Hello Catherine-
Excellent question, as this is exactly what I am looking into for the rest of my dissertation research. While I have currently been working with pure culture isolates in the lab, which has helped me get to this hypothesis of modular denitrifiers, my next step is to move up to the microbial community and ecosystem scale to see if microbial modularity could affect denitrification kinetics or whether soil biophysical properties are more of a driving factor. Lauren and I are currently working at her sites near Ithaca, NY which show variable nitrous oxide fluxes to see whether the microbial communities vary, especially in regard to the active communities with the nitrous oxide reductase gene. Preliminary sampling has indicated differences in the bacterial communities that harbor the the nitrous oxide reductase gene, but more intensive research will occur this summer and fall. Thanks for your question!
-Armanda

Thank you, Constance.
Catherine

Hello Patricia,
Thanks for your great question! From what I’ve seen in the modeled results and the observed measurements, I think the over-prediction is a product of a couple factors. Our observed measurements were made using the push-pull method that Lauren is using for the Landscape Scale measurements, which quantifies denitrification in the saturated zone and overlooks denitrification in the partially saturated regions. This bias occasionally leads to an underestimation in the observed values. When I look at the data points with zero observed denitrification, there is nothing anomalous in the factors we currently consider that explains why the observed rate was zero. Our hope is that as we gain a better understanding of the microbial and environmental drivers of denitrification, our models will reflect more accurately what we see in the landscape. Thanks for your question! Please let me know if you would like more information.
- Janet

Hello Liliana-
Thanks very much for your feedback! We highlighted temperature and groundwater flow in the discussion of the landscape scale measurements because those were the most important drivers of denitrification at these riparian study sites where I have most recently been working. However, we did measure many other environmental parameters that could have an influence on denitrification, such as dissolved organic carbon, dissolved oxygen, ambient nitrate, ammonium, and a suite of cations including iron. We didn’t discuss these in depth on the poster since they were not the primary drivers for the patterns observed at these riparian sites, where dissolved organic carbon was consistently high and thus didn’t appear to be limiting and the saturated conditions led to chronically low dissolved oxygen at all sites. At another denitrification research site which includes more upland landscape, a fellow graduate student measured all of these environmental parameters (dissolved carbon, dissolved oxygen, nitrate, temperature, etc), and some of the resulting relationships were included in Janet’s denitrification model. Regarding soil, the main way that we factor in influences from differing soil types is by also quantifying soil carbon along the soil profile at each site.
Soil carbon is additionally incorporated into Janet’s model. Thanks again for your questions, and please let me know if you would like any clarification.

-Lauren

Hello Alan-
Thanks for the questions about how we’re specifically integrating our cross-scale work- it’s certainly a complicated task. Janet’s landscape denitrification model incorporates several environmental variables that are measured in the plot-scale studies that are considered to influence denitrification- dissolved organic carbon, ambient nitrate, temperature, soil carbon, pH, and soil moisture. For the finer scale, Armanda has primarily been working with pure culture isolates in the lab at this point, exploring what genes from the denitrification pathway different isolates have. This summer and fall, Armanda will begin to quantify the various denitrification genes in the environment (both at the riparian research site and other research sites) along with measurements of environmental variables such as pH, dissolved oxygen, dissolved carbon, as well as production of denitrification gases. Her main question is whether or not the the abundance of genes controlling various parts of denitrification and the active bacterial community are the primary limiting factor controlling observed denitrification patterns, or whether it’s more the environmental variables that are simply controlling denitrification. If we find that there are fundamental differences in microbial communities and denitrification gene abundance between sites, we will begin to try to incorporate these dynamics directly into the landscape model as well.
Thanks for your question,
Lauren

Thanks very much for the kind words, Tony!