Fernando Borie

Glomalin-related soil protein in a Mediterranean ecosystem affected by a copper smelter and its contribution to Cu and Zn sequestration.

The amount of glomalin-related soil protein (GRSP), a glycoprotein produced by arbuscular mycorrhizal fungi (AMF), its contribution to the sequestering of Cu and Zn in the soil, and the microsite variation of other soil traits (pH, water-stable aggregates--[WSA], soil organic carbon--[SOC]) was studied in a semi-arid Mediterranean ecosystem near a copper smelter and affected by deposit of metal-rich particles since 1964. Rhizospheric (R) and non-rhizospheric (NR) soil of four representative plants (Argemone subfusiformis, Baccharis linearis, Oenothera affinis and Polypogon viridis) was analyzed. The results showed a strong variability in GRSP (6.6-36.8 mg g(-1)), Cu content (62-831 mg kg(-1) for the total Cu and 5.8-326 mg kg(-1) for the available Cu) and pH (4.2-5.5) in the different plant and rhizospheric zones analyzed. A strong relationship between the GRSP with the soil Cu and Zn contents was found (r=0.89 and 0.76 for Cu and Zn respectively, p<0.001). The GRSP-bound Cu ranged from 3.76 to 89.0 mg g(-1) soil and represents 1.44-27.5% of the total Cu content in soil. Moreover, the WSA reached 89% in P. viridis R. For this plant, the C contained in GRSP represented up to 89% of SOC, and this coincided with the most extreme conditions of soil degradation within the ecosystem (the highest content of heavy metals and low pH values). This study provides evidence on the role of the GRSP in Cu and Zn sequestration and suggests a highly efficient mechanism of AMF to mitigate stress leading to stabilization of soils highly polluted by mining activities.

Phytoremediation of Metal-Polluted Soils by Arbuscular Mycorrhizal Fungi

Human activities generate wastes, some of which contain large amounts of heavy metals/metalloids that could enter natural ecosystems and alter the activities and functioning of soil micro- and macroorganisms. Microorganisms can adapt/resist to metal stress, and some of them are able to promote the plants establishment and therefore the phytoremediation process. In this context, the use of arbuscular mycorrhizal fungi (AMF), and their role in phytoremediation, has emerged as a new and interesting choice. In addition to AMFs well-known contribution to plant nutrient acquisition and growth, these fungi develop diverse mechanisms that encourage plants to grow in soils with high toxic metals concentrations. The authors are concerned about the AMF metal tolerance mechanisms and its role in the promotion of in phytoremediation processes.

The role of arbuscular mycorrhizas in decreasing aluminium phytotoxicity in acidic soils: a review

Soil acidity is an impediment to agricultural production on a significant portion of arable land worldwide. Low productivity of these soils is mainly due to nutrient limitation and the presence of high levels of aluminium (Al), which causes deleterious effects on plant physiology and growth. In response to acidic soil stress, plants have evolved various mechanisms to tolerate high concentrations of Al in the soil solution. These strategies for Al detoxification include mechanisms that reduce the activity of Al3+ and its toxicity, either externally through exudation of Al-chelating compounds such as organic acids into the rhizosphere or internally through the accumulation of Al–organic acid complexes sequestered within plant cells. Additionally, root colonization by symbiotic arbuscular mycorrhizal (AM) fungi increases plant resistance to acidity and phytotoxic levels of Al in the soil environment. In this review, the role of the AM symbiosis in increasing the Al resistance of plants in natural and agricultural ecosystems under phytotoxic conditions of Al is discussed. Mechanisms of Al resistance induced by AM fungi in host plants and variation in resistance among AM fungi that contribute to detoxifying Al in the rhizosphere environment are considered with respect to altering Al bioavailability.

Effects of arbuscular mycorrhizae and liming on growth and mineral acquisition of aluminum‐tolerant and aluminum‐sensitive barley cultivars

Abstract Acidification and aluminum (Al) phytotoxicity are the most important constraints for plant growing in volcanic soils from southern Chile. This study was conducted to evaluate the effects of arbuscular mycorrhizal (AM) fungus inoculation and liming on growth and mineral acquisition of two barley (Hordeum vulgare L.) cultivars with different tolerances to Al when they grow in an acidic Andisol. The plants were grown in pots under greenhouse conditions with and without calcium (Ca) amendment [equivalent to 2 tons lime ha‐1 as calcium carbonate (CaCO3)] and AM fungi Glomus etunicatum CH 110 (Morton and Bentivenga). Another experiment was conducted in nutrient solution for studying root pH changes produced by the same barley cultivars. The AM treatment appeared to ameliorate Al phytotoxicity more than CaCO3, especially for the Al‐tolerant genotype. Benefits of AM inoculation for the tolerant genotype included increases in root and shoot dry matter, and increased Ca, magnesium (Mg), and phosphorus (P) ...

Influence of copper on root exudate patterns in some metallophytes and agricultural plants.

A hydroponic experiment was carried out to determine the root exudation patterns in two Cu-metallophytes (Oenothera picensis and Imperata condensata) and two agricultural plants (Lupinus albus and Helianthus annuus). Plants were grown in nutrient solution at increasing Cu doses (0, 0.125, 0.25, 0.5, 1 and 2mgCuL(-1)), and plant growth, root elongation, Cu accumulation and root exudates were measured. All plants showed a decrease of over 60% in root elongation at the highest Cu supply level, being O. picensis the most sensitive specie and showing the highest shoot and root Cu concentrations (116 and 2657μgCug(-1), respectively), which were six fold higher than the other species. Differences in root exudation patterns of low molecular weight organic acids were found, with extremely high amounts of succinic acid exuded by O. picensis (1049μmolg(-1)h(-1)), and citric acid by I. condensata (164μmolg(-1)h(-1)). In metallophytes, the organic acid exudation was increased even with no root elongation, meanwhile agricultural plants exuded citric acid at constant levels. Exudation of phenolic compounds was highly species-dependent, with catechin mainly exuded by I. condensata, (2.62μmolg(-1)h(-1)) cinnamic acid by O. picensis (5.08μmolg(-1)h(-1)) and coumaric acid exclusively exuded by H. annuus (13.6μmolg(-1)h(-1)) at high Cu levels. These results indicated that differences in root exudation patterns among metallophytes and agricultural plants could affect their Cu tolerance. Particularly, the higher exudation rate showed by I. condensata can be an effective exclusion mechanism to tolerate high Cu concentrations, supporting its use in Cu phytostabilization programs.

ARBUSCULAR MYCORRHIZAL FUNGI AND SOIL AGGREGATION

Soil aggregation is governed by several biotic and abiotic components including landuse management. Aggregation is essential to maintain soil physical properties and facilitate biogeochemical cycling. Hyphae of arbuscular mycorrhizal fungi (AMF) are considered to be primary soil aggregators and there is a positively correlation between AMF hyphae and aggregate stability in natural systems. Recent evidence suggests that glomalin (GRSP), a glycoprotein produced by AMF hyphae which has a cementing capacity to maintain soil particles together, is mainly involved in such aggregation. However, recently controversial results together with reported shortcoming in glomalin determinat suggest to proceed with caution when studying glomalin in connection with soil aggregation. Relationships between glomalin and soil aggregates found in Chilean soils are discussed.

Acid phosphatase activity and vesicular‐arbuscular mycorrhizal infection associated with roots of four wheat cultivars

Abstract Acid phosphatase activity and vesicular‐arbuscular mycorrhizal (VAM) infection associated with four spring wheat genotype roots were investigated. Plants were grown in a typic low P volcanic soil with and without P‐fertilizer addition and harvested at 21, 42, 63, 84 and 96 days. Results show that phosphatase activity, expresed as ug p‐nitrophenol released per g dry root, decreased from 21 to 96 days in all cultivars. Conversely, trends of VAM infection were similar in all genotypes being higher in P added plants at 63 days after sown. This opposite effects may be viewed as alternative and/or complementary adaptations for P‐uptake by plants growing in low nutrient situations. It was concluded that one of the ways of P‐alleviation in wheat growing in our volcanic soils might be the search of genotypes having high biochemical and/or biological root activities.

Crop residue stabilization and application to agricultural and degraded soils: A review

Agricultural activities produce vast amounts of organic residues including straw, unmarketable or culled fruit and vegetables, post-harvest or post-processing wastes, clippings and residuals from forestry or pruning operations, and animal manure. Improper disposal of these materials may produce undesirable environmental (e.g. odors or insect refuges) and health impacts. On the other hand, agricultural residues are of interest to various industries and sectors of the economy due to their energy content (i.e., for combustion), their potential use as feedstock to produce biofuels and/or fine chemicals, or as a soil amendments for polluted or degraded soils when composted. Our objective is review new biotechnologies that could be used to manage these residues for land application and remediation of contaminated and eroded soils. Bibliographic information is complemented through a comprehensive review of the physico-chemical fundamental mechanisms involved in the transformation and stabilization of organic matter by biotic and abiotic soil components.

TILLAGE EFFECT ON SOIL ORGANIC MATTER, MYCORRHIZAL HYPHAE AND AGGREGATES IN A MEDITERRANEAN AGROECOSYSTEM

Arbuscular mycorrhizal fungi (AMF) and their product glomalin (GRSP) play a decisive role in the soil aggregation, affecting the carbon (C) dynamics in agroecosystems. Tillage affects the AMF activity and GRSP content, influencing the stability and the soil C forms as well. The aim of this study was to compare the effect of no tillage (NT) and conventional tillage (CT) on: i) arbuscular mycorrhizal hyphal length and GRSP content; ii) the nature of soil organic matter by means of physical fractionation (free particulate organic matter (fPOM); occluded particulate organic matter (oPOM) and mineral-associated soil organic matter (Mineral)), as well as chemical fractionation (fulvic acid, humic acid and humin), and iii) the relationships between AMF parameters, soil carbon and water stable aggregates (WSA) in a Mollisol of Central Chile managed for 6 years under NT and CT using a wheat-corn rotation. Higher values in the AMF hyphal length, GRSP and WSA in NT compared with CT were observed. Significant relationships were found between GRSP and WSA (r = 0.66, p < 0.01) and total mycelium and GRSP (r = 0.58, p< 0.05). The total carbon increased 44% under NT compared with CT. The chemical fractionation showed percentage greater than 95% for humim in both treatments. Physical fractionation indicates that the higher part of the SOC (89.4 - 95.1%) was associated with the mineral fraction.

Relación entre densidad de hifas de hongos micorrizógenos arbusculares y producción de glomalina con las características físicas y químicas de suelos bajo cero labranza

La labranza reducida y la cero labranza (CL) son las principales practicas de manejo agricola que contribuyen a la estabilidad de los suelos. En este estudio se determino las relaciones existentes entre algunos parametros micorricicos, tales como la densidad del micelio extraradical y la producion de glomalina, una proteina exudada por las hifas del hongo, con las propiedades fisicas y quimicas de un alfisol bajo CL. Se muestrearon suelos en postcosecha a diferentes profundidades (0-50, 50-100 y 100-200 mm) desde sitios con manejo de CL durante cuatro (4 CL), siete (7 CL) y veinte (20 CL) anos y tambien un suelo con pradera natural, como testigo. Los resultados mostraron en todos los suelos a las tres profundidades un incremento del pH, P total, P disponible y carbono organico en la medida del incremento en los anos con CL. La porosidad decrecio sustantivamente en los primeros horizontes del suelo bajo 20 anos de CL. La estabilidad al agua de los agregados de suelo se mantuvo similar en todos, con excepcion del suelo con 7 CL debido a que Lupinus albus fue el cultivo precedente. La glomalina total y la facilmente extractable se incrementaron en los suelos desde los 4 a los 20 anos bajo CL, lo que representa alrededor del 0.36% de la materia organica en el horizonte superficial de este ultimo. Se encontro una estrecha relacion entre glomalina total y la facilmente extractable (r2 = 0,97) , entre carbono organico y glomalina total (r2 = 0,96), entre pH y densidad de las hifas de las micorrizas (r2 = 0,72) y entre densidad de hifas y P total (r2 = 0,74). No se encontro correlacion entre agregados estables al agua y glomalina o densidad del micelio, sugiriendo de que la agregacion y estabilizacion en esos suelos podria estar gobernada por otro tipo de interacciones