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We ascertained the relationship between the zonal pattern and the pasture vegetation of a volcanic soil polluted with dust from a cement factory after 70 years of operation, with parameters linked to soil microbial activity (soil basal respiration and hydrolases) and physicalchemical properties. Six sampling zones were established at distances of 1, 2, 3, 4, 5 and 6 km away from the cement plant, considering the latter one as the zone where the pastures were unaffected by the cement dust. Plant cover was negatively affected by cement dust, showing a sharp decline with decreasing distance to the cement factory. The values of pH and extractable K were two units and 2·3-fold higher, respectively, in the sampling zone nearest to the factory, in comparison with those in the unaffected zone. The levels of total Cr, Pb, Ni and Cd were normal and did not vary significantly with distance to the cement factory. Soil respiration and the protease, phosphomonoesterase and β-glucosidase activities declined significantly with decreasing distance to the cement factory. Urease activity was only decreased in the zone nearest to the factory, in comparison with that in the unaffected zone. The soil respiration and hydrolase activities were correlated positively with soil organic matter and plant cover and negatively with soil pH and extractable K concentration. The prolonged exposure to cement dust has resulted in shifts in the soil microbial function, which follows a spatial pattern related to soil alkalization and the decrease in pasture production.

Arbuscular mycorrhizal fungi (AMF) play important roles as plant protection agents, reducing or suppressing nematode colonization. However, it has never been investigated whether the galls produced in roots by nematode infection are colonized by AMF. This study tested whether galls produced by Meloidogyne incognita infection in Prunus persica roots are colonized by AMF. We also determined the changes in AMF composition and biodiversity mediated by infection with this root-knot nematode. DNA from galls and roots of plants infected by M. incognita and from roots of noninfected plants was extracted, amplified, cloned, and sequenced using AMF-specific primers. Phylogenetic analysis using the small-subunit (SSU) ribosomal DNA (rDNA) data set revealed 22 different AMF sequence types (17 Glomus sequence types, 3 Paraglomus sequence types, 1 Scutellospora sequence type, and 1 Acaulospora sequence type). The highest AMF diversity was found in uninfected roots, followed by infected roots and galls. This study indicates that the galls produced in P. persica roots due to infection with M. incognita were colonized extensively by a community of AMF, belonging to the families Paraglomeraceae and Glomeraceae, that was different from the community detected in roots. Although the function of the AMF in the galls is still unknown, we hypothesize that they act as protection agents against opportunistic pathogens.

Due to the important role of arbuscular mycorrhizal fungi (AMF) in ecosystem functioning, determination of the effect of management practices on the AMF diversity in agricultural soils is essential for the sustainability of these agro-ecosystems. The objective of this study was to compare the AMF diversity in Prunus persica roots under two types of fertilisation (inorganic, with or without manure) combined with integrated or chemical pest management in a Venezuelan agro-ecosystem. The AM fungal small-subunit (SSU) rRNA genes were subjected to PCR, cloning, sequencing and phylogenetic analyses. Twenty-one different phylotypes were identified: 15 belonged to the genus Glomus, one to Claroideoglomus, two to Paraglomus, one to Acaulospora, one to Scutellospora and one to Archaeospora. The distribution of the AMF community composition differed as a consequence of the treatment effects. The treatment combining organic and inorganic fertilisation with chemical pest control had the highest AMF richness and the treatment combining inorganic fertilisation with chemical pest had the lowest. The real causes and effects of these differences in the AMF community are very difficult to establish, since the crop management regimes tested were composed of several interacting factors. In conclusion, the crop management practices can exert a significant influence on the populations of AMF. The treatment combining organic and inorganic fertilisation with chemical pest control appears to be the most suitable agricultural management strategy with respect to improving the AMF diversity in this crop under tropical conditions, and thus for maintaining the agricultural and environmental sustainability of this agro-ecosystem.