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Keith R. Skene

Bio: Keith R. Skene is an academic researcher from University of Dundee. The author has contributed to research in topics: Cluster root & Lateral root. The author has an hindex of 18, co-authored 35 publications receiving 1114 citations.

Papers
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Journal ArticleDOI
TL;DR: It is argued that cluster roots are the third great adaptation for nutrient uptake in plants and, as such, demand greater attention from the ecologist than they presently receive.
Abstract: It has been said that the 'roots of ecology are in the ecology of roots' (Sen 1980). The study of resource acquisition by roots is a vibrant and challenging field today, and an important meeting point between ecology, physiology and developmental biology. Most of the essential elements for all life forms enter the biosphere through the roots of plants, and so the subject demands careful consideration (Nissen 1991). The determinance of plant community structure also has its roots firmly embedded in the soil. While much emphasis is placed on the ecological significance of mycorrhizas and nitrogen-fixing symbioses, it is surprising that so little attention has been paid to another root adaptation that occurs throughout the world, namely the cluster root. In this short article, it is argued that cluster roots are the third great adaptation for nutrient uptake in plants and, as such, demand greater attention from the ecologist than they presently receive. The term 'cluster root' is used to refer to a region of parent root (usually a primary or secondary lateral root) where many short rootlets are produced in a compact grouping, giving the appearance of a bottle brush (Fig. 1) (Purnell 1960). First noted by Engler (1894), the rootlets develop opposite every protoxylem pole and are determinate, the meristem itself eventually differentiating. Their gross morphology differs between different species, in that they may be simple, complex or compound (Fig. 1; adapted from Skene 1997). Compound cluster roots can form large mats in the upper surface of the soil, and, where they are produced by trees, often extend beyond the canopy.

147 citations

Journal ArticleDOI
TL;DR: The use of continuous percolation of solid cultivation medium with adjustment of nutrient-solution strength appears to be a promising methodology for the determination of root exudation rates and qualitative composition of exuded compounds.
Abstract: The aim of this work is to review the current knowledge on the effects of plant metabolism (C3, C4, and CAM) on root exudation and on the methods of exudate collection as well as the use of such exudates for analyses, testing of microbial response, degradation of pollutants, enzymatic activities, and occurrence of allelochemicals. We examine the advantages and disadvantages of each method as related to the downstream use of the exudates. The use of continuous percolation of solid cultivation medium with adjustment of nutrient-solution strength appears to be a promising methodology for the determination of root exudation rates and qualitative composition of exuded compounds. The method mimics rhizosphere conditions, minimizing the artificial accumulation of compounds, alteration of plasma-membrane permeability, ATPase activity, and the impacts of inhibitors or stimulators of root enzymes. Of particular significance is the fact that the adjustment of strength of nutrient solution and percolation enables universal and also long-term use of the method, allowing high exudation yield by minimizing influx and maximizing efflux rates of exuded compounds at high nutrient-solution strength. Furthermore, it facilitates assessment of the effect on soil microbial populations and their ability to degrade pollutants. Enzymatic activities can be assessed when a low strength of nutrient solution is used, with percolation of the exudates directly into tested soils. Composition of root exudates, regulation of root enzymes, and plant response to nutrient deficiency can be assessed by measuring net efflux or influx rates. The impact of heavy metals and other type of mechanical, chemical, and biological stresses differs according to the type of plant metabolism. This has significant consequences on transformations in plant communities, both structurally and functionally, and impacts upon crop nutrition, with respect to global climate change, and the use of plants for phytoremediation purposes. Understanding the effects of different types of plant metabolism on root exudation with respect to genetic regulation of synthetic pathways through root enzymes and transport systems presents an important direction for future research.

142 citations

Journal ArticleDOI
TL;DR: This review attempts to appraise the literature related to non-protein amino acids, both in terms of their metabolism, plant–soil interactions and at the level of the ecosystem, where they are seen as significant drivers of structure and function.
Abstract: Non-protein amino acids are a significant store of organic nitrogen in many ecosystems, but there is a lack of knowledge relating to them. Research has indicated that they play important roles as metabolites, as allelopthic chemicals, in nutrient acquisition, in signalling and in stress response. They are also thought to be responsible for significant medical issues in both invertebrate and vertebrate animals. This review attempts to appraise the literature related to non-protein amino acids, both in terms of their metabolism, plant–soil interactions and at the level of the ecosystem, where they are seen as significant drivers of structure and function. Finally, important areas for future research are discussed.

120 citations

Journal ArticleDOI
TL;DR: Assessment of nematode diversity using both univariate and multivariate analysis produced contradictory results, with a trend was apparent of increasing numbers of omnivorous nematodes along the succession in relation to increasing organic matter and/or litter accumulation.
Abstract: Changes in below-ground nematode communities, in terms of abundance, diversity and trophic structure and the composition of the community in terms of sex bias and adult:juvenile ratio were related to edaphic factors from sites that represented a known sand dune succession. Nematode abundance increased along a 1-km transect from sandy beach (no vegetation cover, early successional stage) through active dune systems [Ammophila arenaria (L.) and Leymus arenarius (L.) dominated] to mature dunes (heath covered, mature successional stage). Furthermore, as the succession progressed, the adult nematode sex ratio changed from male biased to highly female biased. Consequently, the adult:juvenile ratio decreased as the nematode community became more female dominated. An assessment of nematode diversity using both univariate and multivariate analysis produced contradictory results. The univariate indices, Shannon-Weaver and evenness, were significantly lower (P<0.05) at the dune heath than the other sites whereas the maturity index was significantly lower (P<0.05) at the beach site. Multivariate analysis clearly separated the beach and dune heath samples from the other samples and each other, and to a lesser extent separated the fore dune samples from the grey and yellow dune. Omnivorous nematodes represented the largest trophic component of the nematode community in all successional stages of the terrestrial sites. Epistrate/epigrowth feeders represented ca. 80% of the nematode community at the beach site. A trend was apparent of increasing numbers of omnivorous nematodes along the succession in relation to increasing organic matter and/or litter accumulation.

91 citations

Journal ArticleDOI
TL;DR: The first evidence of cluster roots having arisen only once within the Lupinus genus is presented and the case of the genus Lupinus is taken as a means of exploring the phylogenetic relationships of species with cluster roots.

86 citations


Cited by
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TL;DR: This paper provides an international methodological protocol aimed at standardising this research effort, based on consensus among a broad group of scientists in this field, and features a practical handbook with step-by-step recipes, for 28 functional traits recognised as critical for tackling large-scale ecological questions.
Abstract: There is growing recognition that classifying terrestrial plant species on the basis of their function (into 'functional types') rather than their higher taxonomic identity, is a promising way forward for tackling important ecological questions at the scale of ecosystems, landscapes or biomes. These questions include those on vegetation responses to and vegetation effects on, environmental changes (e.g. changes in climate, atmospheric chemistry, land use or other disturbances). There is also growing consensus about a shortlist of plant traits that should underlie such functional plant classifications, because they have strong predictive power of important ecosystem responses to environmental change and/or they themselves have strong impacts on ecosystem processes. The most favoured traits are those that are also relatively easy and inexpensive to measure for large numbers of plant species. Large international research efforts, promoted by the IGBP–GCTE Programme, are underway to screen predominant plant species in various ecosystems and biomes worldwide for such traits. This paper provides an international methodological protocol aimed at standardising this research effort, based on consensus among a broad group of scientists in this field. It features a practical handbook with step-by-step recipes, with relatively brief information about the ecological context, for 28 functional traits recognised as critical for tackling large-scale ecological questions.

3,288 citations

Journal ArticleDOI
TL;DR: Physiological, biochemical, and molecular studies of white lupin and other species response to P-deficiency have identified targets that may be useful for plant improvement, and Genomic approaches involving identification of expressed sequence tags found under low-P stress may also yield target sites for plant improved.
Abstract: Contents I. Introduction 424 II. The phosphorus conundrum 424 III. Adaptations to low P 424 IV. Uptake of P 424 V. P deficiency alters root development and function 426 VI. P deficiency modifies carbon metabolism 431 VII. Acid phosphatase 436 VIII. Genetic regulation of P responsive genes 437 IX. Improving P acquisition 439 X. Synopsis 440 Summary Phosphorus (P) is limiting for crop yield on > 30% of the world's arable land and, by some estimates, world resources of inexpensive P may be depleted by 2050. Improvement of P acquisition and use by plants is critical for economic, humanitarian and environmental reasons. Plants have evolved a diverse array of strategies to obtain adequate P under limiting conditions, including modifications to root architecture, carbon metabolism and membrane structure, exudation of low molecular weight organic acids, protons and enzymes, and enhanced expression of the numerous genes involved in low-P adaptation. These adaptations may be less pronounced in mycorrhizal-associated plants. The formation of cluster roots under P-stress by the nonmycorrhizal species white lupin (Lupinus albus), and the accompanying biochemical changes exemplify many of the plant adaptations that enhance P acquisition and use. Physiological, biochemical, and molecular studies of white lupin and other species response to P-deficiency have identified targets that may be useful for plant improvement. Genomic approaches involving identification of expressed sequence tags (ESTs) found under low-P stress may also yield target sites for plant improvement. Interdisciplinary studies uniting plant breeding, biochemistry, soil science, and genetics under the large umbrella of genomics are prerequisite for rapid progress in improving nutrient acquisition and use in plants.

2,429 citations

Book
01 Jan 2013
TL;DR: In this article, the authors defined the sources of heavy metals and metalloids in Soils and derived methods for the determination of Heavy Metals and Metalloids in soil.
Abstract: Preface.- Contributors.- List of Abbreviations.- Section 1: Basic Principles: Introduction.-Sources of Heavy Metals and Metalloids in Soils.- Chemistry of Heavy Metals and Metalloids in Soils.- Methods for the Determination of Heavy Metals and Metalloids in Soils.- Effects of Heavy Metals and Metalloids on Soil Organisms.- Soil-Plant Relationships of Heavy Metals and Metalloids.- Heavy Metals and Metalloids as Micronutrients for Plants and Animals.-Critical Loads of Heavy Metals for Soils.- Section 2: Key Heavy Metals And Metalloids: Arsenic.- Cadmium.- Chromium and Nickel.- Cobalt and Manganese.- Copper.-Lead.- Mercury.- Selenium.- Zinc.- Section 3: Other Heavy Metals And Metalloids Of Potential Environmental Significance: Antimony.- Barium.- Gold.- Molybdenum.- Silver.- Thallium.- Tin.- Tungsten.- Uranium.- Vanadium.- Glossary of Specialized Terms.- Index.

1,684 citations

Journal ArticleDOI
TL;DR: The legal and regulatory status of biostimulants are described, with a focus on the EU and the US, and the drivers, opportunities and challenges of their market development are outlined.

1,340 citations

Journal ArticleDOI
TL;DR: It is hypothesised that roots gradually evolved from rhizomes to provide more suitable habitats for mycorrhizal fungi and provide plants with complex branching and leaves with water and nutrients.
Abstract: Summary Here, the coevolution of mycorrhizal fungi and roots is assessed in the light of evidence now available, from palaeobotanical and morphological studies and the analysis of DNA-based phylogenies. The first bryophyte-like land plants, in the early Devonian (400 million years ago), had endophytic associations resembling vesicular‐ arbuscular mycorrhizas (VAM) even before roots evolved. Mycorrhizal evolution would have progressed from endophytic hyphae towards balanced associations where partners were interdependent due to the exchange of limiting energy and nutrient resources. Most mycorrhizas are mutualistic, but in some cases the trend for increasing plant control of fungi culminates in the exploitative mycorrhizas of achlorophyllous, mycoheterotrophic plants. Ectomycorrhizal, ericoid and orchid mycorrhizas, as well as nonmycorrhizal roots, evolved during the period of rapid angiosperm radiation in the Cretaceous. It is hypothesised that roots gradually evolved from rhizomes to provide more suitable habitats for mycorrhizal fungi and provide plants with complex branching and leaves with water and nutrients. Selection pressures have caused the morphological divergence of roots with different types of mycorrizas. Root cortex thickness and exodermis suberization are greatest in obligately mycorrhizal plants, while nonmycorrhizal plants tend to have fine roots, with more roots hairs and relatively advanced chemical defences. Major coevolutionary trends and the relative success of plants with different root types are discussed.

1,308 citations