Nitrogen availability is a key factor governing plant growth and soil fertility, and maintaining agricultural productivity. In agroecosystems, crops form the nexus for nutrient cycling, fueling the activity and characterising the composition of soil microbial communities. Annual and perennial crop management results in fundamentally different rhizospheres. Perennial crops form larger root systems that progressively develop over years or even decades and result in more carbon input into the soil, more complex structures of roots and rhizosphere deposits, and larger root columns. Rhizospheres create microbial habitats rich in resources and fuelling microbial communities with rhizosphere C, which often triggers microbial mining of nutrients from organic matter, a phenomenon known as the “rhizosphere priming effect” (RPE). As such, perennial agriculture likely leads to improved nutrient provisioning to the plant via aboveground-belowground interactions. However, to date, these are theoretical predictions and remain unexplored by experimentation. Thus, it still remains unclear whether perennial crops consistently stimulate microbial nitrogen mining and how this varies along depths in agricultural soils. This is the target of the proposed project.
Supervisors: Xiaojing Yang & Johannes Rousk
https://portal.research.lu.se/en/persons/xiaojing-yang
https://portal.research.lu.se/en/persons/johannes-rousk
Objectives
This project seeks to evaluate the extent to which perennial crops can stimulate nitrogen mining by soil microorganisms and identify the underlying drivers of this process. Specifically, we will draw on the SAFE (Swedish Agricultural Field Experiment) site in Löntorp to quantify microbial nitrogen mining activity in soils under perennial crop cultivation compared to annual crops. We will assess the role of root input in stimulating microbial nitrogen mining and examine how soil conditions (e.g., organic matter content, nitrogen availability) and crop traits (e.g., root biomass) influence microbial nitrogen mining. The study can involve both controlled laboratory experiments, greenhouse experiments, and field studies in agroecosystems dominated by perennial crops. The project is open to adjustments according to your interest in the topic, with the possibility of matching your research interests
Methodology
- Determine bacterial and fungal growth rates by isotope tracing.
- Measure soil respiration rates using gas chromatography.
- Tracking rhizosphere carbon (13C) into CO2 with online ring-down spectroscopy.
- Determine soil characteristics including soil moisture, C, N, pH, organic matter etc.
- Characterize microbial community composition by PLFA method.
- Collect and analyze root biomass from crops to identify carbon substrates that stimulate microbial activity.
- 15N pool-dilution method to estimate gross N mineralization rates
Skills and Techniques Acquired
- Experimental Design: Learn how to design and implement experiments to assess soil-plant-microbe interactions.
- Field and Laboratory Skills: Develop proficiency in isotope tracing, soil respiration measurement, and microbial community analysis.
- Data Analysis and Interpretation: Gain expertise in statistical analysis of environmental data and interpretation of patterns in nitrogen cycling and microbial activity.
- Critical Literature Review: Learn how to identify and synthesize relevant scientific literature on rhizosphere processes, nitrogen cycling, and soil-microbe interactions.
- Problem-Solving: Build problem-solving skills by troubleshooting challenges in both field and laboratory experiments.
Application Process
If you are interested, please contact: Xiaojing Yang xiaojing.yang@biol.lu.se and/or Johannes Rousk johannes.rousk@biol.lu.se