The molecular characteristics of DOMs derived from bio-stabilized wastewater activated sludge and its effect on alleviating Cd-stress in rice seedlings (Oryza sativa L.)

To recycle fertilizing contents in wastewater activated sludge (WAS) is attracting increasing interest. Dissolved organic matters (DOMs) in WAS with high content are biologically active. In this work, the molecular composition of DOMs derived from two typical bio-stabilized WAS (DOMBWS), aerobic composting (DOMACS) and anaerobic digestion (DOMADS), were analyzed. The mitigative effect and molecular mechanisms of DOMBWS on rice seedlings (Oryza sativa L.) under Cd-stress were investigated. Our study indicated that DOMBWS significantly alleviated Cd-stress and facilitated growth recovery of rice seedlings with distinct absorption mechanisms. DOMACS, primarily composed of CHO class with low molecular weight rich in carboxyl groups, forming labile Cd-DOM complexes, which promoted Cd-absorption of rice seedlings. While DOMADS comprised large molecular weight of CHON class interacted with Cd to produce stable macromolecular complexes in the form of microaggregates, consequently reducing Cd-absorption. At transcriptional level, DOMBWS restored auxin signal transduction and phenylpropanoid biosynthesis pathways in root cells, and got the expression of glutathione S-transferase well. Besides, DOMACS significantly promoted the metabolism of amino acids to alleviate phytotoxicity, while DOMADS improved the DNA repair function of rice seedlings. These findings provided novel insights into land-use of bio-stabilized WAS for remediation of heavy metals contaminated soils and food security. [Display omitted] •The molecular composition of DOMs derived from BWS were different.•DOMACS rich in carboxyl groups of CHO formula in small molecular weight•DOMADS mainly composed of high molecular weight protein-like substances•DOMACS increased the Cd absorption of rice seedlings while DOMADS reduced that.•DOMBWS got significantly differential metabolic pathways right to recover growth.