Effect of Biochar on Root Morphological Characteristics of Wetland Plants and Purification Capacity of Constructed Wetland

Abstract

A constructed wetland with Acorus calamus L. was built. Straw biochar, reed biochar, and sawdust biochar was added into the constructed wetland individually to study the effect of different biochars on the root morphology, dissolved oxygen, and purification ability of the constructed wetland. The results show that the total root length, total projection area, total volume, total surface area, root number, branch number, and root dry weight of Acorus calamus L. significantly increased when all three kinds of biochar were added into the constructed wetland (P<0.05). Similarly, adding the biochars into the constructed wetland also significantly increased dissolved oxygen content in the wetland (P<0.05). Addition of sawdust biochar into the constructed wetland increased the root length, projection area, surface area, total volume, number of root tips, number of branches, and root dry weight of Acorus calamus L. by 96.1%, 106.2%, 185.6%, 172.5%, 75.3%, 121.6%, and 84.9%, respectively. After adding biochars into the constructed wetland, the root morphology of Acorus calamus L. and dissolved oxygen content was significantly correlated with removal rate of TN, TP, and COD, respectively. Addition of sawdust biochar into the constructed wetland significantly increased the removal rates of total nitrogen, total phosphorus, and COD when the hydraulic load was 0.022 m3·(m2·d)-1 (P<0.05). These results suggested that the addition of sawdust biochar to the constructed wetland increased the root growth of Acorus calamus L. and enhanced dissolved oxygen content, resulting in purification capacity of the constructed wetland.