This study assessed the effects of nitrogen (N) fertilization source on forage yield, nutritional status, and the activity/abundance of autochthonous root symbionts in fescue–lotus mixtures. Specifically, the contribution of arbuscular mycorrhizal fungi (AMF) and N-fixing rhizobia (NFR) was assessed under manure (M) and urea (U) fertilization. The aim was to determine whether autochthonous root symbiont populations enhance pasture productivity and nutritional status, mainly under organic fertilization. A nine-month pot experiment was conducted growing fescue–lotus mixtures under two soil conditions: A-soil, with autochthonous root symbiont populations; and R-soil, in which root symbiont populations (AMF and NFR) were reduced via formaldehyde application + UV treatment. Both soil conditions received either no fertilizer (Control) or equal N doses (120 kg N ha− 1 y− 1) supplied as cattle dry manure or urea. Fertilization with M resulted in root symbionts activity/abundance similar to the Control. Fertilization with U reduced root mycorrhizal colonization and nodulation. Plant growth was significantly higher in A-soil than in R-soil, with the legume component showing positive response. Under R-soil conditions, U fertilization resulted in the highest pasture growth, favoring grasses at the expense of legumes. Overall, M appears to be a more suitable fertilizer than U, as it better preserves root symbionts and may also contribute to increased productivity in the mixture. These findings suggest that M may be less disruptive to the studied root symbionts (AMF and NFR) than U under these conditions. These findings could have implications for the development of management strategies designed to preserve potentially beneficial root symbionts in pasture-based livestock systems. Root symbionts enhance the forage yield and nutritional status of a fescue–lotus mixture. Greater benefits were reached in the legume-root symbionts relationship. Dry manure fertilization did not negatively affect AMF or NFR activity/abundance. Urea fertilization negatively affected root mycorrhization and nodulation. The sources of fertilization affected the fescue–lotus mixture components differently but not total yield.

This study examines the effects of organic amendments (OA) on arbuscular mycorrhizal fungi (AMF), wheat productivity, and soil properties. A field experiment (4 replicates) tested application rates (100 and 200 kg N ha-1) of OA: chicken litter (CL), liquid pig manure (LPM), and digestate (DIG); synthetic fertilizer (urea: U) and a non-fertilized Control. Fertilization (except LPM) reduced AMF root colonization at tillering but had no later-stage effects. OA fertilization increased soil inorganic nitrogen concentration and microbial respiration at sowing, without affecting total organic carbon. LPM application was positively associated to soil pH, extractable phosphorus, electrical conductivity, and microbial respiration, suggesting enhanced nutrient availability and biological activity in the soil after its application, mainly at sowing. AMF multiplied-spore abundance was similar across treatments, although Control soils had three times more spores than fertilized ones. AMF diversity (Glomeraceae), assessed via SSCP gel electrophoresis, was unaffected by fertilization but was slightly higher in OA-treated soils (excluding CL). Wheat productivity under OA were similar than Urea fertilized plants, but higher than the Control. Our findings suggest that OAs, can sustainably enhance soil fertility and crop yield without harming beneficial fungal communities (focused on AMF), supporting their use as alternatives to conventional fertilization of wheat.

Soil health has deteriorated due to monoculture predominance and lack of crop rotations, impacting on soil organic carbon dynamics and beneficial microbial communities. This study analyzes data collected over a 12-year period within a long-term field experiment (> 16 years) to explore how different cropping systems- Monocrop (soybean, Glycine max L. Merr), Cover crop (oat, Avena sativa L./soybean), and Rotation (oat/soybean-corn, Zea mays L.-wheat, Triticum aestivum L.)-, influence soil organic carbon fractions, arbuscular mycorrhizal fungi related protein (glomalin-related soil protein), and soil respiration (flush of CO2). We assessed the upper soil layer (0–5 cm) at three points in time, evaluating total, particulate, and associated organic carbon, glomalin-related soil protein, and flush of CO2. Across the assessed period, the intensified cropping systems (Cover crop and Rotation) significantly enhanced total organic carbon and microbial activity (glomalin-related soil protein and flush of CO2) compared to Monocrop systems. Particulate organic carbon showed to be responsive to environmental stressors while associated organic carbon increased progressively, suggesting a potential improvement in soil stability. Although glomalin-related soil protein levels showed a decreasing trend, it was positively correlated with total organic carbon and flush of CO2. Our finding emphasizes that sustainable crop management enhances soil carbon storage and microbial function, which are the key for addressing climate challenges.

Agriculture in the Argentine Puna faces significant challenges due to adverse climatic conditions and poor sandy soils prone to erosion and nutrient loss, particularly nitrogen (N), which is essential for plant growth. Despite these challenges, there is limited information on the role of beneficial soil microorganisms in nutrient cycling and uptake in this extreme environment. This study aimed to investigate the impact of agricultural practices on Ncycling microorganisms and arbuscular mycorrhizal fungi (AMF) interactions in Abra Pampa soils, located 3487 m above sea level. We conducted three annual samplings during the summers of 2020, 2021, and 2022 across four treatments: two agricultural plots (A1 and A2) amended with llama manure, each under different crop rotations - A1: Andean potato-quinoa-mallow and A2: quinoa-triticale-mallow; one soil under decomposing llama manure (BG) adjacent to agricultural plots; and a pristine control soil covered with native vegetation. We quantified the N-cycling genes (nifH, amoA from Archaea (AOA) and Bacteria (AOB), nirK, nirS and nosZ), and assessed AMF functional activity (percentage of colonization, arbuscule formation and number of spores in soil) and AMF diversity (Glomeraceae family) using PCR-SSCP analysis. Climate conditions were found to significantly influence the abundance of denitrification genes (nirK and nosZ) and AMF functional parameters, correlating with soil ammonia and nitrate concentrations. Variations in nifH abundance and the AOA/AOB ratio were associated with agricultural practices and soil parameters such as ammonia and available phosphorus content, respectively. Notably, associations between N-cycling bacteria and AMF functions suggest synergistic rather than antagonistic interactions between these groups. Agricultural activities were found to adversely affect AMF genetic diversity. The BG site emerged as a hotspot with a significant abundance of denitrification genes, warranting further investigation in future studies. This study provides valuable insights into the potential interactions among microorganisms involved in N cycling and AMF under various land use scenarios in the Argentine Puna, highlighting considerations for developing sustainable agricultural strategies in the region.

Arbuscular mycorrhizal fungi (AMF) and Trichoderma spp. (T) are known as plant-beneficial fungi effective against root-knot nematodes, but their interactions in the rhizosphere are not well understood. This study examined how Meloidogyne javanica influences AMF colonization and community diversity at the root-soil interface of tomato plants. A 60-day growth chamber experiment was conducted with tomato plants grown in non-sterile agricultural soil, either infected or not with M. javanica, that received a single inoculation with AMF or Trichoderma (strains T363 or TJ15), combined AMF + T inoculations, or no inoculation (Control). Both single and combined inoculations significantly reduced root galls, eggs, and soil nematode larvae. An AMF community analysis via single-strand conformation polymorphism of the D1 region of 28S rDNA gene (Glomeraceae family) revealed that M. javanica decreased AMF diversity and altered community structure, in plants single-inoculated with AMF. However, a combined inoculation with Trichoderma appears to prevent this reduction and maintain AMF diversity. While M. javanica reduced root mycorrhizal colonization, it did not affect Trichoderma abundance. These results suggest that Trichoderma may be more resilient to nematode infection, helping stabilize AMF communities and enhance biocontrol. Thus, combining AMF and Trichoderma inoculations could better preserve root health and improve biological control effectiveness against M. javanica.

Anaerobically mineralized nitrogen (AN) is a suitable soil health indicator. The AN is sensitive to soil use changes and is related to soil and particulate organic carbon and aggregate stability. This work aims to evaluate the relationship between AN and 1) easily extractable glomalin-related soil proteins; 2) abundance of arbuscular mycorrhizal fungi measured by the number of arbuscular mycorrhizal fungi spores, and 3) arbuscular mycorrhizal fungi activity (root colonization). Soil samples were taken at depths of 0-5 and 5-20 cm from cultivated and uncultivated plots throughout the southeastern province of Buenos Aires. Anaerobically mineralized nitrogen, soil organic carbon, particulate organic carbon, aggregate stability, easily extracted glomalin-related soil proteins and the logarithm of the number of arbuscular mycorrhizal fungi spores (log spores) at 0-5, 5-20 and 0-20 cm depths were determined. In wheat roots, the percentages of total infection and arbuscules at 0-20 cm were measured. At all depths, AN was positively correlated to easily extractable glomalin-related soil proteins (r=0.34-0.65), which is an indicator of arbuscular mycorrhizal fungi activity and abundance. Likewise, AN was positively related to log-spores (r=0.58-0.78), which is an indicator of arbuscular mycorrhizal fungi abundance. However, AN was not related to root colonization (the percentages of total infection and arbuscules) that manifests the activity of arbuscular mycorrhizal fungi at a specific moment. Thus, anaerobically mineralized nitrogen would be an indicator of mid- to long-term changes in arbuscular mycorrhizal fungi abundance and activity (easily extractable glomalin-related soil proteins and log-spores) resulting from soil use. Consequently, the AN would allow monitoring an important aspect of soil microbiological health associated with arbuscular mycorrhizal fungi. However, it is necessary to evaluate the relationships studied in this work in a wider range of soil situations.

Abstract Introduction Inoculation of plants with beneficial microorganisms may improve plant performance yet suffers from efficacy variability. A solution might be the combined application of different inoculants as consortium. The objective of the present study was to evaluate the effects of single or combined inoculation of Trichoderma harzianum, strain TGFG411, and a consortium of arbuscular mycorrhizal fungi (AMF) on plant growth, and native microbial communities (here bacteria/archaea, fungi and AMF) in root‐associated soil (RAS) and rhizosphere (RH), that is, soil loosely or tightly attached to the roots, respectively. Materials and Methods A greenhouse experiment was carried out with non‐sterile agricultural soil and the model crop maize, which was single inoculated with either TGFG411 or AMF or received a combined inoculation of TGFG411 + AMF. Control plants received only water. Seven weeks after the second AMF inoculation, the plant growth promotion capacity of the inoculants was measured based on shoot and root parameters. Furthermore, RAS and RH microbiota (fungi including AMF, bacteria and archaea) were assessed via a combination of different cultivation‐dependent, microscopic and DNA‐based methods. Results After 7 weeks of maize growth, both single and combined inoculation of AMF and TGFG411 enhanced shoot dry weight and led to a significant reduction in root biomass. The TGFG411 strain successfully established in the soil. However, no definite evidence for the establishment of the inoculated AMF was found. Single or combined inoculation of TGFG411 and AMF modified the composition of total bacterial in the RH, whereas modulated total fungal communities in the RAS. Conclusion The combined inoculation did not result in a significant improvement of plant performance compared with single inoculation likely due to optimal nutrient supply. However, samples receiving the combined inoculation exhibited a distinct modulation of the native RAS/RH microbiota, which may influence the inoculant efficacy under less favourable conditions.

Approaches to rapidly collecting global biodiversity data are increasingly important, but biodiversity blind spots persist. We organized a three-day Datathon event to improve the openness of local biodiversity data and facilitate data reuse by local researchers. The first Datathon, organized among microbial ecologists in Uruguay and Argentina assembled the largest microbiome dataset in the region to date and formed collaborative consortia for microbiome data synthesis.

Background: A rapid production of tree seedlings in nurseries with a high survival rate after transplanting is important to respond to the current demand for programs of restoration of arid environments by forestation. The low level of seedlings’ survival and establishment, caused by low moisture and nutrient content of soils, has been a bottleneck to reaching the target of the forest national restoration in Ethiopia of last years. It is suggested that, inoculation with root-associated plant growth promoting microorganisms could help to ameliorate this scenario and also respond to the Ethiopia's Green Legacy Program. Objective: To assess the potential of inoculation with arbuscular mycorrhizal fungi (AMF) native to Ethiopia to improve the survival and growth of trees that could be used in afforestation programs in Ethiopia. Methodology: The study was carried out in three stages: (1) soil samples associated with roots of selected acacia species (T1-AMF of A. abyssinica, T2-AMF of A. seyal, T3-AMF of A. tortilis and T4-Control) were collected of highland and lowland areas from Ethiopia, (2) Sorghum (Sorghum bicolor (L.), provided by the Melkasa Agricultural Research Center-(MARC) served as a trap plant for the AMF consortium multiplication and (3) plant growth promotion by AMF was assessed throughout inoculations of seedlings of Delonix regia (Hook.) Raf., Sesbania grandiflora (L.), Cassia fistula L., and Azadirachta indica A. Juss., trees. Results: All inoculated seedlings showed significantly greater responses in all growth and mycorrhizal parameters over the non-inoculated trees. Consortium T2-AMF associated to roots of A. seyal from lowlands of Batu, showed significantly greater responses in all plant growth and mycorrhizal parameters over the AMF inoculums associated to other tree species evaluated. Significant and positive correlations were found between mycorrhizae and plant-growth parameters. Implications: Our results suggest that inoculation with native arbuscular mycorrhizal fungi indigenous from Ethiopia has the potential to significantly enhance survival and growth rates of tree seedlings. This could thereby advance national reforestation goals and addressing challenges in seedling establishment in arid environments. Conclusion: The potential for growth promotion and establishment of tree seedlings evidenced, implies that further efforts should be directed towards the in-mass production of AMF-based inoculants, particularly associated with A. seyal roots.

Low crop diversification in highly productive areas has led to declines in total organic carbon (TOC) in soil, essential nutrients for plant’s growth and microbial diversity/activity. This could have an impact on the movement of water in the soil profile and, consequently, on the production of crops. To address these challenges there is growing support for crops intensification, which involves increasing the number/variety of crops throughout the year. The purpose of this study was to assess the influence of crop intensification on the initial infiltration of water in the upper layer of the soil profile and the activity/abundance of soil microorganisms involved in the turnover of TOC and phosphorus (P). Three crop regimes were assessed in a long-term experiment established in the southeast of the Argentinean Pampas: without intensification (Monocrop: soybean), intensified (Cover crop: CC [oat]/soybean) and Rotation (CC [oat]/soybean-corn-wheat). Soil in the Monocrop regime exhibited the highest sorptivity values and a lower TOC, suggesting a higher initial rate of water entry into the profile, which could break down soil aggregates. Under rotation, the highest infiltration rate was recorded, which would guarantee more water flow into the profile. Intensified soils showed the highest total glomalin content and root colonization with arbuscular mycorrhizal fungi (AMF), which are known to contribute to plant nutrient uptake and growth and soil aggregate stability. Trichoderma abundance and their P-solubilizing capacity were also higher under Rotation, which could favor AMF activity. Correlation analysis revealed a significant positive correlation between sorptivity and glomalin under Rotation. Our study suggests that soils from the Argentinean south-eastern Humid Pampas under crop intensification promote soil water storage and maintenance of soil structure in the upper layers compared to Monocrop, which could be attributed —at least in part— to a greater microbiological activity and TOC content.

Drought stress (DS) is one of the main environmental stresses that determines crop productivity. It has been estimated that DS depresses over 40%-60% of soybean (Glycine max (L.) Merr.) and common bean (Phaseolus vulgaris L.) production worldwide, respectively. Although different agronomic strategies are sometimes implemented, the current goal in sustainable agriculture could involve the inoculation with native microorganisms to mitigate DS effects. A potential fungal candidate is Trichoderma, which is recognized as a ubiquitous soil inhabitant with growth-promoting and biocontrol potentiality. However, its potential for mitigating the stress for water deficit is less well-documented. Our objective was to evaluate the effect of inoculation with native Trichoderma harzianum strains on soybean and common bean growth under contrasting conditions of water availability. Seeds were independently inoculated (or not) with IB-J15 and IB-363 strains, and plants were submitted to DS or were kept under optimal irrigation (well-watered, WW). In both legumes, the most evident effect after being inoculated was the modification of plant root architecture, the increase in root area and the development of lateral roots in plants under WW and DS conditions. In soybean, both Trichoderma strains had a positive inoculation response, both fresh and dry root biomass increased under WW, and remarkably under DS conditions. The main effect was an increase of about 110% in root dry weight under WW and, about 330% in DS in plants inoculated with IB-J15 strain, meanwhile, plants inoculated with IB-363 increased root dry weight 60% in WW and 177% in DS conditions. Notably in soybean, the inoculation with both Trichoderma strains increased the root area more than 70% in both WW and DS conditions. Common beans inoculated with IB-363 under WW conditions, reached a positive inoculation responsiveness of around 247% in shoot dry weight biomass, and under WW both strains increased the root area more than 50%. Further, IB-363 increased leaf area by 25% in WW and 72% in DS. Additionally, the in vitro co-culture between both Trichoderma strains and nodulating Rhizobium etli and Bradyrhizobium japonicum E109 showed compatibility between microorganisms, since no inhibition of their growth was observed. We emphasize that plants inoculated with Trichoderma showed better resistance to water deficit, as seen by redistribution of photosynthates, prioritizing mainly, the development of the root system. (c) 2024 Association of Applied Biologists.

Arbuscular mycorrhizal fungi (AMF) and some rhizobacteria are known as plant growth-promoting microorganism (PGPM) as they play significant roles in improving soil fertility structure, plant nutrition, growth, and health. However, little is known about the PGPM potential of AMF and rhizobacteria native to the Rift Valley and highland regions of Ethiopia. Hence, this study aimed to investigate the PGPM effect of single and co-inoculation of AMF and the Bacillus subtilis ALCR46 strain, on tomato (Lycopersicum esculentum L.), onion (Allium cepa L.), and squash (Cucurbita pepo L.) plants. The experimental setup was a randomized complete block design with three replications of the following treatments: (i) inoculation with a consortium of AMF, (ii) co-inoculation with a consortium of AMF and the Bacillus subtilis, (iii) inoculation with Rhizophagus clarus, (iv) co-inoculation with R. clarus and B. subtilis, (v) inoculation with B. subtilis, (vi) plants without inoculation (negative control), and (vii) plants treated with chemical fertilizer (positive control). Plants were maintained in a greenhouse for 60 days, and after harvest, plant growth parameters, percentage of AMF root colonization, and spore number were analyzed. The result shows that the growth of crops significantly increased by co-inoculation with the consortium of AMF and B. subtilis. AMF spore density and root colonization rate were also increased in co-inoculated plants. Highest root colonization, spore number, and mycorrhizal dependency were observed in A. cepa. Our results suggest that there is a synergistic effect between the AMF and B. subtilis ALCR46, and between AMF inoculants. However, the application of present findings under field conditions is required to be confirmed by further studies.

The aim of this study was to find ways to improve the forage yield of grass-legume mixtures without compromising soil biodiversity. In Argentinean Patagonia, the effects of applying cattle dry manure (M) and urea (U) (0, 60, 120, or 240 kg N ha-1 year-1) were assessed on herbage production of irrigated fescue-lotus mixtures, as well as on the activity/abundance of autochthonous arbuscular mycorrhizal fungi and N-fixing rhizobium bacteria. We hypothesised that manure has advantages over urea in increasing forage yields while maintaining the proportion of legumes and root-associated microbiota. The 120 U, 240 U, and 240 M resulted in the greatest forage production; however, yield varied depending on the source applied. The high productivity of the 120 U and 240 U was probably due to the fast grass growth immediately after fertilization, which resulted in a depressed growth of the legume. The high yield of the swards fertilized with 240 M was probably due to slight and delayed growth of grass without legume yield decline. The highest radiation interception was found in swards with a low legume proportion, suggesting a light competition from grass fertilized with the highest urea doses, which were also consistent with the highest N and P nutritional status. The microbial activity/abundance were not affected by fertilization, but the final number of nodules was positively associated with the legume proportion. In conclusion, manure fertilization increased forage yield of the mixtures, while preserving the legume proportion and the root-associated microbiota. Our findings aid in reducing synthetic-N fertilizers applied in pasture-based livestock systems.

ABSTRACT This work aimed to evaluate the capacity of anaerobically mineralized nitrogen (AN) within large (ANLM), small (ANSM), and total macroaggregates (ANTM) to predict grain yield, aboveground biomass, and total nitrogen (N) content of wheat (Triticum aestivum L.) plants as compared to AN in bulk soil (ANBS). Eight fields with non-N-fertilized wheat on Mollisols of the southeastern Argentinean Pampas were studied. Soil ANBS, ANLM, ANSM, and ANTM, and wheat grain yield, aboveground biomass, and plant total N content were determined. The ANLM, ANSM, and ANTM were positively related to grain yield, aboveground biomass, and plant total N content (R2=0.34-0.65). The relationships between ANBS and all those crop variables showed similar predictive capacity. Therefore, AN within macroaggregates was not a better indicator of soil nitrogen supply capacity than ANBS.

The evolutionary history of the symbiotic association between arbuscular mycorrhizal fungi (AMF) and embryophytes dates back to the Devonian period. Previous ecological and physiological studies have described the presence of arbuscules, inter- and intracellular hyphae, vesicles, coils and spores, in liverworts and hornworts, which are considered absent in mosses. This study aimed to report the presence of AMF in a community of bryophytes (mosses and liverworts) from Punta Lara Natural Reserve, Argentina. Senescent and green sections of gametophytes were stained and, following microscopic observation, revealed AMF structures. We found intracellular hyphae, vesicles, spores and sporocarps associated with thallus and rhizoids of mosses and liverworts and senescent moss caulidia. The morphological characterization of spores resulted in the determination of Rhizophagus intraradices and Dominikia aurea. The species D. aurea is reported for the first time for Argentina. Sequencing of the D1 variable domain of the LSUrDNA from AMF spores mixes plus hyphae resulted in high similitude to the Dominikia sequences available from NCBI. This study reported the presence of AMF associated with declining and senescent gametophytes of bryophytes (mosses and liverworts) in a Natural Reserve in Argentina. These findings open up new lines of study, which should further investigate these associations and their diversity, physiology and significance.

This study aimed to evaluate the root colonization and diversity of arbuscular mycorrhizal fungi (AMF) associated with Lotus tenuis grown in natural and L. tenuis-promoted grasslands (by herbicide application, which consists in removing above-ground biomass to favor the establishment and growth of L. tenuis) in the Salado River Basin (Argentina). Soils ranged from saline and/or sodic to neutral and non-saline. AMF colonization was slightly higher in natural grasslands than in L. tenuis-promoted sites (93% and 86%, respectively). A total of 22 AMF species were identified in root-associated soil. The Glomeraceae was the only family present in all sites, and Funneliformis mosseae was the only species found in all the sites studied, regardless of the soil properties and management. Claroideoglomus etunicatum and Septoglomus constrictum were present in all sites except in one of the L. tenuis-promoted sites studied. The PCR-Single-Strand Conformation Polymorphism analysis showed that amplicons of AMF-Glomeraceae did not cluster in a site-specific or management-specific way. The sequences obtained were highly similar to sequences of Glomeraceae detected by morphological spore taxonomy. L. tenuis promotion by herbicide application did not negatively affect AMF colonization or diversity. L. tenuis contributed to maintaining AMF diversity through high root colonization, regardless of soil properties or management. This should be considered for the maintenance of L. tenuis and AMF-associated communities.

The glomalin-related soil proteins (GRSPs) are currently used to describe different fractions of the protein, which are linked to the arbuscular mycorrhizal fungal activity and include the easily or total GRSP (named EE or T, respectively) extracted. The GRSP would represent part of the carbon storage, but there are still disagreements whether the GRSP is a reliable indicator of changes in agricultural practices. We aimed (i) to determine the sensitivity of GRSP as an indicator of soil changes in different cropping systems, (ii) to evaluate the accuracy of relationships between GRSP and soil organic carbon (SOC) and (iii) to improve the T-GRSP standard procedure. Three long-term field trials were studied in the Argentine Pampas during winter and autumn over two growing seasons of soybean under three cropping regimes: soybean monoculture (Sb) and agricultural intensification that included cover crop (CC) before soybean (CC/Sb) or CC/soybean-corn-double cropping with wheat and soybean, called crop rotation (CR). Significant SOC increases were found only in the intensified plots with a low initial SOC. The optimization of T-GRSP procedure that included the sum of GRSP content across all generated extracts, and having stopped the extraction procedure when the value of absorbance reached 0.04–0.09, rather than processing samples based on their color, allowed us to achieved more accurate results; also, lower volume of the centrifuge tubes used reduced the processing time. The GRSP positively correlated to SOC and, in general, highest EE-GRSP and T-GRSP concentrations were recorded (mainly in winter-fallow) under agricultural intensification. This should be considered before planning agricultural production decisions in order to maintain soil sustainability.

Climate change, the shortage of fertilizers and reduced land for cultivation have drawn attention to the potential aid provided by soil-borne organisms. Arbuscular mycorrhizal fungi (AMF) offer a wide range of ecosystem benefits and hence, understanding the mechanisms that control AMF occurrence and maintenance is essential for resilient crop production. We conducted a survey of 123 soybean fields located across a 75,000-km 2 area of Argentina to explore AMF community composition and to quantify the impact of soil, climate, and geographical distance on these key soil organisms. First, based upon morphological identification of spores, we compiled a list of the AMF species found in the studied area and identified Acaulospora scrobiculata and Glomus fuegianum as the most frequent species. G. fuegianum abundance was negatively correlated with precipitation seasonality and positively correlated with mean annual precipitation as well as mycorrhizal colonisation of soybean roots. Second, we observed that species richness was negatively correlated with soil P availability (Bray I), clay content and mean annual precipitation. Finally, based on partitioning variation analysis, we found that AMF exhibited spatial patterning at a broad scale. Therefore, we infer that geographical distance was positively associated with spore community composition heterogeneity across the region. Nevertheless, we highlight the importance of precipitation sensitivity of frequent species, overall AMF richness and community composition, revealing a crucial challenge to forthcoming agriculture considering an expected change in global climate patterns.

La expansión del cultivo de soja en la Argentina reemplazó a otros cultivos, a la ganadería extensiva y a ecosistemas forestales. Se desconoce el impacto sobre poblaciones microbianas nativas edáficas que podrían brindar servicios ecosistémicos, como los hongos micorrícicos arbusculares (HMA). Los HMA son simbiontes de las raíces de la mayoría de las plantas superiores y son reconocidos por favorecer la nutrición y el crecimiento del hospedador, y la sustentabilidad edáfica. La magnitud del aporte por los HMA depende, en parte, de su abundancia en el suelo y de su potencial para formar micorrizas con las raíces. Nuestro objetivo fue analizar variaciones en la infectividad micorrícica (IMS50) del suelo y en la colonización micorrícica arbuscular (MA) espontánea en raíces de cultivos de soja implantados en tres sitios agrícolas del norte de la Región Pampeana (Córdoba), en relación con el historial de uso de suelo (Agrícola [soja por más de 60 años], Mixto agrícolaganadero [A-G, soja en los últimos 35 años], y Sierras [soja en los últimos 20 años]). Un bioensayo in vivo permitió determinar que las mayores IMS50 ocurrieron en el sitio Agrícola y en el de Sierras, en relación con el Mixto A-G, cuyo contenido de P disponible en el suelo es mayor. Tanto la IMS50 como la micorrización correlacionaron negativamente con el P del suelo; la IMS50 se asoció negativamente con el contenido de arena y positivamente con el de agua, carbono y arcilla. Se detectó un alto grado de potencialidad infectiva por HMA nativos en suelos destinados al cultivo de soja con diferente historial de uso. El IMS50 fue un método de detección más sensible que la determinación de la colonización MA a campo. Se concluye que la IMS50 podría utilizarse para definir estrategias de manejo agrícola tendientes a mantener/favorecer las comunidades de HMA nativos.