Location: Forage-animal Production ResearchTitle: Long-term tillage and nitrogen fertilization in maize influences the ammonia-oxidizing bacterial community
|LIU, SHUANG - University Of Kentucky|
|COYNE, MARK - University Of Kentucky|
|GROVE, JOHN - University Of Kentucky|
Submitted to: Applied Soil Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/3/2018
Publication Date: 5/31/2018
Citation: Liu, S., Coyne, M.S., Grove, J.H., Flythe, M.D. 2018. Long-term tillage and nitrogen fertilization in maize influences the ammonia-oxidizing bacterial community. Applied Soil Ecology. 129:98-106.
Interpretive Summary: An abundance of nitrogen fertilizer is applied world-wide each year. A major type of inorganic nitrogen, ammonium (NH4+), is converted to nitrate (NO3-) by nitrifying soil microorganisms (nitrifiers). Both ammonium and nitrate are available N nutrients for plants and microorganisms, but nitrate leaches into the groundwater as a contaminant more easily. At the same time, nitric oxide (NO) and nitrous oxide (N2O) are byproducts of nitrification and also cause environmental problems. For economic and environmental benefits, better managing nitrifiers promises to increase N fertilizer use efficiency and decrease water and air contamination. Before managing nitrifiers, we need to understand their community structure. In this study, we focused on an important group of nitrifiers – ammonia-oxidizing bacteria (AOB). AOB not only catalyze the rate-limiting step of nitrification but they are the functionally dominant nitrifier group in cropland. We examined how soil management such as tillage and N fertilizer rate, influenced AOB the community, because different AOB species have functional differentiation and do not equally contribute to nitrification. Our results showed that fertilizer rates, sample season, tillage method, and their interaction all changed the AOB diversity. AOB were more diverse with N fertilizer applied; more diverse in summer samples than winter samples; and more diverse in no-tillage plots than plow tillage plots. Additionally, unique groups were discovered that showed the environmental selection. This information may facilitate new approaches to optimize nitrification in cropping systems and mitigate its adverse consequences.
Technical Abstract: Nitrification is a biological oxidation of NH3 to NO2- and then to NO3-. Managing nitrifiers to increase nitrogen (N) fertilizer use efficiency, decrease NO3- leaching, and reduce NO and N2O emissions could benefit the environment. But one must first understand the structure of the nitrifier community. In cropland, ammonia-oxidizing bacteria (AOB) are the functionally dominant group responsible for the rate-limiting nitrification step - NH3 oxidation. However, different AOB species have functional differentiation and do not equally contribute to nitrification. This study examined how long-term N fertilization and tillage influenced AOB community structure. The study site was a long-term (>50 years) continuous maize (Zea mays L.) experiment with three N fertilization rates (0, 168, and 336 kg ha-1) and either no-tillage (NT) or plow tillage (PT). Denaturing gradient gel electrophoresis (DGGE) was used to analyze PCR-amplified bacterial ammonia monooxygenase (amoA) genes to detect the dynamics of NH3-oxidizing bacteria. Tillage, fertilization, sample season, and their interaction all significantly influenced the AOB community. AOB became more diverse with increasing N input; compared to winter samples, AOB were more diverse in summer; and AOB were more diverse in no-tillage compared to plow tillage soils when N fertilizer was applied. Nitrosomonas-like and Nitrosospira-like groups were identified based on migration patterns in the gel. Unique bands were discovered in different treatments, manifesting the environmental selection. The long-term field trial provided clear evidence that soil management changes AOB communities, which may facilitate new approaches to optimize nitrification in cropping environments for greater N use efficiency and less environmental stress.