing calculated metal activities with measured toxic responses to a genetically modified, luminescent bacterium, Escherichia coli. The toxicity of Cd, Cu, and Zn sulphate salts in the presence of EDTA and fulvic acid in well-defined solutions was measured. Good agreement between free metal activity and toxicity was found for Cu but not for Zn and Cd. The toxicity relationships were altered by glucose addition to the organism. Stable chloride complexes may have contributed to the toxicity of Cd under the test conditions. The results suggest that there is not always a simple relationship between toxicity and free-ion metal concentration and that further account should be taken of competitive interactions between living cells and ligands and the physiological status of the organism.

Better knowledge of spatial and temporal delivery of dissolved organic carbon (DOC) in small catchments is required to understand the mechanisms behind reported long-term changes in C fluxes from some peatlands. We monitored two storms with contrasting seasons and antecedent conditions in a small upland UK moorland catchment. We examined DOC concentrations and specific UV absorbance (SUVA at 285 nm), together with solute concentrations required to undertake end-member mixing analyses to define dominant flow paths contributing to streamflow. This was combined with laboratory soil-solution equilibrations. We aimed to resolve how seasonal biogeochemical processing of DOC and flowpath changes in organo-mineral soils combine to affect DOC exported via the stream. An August storm following a dry period gave maximum DOC concentration of 10 mg l−1. Small DOC:DON ratios (16–28) and SUVA (2.7–3.6 l mg−1 m−1) was attributed to filtration of aromatic compounds associated with up to 53% B horizon flow contributions. This selective filtration of high SUVA DOC was reproduced in the experimental batch equilibration system. For a November storm, wetter antecedent soil conditions led to enhanced soil connectivity with the stream and seven times greater DOC stream-load (maximum concentration 16 mg l−1). This storm had a 63% O horizon flow contribution at its peak, limited B horizon buffering and consequently more aromatic DOC (SUVA 3.9–4.5 l mg−1 m−1 and DOC:DON ratio 35–43). We suggest that simple mixing of waters from different flow paths cannot alone explain the differences in DOC compositions between August and November and biogeochemical processing of DOC is required to fully explain the observed stream DOC dynamics. This preliminary evidence is in contrast to other studies proposing hydrological controls on the nature of DOC delivered to streams. Although our study is based only on two storms of very different hydrological and biogeochemical periods, this should promote wider study of DOC biogeochemical alteration in headwaters so that this be better incorporated in modelling to predict the impacts of changes in DOC delivery to, and fate in, aquatic systems.

We present results from modelling studies, which suggest that, at most, only about 10–20% of recently observed soil carbon losses in England and Wales could possibly be attributable to climate warming. Further, we present reasons why the actual losses of SOC from organic soils in England and Wales might be lower than those reported.