Temperature and moisture mediated changes in chemical and microbial properties of biochars in an Anthrosol.

Sequestration of soil carbon is considered as a promising strategy for mitigating climate change. As a source of recalcitrant carbon, biochar has been widely used in agricultural soil as a mean of stabilizing soil organic carbon (SOC). However, limited reports focused on the changes of biochar itself in soil when compared with the bulk SOC after biochar addition. To explore how environmental conditions influence the stability of biochar, isolated straw-derived biochar particles (0.25-2 mm) were embedded in an Anthrosol for 12 months under varied environmental conditions of incubation temperature (15 °C, 25 °C and 35 °C) and moisture (60 % and 150 % of saturated water content). Within the early 1 month of incubation, pH and inorganic nitrogen contents of biochar changed significantly as a function of moisture and temperature (p < 0.01), whereas water extractable organic carbon (WEOC) content was only influenced by moisture content (p < 0.01). The highest temperature (35 °C) and saturated water content (150 %) induced the largest aging response reflected by increases in oxygen-containing surface functional groups of biochar, including C-O-C (51.35 % - 149 %) and N-C-O (65.55 % - 119 %). Pearson correlation and RDA analysis indicated that the chemical properties of biochar contribute more to the carbon-source utilization properties of biochar colonized microbial community within 1 month of incubation, while the bulk soil chemical properties (pH, DOC, MBC and NO) had a higher contribution until the end of incubation. Moisture rather than temperature was the dominant factor in regulating the functional diversity of biochar colonized microbial community.