Rosa Rubio

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) ...

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.

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

Effect of Compost Application on Some Properties of a Volcanic Soil from Central South Chile

Soil compost application is a common soil management practice used by small farmers of Central-South Chile that produces positive effects on soil properties and also promotes presence and activity of arbuscular mycorrhizal fungi (AMF). This fungi form symbiosis with plant roots improving plant nutrition, as well as producing glomalin, a glycoprotein that has been associated with soil aggregation stability. Therefore, the aim of this study was to evaluate, in an Ultisol from Central-South Chile, the effect of different doses of compost on some soil characteristics at the end of the third year of a crop sequence including wheat (Triticum aestivum L.), bean (Phaseolus vulgaris L.), and grassland (Lolium multiflorum Lam. associated with Trifolium repens L.). Studied soil characteristics included chemical (pH, available-P, organic C), biological (C and N biomass, AMF spore number, root colonization percentage, mycelium length, and glomalin content), as well as physical parameters (water holding capacity [WHC], and water stable aggregates [WSA]). Results showed that, in general, compost application increased soil

ARBUSCULAR MYCORRHIZAE IN AGRICULTURAL AND FOREST ECOSYSTEMS IN CHILE

Arbuscular mycorrhizal (AM) association plays a key role in the sustainability of terrestrial plant ecosystems, in particular those presenting limitations for the establishment and subsequent growth of plants. In Chile, more than 50% of arable soils are originated from volcanic ashes, showing in general several constraints to crop production, such as low pH, high exchangeable aluminum content and low levels of available P. Under these conditions, the management of AM fungal propagules using adequate cultural management practices emerges as a successful alternative in order to maximize the positive effects of AM symbiosis on plant growth in these types of soil. This review presents the results of several years of research about the effect of different agronomic and forest management practices on the density and functionality of the native fungal populations in volcanic soils from Southern Chile, and their subsequent effect on the improvement of soil characteristics. These investigations have contributed to a better understanding of the role played by AM symbiosis in such soils and provide guidance on the most appropriate alternatives to increase its presence and functionality.

Mycorrhizal Propagule Persistence in a Succession of Cereals in a Disturbed and Undisturbed Andisol Fertilized with Two Nitrogen Sources

Arbuscular mycorrhizal fungi (AMF) form symbiosis with plant roots, improving its establishment, nutrition, and tolerance to adverse soil conditions. In annual crop rotations, some aspects such as the type of N fertilizer and tillage system used can affect the AMF propagule density and its functionality in the following crop. To analyze the effect of the agronomic practices previously mentioned on the persistence and density of AMF propagules, a study in a succession of cereals was carried out. For this, soil previously cropped with wheat (Triticum aestivum L.) and fertilized with urea (NH4 + ) or sodium nitrate (NO3 ) was disturbed in each case by simulating conventional tillage (CT) or maintained without disturbing, simulating no-tillage (NT). It was then cultivated with oat (Avena sativa L.) using the same N sources. Higher densities of AMF active mycelium and colonized root length in the NT soil were observed (76 and 497% higher than in CT soil, respectively, P < 0.001). Moreover, NT + NO3 interaction produced a higher density of AMF spores (75% higher than in the rest of the treatments, P < 0.05), although showing a decrease in comparison with the previous wheat crop. These results suggest that N source and tillage system interact to

PLANT GROWTH RESPONSES IN NATURAL ACIDIC SOIL AS AFFECTED BY ARBUSCULAR MYCORRHIZAL INOCULATION AND PHOSPHORUS SOURCES

ABSTRACT The effect of arbuscular-mycorrhizal (AM) fungus Glomus etunicatum inoculation in interaction with two sources of phosphorus (P) [soluble P and partially acidulated phosphate rock (pa-PR)] at three rates (17, 43, and 86 kg P ha−1) was studied in an acidic natural soil using wheat (Triticum aestivum L.) as host plant. Shoot and root dry biomass, AM colonized root length, macro-micronutrients content and soil phosphatase (P-ase) activity were determined after six months of plant growth. The inoculated G. etunicatum fungus, a fungal strain adapted to the prevailing soil conditions, enhanced plant growth (shoot and root biomass) and mineral acquisition of some elements when plants were fertilized with pa-PR but not with soluble P. The nutrient acquisition by AM inoculated plants varied with the source and amount of applied P. When pa-PR was supplied, the inoculated AM fungus enhanced P, potassium (K), aluminum (Al), and manganese (Mn) plant acquisition in comparison with indigenous endophytes alone. Shoot zinc (Zn) and copper (Cu) uptakes were also enhanced by G. etunicatum inoculation only at the intermediate assayed pa-PR level (43 kg ha−1). AM root colonization in the efficient pa-PR treatments, did not relate well to the plant growth and nutrient acquisition in most cases. Nutrients (Ca and Mg) that increased in AM inoculated plants were not those commonly deficient in acidic soils. Nevertheless, some nutrients, which often become limiting under low pH conditions such as P and K were increased by G. etunicatum inoculation plus pa-PR. Changes in rhizospheric soil pH under pa-PR application may be involved in these mycorrhizal effects on nutrient acquisition. The increases in plant biomass as a result of mycorrhizal inoculation do not seem to account for all the changes observed in mineral acquisition. The highest soil P-ase activity was observed at the lowest pa-PR dose showing a negative relationship with P-availability. The inoculation of G. etunicatum was effective in this natural acidic soil in overcoming factors that restrict plant growth and nutrition when pa-PR was applied.

Mycorrhizal Effectiveness on Wheat Nutrient Acquisition in an Acidic Soil from Southern Chile as Affected by Nitrogen Sources

ABSTRACT Acidity, aluminium (Al) and manganese (Mn) phytotoxicity, and low levels of available phosphorus (P) are the main constraints for plants growing in Andisols from southern Chile. This study was carried out to evaluate the effect of arbuscular mycorrhizal (AM) fungus inoculation and two nitrogen (N)-sources on the growth and mineral uptake of wheat (Triticum aestivum L.) plants grown in an acidic Andisol at 120 and 150 days after sowing (DAS). The plants were grown in pots under greenhouse conditions with or without inoculation with the AM fungus Glomus etunicatum CH110 (Morton and Bentivenga) and fertilized with N-ammonium (NH4 +) or N-nitrate (NO3 −). The biomass production was not affected for any treatment used, but the inoculation with G. etunicatum increased the shoot contents and specific absorption rate (SAR) of P and zinc (Zn) at 120 and 150 DAS, especially when N-NH4 + was used. On the other hand, the use of N-NO3 − increased the N (at 120 DAS), potassium (K) (120 and 150 DAS), and copper (Cu) (120 DAS) shoot content, reduced the Al shoot content and Mn SAR (both at 120 DAS). The combined use of G. etunicatum inoculation and N-NO3 − use decreased significantly (P < 0.001) the Mn shoot content and the Al SAR at 150 DAS. The results suggest the selection of NO3 − as N-source to address practical and ecological fertilization management, which is important for acidic volcanic soils from southern Chile, with a natural tendency to produce Mn and Al phytotoxicity.