Habitat and nutrient enrichment affect decomposition of maize and willow oak detritus in Lower Mississippi River Basin bayous

Few investigators have studied leaf breakdown in bayous or oxbow lakes, dominant aquatic features in fertile floodplains that potentially influence storage and processing of detritus in agricultural landscapes. We compared decomposition rates of maize (Zea mays) and willow oak (Quercus phellos) from 3 bayous in the Lower Mississippi River Basin of northwestern Mississippi and in bayou mesocosms enriched to agriculturally relevant concentrations of N, P, and N+P. We hypothesized that maize would break down faster than willow oak and that bayou nutrient and habitat factors would influence decomposition for each species. Breakdown rates were significantly higher for maize (k = 0.0229-0.0386/d) than for willow oak (0.0026-0.0240/d). Decomposition was faster in lentic than lotic habitats for willow oak but not maize. In mesocosms, breakdown rates were higher for maize than willow oak, and decomposition of both species increased significantly in mesocosms enriched with N or N+P. Maize leaf C:N and C:P ratios were lower than willow oak, decreased with time, and did not differ between lotic and lentic habitats in the field study. Maize and willow oak leaf nutrient-ratio responses to enrichment in mesocosms varied with time. By the end of the experiment, C:N ratios were lower in mesocosms enriched with N or N+P, and C:P ratios were lower in mesocosms enriched with N+P for both litter species. Microbial respiration rates for maize were double that of willow oak, and enrichment effects varied with time, but N+P enrichment increased respiration for both species by the end of the experiment. Differences in breakdown between crop and native organic-matter sources combined with nutrient enrichment may affect water bodies in highly modified aquatic agroecosystems by increasing organic-matter breakdown rates and overall microbial respiration.