LB 29-290 - Volatile Methanol and Biochar both increase microbial activity and reduce soil nitrate

Background/Question/Methods:

Soil microbial communities rely on external carbon (C) sources to fuel metabolism, including volatile organic compounds (VOCs). VOCs from decomposition often contain high quality C compounds that can drive microbial community composition, and soil biogeochemistry. Soil additives such as biochar have the potential of sorbing added carbon compounds limiting their microbial availability. In order to compare determine if biochar inhibits the effects of the most abundant soil VOC, methanol, we performed a full factorial microcosm experiment with four biochar treatments (switchgrass, softwood, hardwood, and a no biochar control), and two levels of VOC amendment: a no VOC control, methanol addition. We measure respiration throughout, and at the end of the experiment we measured the active microbial biomass, NO₃^-, and NH₄⁺. We also extracted leachable C from each biochar and measured the soil respiratory response to that extract.

Results/Conclusions:

We found that both methanol and biochar increased soil respiration, and the active microbial biomass. Additionally, both treatments decreased soil nitrogen, especially evident in the NO₃^-. It appears that leachable C from biochar is the major driver of increased microbial activity. And, biochar may have slightly reduced the methanol effect. It is unclear whether this tempering effect was due to sorbtion or not. However, this study does confirm the effects of biochar and VOC on soil respiration and N cycling. And, establishes a useful method for measuring the effects of leachable biochar C on soil communities, providing a concrete mechanism for observed increases in respiration and immobilization of nitrogen.