One of Mike’s and my papers just came out this morning in Soil Biology and Biochemistry (link here). We compared nitrogen concentration data from our lysimeter samples of soil pore water and our extracted samples from soil cores and found were were seeing a lot more nitrogen in the soil core samples. This seemed to support the idea from a paper by John and Erik Hobbie a few years ago in which they suggested that soil amino acid concentrations seemed a little too high given the strong uptake capability of microbes, and that thus some of it might not be biologically available. Here’s our key figure showing the relative magnitude of nitrogen pool sizes and suggesting a sizable “inaccessible” pool:
You can see that the cores (red and dark blue lines), even though quite variable, definitely get more nitrogen than the lysimeters (light blue), which spike at the beginning of the season and then drop to low levels. It also looks like the adsorbed pool (mostly ammonium bound to the soil matrix) and the inaccessible pool can change throughout the season, so the inaccessibility isn’t permanent. Overall, a fun comparison of techniques that I think has implications for the way nitrogen is actually cycled in soils.