Utilization of marigold (Tagetes erecta) flower fermentation wastewater as a fertilizer and its effect on microbial community structure in maize rhizosphere and non-rhizosphere soil

Abstract

Marigold (Tagetes erecta L.) flowers can be used to produce lutein, but the production process generates fermentation wastewater, which is rich in lactic acid. Currently, most fermentation wastewater treatment methods are relatively expensive and time-consuming. To develop a practical marigold flower fermentation wastewater treatment method, in this study, we treated the fermentation wastewater with calcium oxide to prepare a neutralization solution, which was then used to irrigate maize that in turn exhibited a significant increase in growth. Then, we investigated soil pH, conductivity and enzyme activity, as well as microbial community and diversity of the maize rhizosphere and non-rhizosphere soil. Compared with the control group, the neutralization solution had no significant effect on soil pH and four kinds of enzyme (soil urease, catalase, sucrase and acid phosphatase) activity, but the electrical conductivity of the treatment group increased by 24.3%. The 16s rDNA and ITS rDNA sequencing results showed that the neutralization solution treatment influenced the diversity and abundance of bacteria and fungi in the non-rhizosphere samples, as well as the number of bacterial species in rhizosphere soil. The effect of neutralization solution treatment on bacteria was greater than that on fungi. Proteobacteria and Ascomycota were the predominant bacterial and fungal phyla in maize rhizosphere soil. The relative abundance of Paenibacillus, Bacillus and Penicillium genera significantly increased in non-rhizosphere soils. We hereby present a potential method for treating marigold flower fermentation wastewater for fertilizer utilization and show that the neutralization solution promotes maize growth and influences the soil microbial structure.