Monday afternoon we started the Alyssum germination counts. As I type (10AM Wed) the crew is finishing counts on a total of 44 plates some of which have had up to 365 little Alyssum seedlings on them. I'll update the data later.
Above: Counting Alyssum
Below: Two Alyssum seedlings
Tuesday was a day of science. We spent the morning calculating the amount of 15N (stable isotope of nitrogen 14N) we would be adding the in the form of 15N-Ammonium sulfate or 15N-Potassium Nitrate. Ammonium is the initial substrate that is produced by soil prokaryotes (bacteria and archaea) that break down organic matter which contains primarily carbon and nitrogen. After the initial step of prokaryotic decomposition takes place ammonium (NH4+) is produced and this is a plant available source of nitrogen. But there are other prokaryotes that utilize ammonium as a nitrogen source and therefore compete with plants for nitrogen. There are ammonia oxidizing bacteria and archaea that produce and release nitrite (NO2-) which in functioning soils is rapidly utilized by nitrite oxidizing bacteria to produce nitrate (NO3-) which is also a plant avaiable source of nitrogen. The process of denitrification has nitrite as the middle point as bacteria reduce NO3- and NO2- as energy sources which produces NO, N2O, and N2. We detected NO production in the invaded Cinnabar site last week but not in the Mudslide Creek undisturbed native remnant.
So back to our experiment. By using 15N-NH4 we will be able to quantify potential nitrification rates and by using 15N-NO3 we will be able to quantify potential mineralization rates. Back in the lab next week and continuing this summer we will perform laboratory incubations under controlled conditions. But this field experiment is the best way to approximate in situ conditions.
In this picture Will and Cozy (it was cold and very windy) are injecting the 15N solution into a soil core that was collected by pounding a plastic centrifuge tube that had the bottom cut off into the soil. This method gives an intact core that we can apply the 15N label to and then put back in the ground for incubation (See purple caps in the soil below).
After labeling cores at the Mudslide Creek remnant site we headed to the Cinnabar exclosure site. We collected and labeled cores from out and inside the exclosure. The barley that was planted last year has added root biomass to the soil and this may have an effect on N-mineralization and nitrification when compared to cores from outside the exclosure which has a high density of Alyssum growing.
By this point in the day it was extremely windy and Wilson and Cozy set up in the Suburban to do the label injections. Not a bad portable lab.