Bio-stimulating effect and mechanism of rice straw amendment for enhancing the elimination of soil benzo[a]pyrene

In this study, we conducted four treatments for soil contaminated with benzo[a]pyrene (BaP) using various doses (w/w) of rice straw (CK, 0 %; SL, 0.5 %; SM, 1.5 %; SH, 4.5 %) over a 100-day incubation period to investigate the bio-stimulating effect and underlying microbial mechanism of straw amendment for BaP elimination. The results indicated that the SL and SM treatments improved the BaP elimination rate (BER) by 6.40 % and 8.09 %, respectively, compared with that of CK, but SH treatment decreased it by 34.58 %. The soil BER showed significant correlations with the prokaryotic community structure (bacteria and archaea), which had a positive and negative relationship with microbial biomass nitrogen (MN) and the ratio of microbial biomass carbon (MC) to MN, respectively. Straw amendment enriched several known polycyclic aromatic hydrocarbon (PAH) degrading microbes, including Agromyces, Sphingomonas, Rhizopus, Steroidobacter, Xylaria, Chaetomium, Mesorhizobium, Fusarium, Nocardioides, Micromonospora, and an unclassified Pseudomonadota genus. Furthermore, genes encoding both upstream (cmtAb, cmtB, and phtB; dioxygenase and dehydrogenase) and downstream (bphI, xylK, nahM, or tesG; aldolase) enzymes responsible for the degradation of aromatic compounds showed a significantly positive relationship with the soil BER. These results suggest that moderate-dose amendment with straw can improve soil BER by promoting the growth of PAH-degrading bacteria and enriching the key genes responsible for BaP degradation.