Preceding crop and weed management history affect denitrification and denitrifier community structure throughout the development of durum wheat

Aside from negative impacts on crop yield, the role of weeds in agricultural systems, particularly with respect to below ground function, is not well understood. In this study, we utilised a mesocosm approach with soils collected from a long-term rotation study to compare legacy effects of previous flax (Linum usitatissimum L.) or canola (Brassica napus L.) and different levels of weediness established over a decade by different herbicide use patterns. Despite few significant differences in initial soil chemical properties, the impact of level of weediness superseded that of the preceding crop and altered the growth of durum wheat (Triticum durum L.) during early development and the temporal dynamics of denitrification and the nirK denitrifier communities. The impact of the presence of durum plants in the mesocosm experiment was relatively small, however, the presence of durum plants did modify the legacy effects of preceding crop and weediness on the denitrifier community. Differences in denitrifier community structure were due to differential presence/absence and differential abundance of multiple T-RFs. To our knowledge, this is the first study to investigate the effects of long-term weed management strategies on denitrification. Our results indicate that weediness contributes to priming effects and unexplained variation associated with these soil processes and that weed management history should be taken into consideration when determining soil function and soil microbial community dynamics in agricultural systems. (C) 2015 Elsevier B.V. All rights reserved.