Soils are complex systems, in which physical, geochemical and biological processes interact in a variety of aggregate structures that experience dramatic shifts in the fraction of gas and liquid surrounding them. As a result, it is both difficult to adequately sample soil properties and to model processes related to those soil measurements. These challenges were discussed in a stimulating three-day conference on Complex Soils Systems in Berkeley a few weeks ago. Attendees came from an incredible diversity of backgrounds with a related interest in tackling issues in soil science. An overarching concern was to better understand soils to know “How to feed the soil and the planet?” in the anthropocene, which was asked early on by Professor John Crawford. I presented a poster on the soil microbial imprint on atmospheric COS.
Issues of scale were brought up explicitly or were evident implicitly in many of the presentations. Namely, that relevant processes in biogeochemical cycles occur over a wide range of spatial (nano- to mega-meter) and temporal (seconds to millennia), but our observations are typically limited to a much narrower range given measurement and resource constraints. These issues were elegantly summarized in the article “Digging Into the World Beneath Our Feet: Bridging Across Scales in the Age of Global Change” by Hinckley, Wieder, Fierer and Paul in Eos, Transactions American Geophysical Union 95 (11), 96-97. In a real sense, the scale issue presents problems when societal decisions regarding soil sustainability and ecosystem services are made using data and models derived from different (often smaller) spatial scales than the policies themselves.
Thanks to California College of the Arts (CCA) student Sakurako Gibo, the concept of a spatially complex soil system can be illustrated with the figure below. The image depicts a theoretical assemblage of soil microbes with different morphologies (for instance round spores versus stringy mycelia). In the second figure, the complex system is “pulled apart” into bins that might represent the effect of a sampling strategy that subsamples the whole system or measurements that only count certain members of the communities. The information about the original complex assemblage and connections is not retained, and as a result, rules based off of the binned samples may not apply to the intact community.
What to do? Well, let’s just say I walked away from the meeting knowing that there are plenty of unanswered questions on complexity and scale. Perhaps with the increasing technical capability in soil and microbial measurements, we’ll get there soon.
I’ll end with another neat set of figures produced by CCA student Leslie Greene who illustrated an emergent pattern of predicted H2 consumption (o) based on the availability of H2 (•) from the atmosphere (distributed) and from N2-fixing root nodules (gray filled circles). She based the pattern of H2 consumption based on one rule, soil moisture had to be above 10% and below 50%, as indicated by the concentric rings around water-logged soil sites (red filled circles). From this simple scheme, an irregular pattern emerges of sites where properties converge to promote H2 consumption. Perhaps we can use a simple approach like this to embrace and move beyond the paralysis (that at least I tend to feel) when faced with complexity.
Thank you for the BioDesign course organizers at California College of the Arts (Tobi Lyn Schmidt and Mike Bogan)!Share on Facebook