Carbon and Nitrogen cycling: examples at microscales in Biological Soil Crusts

We propose to study the microscale biogeochemical cycling of Carbon and Nitrogen in biofilm-like microbial communities forming cryptic but abundant topsoil crusts in much of the arid Western US rangelands. Soil crusts are though to be responsible for much of the net inputs of nitrogen into arid lands through nitrogen-fixation, but the fate of these nitrogen inputs has been difficult to establish, and remains controversial. The extent to which some of it is lost either to the atmosphere or to deeper soil horizons, is key to determine the role that these crusts play in aridland fertility. But the biogeochemical mechanisms that determine the fate of nutrients in these communities occur at scales smaller than 1 cm, in an apparently tightly coupled and spatially organized fashion. We will use chemical profiling of oxygen, pH, nitrate, nitrite and nitrous oxide using microsensors that yield µm-scale spatial resolution to describe and interrogate these systems. With the aid of diffusion/reaction modeling of profiles, and experiments using specific inhibitors we hope to assess nitrification, denitrification, net nitrogenous efflux to deeper horizons and to the atmosphere. Complementing this effort with standard assay incubation and tracer experiments, we will link microscale processes to more standard measurements of emergent system properties. We will study three types of soil crusts, spanning the successional pattern seen after human disturbance of arid soils. With this work a mechanistic understanding will be gained that has the potential to guide efforts in rangeland management and conservation efforts. This project is funded by the US Department of Agriculture and the National Resources Institute.

See an example in: Johnson S. L., C. R. Budinoff, J. Belnap, F. Garcia-Pichel. 03 2005. Relevance of ammonium oxidation within biological soil crust communities. Environmental Microbiology 7(1):1-12