Enzymatic activities and microbial biomass as affected by glyphosate under conservation and conventional agriculture.

Glyphosate (N-phosphonomethyl glycine) plays an important role in weed control. Since microorganisms are major soil decomposers driving key biogeochemical processes, effects of glyphosate on soil microorganisms need to be assessed. The influence of glyphosate under conservation (NY) and conventional agriculture (CT) on the soil microbial biomass and soil enzymatic activities was investigated. Soil samples (0-10 cm depth) were collected in 2013-2015 (2th-5th years of the field trial) before and 20 days after glyphosate application (2 kg ha-1). Soil microbial biomass was assessed through an high-throughput dsDNA-based method based. Eight soil enzymatic activities were determined: acetate esterase, β-glucosidase, leucine-amminopeptidase, chitinase, alkaline and acid phosphatase, pyrophospatase phosphodiesterase, phosphodiesterase. These activities were determined using a 384-well microplate-, desorption-based fluorometric enzyme assay. All enzyme activities and dsDNA were not significantly affected by the glyphosate application either under CT and NT. In NT treatment we also observed that all soil enzymatic activities were nearly doubled in three years. Leucine-amminopeptidase, alkaline phosphomonoesterase and β-glucosidase were the enzymes that showed the highest increased over time under NT, respectively of 45%, 64% and 38%. These enzymes under CT showed instead a nearly constant activity. dsDNA was found higher under NT (18g dsDNA gsoil-1) compared to CT (11g dsDNA gsoil-1). Soil enzymes and dsDNA measured with this high-throughput method helped to reveal the non-target effect of glyphosate on soil microbial community and the positive effects of adopting NT.