Effect of Natural Vegetation Strips and Herbicides on Enzyme Activities and Bacterial Diversity in Olive-Orchard Systems

The use of vegetation strips in mountainous olive-orchards is of major importance in reducing soil erosion and minimizing the adverse effects of the herbicides transfer to surface waters. This study was carried out to evaluate the effects of natural vegetation strips and herbicides on soil enzyme activities and changes in bacterial community structures. Thus, four enzyme activities were determined in soil samples from different zones in an integrated olive-orchard system on slopes. Changes in microbial population were analysed by using PCR assays to target 16S rDNA genes and denaturing gradient gel electrophoresis. Soil samples were collected at a depth of 0–5 cm from the experimental plot upslope and downslope: (1) under the vegetation strips before and after application of glyphosate, (2) from bare soil between the strips and under the olive trees treated with oxyfluorfen and glyphosate, (3) native soil from a non-cultivated area. Enzyme activities and bacterial diversity were lower in soils from the olive-orchard system than in the native soil. In the olive-orchard system, the enzyme activities in soils from the strips were higher than in bare soils and soils under trees. In the soils under strips, the level of β-glucosidase and phosphatase activities increased after the application of glyphosate while dehydrogenase and urease activities decreased. The presence of natural vegetation in the strips as well as herbicide application modified the bacterial community structure and the biodiversity indices. Soil sampled in the downslope strip and after glyphosate addition showed the highest biodiversity values and dominance indices.