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Aims:  To study phosphate solubilization in Penicillium purpurogenum as function of medium pH, and carbon and nitrogen concentrations. Methods and Results:  Tricalcium phosphate (CP) solubilization efficiency of P. purpurogenum was evaluated at acid or alkaline pH using different C and N sources. Glucose‐ and (NH4)2SO4‐based media showed the highest P solubilization values followed by fructose. P. purpurogenum solubilizing ability was higher in cultures grown at pH 6·5 than cultures at pH 8·5. Organic acids were detected in both alkaline and neutral media, but the relative percentages of each organic acid differed. Highest P release coincided with the highest organic acids production peak, especially gluconic acid. When P. purpurogenum grew in alkaline media, the nature and concentration of organic acids changed at different N and C concentrations. A factorial categorical experimental design showed that the highest P‐solubilizing activity, coinciding with the highest organic acid production, corresponded to the highest C concentration and lowest N concentration. Conclusions:  The results described in the present study show that medium pH and carbon and nitrogen concentrations modulate the P solubilization efficiency of P. purpurogenum through the production of organic acids and particularly that of gluconic acid. In the P solubilization optimization studies, glucose and (NH4)2SO4 as C and N sources allowed a higher solubilization efficiency at high pH. Significance and Impact of the Study:  This organism is a potentially proficient soil inoculant, especially in P‐poor alkaline soils where other P solubilizers fail to release soluble P. Further work is necessary to elucidate whether these results can be extrapolated to natural soil ecosystems, where different pH values are present. Penicillium purpurogenum could be used to develop a bioprocess for the manufacture of phosphatic fertilizer with phosphate calcium minerals.

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The influence of tillage and monoculture on arbuscular mycorrhizae (AM) fungal species diversity in a field site of the Buenos Aires province (Argentina) was investigated through the morphological characterization of AM spores. Glomalean spores were isolated by wet sieving and decanting from three plots cropped either to wheat, barley or clover and from a grassland at the margins of the cultivated plots. Seventeen different Glomalean species were detected overall and seven of them were identified. Total species number as well as spore and species richness found in grassland and clover soil were higher than those found in soils planted either with barley or wheat. The most frequently occurring species in the site were Glomus mosseae, Scutellospora pellucida, Glomus sp. 7 and Gigaspora sp. 1. The first three were also the most dominant species and were found in the four types of analysed soils. In grassland soil and wheat, the dominant species was Glomus sp. 6. S. pellucida was dominant in barley, and in red clover the dominant species were G. mosseae and S. pellucida. Tillage and cereal monoculture negatively affected diversity of AM fungal species. Natural re-colonization of indigenous AM fungi was observed in cultivated soil with red clover for 3 years, suggesting that this host could be used as a cover crop to increase AM fungal inocula in disturbed soils. Arbuscular mycorrhizal populations were associated with natural and cultivated vegetation on a site of Buenos Aires province, Argentina.