Resumen Los parámetros biológicos son usados como indicadores tempranos en la calidad de un suelo (ICS) agrícola, ya que responden rápidamente al manejo antrópico. El objetivo de esta investigación fue determinar el efecto del sistema de labranza: siembra directa (SD) y labranza convencional (LC), y de la fertilización nitrogenada después de los cultivos de fréjol y maíz, sobre ciertos indicadores biológicos de la calidad del suelo. El estudio se realizó sobre un molisol de la región andina del Ecuador. Se determinó la biomasa microbiana (BM), respiración microbiana (RM), y actividad enzimática (fosfatasa ácida, hidrólisis de la fluoresceína-diacetato [FDA], y β-glucosidasa [β-G]). Los resultados mostraron que la fosfatasa presentó la mayor actividad bajo LC, la FDA respondió al efecto de los niveles altos de nitrógeno (N), la actividad de la enzima β-G fue mayor en LC. Adicionalmente, el análisis de componentes principales seleccionó a los indicadores biológicos estudiados, como ICS. Se concluye que los indicadores biológicos del suelo fueron afectados por las prácticas de manejo estudiadas.

Abstract Biological parameters are used as early indicators of the quality of an agricultural soil (ICS), due to their quick response to the anthropic soil management. The main objective of this research was to determine the effect of the tillage system: no-till (SD) and conventional tillage (LC), and to the nitrogen fertilization in bean and corn crop on certain biological indicators of soil quality. The study was carried out on a mollisol from the Andean region of Ecuador. Microbial biomass (MB), microbial respiration (RM), and enzyme activity (acid phosphatase, hydrolysis of fluorescein diacetate [FDA], and β-glucosidase [β-G]) were determined. The results showed that the phosphatase presented the highest activity under LC, the FDA responded to the effect of high nitrogen levels application (N), the activity of the β-G enzyme was higher under LC. Additionally, the principal component analysis selected these biological indicators studied as ICS. It is concluded that the biological indicators of the soil were affected by the management practices studied.

Abstract: This research study seeks to describe university students’ perceptions of social responsibility from the perspective of social outbreaks (“Estallido Social”) and the COVID-19 pandemic in Chile. An instrument is applied to a non-probabilistic sample of 153 university students from southern Chile. An exploratory factor analysis is performed and statistically significant differences are examined considering the sociodemographic characteristics of the sample. The results show differences according to occupation, socioeconomic level, and the criterion variable. The most significant correlation is observed between “personal discovery of values” and “professional practice with social commitment.” It is concluded that universities must develop efforts to design policies, strategies, practices, and actions for training in socially responsible behavior by considering current contexts and the challenges of a society damaged by the pandemic.

Resumen: La presente investigación busca describir la percepción del estudiante universitario sobre la responsabilidad social desde la perspectiva de las protestas (“Estallido Social”) y la pandemia COVID-19 en Chile. Se aplica un instrumento a una muestra no probabilística de 153 estudiantes universitarios de la zona sur de Chile. Se realiza un análisis factorial exploratorio y se examinan diferencias estadísticamente significativas considerando las características sociodemográficas de la muestra. Los resultados muestran diferencias según ocupación, nivel socioeconómico y variable criterio. Se observa en todos los casos una correlación alta y positiva entre las dimensiones. La mayor correlación se encuentra entre la dimensión “descubrimiento personal de los valores” y “planteamiento del ejercicio profesional desde el compromiso social”. Se concluye que las universidades deben desarrollar esfuerzos para el diseño de políticas, estrategias, prácticas y acciones para la formación en comportamiento socialmente responsable considerando el contexto actual y los desafíos de una sociedad dañada por la pandemia.

ABSTRACT Conventional tillage (CT) is a soil management system commonly used by small farmers in the Ecuadorian highlands; they remove the soil during seedbed preparation to eliminate weeds, improve soil aeration, avoid compaction, and develop adequate rooting space. CT causes changes in physical, chemical, and biological soil properties but, in the long run, have negative effects on crop performance. Most of these effects can be avoided by using no-tillage (NT). The objective of this study was to determine the initial effects of NT, different fertilization rates and depth levels of sampling on yield and soil chemical and physical properties after the first crop cycle (prior to crop rotation scheme). A long-term field experiment was established to study the soil changes derived from the transition from CT to NT systems in a volcanic soil of the Ecuadorian highlands cultivated with the following crop rotation schemes: beans (Phaseolus vulgaris L.)-corn (Zea mays L.)-beans and beans-amaranth (Amaranthus caudatus L.)-beans. The results for the first crop cycle show that bean yield was 42% higher under NT compared to CT, indicating that the soil improvements promoted by NT had effects on crop yield; however, only the changes in pH and water storage capacity presented significant differences, levels of soil organic matter, total N, available P, and bulk density showed a trend towards improvements under NT. This suggests that NT allows for increased crop yield and improved crop rotation performance in the medium and long term.

RESUMEN La labranza convencional (CT) es una práctica agrícola ampliamente usada por los pequeños agricultores de la sierra del Ecuador. En la operación de labrado, se remueve suelo durante la preparación de la cama de siembra, para eliminar malezas, mejorar la aireación, evitar compactación y desarrollar un adecuado ambiente para el crecimiento radicular. Esta remoción causa cambios en las propiedades físicas, químicas y biológicas del suelo, que con el tiempo tienen efectos negativos en los cultivos. Muchos de estos efectos se pueden evitar usando siembra directa (NT). El objetivo de este estudio fue determinar los efectos iniciales de la siembra directa, diferentes tasas de fertilización y niveles de profundidad del muestreo sobre el rendimiento y las propiedades químicas y físicas del suelo después del primer ciclo de cultivo. Se implementó un experimento a largo plazo para determinar los cambios promovidos por la transición de labranza convencional (CT) a siembra directa (NT) en un suelo volcánico de la sierra del Ecuador cultivado bajo dos esquemas de rotación: fréjol (Phaseolus vulgaris L.)-maíz (Zea mays L.)-fréjol y fréjol-amaranto (Amaranthus caudatus L.)-fréjol. Los resultados correspondientes al primer ciclo de cultivo indican que el rendimiento del fréjol fue 42% más alto con la siembra directa, sugiriendo que los cambios en el suelo promovidos por este sistema de labranza tienen efecto en el rendimiento del cultivo. A pesar de que solamente fueron significativos los cambios en pH y contenido de capacidad de almacenamiento de agua, los resultados sobre materia orgánica del suelo, nitrógeno total, P disponible y densidad aparente muestran una tendencia de mejoramiento con la siembra directa, lo que sugiere que esta práctica mejora el rendimiento inicial y promovería un mejor comportamiento de las rotaciones a mediano y largo plazo.

Abstract: Selenium (Se) is an important antioxidant considered among the fertilization programs in developed countries. In Chile, chemical fertilization based in Se is inefficient due the physicochemical characteristics of Andisol that sustain the 60% of crop production. Andisol also are highly conductive to take-all disease caused by Gaeumannonyces graminis var tritici (Ggt). Here, we evaluated the effect of Bacillus sp.E5 and Acinetobacter sp.E6.2 and Claroideoglomus claroideum as potential inocula for Se biofortification and Ggt bicontrol in wheat. Plants inoculated with Acinetobacter sp.E6.2 showed major root growth and major Se content in shoots and grains. The antioxidant role of Se regarding DPPH activity was shown in Se-supplemented plants with small Se nanoparticles founded inside the roots. Mycorrhizal plants showed major SOD activity in shoots but no affected the Se uptake. Respect to pathogen biocontrol, plants inoculated with both bacteria showed an efficient control against Ggt independent to mycorrhization. Thus, our inocula could make important contributions to produce enriched Se flours for human nutrition and biocontrol against Ggt.

Abstract Volcanic eruptions have a significant effect on ecosystems, including soil and its fungal communities. Due to the eruption of the Puyehue-Cordón Caulle in 2011, thick tephra deposits accumulated in several Nothofagus pumilio forests in Northern Patagonia. The tephra deposition affected plant establishment and development during the post-eruption period. In this work we analyzed rhizosphere fungal communities associated with N. pumilio seedlings at three study sites sampled three years after the eruption, two with a thick tephra layer (50 cm) and a third site with no tephra deposition. Denaturing gradient gel electrophoresis (DGGE) was performed for the different fungal communities (Ascomycetes, Basidiomycetes and Total fungi). We found clear shifts in rhizosphere fungal communities, especially for Basidiomycetes and Total fungi. Site-related characteristics, such as type of substrate, light intensity and the existence of understory and previous mycelial networks, seemed to be the main factors determining the structure of these fungal communities. Given their sensitivity to different types of environmental change, these microbial communities could be used as bioindicators. Specifically, Basidiomycetes and total fungi seem to be better bioindicators of environmental changes than ascomycetes. The results shown here contribute to the understanding of how fungal communities respond to disturbance, an important issue in the evaluation of how ecosystem processes might be affected in areas commonly subjected to geological risks, such as volcanism. This information is also relevant to the planning and successful implementation of restoration activities based on seedling optimization by rhizosphere fungi.

Abstract The 2011 Puyehue-Cordón Caulle volcanic eruption left vast areas of Nothofagus pumilio forests covered by high volumes of tephra, which buried the understory. This event offered a unique opportunity to analyse the impact of recent tephra deposition and the main environmental factors affecting the growth of N. pumilio seedlings. To this end, three study sites were selected and sampled three years after the eruption, two with a thick tephra layer (50 cm) but with different tree conditions: i) most trees alive or ii) most trees dead, and a third site, iii) with minimal tephra deposition. From each site, five N. pumilio 18-month-old seedlings were collected, morphometrically measured (shoot, epicotyl and main root length; shoot, epicotyl and root collar diameter), and environmental factors were also registered (light intensity, soil pH and conductivity, available P, bulk and particle soil density, and porosity). The main results indicated that three years after eruption the site with tephra deposition and dead trees (the most near to the crater) had the biggest seedlings, the lowest pH and the highest values for available P and light intensity. This temporally unique geological event showed that the regeneration potentiality of N. pumilio is high when environmental factors allow direct incident light on a substrate with high mineral content, even when the environment has previously been subjected to a significant degree of disturbance. Given the recurrence of volcanic events in Northern Patagonia, this subject merits further long-term study.

ABSTRACT Crotalaria juncea is used as plant cover in grape vineyards in Brazil, which usually present soils with high copper (Cu) levels due to the application of Cu-based phyto-sanitary products. Under this condition an increase growth and cover of C. juncea is needed to improve the phytoremediation processes in those soils. Some alternatives to achieve this condition is the inoculation with arbuscular mycorrhizal fungi (AMF), which has demonstrated an important increase of plant growth in Cu-contaminated soils at different soil P levels. The aims of this study were to evaluate the effect of AMF inoculation in soils with high Cu contents on the growth of C. juncea, the acid phosphatase (APase) enzyme activity in plants and soil, and the presence of glomalin under different P supply conditions, as a basis to identify if there is a synergistic interaction between AMF inoculation and P supply on soils with high Cu levels. The experiment was carried under greenhouse conditions in a factorial 3 × 2 design (natural P content, addition of 40 and 100 mg kg-1 P, with and without the inoculation of the AMF Rhizophagus clarus with three replicates) in a soil with high Cu content (60 mg kg-1). The addition of 40 and 100 mg kg-1 P favored plant growth both in the presence and in the absence of AMF. However, when plants were grown in soil with a natural P level, the inoculation with AMF increased by 116 % the shoot biomass, compared to the non-inoculated treatment. Our results showed that the combination of P supply and R. clarus inoculation could be an adequate strategy to reduce Cu phytotoxicity in C. juncea, as it increases plant biomass and modify the APase enzyme activity in the soil and plant. Additionally, glomalin produced by the AMF and accumulated in the soil can decrease the availability of Cu to the plants by means of sequestration beyond the root surface, with a consequent plant protective effect.

The Bradford-reactive soil protein (BRSP) fraction includes glomalin, a glycoprotein produced by arbuscular mycorrhizal (AM) fungi able to bind some metals, such as copper (Cu), which could promote the bioremediation of Cu-polluted soils. This study aimed to analyze the Cu-binding capacity of BRSP in Oenothera picensis that was inoculated or not inoculated with AM fungi. O. picensis plants were established in a Cu contaminated sterilized soil and treated with the following: i) uninoculated (-M); ii) inoculated with native AM fungal propagules (+M); or iii) inoculated with a Claroideoglomus claroideum (CC) strain isolated from non-contaminated soil. In each case, five Cu levels were applied to the soil (basal level 497.3 mg Cu kg-1): 0 (T1); 75 (T2); 150 (T3); 225 (T4); and 300 mg Cu kg-1 (T5). A high BRSP accumulation in AM inoculated treatments, especially with CC, was observed. A higher Cu-bound-to-BRSP content was found with increasing Cu concentrations, representing up to 20-22% of the total Cu in the soil. Moreover, a higher root Cu concentration in +M was observed. These results suggest a high Cu binding capacity by BRSP, which is a relevant aspect to consider in the design of bioremediation programs together with the selection of endemic metallophytes and AM fungal strains, which are able to produce glomalin at high quantities.

Southern Chilean pristine temperate rainforests have been floristically stable during the Holocene, thus representing a pre-industrial baseline of forest ecology. Given this and its edaphic limitations, it is imperative to better understand these forests ecological patterns of mycorrhizal symbiosis. Therefore, here we compare the arbuscular mycorrhizal (AM) communities in three tree line Nothofagus pumilio contrasting plots of Chilean Andes (a volcano crater, pristine forest, and disturbed forest). The AM community assemblages were determined by morphological identification and spore counting, in three A horizon soil samples by plot. In the same nine soil samples, standard chemical analysis was performed. Eighteen AM species were described; Acaulospora was the most abundant genus. The forest plot had the highest AM species richness compared to the disturbed and crater plots. Interestingly, soils Olsen P (plant available phosphorus), pH, and Al+++ saturation similarly affected the AM assemblages. We suggest that some AM species could be specially adapted to extremely high Al saturation and extremely low plant available P conditions, as those experienced on Andean Nothofagus forests. These species may help initiate biological succession on highly disturbed ecosystems. We suggest that mycorrhizal fungi play a key role in seedling colonization of extreme environments such as the Andean tree line.

Aluminum phytotoxicity in acid soils is an important environmental stress that negatively affects crop production, but arbuscular mycorrhizal (AM) fungi performance would allow plants to better withstand this environmental condition. This study aimed to analyze the effect of soil Al on early AM colonization of wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.) cultivars. Near-isogenic Crac, Invento, and Porfiado wheat cultivars and Sebastián and Aurora barley cultivars were sown in pots in an acid soil at three Al saturation levels (60, 34, and 11%). At 20 d after sowing (DAS) ’Crac’ presented higher AM colonization (27%) than other cultivars. However, ’Invento’ had the fastest colonization at 41 DAS, which was inhibited in short term at lower Al-saturation. Moreover, roots of ’Aurora’ were colonized 28 and 51% at 20 and 66 DAS, respectively, and also decreased at lower Al-saturation. In soil with 60% Al-saturation a great spore production was observed at 41 DAS, ’Aurora’ had the highest spore density at 66 DAS. At 20 DAS a negative relationship (r = -0.37; p < 0.001) was observed between the early root colonization and root weight. In addition, such relation was stronger (r = -0.49; p < 0.001) when plants were grown at high Al saturation. An early AM colonization was observed in all cultivars essayed when growing at high Al saturation being higher in cultivars apparently more Al tolerant, suggesting that an early AM colonization can be an important factor in Al tolerance for agricultural plants cropped in acid soils.

La fitotoxicidad por Al en suelos ácidos es un importante estrés que afecta negativamente la producción de cultivos, pero la actividad de hongos micorrícicos arbusculares (MA) permitiría que las plantas soporten mejor esta condición ambiental. Este estudio tuvo como objetivo analizar el efecto del Al en la colonización MA temprana de cultivares de trigo (Triticum aestivum L.) y cebada (Hordeum vulgare L.). Cultivares de trigo Crac, Invento, y Porfiado, y de cebada Sebastián y Aurora fueron sembrados en macetas en un suelo ácido con tres niveles de saturación de Al (60, 34, y 11%). A los 20 días después de la siembra (DDS) ’Crac’ presentó la mayor colonización MA (27%); sin embargo, ’Invento’ tuvo la más rápida colonización a los 41 DDS, la cual fue inhibida a corto plazo a una menor saturación de Al. Por otra parte, las raíces de ’Aurora’ fueron colonizadas 28 y 51% a los 20 y 66 DDS, respectivamente, y también se redujo a una menor saturación de Al. En suelos con 60% de saturación de Al se observó una gran producción de esporas a los 41 DDS, siendo ’Aurora’ el de más alta densidad de esporas a los 66 DDS. A los 20 DDS se observó una relación negativa (r = -0.37, p < 0,001) entre la colonización MA temprana y la masa de las raíces. Además, dicha relación fue más fuerte (r = -0.49, p < 0,001) cuando las plantas fueron cultivadas en alta saturación de Al. Una temprana colonización MA se observó en todos los cultivares ensayados cuando se cultivaron en alta saturación de Al y fue superior en las variedades aparentemente más tolerantes a Al, sugiriendo que una temprana colonización MA puede ser un factor importante en la tolerancia a Al para plantas agrícolas cultivadas en suelos ácidos.

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.

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 paniculate organic matter [fPOM]; occluded paniculate 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.

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 influence persistence and density of AMF propagules, an important aspect to consider in acidic soils intended for annual crops.

Los hongos micorrícico-arbusculares (AMF) forman simbiosis con las raíces de las plantas, favoreciendo su establecimiento, nutrición y tolerancia a condiciones adversas del suelo. En rotaciones de cultivos anuales algunos aspectos como el tipo de fertilizante nitrogenado utilizado y el sistema de labranza pueden afectar la densidad de propágulos de AMF y su funcionalidad en el cultivo siguiente. Para analizar el efecto de las prácticas agronómicas previamente mencionadas sobre la persistencia y densidad de los propágulos de AMF, se realizó un estudio en microcosmos simulando una rotación de cereales. Para esto, suelo previamente cultivado con trigo (Triticum aestivum L.) y fertilizado con urea (NH4+) o nitrato de sodio (NO3-) fue, en cada caso, disturbado simulando una labranza convencional (CT) o mantenido sin disturbar simulando cero labranza (NT) y cultivado con avena (Avena sativa L.), utilizando las mismas fuentes de N. Se observaron mayores densidades de micelio activo de AMF y longitudes de raíz colonizada en el suelo NT (76 y 497% mayor que en suelo CT, respectivamente; P < 0,001). Por otra parte, la interacción NT + NO3- produjo una mayor densidad de esporas de AMF (75% mayor que en el resto de los tratamientos, P < 0,05), aunque mostrando una disminución respecto del cultivo previo de trigo. Estos resultados sugieren que la fuente de N y el sistema de labranza influyen interactivamente sobre la persistencia y densidad de propágulos de AMF, aspecto importante de considerar en suelos ácidos destinados a cultivos anuales.

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 pH, mycorrizal roots, mycelium length, glomalin levels, and WSA. Significant relationships were found between C and N biomass, C biomass and WSA, C biomass and glomalin, WSA and WHC, among others. Results suggest that compost application to this type of soil is a feasible option as a fertilizer substitute, and a way to avoid soil erosion by small local farmers involved in organic agriculture.

La aplicación de compost al suelo, práctica habitual en predios de pequeños agricultores de la región centro-sur de Chile, produce efectos positivos en sus propiedades y promueve la presencia y actividad de los hongos micorrícicos arbusculares (AMF). Estos hongos forman simbiosis con las raíces de las plantas mejorando su nutrición y además producen una glicoproteína llamada glomalina, la cual ha sido relacionada con la estabilidad de los agregados de suelo. Por lo anterior, el objetivo de este estudio fue evaluar el efecto de la aplicación de distintas dosis de compost sobre algunos parámetros de un Ultisol de la zona centro-sur de Chile, al finalizar el tercer año de una secuencia de cultivos formada por trigo (Triticum aestivum L.), frejol (Phaseolus vulgaris L.) y pradera permanente (Lolium multiflorum Lam. asociada con Trifolium repens L.). Se estudiaron parámetros químicos (pH, C orgánico, P-Olsen), biológicos (C y N biomásico, número de esporas de AMF, micorrización de raíces, longitud de micelio y niveles de glomalina), y físicos (capacidad de retención de agua, WHC, y agregados estables al agua, WSA). Los resultados mostraron que, en general, la aplicación de compost incrementó el pH, micorrización radical, niveles de glomalina, longitud del micelio fúngico y porcentaje de WSA. Se encontraron correlaciones entre C y N biomásico, C biomásico y WSA, C biomásico y glomalina, WSA y WHC. Los resultados aportan antecedentes sobre el uso beneficioso de compost como una alternativa viable de sustitución de insumos y disminución de la erosión en asentamientos de pequeños agricultores orientados a la agricultura orgánica.

Nitrogen fertilization influences plant growth and rhizospheric properties, affecting the functionality and persistence of arbuscular mycorrhizal fungi (AMF). In order to analyze the effect of two N-sources (NH4+ and NO3-) on the persistence of AMF propagules (colonized root, mycelium and spores) and some rhizospheric parameters (pH, P available), a greenhouse experiment was carried out using two wheat (Triticum aestivum L.) cvs. Otto and Metrenco, which were grown in an Andisol. Plant biomass was determined at the dry grain stage (Zadocks 99, 150 days after sowing, DAS), the density of AMF propagules was determined three months later (240 DAS), and pH and available P were determined at both stages. The results showed that N-source and cultivar influenced most of the studied variables. The NO3- + Metrenco combination showed the highest values for biomass, pH, available P and AMF spores (150, 13, 5 and 375% more than NH4+ + Otto interaction, respectively; p < 0.001). On the other hand, close relationships were found between biomass production and density of AMF spores (r² = 0.89; p < 0.001), suggesting that this propagule is quantitatively affected by host plant biomass production. This propagule is probably also indirectly affected by rhizospheric conditions. This result is of a special agronomic and ecological interest in acidic soils destined to annual crops, in which nitrogen fertilization is a habitual practice, being the N-source very influential in yields.

La fertilización nitrogenada influye en el crecimiento vegetal y propiedades rizosféricas, afectando la funcionalidad y persistencia de hongos micorrícico-arbusculares (AMF). Para analizar el efecto de dos fuentes de N (NH4+ y NO3-) sobre la persistencia de propágulos de AMF (raíz colonizada, esporas e hifas) y algunos parámetros rizosféricos (pH, P disponible), se realizó un experimento en invernadero utilizando dos cultivares de trigo (Triticum aestivum L.), cvs. Otto y Metrenco en un Andisol. La biomasa se determinó en grano seco (Zadocks 99, 150 días después de la siembra, DAS), la densidad de propágulos de AMF se determinó tres meses más tarde (240 DAS), y el pH y P disponible se determinaron en ambas etapas. Los resultados indicaron que la fuente de N y el cultivar influyeron en la mayoría de las variables estudiadas. La combinación NO3- + Metrenco presentó mayores valores de biomasa, pH, P disponible y esporas de AMF (150; 13; 5 y 375% más que la interacción NH4+ + Otto, respectivamente; p < 0,001). Por otra parte, se encontraron estrechas relaciones entre producción de biomasa y densidad de esporas de AMF (r² = 0,89; p < 0.001), que sugiere que este propágulo es cuantitativamente afectado por la producción de biomasa de la planta hospedera. Este propágulo es probablemente afectado de forma indirecta por las condiciones rizosféricas. Este resultado es de especial interés ecológico y agronómico en suelos ácidos destinados a cultivos anuales, donde la fertilización nitrogenada es una práctica habitual, siendo la fuente de N muy incidente en los rendimientos.