Resumen El bosque seco tropical concentra la mayor parte de la biodiversidad del mundo y, sin embargo, es uno de los ecosistemas más degradados en Colombia. Para su conservación es importante conocer la diversidad de microorganismos del suelo que lo integran, como los hongos micorrízicos arbusculares (HMA). En este estudio se evaluó el efecto del fuego y los depósitos fluviovolcánicos en la composición, abundancia y diversidad de los HMA en suelos de bosque seco tropical del departamento del Tolima, Colombia. El estudio se desarrolló en cuatro áreas: dos con vegetación nativa en la Reserva Natural Santafé de los Guaduales (RN) y en Armero (AN), otra afectada por el fuego de un incendio forestal (RQ) y la cuarta por depósitos fluviovolcánicos (ADV). La identificación de las morfoespecies de HMA se hizo mediante la extracción de esporas directamente del suelo (SD) y en cultivos trampa (CT) con el método de tamización en húmedo con posterior montaje en láminas y observación microscópica de la morfología de las esporas. Se identificaron 64 morfoespecies pertenecientes a cuatro órdenes, nueve familias y 17 géneros, de las cuales la familia Glomeraceae presentó el mayor número de morfoespecies indicadoras. En las cuatro áreas evaluadas se registraron diferencias significativas en la composición, abundancia y diversidad de las comunidades de HMA, siendo RQ el área con la mayor abundancia y diversidad, seguida de AN. Estos resultados representan un importante aporte al conocimiento de las comunidades de microorganismos del bosque seco tropical y su respuesta ante diferentes eventos antrópicos y naturales, y contribuye al inventario nacional de los HMA.

Abstract The tropical dry forest (TDF) concentrates most of the world's biodiversity nut currently it is one of the most degraded ecosystems in Colombia. For its conservation, it is important to understand the diversity of soil microorganisms that are part of it, such as the arbuscular mycorrhizal fungi (AMF). Here we evaluated the effect of fire and fluviolcanic deposits on the composition, abundance, and diversity of the AMF in tropical dry forest soils in the department of Tolima, Colombia. We selected four areas: two with native vegetation in Santafé de Los Guaduales Natural Reserve (RN) and Armero (AN), one affected by a forest fire (RQ), and another one by fluviolcanic deposits (ADV). We identified the AMF morphotypes by extracting spores directly from the soil (SD) and from trap cultures (TC) using the wet sieving method and subsequently mounting them on plates for the microscopic observation of their morphology. A total of 64 morphotypes were identified distributed in four orders, nine families, and 17 genera, the Glomeraceae family registering more indicator morphospecies. The four areas showed significant differences in their AMF communities' composition, abundance, and diversity; RQ was the area with the highest abundance and diversity followed by AN. Our results are an important contribution to the knowledge of TDF microorganism communities and their behavior in soils affected by different natural events. They also contribute to the national inventory of fungi with adaptive capacities.

Resumen La melina (Gmelina arborea Roxb) es una especie de amplia distribución mundial y de elevado valor comercial por su crecimiento rápido y las excelentes propiedades físicas y mecánicas de su madera; sin embargo, constantemente se ve amenazada por diversos factores físicos, químicos y biológicos, siendo los hongos y las bacterias los microorganismos que más pueden afectar su producción. El presente estudio tuvo como objetivo aislar e identificar hongos y bacterias asociados con fustes enfermos de G. arborea en plantaciones ubicadas en el departamento del Tolima (Colombia). La caracterización morfológica de las colonias fúngicas se realizó en el medio Papa-Dextrosa-Agar (PDA) con posterior identificación microscópica, después de inducir la producción de las estructuras reproductivas. El aislamiento de las bacterias se realizó en Agar Nutritivo (AN), con posterior caracterización bioquímica. La identificación molecular fue realizada mediante la amplificación de la región ITS para hongos y 16S para bacterias. Se identificaron los hongos Lasiodiplodia theobromae, Coniothyrium aleuritis, Curvularia geniculata, Chaetomium globosum, Phomopsis columnaris, Diaporthe sp y un aislamiento perteneciente a la clase Dothideomycetes. Las bacterias correspondieron a Bacillus cereus, Pseudomonas alcaligenes y Pantoea dispersa. Mediante pruebas de patogenicidad se determinó que los microorganismos causantes de la pudrición del tejido vascular en fustes jóvenes de melina fueron L. theobromae y C. geniculata.

Abstract Gmelina (Gmelina arborea Roxb) is a species of global distribution with a high commercial value due to its rapid growth and excellent physical, chemical, and biological features. Fungi and bacteria are the most important microorganisms that can affect its production. The present study aimed at isolating and identifying fungi and bacteria associated with G. arborea stem diseases in plantations located in the department of Tolima (Colombia). The morphological characterization of the fungal colonies was carried out in Potato Dextrose Agar medium (PDA) with subsequent microscopic identification after inducing the reproductive structures. Bacteria isolation was conducted in nutrient agar with subsequent biochemical characterization. The molecular identification was made by the amplification of the ITS region for fungi and the 16S for bacteria. We identified the fungi Lasiodiplodia theobromae, Coniothyrium aleuritis, Curvularia geniculata, Chaetomium globosum, Phomopsis columnaris, Diaporthe sp, as well as an isolate belonging to the Dothideomycetes class. The bacteria corresponded to Bacillus cereus, Pseudomonas alcaligenes, and Pantoea dispersa. The pathogenicity tests determined that L. theobromae and C. geniculate caused rot of vascular tissue in young candahar stems.

Abstract Spore counts, species composition and richness of arbuscular mycorrhizal fungi, and soil glomalin contents were evaluated in a soil contaminated with Zn, Cu, Cd and Pb after rehabilitation by partial replacement of the contaminated soil with non-contaminated soil, and by Eucalyptus camaldulensis planting with and without Brachiaria decumbens sowing. These rehabilitation procedures were compared with soils from contaminated non-rehabilitated area and non-contaminated adjacent soils. Arbuscular mycorrhizal fungi communities attributes were assessed by direct field sampling, trap culture technique, and by glomalin contents estimate. Arbuscular mycorrhizal fungi was markedly favored by rehabilitation, and a total of 15 arbuscular mycorrhizal fungi morphotypes were detected in the studied area. Species from the Glomus and Acaulospora genera were the most common mycorrhizal fungi. Number of spores was increased by as much as 300-fold, and species richness almost doubled in areas rehabilitated by planting Eucalyptus in rows and sowing B. decumbens in inter-rows. Contents of heavy metals in the soil were negatively correlated with both species richness and glomalin contents. Introduction of B. decumbens together with Eucalyptus causes enrichment of arbuscular mycorrhizal fungi species and a more balanced community of arbuscular mycorrhizal fungi spores in contaminated soil.