So, for those of you who don’t know, I’m currently working through my honours year in Plant Science at The University of Queensland. I’m a little over halfway through, and with a few months to go, I’m starting a new experimental series – looking for different forms of nitrogen in agricultural soils, using a neat system called microdialysis.
These systems are generally used in fields of research unrelated to plants and soil – namely animal physiology and neuroscience (as demonstrated by the helpful instruction manual describing the process of inserting probes into rats).
Instead of inserting probes into a rat’s brain, I will be inserting them into soils. This way of using the microdialysis system is new, but I’m definitely not the first to start probing the soily depths. Some very smart people (see examples – Sulyok et al. 2005; Inselsbacher et al. 2011) have found some very surprising results from using microdialysis, especially when compared to traditional techniques of soil analysis. The trick is, microdialysis is a very non-invasive method of looking at what’s in the soil, whereas traditional techniques involve lots of digging, sieving and turbulent water/salt extractions that can completely change the nature of the soil, and confound results.
I like to think of microdialysis as soil surgery – especially since the machine looks like it belongs in a hospital.
How it works is that a series of probes, each with a permeable membrane, are inserted into something you wish to sample. In this case I’m sampling a known solution of nitrogen forms (nitrate + amino acids).
A series of electronically-controlled syringes (hooked up to the probes by a tangle of annoying tiny tubes) pushes through a ‘perfusate’ – in this case, ultra-pure water – through to the probes.
Molecules, floating around in the solution being sampled, move across the permeable membrane of the probes, and mixes with the pure water. This is then carried out of the probes and to a refridgerated sample collector.
You can then take these samples and analyse their contents. Alongside some hefty carbon analysis in Sweden, I’m going to be using Ultra-Performance Liquid Chromotography (UPLC) to look at ammonium and amino acids in my samples, and nitrate assays to look for… well, nitrate.
I’ll also be pushing the boundaries of this machine’s capabilities – using very slow flow rates (0.2µL/min) to sample continuously for 5 days straight, inside a rather humid growth cabinet. Eep. Toys are fun, but when they are expensive and fragile, I tend to freak out a little. Clumsy piano hands with tendonitis aren’t ideal for this kinda work ;).
Sulyok, M, Miró, M, Stingeder, G & Koellensperger, G 2005, ‘The potential of flow-through microdialysis for probing low-molecular weight organic anions in rhizosphere soil solution’, Analytica Chimica Acta, vol. 546, no. 1, pp. 1-10.
Inselsbacher, E, Öhlund, J, Jämtgård, S, Huss-Danell, K & Näsholm, T 2011, ‘The potential of microdialysis to monitor organic and inorganic nitrogen compounds in soil’, Soil Biology and Biochemistry, vol. 43, no. 6, pp. 1321-32.