Research Feature: Markus Kleber, new SBI faculty member in Soil Science

Posted: February 27, 2007

Markus Kleber joined the faculty of the OSU Crop and Soil Science Department in Fall 2006. His position is partially funded by the Subsurface Biosphere Initiative. This short Web interview is designed to profile Markus and introduce the expertise he brings to campus.

What is the focus of your research?

My central interest is in poorly crystalline mineral phases in soils and what role they play in the biosphere. I’ve posted this excerpt outside of my door to give students an idea of my scientific credo:

“New discoveries are taking place across the full front of organic geochemistry. Intimate, and seemingly protective, associations of organic substances with inorganic particles are now evident. Such challenging substrates as kerogens, coals and humus are subject to oxic degradation so severe that preservation must result from highly unusual structures or environmental conditions. As such recalcitrant substrates are destroyed, nitrogen-rich aliphatic remains of microorganisms are produced and preserved in association with fine grained minerals. Within this scenario, the interactions of organic remains with minerals in soils and sediments take on a new, less passive role.”

- Hedges, J. I. and J. M. Oades (1997). “Comparative organic geochemistries of soils and marine sediments.” Organic Geochemistry 27(7-8): 319-361.

Photo of Markus Kleber.
Markus Kleber,
Assistant Professor,
Soil Microbiology and Chemistry

For a long time, soil scientists have known that mineral particles stabilize soil organic matter against decomposition -- but the biogeochemistry of this relationship hasn’t been understood. One of my main projects recently has been to develop a conceptual model of the contact zone between soil organic material and mineral particles.  

My work on this started when I was a member of the group of Margaret Torn at Lawrence Berkeley National Lab. Margaret introduced me to Rebecca Sutton of UC Berkeley and Phil Sollins here at OSU [Forest Science]. Rebecca got me interested in the physical biochemistry of soil organic matter fragments, while Phil pointed out to me that nitrogen plays a role and is present in most associations between minerals and organics. Together the three of us set out to assemble a conceptual model that would explain organo-mineral interactions in soils reconciling two previously unaccounted facts: a) the amphiphilicity of most decaying organic molecular fragments and b) the particularly high affinity of nitrogen containing, proteinaceous organic moieties for mineral surfaces. The model is in the process of being published by Biogeochemistry.

The image below is one that you use in slide shows to depict the organo-mineral interface - can you explain what it shows?

Xray image of an organic film on a soil mineral particle..

Scanning Transmission X-ray Microscopy is an imaging technique which allows to obtain nanoscale information about the spatial distribution of an element in a sample. For any point in the image, there is also the possibility to obtain spectroscopic information (C 1s-NEXAFS). This technique enables us to determine the chemistry of organic moieties in close contact with mineral surfaces.

The above picture shows a patch of organic matter on a mineral grain. The mean turnover time of this organic matter in close contact with the mineral surface has been calculated at 680 years, although the sample was taken from a surface (A) soil horizon. The blueish-white area shows where soft x-rays of an element specific energy (280-290 eV, Carbon – K-edge in this case) are absorbed by carbon atoms. In this way, we can obtain a map of carbon distribution and we can make inferences about the chemistry on the surface of soil particles.

How did you become interested in soil chemistry?

I started working in plant ecology and physiology when I did my master's work at the University of Hohenheim (Stuttgart, Germany).  I had been in the military before that for ten years and I left feeling like I wanted to do something related to the biosphere and so I became a plant person. My master's work was on the calibration of the simulation model EPIC (Erosion productivity impact calculator) for a three year crop rotation on an agricultural test site.  In the end, the model fit the data very well, but it was all a function of adjusting rate coefficients.  It was not very satisfying – I wanted a more mechanistic explanation of what was happening and that is what helped me make the decision to stay in academia and what drives my approach to research.

I then did my PhD work on a project that dealt with carbon exchange in humid grassland soils. This was part of a major project to assess the sustainability of agriculture in montane grasslands. Later, I moved from Hohenheim in southwestern Germany to the City of Halle in former east Germany to be the assistant of newly installed professor Reinhold Jahn at the Institute of Soil Science and Plant Nutrition, Martin-Luther-University Halle-Wittenberg. At Halle I was in charge of the mineralogy lab and began to become interested in mineral-organic associations, mainly because there was an obvious lack of mechanistic information regarding the mineral-organic interface, so this area seemed to be a good choice for a carbon-minded person in search of a scientific problem to solve.

What other topics are you working on?

An unfolding issue seems to be the pedogenic cycling of the second most abundant element in the Earth's crust – silicon. The mechanisms of silicon redistribution within soil profiles and desilication remain poorly quantified, particularly those concerning the pools involved, rates of turnover, driving forces and general process-knowledge.

The issue is important, because there is increasing evidence for a major disturbance of the global silicon cycle involving the land-ocean transfer of dissolved silica. A general trend of decreasing levels of dissolved silica in rivers, lakes, and coastal marine areas has been observed during the last half of the twentieth century. Human emissions of nitrogen and phosphorus causes silica dependent phytoplankton (diatoms) to bloom and consume soluble silica. The resulting dissolved silica limitation has inhibited diatom growth in aquatic systems, with novel and often phytotoxic plankton species taking their place.

How does your work relate to the subsurface biosphere?

Many transformations of soil organic material are done by biota. I believe it is a mistake to look at fluxes without looking at the major players and that’s the biota – they are the ones who are doing things. Sometimes the biota is intentionally excluded – microbes are hard to work with – analyses have to be done fast before things change so they add challenging time constraints – but the biota are a critical part of the story.

Markus Kleber.

Markus competing in a Triathlon in Tempe, Arizona, April 2006.

What courses will you teach?

I am teaching a new graduate course this spring called, "The Mineral Organic Interface," Crop and Soil Science 525.  I'm also working with other faculty on developing a new undergraduate course, covering practical field assessments of soil fertility.

Are you looking for new graduate students?

Yes, I’m looking for students. They might work on either of the two projects I described – mineral/organic interactions in soils or silica mobilization in the landscape. It would be a good fit for either someone with an environmental/agricultural background or interests in sediments.

What are you liking most about being at OSU?

On campus I’m enjoying the easy access to the Dixon Rec Center. I try to keep up my physical fitness through endurance sports and Corvallis is a great place to swim, run, and bike. It’s very convenient that those interests fit with the culture of the department – we’ve been discussing the new undergrad course while we run. Other great things? Volcanoes, the ocean shore, seafood, Columbia Riesling and Willamette Pinot Noir.

What other Web pages or scientific papers will give readers an idea of your interests and background?

Some of my recent publications are:

Three papers that have influenced my thinking are:

For more information, reach Markus through the Crop and Soil Science Department.