Hamid Amir

Bio: Hamid Amir is an academic researcher from Institut national de la recherche agronomique. The author has contributed to research in topics: Cyperaceae & Arbuscular mycorrhiza. The author has an hindex of 14, co-authored 28 publications receiving 502 citations.

Arbuscular mycorrhizal fungi from New Caledonian ultramafic soils improve tolerance to nickel of endemic plant species

Abstract: In order to improve knowledge about the role of arbuscular mycorrhizal fungi (AMF) in the tolerance to heavy metals in ultramafic soils, the present study investigated the influence of two Glomus etunicatum isolates from New Caledonian ultramafic maquis (shrubland), on nickel tolerance of a model plant species Sorghum vulgare, and of two ultramafic endemic plant species, Alphitonia neocaledonica and Cloezia artensis. In a first step, plants were grown in a greenhouse, on sand with defined concentrations of Ni, to appreciate the effects of the two isolates on the alleviation of Ni toxicity in controlled conditions. In a second step, the influence of the AMF on A. neocaledonica and C. artensis plants grown in a New Caledonian ultramafic soil rich in extractable nickel was investigated. Ni reduced mycorrhizal colonization and sporulation of the fungal isolates, but the symbionts increased plant growth and adaptation of endemic plant species to ultramafic conditions. One of the two G. etunicatum isolates showed a stronger positive effect on plant biomass and phosphorus uptake, and a greater reduction in toxicity symptoms and Ni concentration in roots and shoots. The symbionts seemed to act as a barrier to the absorption of Ni by the plant and reduced root-to-shoot Ni translocation. Results indicate the potential of selected native AMF isolates from ultramafic areas for ecological restoration of such degraded ecosystems.

Is a mixture of arbuscular mycorrhizal fungi better for plant growth than single-species inoculants?

Abstract: Inoculation of arbuscular mycorrhizal fungi (AMF) as plant growth promoters has mostly been conducted using single-species inoculum. In this study, we investigated whether co-inoculation of different native AMF species induced an improvement of plant growth in an ultramafic soil. We analyzed the effects of six species of AMF from a New Caledonian ultramafic soil on plant growth and nutrition, using mono-inoculations and mixtures comprising different numbers of AMF species, in a greenhouse experiment. The endemic Metrosideros laurifolia was used as a host plant. Our results suggest that, when the plant faced multiple abiotic stress factors (nutrient deficiencies and high concentrations of different heavy metals), co-inoculation of AMF belonging to different families was more efficient than mono-inoculation in improving biomass, mineral nutrition, Ca/Mg ratio, and tolerance to heavy metals of plants in ultramafic soil. This performance suggested functional complementarity between distantly related AMF. Our findings will have important implications for restoration ecology and mycorrhizal biotechnology applied to ultramafic soils.

Mines et environnement en Nouvelle-Calédonie : les milieux sur substrats ultramafiques et leur restauration

Abstract: Presentation de l'editeur : Les substrats ultramafiques - ou terrains miniers - a l'origine du minerai de nickel, couvrent pres du tiers de la Nouvelle-Caledonie, qui se place parmi les premiers producteurs de ce metal dans le monde. Mais l'exploitation miniere a ciel ouvert necessite d'importants decapages qui generent des problemes d'erosion des sols, de dereglement des debits hydriques, de pollution des cours d'eau et de perte de biodiversite. Ces substrats datant de 37 millions d'annees portent une flore riche et originale, qui a largement contribue au classement de la Nouvelle-Caledonie comme un des principaux hotspots de biodiversite de la planete. Elle comprend environ 2150 especes vegetales dont 82 % sont endemiques. Ces especes sont en outre specialisees, adaptees a des sols tres pauvres en plusieurs elements nutritifs et inversement tres riches en magnesium, en nickel et en d'autres metaux. Ces milieux abritent egalement une faune d'une grande diversite. Ainsi la Nouvelle-Caledonie est confrontee a un double defi : celui d'exploiter une ressource miniere considerable a meme d'assurer au pays un developpement economique important, et celui de proteger cette biodiversite exceptionnelle au nom des principes fondamentaux edictes mondialement. Dans ce contexte, la conservation des milieux abritant la plus grande part de la biodiversite, ainsi que la restauration des sites degrades par l'exploitation miniere s'imposent comme des necessites incontournables. L'ouvrage decrit et illustre tout d'abord la variete des substrats ultramafiques, ainsi que la diversite des ecosystemes et de leurs composantes floristiques, zoologiques et microbiologiques. Le concept de restauration ecologique des sites degrades et les moyens necessaires pour sa mise en oeuvre sont ensuite developpes ; puis les modes de collecte, de germination, de conservation des semences et de production de plants d'especes locales sont decrits, de meme que les methodes de revegetalisation. Enfin pres de 100 especes vegetales utiles pour la restauration sont presentees. Cet ouvrage est destine a un large public, allant des professionnels du secteur minier (societes minieres, operateurs de la revegetalisation, bureaux d'etude...) aux personnels des collectivites impliquees dans la gestion du patrimoine minier et biologique du pays, ainsi qu'aux scientifiques, enseignants, etudiants, et plus largement a toute personne interessee par les terrains miniers et leur gestion environnementale

New insights into the mycorrhizal status of Cyperaceae from ultramafic soils in New Caledonia.

Abstract: In New Caledonia, a hot spot of biodiversity, plants from the Cyperaceae family are mostly endemic and considered pioneers of the nickel-rich natural serpentine ecosystem. The aim of the study was ...

Streptomyces yatensis sp. nov., a novel bioactive streptomycete isolated from a New-Caledonian ultramafic soil.

Abstract: The taxonomic position of an actinomycete isolated from an ultramafic soil in New Caledonia was examined using a polyphasic approach. The organism, which was designated SFOCin 76, was found to have chemical and morphological properties typical of streptomycetes and formed a distinct phyletic line in the Streptomyces violaceusniger clade of the 16S rDNA tree. It also showed a unique pattern of phenotypic properties that distinguished it from representatives of all of the validly described species classified in this clade. It is, therefore, proposed that strain SFOCin 76 be classified in the genus Streptomyces as Streptomyces yatensis sp. nov.

Clinical and Laboratory Features of the Nocardia spp. Based on Current Molecular Taxonomy

Abstract: The recent explosion of newly described species of Nocardia results from the impact in the last decade of newer molecular technology, including PCR restriction enzyme analysis and 16S rRNA sequencing. These molecular techniques have revolutionized the identification of the nocardiae by providing rapid and accurate identification of recognized nocardiae and, at the same time, revealing new species and a number of yet-to-be-described species. There are currently more than 30 species of nocardiae of human clinical significance, with the majority of isolates being N. nova complex, N. abscessus, N. transvalensis complex, N. farcinica, N. asteroides type VI (N. cyriacigeorgica), and N. brasiliensis. These species cause a wide variety of diseases and have variable drug susceptibilities. Accurate identification often requires referral to a reference laboratory with molecular capabilities, as many newer species are genetically distinct from established species yet have few or no distinguishing phenotypic characteristics. Correct identification is important in deciding the clinical relevance of a species and in the clinical management and treatment of patients with nocardial disease. This review characterizes the currently known pathogenic species of Nocardia, including clinical disease, drug susceptibility, and methods of identification.

The role of plant-associated bacteria in the mobilization and phytoextraction of trace elements in contaminated soils

Abstract: Phytoextraction makes use of trace element-accumulating plants that concentrate the pollutants in their tissues. Pollutants can be then removed by harvesting plants. The success of phytoextraction depends on trace element availability to the roots and the ability of the plant to intercept, take up, and accumulate trace elements in shoots. Current phytoextraction practises either employ hyperaccumulators or fast-growing high biomass plants; the phytoextraction process may be enhanced by soil amendments that increase trace element availability in the soil. This review will focus on the role of plant-associated bacteria to enhance trace element availability in the rhizosphere. We report on the kind of bacteria typically found in association with trace element – tolerating or – accumulating plants and discuss how they can contribute to improve trace element uptake by plants and thus the efficiency and rate of phytoextraction. This enhanced trace element uptake can be attributed to a microbial modification of the absorptive properties of the roots such as increasing the root length and surface area and numbers of root hairs, or by increasing the plant availability of trace elements in the rhizosphere and the subsequent translocation to shoots via beneficial effects on plant growth, trace element complexation and alleviation of phytotoxicity. An analysis of data from literature shows that effects of bacterial inoculation on phytoextraction efficiency are currently inconsistent. Some key processes in plant–bacteria interactions and colonization by inoculated strains still need to be unravelled more in detail to allow full-scale application of bacteria assisted phytoremediation of trace element contaminated soils.

A Definitive Book on Seed Ecology@@@Seeds: Ecology, Biogeography, and Evolution of Dormancy and Germination

Abstract: Introduction. Ecologically Meaningful Germination Studies. Types of Seed Dormancy. Germination Ecology of Seeds with Nondeep Physiological Dormancy. Germination Ecology of Seeds with Morphophysiological Dormancy. Germination Ecology of Seeds with Physical Dormancy. Germination Ecology of Seeds in the Persistent Seed Bank. Causes of Within-Species Variations in Seed Dormancy and Germination Characteristics. A Geographical Perspective on Germination Ecology: Tropical and Subtropical Zones. A Geographical Perspective on Germination Ecology: Temperate and Arctic Zones. Germination Ecology of Plants with Specialized Life Cycles and/or Habitats. Biogeographical and Evolutionary Aspects of Seed Dormancy. Subject Index.