Soil microbiome-induced changes in the priming effects of ¹³C-labelled substrates from rice residues

Knowledge gap exists to understand the soil CO₂ emission and microbial group response to substrates of whole plant residues and derived biochar. We used ¹³C-labelled substrates (rice straw, roots and biochar) to track influences of their decomposition on soil priming effect (PE) and phospholipid fatty acid (PLFA) composition during one-year incubation. Organic substrates at 1% (w/w) level increased soil pH, available nitrogen (AN) and available phosphorus (AP), especially during the first 45 days of incubation. After incubation, 44% of the added straw was mineralized to ¹³CO₂, followed by roots (~35%) and biochar (~5%). Straw and roots amendment caused positive PE during 4-360 day of the incubation, where a lowest value of 41.9 mg C kg^-1 was observed. Biochar amendment caused negative PE during 56-150 day of the incubation, where a largest value of -99.0 mg C kg^-1 was observed. Analysis of ¹³C-labelled PLFA enabled the differentiation of microbial groups during substrates utilization. Gram positive bacteria (G⁺) and general bacteria groups were dominated in co-metabolizing both the native soil organic carbon (SOC) and substrates after straw and roots amendment. Gram negative bacteria (G^-), especially identified by PLFA biomarkers cy17:0 and cy19:0, preferentially utilizes the ¹³C-labelled biochar but not promoting soil priming effect. Soil pH, SOC, AN and AP all explained changes of total and ¹³C-labelled PLFA contents (>75%, p < .05). Evidences showed that biochar is best in sequestering soil C pool, followed by straw and roots, and soil microbial groups in utilization of organic substances mediated SOC mineralization.