[Influences of Biochar Application on Root Aerenchyma and Radial Oxygen Loss of Acorus calamus in Relation to Subsurface Flow in a Constructed Wetland].

In the subsurface flow of a constructed wetland (CW) used for treating wastewater, low oxygen diffusion results in long-term anoxic or anaerobic surroundings, which cannot meet the needs of plant respiration and poses a threat to the survival of macrophytes. Although sweet sedge (Acorus calamus L.) has a significant ability to resist hypoxia, membrane lipid oxidation would still occur in the plant due to the long-term hypoxia in the CW. According to reports in the existing literature, activation of the antioxidative response system could be promoted by adding biochar, thereby significantly decreasing the malonic dialdehyde in the plants. However, the specific reasons why biochar alleviates the stress from anoxia are still not clear. Thus, the responses of macrophyte roots to biochar application were studied in five different CWs built in a greenhouse, using plant ecology analyses combined with root aerenchyma, root porosity, and radial oxygen loss (ROL). The results showed that adding biochar to CW was beneficial for sweet sedge to form root aerenchyma and to increase root porosity. Moreover, there was a significant positive correlation between root porosity and the amount of biochar applied. Photosynthetic metabolism could be indirectly promoted by biochar application by increasing oxygen partial pressure in the blades, helping to transport O₂ to underground parts through aerenchyma, and spreading O₂ to the rhizosphere in the form of ROL. The reduction environment could be improved by applying biochar in CWs, which was also beneficial for ROL. Compared with other light conditions, 3000 μmol·(m²·s)^-1 was more suitable for the growth of A. calamus in CWs with biochar, where the ability of the plants to secrete oxygen would be stimulated and enhanced. However, the effect of the biochar application ratio on ROL was not significant.