Investigating the impact of long-term nutrient additions on soil microbial biodiversity and carbon sequestration potential
Anthropogenic nutrient additions have the potential to cause dramatic shifts in plant and microbial communities ultimately influencing global carbon cycling. Nutrient availability can impact microbial mineralization of soil organic matter as a consequence of increased plant inputs (i.e., rhizodeposition) and changes in soil microbial community composition. Nutrient availability impacts microbial metabolic potential, thus, influencing rates of carbon turnover and carbon sequestration potential. We hypothesize that history of nutrient availability influences decomposition rates, limiting carbon turnover under long-term nutrient-limited conditions. We explored relationships among nutrient availability, plant communities, and microbial communities to test effects of long-term fertilization in a wetland ecosystem in east central North Carolina. This long-term experiment provides the opportunity to study the effects of anthropogenic nutrient addition and disturbance on wetland biodiversity and ecosystem function. For 12 years, a 2×2 factorial experiment has been maintained to test the effects of nutrient addition (N-P-K fertilizer), disturbance (mowing), and their interaction on wetland community diversity and function in a randomized block design on an array of eight 20×30 m blocks. Using molecular and culture-based techniques, we assessed microbial community composition and carbon cycling function in response to nutrient conditions. We additionally surveyed plant community composition and measured soil chemical factors.
Soil organic carbon and nitrogen and soil temperature were higher in nutrient addition compared to control plots. In addition, we documented significant effects of fertilization on the diversity and composition of the plant and microbial communities. This difference in soil conditions supports higher plant biomass and potentially a higher ratio of fast growing, copiotrophic compared to slower growing, oligotrophic soil bacteria. Relieving nutrient limitation can support higher carbon turnover rates due to shifts in microbial and plant community composition.