Soil algae composition under different agro-ecosytems in North-Eastern Italy

Soil algae can perform important services for agro-ecosystems and functions as a bioindicator for soil quality. Communities of topsoil algae were studied (species composition and counts) in four different agro-ecosystems in relation to different land uses, including tillage. The chosen agro-ecosystems were an intensively-cultivated corn (Zea mays L.) field, a vineyard, a pasture and a field abandoned for 12 years. In all, 92 algal species were identified in the different ecosystems, which were sampled twice (March and May). In 2001 the main algal species were Cyanophyceae, Chlamydophyceae, and Chlorophyceae. The greatest species richness of algal species was recorded in the pasture, followed by the abandoned field, the corn field and the vineyard. Using a dilution method on solid media to count the algae enabled the distinction and separate quantification of cyanophytes, diatoms and greenish algae (cholorophytes (CH) + xanthophytes (X) + eustigmatophytes (E)). This last group of greenish algae dominated at all four sites, together with cyanophytes in the pasture and the abandoned field, whereas cyanophytes were almost absent in the vineyard. The highest mean abundance of algal cells in the 0-2 cm soil layer was found in the abandoned field and in the pasture, while it was lower in the corn field and in the vineyard. The undisturbed sites (abandoned field and, to some extent, pasture) were also characterised by a greater diversity of algae. Disturbance (tillage and use of pesticides) seemed to have a strong effect on both the composition and the density of the algal communities. Cyanophytes (Calothrix sp., Cylindrospermum sp., Pseudoanabaena sp., Scytonema sp. and Thricormus sp.) seemed to be particularly sensitive to disturbance. Heavy metals residues in the soil, especially Cu (linked to fungicide sprays, used particularly in vineyards), may be a factor affecting the abundance of cyanobacteria. It would be reasonable to conclude that the structure of soil algal communities is affected more by soil use rather than by physico-chemical soil parameters. Cyanobacteria showed the most evident response in the different agro-ecosystems, and therefore seem to be the most suitable group to consider as a soil bioindicator of land use.