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Effects of biochar on cell-cell signaling

PIs:  Silberg, Masiello, Zygourakis, Rudgers

There have been occasional reports of biochar increasing the decomposition rate of bulk soil organic matter in amended soils (or “priming” soil organic carbon decomposition). If this effect were widespread, it could reduce the sequestration of carbon when biochar is added to soils.  One possible explanation for these observations is the sorption of cell-cell signaling compounds by biochar, a process that could reduce or completely shut off the ability of microbes to communicate with each other within soils.  Microbes use nonpolar aliphatic and aromatic compounds to communicate with one another, and this signaling is thought to influence interactions of microbes with plants.  One of the roles of these cell-cell signaling compounds is population control (quorum sensing):  when microbes detect environmental concentrations of specific compounds that exceed some threshold, they reduce their growth rate and reduce their consumption of soil organic matter.  It is possible that biochar’s high sorptivity could temporarily reduce soil concentrations of quorum sensing compounds, leading to a surge in microbial growth and concurrent increase in soil organic matter decomposition. 

We have constructed a microbial sensor that can be used to measure the ability of biochar to interfere with microbial communication in vitro.  We are using this sensor to test the tendency of biochars to alter microbial signaling.

Reaction Engineering

PIs: Zygourakis, Masiello, Hockaday

PhD student:  Sun

We operate two purpose-built reactors, one microscale (mg) and one demo-scale (10s of kg).  We additionally produce biochar using many approaches in our lab furnace at the bench scale (100s of mg).

Our largest reactor is a mobile, trailerable unit designed to produce kg-sized batches of biochar for greenhouse trials.  It is a closed-system reactor designed and built by Bill Hockaday.  It is powered by an external propane tank and production temperature is monitored via thermocouples.

Our microscale fixed-bed pyrolysis reactor is designed to produce mg of biochar under extremely well-controlled temperature and gas-flow conditions, and was designed and built by Hao Sun.  This computer-controlled reactor has a thermocouple embedded within the pyrolyzing biomass and the temperature of the pyrolyzing biochar itself is controlled via a feed-forward/feedback algorithm.  The amount of energy input to the reactor is adjusted continuously to compensate for exothermic and endothermic reactions that occur during pyrolysis, and the deviation from the set point is always less than 15°C.

Biochar characterization

PIs: Zygourakis, Masiello, Dugan, Gonnermann, Hockaday

PhD student:  Sun

We are working to characterize the chemical and physical properties of biochar produced from a variety of feedstocks under a range of temperature and gas flow conditions. 

Chemical characterization

We chemically characterize all our biochar by elemental analysis (%C, %H, %N) using a Costech 4010 EA.  We also measure bulk chemical structure and ring cluster size using a 200 MHz Bruker solid state NMR.  Additionally, we measure surface total elemental composition and C and N functionality using a Phi Quantera XPS and a Nicolet FTIR in attenuated total reflectance mode.

Physical characterization

We use a range of tools to characterize the physical structure of biochar.  We use N2 gas adsorption to understand the micropore structure (Micromeritics ASAP 2010).  We also characterize the macropore structure using SEM.  We characterize skeletal bulk density using He pycnometry and envelope density by dry displacement.  Finally, we are developing new thermogravimetric and modeling techniques to quantitatively assess the macropore structure of biochar particles.

Biochar and soil hydrology

PIs:  Dugan, Masiello, Zygourakis, Hockaday

postdocs:  Gallagher, Barnes

PhD students:  Liu, Ziegelgruber

Biochar alteration of the hydrologic cycle may be its single-most important driver of plant productivity.  We are characterizing the impact of biochar amendment on soil hydrophobicity, water-holding capacity, soil water potential, hydraulic conductivity, and permeability.

We are connecting microscale measurements (XPS, pycnometry) with bench-scale hydrologic measurements (water potential, hydraulic conductivity, water-holding capacity) with the goal of understanding the underlying physical controls on environmental outcomes.

Economic Valuation of Biochar Ecosystem Services

PIs: Medlock, Masiello, Davies (Shell)

postdoc: TBD

Biochar provides added value beyond carbon sequestration:  it can deliver a broad range of ecosystem services.  Key services provided include water retention, nutrient retention, yield improvement, alternatives to gray infrastructure.  We are developing frameworks to value ecosystem services to motivate private sector investment in biochar.

Biochar effects on plant-mycorrhizal symbiosis

PIs: Rudgers, Masiello, Hockaday

postdocs:  Gallagher, Barnes

undergraduate:  LeCroy

Biochar alters the rhizosphere through processes that are poorly understood.  We use greenhouse experiments to understand the effects of biochar soil amendment on plant above- and below-ground NPP, degree of plant fungal colonization, and fungal hyphae length.  We follow these experiments up with XPS analyses of the biochar to understand how plant-fungal interactions alter the surface chemistry of biochar.

Biochar and soil invertebrates

PIs:  Alvarez, Masiello, Hockaday

PhD student:  Li

Biochar alters the chemical and physical environments experienced by soil invertebrates.  Using standard methods, we have showed that biochar applied dry to soil desiccates earthworms, but does not trigger responses indicating any oxidative stress (as would have been indicative of PAH exposure).  Negative effects on earthworms can be mitigated by wetting biochar before soil application. See:  Li et al., Earthworm avoidance of biochar can be mitigated by wetting.  in press 2011, Soil Biology and Biochemistry.

Biochar and dissolved organic matter

PIs:  Hockaday, Masiello, Dugan

postdocs:  Barnes, Gallagher

undergrad:  Vicki Chuang

Biochar releases DOM abundantly into the environment and may be a major source of dissolved humic substances in global soils and watersheds.  We are characterizing the amount and chemical composition of dissolved carbon and nitrogen released by biochars made from a range of feedstocks under a range of pyrolysis conditions.