Microbial Responses to Biochar Soil Amendment and Influential Factors: A Three-Level Meta-Analysis.

Biochar is a multifunctional soil conditioner capable of enhancing soil health and crop production while reducing greenhouse gas emissions. Understanding how soil microbes respond to biochar amendment is a vital step toward precision biochar application. Here, we quantitatively synthesized 3899 observations of 24 microbial responses from 61 primary studies worldwide. Biochar significantly boosts microbial abundance [microbial biomass carbon (MBC) > colony-forming unit (CFU)] and C- and N-cycling functions (dehydrogenase > cellulase > urease > invertase > nirS) and increases the potential nitrification rate by 40.8% while reducing cumulative N2O by 12.7%. Biochar derived at lower pyrolysis temperatures can better improve dehydrogenase and acid phosphatase and thus nutrient retention, but it also leads to more cumulative CO2. Biochar derived from lignocellulose or agricultural biomass can better inhibit N2O through modulating denitrification genes nirS and nosZ; repeated biochar amendment may be needed as inhibition is stronger in shorter durations. This study contributes to our understanding of microbial responses to soil biochar amendment and highlights the promise of purpose-driven biochar production and application in sustainable agriculture such that biochar preparation can be tuned to elicit the desired soil microbial responses, and an amendment plan can be optimized to invoke multiple benefits. We also discussed current knowledge gaps and future research needs.

Aerobic bacterial methane synthesis.

Reports of biogenic methane (CH4) synthesis associated with a range of organisms have steadily accumulated in the literature. This has not happened without controversy and in most cases the process is poorly understood at the gene and enzyme levels. In marine and freshwater environments, CH4 supersaturation of oxic surface waters has been termed the "methane paradox" because biological CH4 synthesis is viewed to be a strictly anaerobic process carried out by O2-sensitive methanogens. Interest in this phenomenon has surged within the past decade because of the importance of understanding sources and sinks of this potent greenhouse gas. In our work on Yellowstone Lake in Yellowstone National Park, we demonstrate microbiological conversion of methylamine to CH4 and isolate and characterize an Acidovorax sp. capable of this activity. Furthermore, we identify and clone a gene critical to this process (encodes pyridoxylamine phosphate-dependent aspartate aminotransferase) and demonstrate that this property can be transferred to Escherichia coli with this gene and will occur as a purified enzyme. This previously unrecognized process sheds light on environmental cycling of CH4, suggesting that O2-insensitive, ecologically relevant aerobic CH4 synthesis is likely of widespread distribution in the environment and should be considered in CH4 modeling efforts.