[Fungal biomass estimation in soils from southwestern Buenos Aires province (Argentina) using calcofluor white stain]. / Estimación de la biomasa fúngica en un suelo del sudoeste de la provincia de Buenos Aires (Argentina) con una tinción directa con blanco de calcoflúor.

Soil microorganisms are vital for ecosystem functioning because of the role they play in soil nutrient cycling. Agricultural practices and the intensification of land use have a negative effect on microbial activities and fungal biomass has been widely used as an indicator of soil health. The aim of this study was to analyze fungal biomass in soils from southwestern Buenos Aires province using direct fluorescent staining and to contribute to its use as an indicator of environmental changes in the ecosystem as well as to define its sensitivity to weather conditions. Soil samples were collected during two consecutive years. Soil smears were prepared and stained with two different concentrations of calcofluor, and the fungal biomass was estimated under an epifluorescence microscope. Soil fungal biomass varied between 2.23 and 26.89µg fungal C/g soil, being these values in the range expected for the studied soil type. The fungal biomass was positively related to temperature and precipitations. The methodology used was reliable, standardized and sensitive to weather conditions. The results of this study contribute information to evaluate fungal biomass in different soil types and support its use as an indicator of soil health for analyzing the impact of different agricultural practices.

Estimación de la biomasa fúngica en un suelo del sudoeste de la provincia de Buenos Aires (Argentina) con una tinción directa con blanco de calcoflúor / Fungal biomass estimation in soils from southwestern Buenos Aires province (Argentina) using calcofluor white stain

Los microorganismos del suelo son vitales para el correcto funcionamiento de los ecosistemas, principalmente por su papel en el ciclado de nutrientes. La intensificación del uso del suelo y las prácticas agrícolas alteran negativamente la actividad microbiana. La biomasa fúngica es uno de los parámetros más utilizados para estudiar el impacto de las actividades agrícolas en la estructura y el funcionamiento del suelo. El objetivo del presente trabajo fue estimar la biomasa fúngica en un suelo del sudoeste bonaerense con el fin de obtener valores de referencia que permitan usar este parámetro como un indicador de cambios en el ecosistema y, por otro lado, demostrar que la metodología empleada es sensible a las variaciones en las condiciones climáticas. Se colectaron muestras de suelos durante 2 años consecutivos. Se prepararon frotis de suelo y se tiñeron con soluciones de distintas concentraciones de blanco de calcoflúor y luego se estimó la biomasa fúngica observando los frotis con microscopio de epifluorescencia. Los valores de biomasa fúngica estimados variaron entre 2,23 y 26,89 μg Cfúngico/g de suelo y estuvieron dentro del rango esperable para el tipo de suelo estudiado. La biomasa fúngica mostró una relación positiva con la temperatura y las precipitaciones. La metodología empleada resultó ser confiable, repetible y sensible a cambios en las condiciones climáticas. Los resultados podrían usarse como valores de referencia para estudiar la biomasa fúngica de suelos bajo distintas condiciones y emplearse como indicadores del impacto de las distintas prácticas agrícolas sobre el ecosistema.

Soil microorganisms are vital for ecosystem functioning because of the role they play in soil nutrient cycling. Agricultural practices and the intensification of land use have a negative effect on microbial activities and fungal biomass has been widely used as an indicator of soil health. The aim of this study was to analyze fungal biomass in soils from southwestern Buenos Aires province using direct fluorescent staining and to contribute to its use as an indicator of environmental changes in the ecosystem as well as to define its sensitivity to weather conditions. Soil samples were collected during two consecutive years. Soil smears were prepared and stained with two different concentrations of calcofluor, and the fungal biomass was estimated under an epifluorescence microscope. Soil fungal biomass varied between 2.23 and 26.89 μg fungal C/g soil, being these values in the range expected for the studied soil type. The fungal biomass was positively related to temperature and precipitations. The methodology used was reliable, standardized and sensitive to weather conditions. The results of this study contribute information to evaluate fungal biomass in different soil types and support its use as an indicator of soil health for analyzing the impact of different agricultural practices.

The phylogenetic position of poroid Hymenochaetaceae (Hymenochaetales, Basidiomycota) from Patagonia, Argentina.

Six poroid Hymenochaetaceae from Patagonia, Argentina, were studied phylogenetically with nuc rDNA internal transcribed spacer (ITS) and partial 28S rDNA sequences, together with morphological data. Two new genera and a new species are introduced as well as two new combinations proposed. Arambarria destruens gen. et sp. nov. is proposed for a taxon fruiting on fallen or standing, dead Diostea juncea and Lomatia hirsuta and previously recorded erroneously as Inocutis jamaicensis; it is distinguished by annual, effused to effused-reflexed basidiomes forming pilei, a monomitic hyphal system, thick-walled and yellowish basidiospores (brownish chestnut in potassium hydroxide solution), lack of a granular core in the context and lack of setoid elements. Nothophellinus gen. nov. is proposed to accommodate Phellinus andinopatagonicus, the main white wood-rotting polypore of standing Nothofagus pumilio and also an important wood-decayer of other Nothofagus species from southern Argentina and Chile. It is morphologically similar to Phellopilus (type species P. nigrolimitatus) but differs by lacking setae. The new combinations Pseudoinonotus crustosus and Phellinopsis andina are proposed for Inonotus crustosus and Phellinus andinus, respectively. Phellinus livescens, which decays the sapwood of several standing Nothofagus species, is closely related to Phellinus uncisetus, a Neotropical species related to Fomitiporia; for the time being P. livescens is retained in Phellinus sensu lato. An unidentified taxon responsible for a white heart-rot in living Austrocedrus chilensis grouped with Phellinus caryophyllii and Fulvifomes inermis, but its generic affinities remain ambiguous. Transmission electron microscopy studies confirm this unidentified taxon has an imperforate parenthesome, which is typical of the Hymenochaetaceae.