Livestock manure and antibiotics alter extracellular enzyme activity

Abstract Soil enzyme activities are commonly used for inferring microbial processes and nutrient limitations. In agroecosystems these enzymes can also be used to determine management effects on soil quality. Here we report the effect of dairy manure inputs and veterinary antibiotics (cephapirin and pirlimycin) on soil enzyme activities, using both a nationwide survey and a controlled field experiment. We found that manure from dairy cows increased ɑ-glucosidase (67.5%), β- d -cellubiosidase (51.4%), β-xylosidase (48.5%), and total measured enzyme activity (34.0%). Manure reduced mass-specific enzyme activity of 5 of the 6 measured enzymes and relieved microbial phosphorus limitation, as β-glucosidase:acid phosphatase activity was 34% higher in the manure treatment. Veterinary antibiotics administered to livestock decreased the activity of individual soil enzymes, yet only pirlimycin elicited a significant decrease in activity for β-D-cellubiosidase (48.1%), leucine aminopeptidase (24.1%), β-xylosidase (41.9%), and total measured enzyme activity (18.6%). We found that microbial resource allocation was largely unchanged by antibiotic treatment; however, mass-specific leucine aminopeptidase was marginally higher (21.4%) in the control treatment than in the cephapirin treatment, potentially linking antibiotics to microbial resource allocation strategies. Our results suggest that administering antibiotics to livestock affects gross ecosystem processes - i.e. decomposition rate – through effects on microbial biomass. Furthermore, manure directly impacts microbial resource allocation while antibiotics administered to livestock appears to have a less pronounced impact on microbial resource allocation. Taken together, administration of antibiotics to livestock can affect overall ecosystem process rates but is unlikely to affect microbial resource allocation.