Sandra Jämtgård: What is plant available nitrogen? – sampling lots of stuff with microdialysis

What a plant root experience as available nitrogen (N) in soil is crucial in its N uptake and N use efficiency. Soil contains many organic N compounds, some of which can be used for plant growth but are rapidly turned over and therefore their importance in plant uptake has been difficult to quantify. Microdialysis is a method that our research group has developed for non-destructive sampling of soil solution chemical composition at the scale of a plant fine root. In contrast to traditional soil sampling methods, microdialysis samples soil in situ through a semipermeable membrane, which enables sampling with minimal disturbance and instantaneous separation of the sample from potential chemical alteration. The use of the method show that plant roots in many environments seem to have access to a larger proportion of organic N than previously thought. In addition, we have applied the low disturbance sampling enabled by this technique in other contexts. For sampling simple carbon compounds in soil, secretion of metabolites during the initiation of ectomycorrhizal symbiosis and we see many possible applications. Furthermore, there are other plant functions influencing plant N availability that can be simulated with this technique. Root exudation is one of these that we are focusing on at the moment. By understanding more about the natural occurrence of N in soil we might be able to find new ways of improving N use efficiency.