Abstract
Nitrogen (N) availability is crucial to maintaining crop productivity in agroecosystems, driven primarily by soil microbial processes such as nitrification and denitrification. Weeds are an integral part of agroecosystems and are involved in many processes related to the N cycle, but how weed management could shift plant–microbe interactions, and thus, N‐cycling is yet to be determined. Using a network of 15 Mediterranean vineyards, we quantified the effect of 5 years of different weed management practices (chemical weeding, tillage, mowing) on the above‐ground and below‐ground functional properties of weed communities and soil microbial N‐cycling. Specific root length (SRL) of the tilled and mowed weed communities were 30% and 44% lower than in the herbicide‐treated weed communities. Soil pH and texture were the main drivers of soil microbial activity as quantified by substrate‐induced respiration (SIR), potential denitrifying enzyme activities to SIR ratio (PDEA:SIR) and potential nitrifying and denitrifying enzyme activity ratio (PNEA:PDEA). SIR was also impacted by the management: Mowed weed communities had 58% higher SIR compared to herbicide‐treated communities. Weed communities with high SRL were associated with soils with a higher nitrifying enzyme efficiency per unit of respired carbon. Synthesis and applications . Overall, our findings indicate that vineyard weed management influences the potential nitrifying enzyme activities by modifying the root strategies of weed communities. This study highlights that the design of sustainable weed management strategies should incorporate unintended effects on soil microbial communities and N‐cycling.