Nitrogen (N) is a principal component of biological activity and quantitatively the most important nutrient involved in plant growth, which in turn may present a significant limiting factor for plant productivity in both natural and anthropogenic ecosystems. Other researchers have identified three key determinants of plant N nutrition. Namely, these are; (1) availability:
specifically the access which the plant has to the N form within the soil, e.g. pool size and nutrient fluxes close to plant roots (2) uptake: does the plant possess the capacity to acquire the target N compounds from the soil, and (3) metabolism: does the plant possess the capacity to assimilate the target N compound into its own biomass? These works focus predominately on number one, availability.
Protein hotspots in soil, such as those associated with decaying soil fauna or plant litter, may produce ephemeral patches of disproportionately high
nitrogen forms . These hotspots may occur at the macro- and microscale in close proximity to plant roots, however, the likely concentration of soluble products produced in these hotspots remains poorly understood.
To address this, we buried two contrasting biomass residues in soil, namely earthworm (Lumbricus terrestris) and clover (Trifolium repens). Their transformation to amino acids, NH4+ and NO3- were monitored continually
over 6 days using microdialysis. Microdialysis is a novel, membrane based sampling technique with origins in medical science, which has seen limited
use in environmental sampling, and to our knowledge, has never been used to quantify fluxes of soil organic matter breakdown products in continuous real time before. For the purposes of our experiment, microdialysis acted biomimetically as a plant root, as it allows bidirectional flow of perfusate across the probe membrane (simulating root exudates and uptake).
Through the use of microdialysis we are able to show that soil nutrienthotspots may provide nearby roots with concentrations of amino acids and NH4+ several orders of magnitude higher than found in the bulk soil solution; a highly significant step towards understanding the mechanistic processes which likely occur in soil nutrient hotspots close to plant roots.