ALTA PRESENCIA DE CADMIO RESULTA EN BAJA DIVERSIDAD DE HONGOS FORMADORES DE MICORRIZAS ARBUSCULARES ASOCIADOS A CACAO (Theobroma cacao L.) / High cadmium concentration resulted in low arbuscular mycorrhizal fungi community diversity associated to cocoa (Theobroma cacao L.)

RESUMEN Los hongos formadores de micorrizas arbusculares (HFMA) son simbiontes obligados presentes en la rizósfera de plantas de cacao y la diversidad de sus comunidades se modifica, dependiendo de diversos factores como la presencia de cadmio (Cd) en el suelo. La persistencia de HFMA en suelos enriquecidos naturalmente con Cd podría ser un indicador de su capacidad para tolerar esta condición. Esta investigación caracterizó la estructura de la comunidad de HFMA locales presentes en la rizósfera de plantas de cacao en dos suelos con baja (B-Cd: 0,1 mg kg-1) y alta (A-Cd: 20,9 mg kg-1) concentración de Cd. Esporas de HFMA se identificaron mediante claves taxonómicas y su abundancia, riqueza y diversidad se determinó en muestras de suelo originales y después de su multiplicación mediante cultivos trampa. Las comunidades de HFMA se compararon usando análisis de componentes principales (ACP) e índices de diversidad alfa y beta. Los resultados indican que A-Cd presentó valores significativamente menores de abundancia (21 %), riqueza (20 %) y diversidad (11 %) de morfoespecies de HFMA con respecto a B-Cd. Las dos comunidades de HFMA presentaron cinco de siete géneros en común, pero solo cuatro de las 23 morfoespecies descritas se encontraron en ambas comunidades. El análisis de diversidad beta y el ACP determinaron baja similaridad y tasa de recambio entre las comunidades de HFMA. La dominancia de Diversispora spurca, Rhizoglomus sp. y Claroideoglomus etunicatum en A-Cd sugiere que estas morfoespecies son estrés-tolerantes y candidatos potenciales para el desarrollo de estrategias de mitigación en suelos con Cd.

ABSTRACT Arbuscular mycorrhizae fungi (AMF) are obligate symbionts present in rhizosphere of cocoa plants and their community diversity is modified depending on several factors, such as cadmium (Cd) presence in soil. AMF persistence on Cd natural enriched soils might be an indicator of their tolerance and their potential in biotechnological applications. In this research we characterized local AMF community structure present in cocoa rhizosphere soils with low (B-Cd: 0.1 mg kg-1) and high (A-Cd: 20.9 mg kg-1) natural Cd concentrations. AMF spore identification was carried out using taxonomic keys and their abundance, richness and diversity were determined in original samples and after multiplication process using onion trap cultures. AMF communities were compared using alpha and beta diversity indexes and principal component analysis (PCA). The results indicated that A-Cd presented significative lower values of abundance (21 %), richness (20 %) and diversity (11 %) of AMF morphospecies in comparison with B-Cd. Both AMF communities presented five of seven genera in common, but only four of 23 morphospecies described were found in two communities. Low similarity and turnover were found among AMF communities throughout beta diversity analysis and PCA. Dominance of Diversispora spurca, Rhizoglomus sp. and Claroideoglomus etunicatum in A-Cd suggests that these morphospecies are stress-tolerant and they are potential candidates for the development of mitigation strategies in cocoa plants under Cd stress.

Micosociología: antecedentes históricos, evolución y proyecciones / Mycosociology: Historical background, evolution and projections

A lo largo de la historia numerosos investigadores han intentado estudiar la sociología de los hongos, también llamada micosociología que se refiere al estudio y la clasificación de las comunidades fúngicas, sus interrelaciones y su dependencia del medio. La mayoría de estos estudios han sido realizados en Europa, donde destacan los trabajos realizados por Darimont (1973) y García Bona (1977). Son pocos los estudios de carácter micosociológico que describen la interacción de ciertos macromicetos con especies de Nothofagus de América del Sur, destacando los de Godeas et al. (1993 a, b, c) en bosques de Nothofagus de Tierra del Fuego y el de Valenzuela et al. (1998). En esta revisión, se exponen los comienzos históricos de la micosociología, su evolución a lo largo de los años y cómo su enfoque ayuda a comprender el funcionamiento de las comunidades fúngicas. También, se destaca la importancia que tiene para nuestro país realizar estudios micosociológicos, especialmente, en bosques nativos dominados por Nothofagus.

Over time many researchers have tried to study the sociology of fungi, or mycosociology, meaning the study and classification of fungal communities, their inter-relations and their dependence on the medium. The majority of these studies have been carried out in Europe, notably the works of Darimont (1973) and García Bona (1977). There are few mycosociological studies which describe the interaction of certain macromycetes with South American Nothofagus species. Important studies are Godeas et al. (1993 a, b, c), in Nothofagus forests in Tierra del Fuego, and Valenzuela et al. (1998). This review examine the historical beginnings of mycosociology, its evolution over time and how its focus helps to understand the functioning of fungal communities. The autor also stress the importance for Chile of carrying out mycosociological studies, especially in native forests dominated by Nothofagus.

Characterization saprobic fungi on leaf litter of two species of trees in the Atlantic Forest, Brazil

Abstract We investigated the composition and structure of fungal communities associated with leaf litter generated by Clusia nemorosa and Vismia guianensis that belong to phylogenetically-related botanical families and exist together in a remnant of the Atlantic Forest in Bahia, Brazil. Samplings were conducted during wet (June 2011) and dry (January 2013) seasons in Serra da Jibóia. The fungi were isolated using particle filtration and the 1,832 isolates represented 92 taxa. The wet season yielded the largest number of isolates (1,141) and taxa (76) compared with the dry season (641 isolates and 37 taxa). The richness and diversity of fungal species associated with C. nemorosa (64 taxa, Simpson=0.95)were higher compared with those of V.guianensis (59 taxa, Simpson =0.90). Analysis of similarity (ANOSIM) revealed significant variations in the composition and community structure of fungi isolated from the two plants as a function of seasons. In contrast, nonmetric multidimensional scaling (NMDS) analysis show that the seasonality was an important influence on the distribution of fungal species. However, the populations of the saprobic fungal communities were dynamic, and several factors may influence such communities in the Atlantic Forest.

Effects of open drainage ditch design on bacterial and fungal communities of cold waterlogged paddy soils

A field experiment established in 1980 was conducted to evaluate the effects of open drainage ditch applied for water removal on bacterial and fungal communities of cold waterlogged paddy soils in 2011. In this experiment, traditional plate counting and temperature gradient gel electrophoresis were employed to characterize the abundance and diversity of soil bacterial and fungal communities. Four different distances from the open drainage ditch, 5, 15, 25 and 75 m with different degrees of drainage were designed for this study. Maximum populations of culturable aerobic bacteria and fungi were at 15-m distance while minimum populations were at 75-m distance. Significant differences (p < 0.05) in fungal populations were observed at all distances from open drainage ditch. The highest diversity of the bacterial community was found at a distance of 25 m, while that of the fungal community was observed at a distance of 5 m. Sequencing of excised TGGE bands indicated that the dominant bacteria at 75-m distance belonged to anaerobic or microaerobic bacteria. Relationships between microbial characteristics and soil physicochemical properties indicated that soil pH and available nitrogen contents were key factors controlling the abundance of culturable aerobic bacteria and fungi, while soil water capacity also affected the diversity of fungal community. These findings can provide the references for better design and advanced management of the drainage ditches in cold waterlogged paddy soils.