Responses of Soil Microbial Community Structure and Activity to Incorporation of Straws and Straw Biochars and Their Effects on Soil Respiration and Soil Organic Carbon Turnover

Like straw, biochar incorporation can influence soil microorganisms and enzyme activities and soil carbon (C) responses; however, few studies have compared the various effects of straw and biochar and the underlying mechanisms. An experiment was performed to study the changes in soil respiration (SR) and soil organic C (SOC) fluxes in response to the incorporation of three kinds of straw (reed, smooth cordgrass, and rice) and their pyrolyzed products (biochars) at Chongming Island, China. In addition, the microbial activity and community structure of some amended soils were also analyzed to clarify the mechanisms of these responses. The results showed that all biochar incorporation (BC) induced lower SR than the corresponding unpyrolyzed straw incorporation (ST), and the average SR in the soils following BC and ST during the experimental periods was 21.69 and 65.32 mu mol CO2 m(-2) s(-1), respectively. Furthermore, the average SOC content was 16.97 g kg(-1) following BC, which was higher than that (13.71 g kg(-1) ) following ST, indicating that compared to ST, BC was a low-C strategy, even after accounting for the C loss during biochar production. Among the BC treatments, reed-BC induced the lowest SR (17.04 mu mol CO2 m(-2) S-1), whereas smooth cordgrass-BC induced the highest SR (27.02 mu mol CO2 m -2 S-1). Furthermore, in contrast with ST, BC significantly increased the abundance of some bacteria with poorer mineralization or better humification ability, which led to lower SR. The lower easily oxidizable C (EOC) and higher total C contents of biochars induced lower SR and higher SOC in the soil following BC compared to that following ST. Among the BC treatments, the higher total nitrogen content of rice biochar led to significantly higher soil microbial biomass, and the lower EOC content of reed biochar led to lower soil microbial activity and SR.