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.