Fungal degradation of complex organic carbon supports denitrification in saturated woodchip bioreactors

Authors: WANG, HAO - University Of Minnesota; Feyereisen, Gary; ZHANG, JIWEI - University Of Minnesota; ISHII, SATOSHI - University Of Minnesota

Submitted to: Bioresource Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/12/2024
Publication Date: 2/1/2025
Citation: Wang, H., Feyereisen, G.W., Zhang, J., Ishii, S. 2025. Fungal degradation of complex organic carbon supports denitrification in saturated woodchip bioreactors. Bioresource Technology. 417. Article 131826. https://doi.org/10.1016/j.biortech.2024.131826.
DOI: https://doi.org/10.1016/j.biortech.2024.131826

Interpretive Summary: The woodchip bioreactor—usually a trench filled with woodchips and through which tile drainage water is routed—is a promising technology to remove nitrate from row crop agricultural runoff. The main engine for nitrate removal is bacterial activity; carbon is needed to propel the action. Little is known about how fungi may be important in the process for breaking down the woodchips and providing carbon to the bacteria. This study investigated where in the bioreactor (inlet vs. outlet) fungi were located and how their abundance changed over time. The results showed greater fungal abundance near the inlet. Previous research showed that bacterial abundance was also greater near the inlet. The collective results suggest that fungi degrade complex carbon structures to provide more readily available carbon for denitrification. The study points out that modifying the fungal community may enhance bioreactor performance. This research is pertinent to researchers and academics, agency personnel, and design engineers and practitioners with interest in using denitrifying bioreactors to remove nitrate-N from water.

Technical Abstract: Woodchip bioreactor (WBR) is a promising technology for the removal of nitrate from agricultural drainage, although low temperatures and large water volumes typical of early spring could reduce the nitrate removal efficiency of WBRs. A key factor influencing the performance of WBRs is the availability of carbon for microbial denitrification. Microbes in WBRs rely on the decomposition of lignocellulosic biomass to obtain carbon. Fungal wood decomposition is generally more efficient than bacterial wood decomposition; however, little is known about the fungal community structure and functions in WBRs. In this study, we investigated the spatial and temporal dynamics of the WBR fungal microbiome and clarified the role of fungi in WBRs. Woodchip samples were collected from near the inlets and outlets of WBRs located in Minnesota, USA. Based on the amplicon sequencing analysis of the fungal internal transcribed spacer (ITS) region, wood-degrading fungi were more abundant near the inlet than the outlet of WBRs, most likely due to higher concentration of dissolved oxygen near the WBR inlet. Confocal microscopic analysis also confirmed the invasion of fungal hyphae into the wood cells. Furthermore, scanning electron microscopy revealed the fungal wood degradation. Since our previous study shows higher denitrification gene abundance near the inlet of WBRs, these results collectively suggest that fungi degrade complex organic carbon in WBRs to provide more readily available carbon to support denitrification. This study points toward a new avenue for future bioaugmentation and biostimulation strategies to improve the nitrate removal efficiency of WBRs.