Pine sawdust biomass and biochars at different pyrolysis temperatures change soil redox processes

To date, no investigation has been carried out to explore the effects of biochars produced at different pyrolysis temperatures on the dynamics of redox potential (E_H) and pH in a contaminated floodplain soil. Thus, we aimed to quantify the dynamics of E_H and pH in contaminated flooded soils treated with 70 t ha^{− 1} of pine sawdust biomass (S&BM) and biochars pyrolyzed at 300 °C (S&BC300) and 550 °C (S&BC550) and pre-incubated for 105 days in an automated biogeochemical microcosm system. Microbial community composition was also determined via analyzing phospholipid fatty acid (PLFA).We found that BC300 and BC550 treatments substantially decreased (3–6.5%) and BM increased (~ 37%) the mean of soil E_H compared to the untreated contaminated soil (CS).·The largest E_H decline in S&BC550 was at the rate of − 80 mV h^{− 1} at 10 h while it was observed at 25 h in S&BC300 and 20–25 h in S&BM or CS, respectively. At high E_H, a higher total PLFA biomass and microbial groups in the CS (71–87%) were found in comparison to treated soils. Higher aromaticity and ash content in BC550 than BC300 and BM led to the greater PLFA biomass and microbial groups which contributed to higher capacity of accepting and donating electrons in soil slurry and were probably one reason for the largest decrease in E_H. Pine sawdust biomass and BCs have a noticeable influence in soil biogeochemical processes relevant to fluctuating redox conditions.