Myriophyllum elatinoides growth and rhizosphere bacterial community structure under different nitrogen concentrations in swine wastewater

doi:10.1016/j.biortech.2020.122776

Bioresource Technology

Volume 301, April 2020, 122776

https://doi.org/10.1016/j.biortech.2020.122776 Get rights and content

Highlights

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Harvesting of Myriophyllum elatinoides at 49 days is recommended.
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Higher N concentrations in plant roots were found under high N conditions.
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Aerobic bacteria increased at low N, while anaerobic bacteria increased at high N.
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pH drove rhizosphere bacterial community distribution.

Abstract

In this study, Myriophyllum elatinoides growth under different nitrogen (N) concentrations (2, 250, 300, 350 and 400 mg L⁻¹) and changes in rhizosphere bacterial community structure were investigated. High N (>300 mg L⁻¹) concentrations caused reduction in M. elatinoides biomass. Growth tended to stabilize at 49 days. N concentration in roots were higher than that in stems and leaves under high N conditions. TN and NH₄⁺ removal efficiencies reached 84.0% and 87.2%, respectively, in M. elatinoides surface flow constructed wetlands (SFCWs). Rhizosphere bacterial diversity increased over time. Proteobacteria, Firmicutes, Cyanobacteria, and Bacteroidetes dominated at the phylum level. Genera Turicibacter, Allochromatium, and Methylocystis increased at low N (<300 mg L⁻¹) concentrations, while Pseudomonas increased at high N concentrations over the experimental period. Redundancy analysis showed that pH was strongly correlated with changes in rhizosphere bacterial community structure. These findings helped to insight into N removal mechanism in M. elatinoides.

Graphical abstract

Introduction

With the rapid development of livestock and poultry breeding, livestock wastewater has become a severe environmental contaminant, which affects water bodies worldwide (Hooda et al., 2000, Wang et al., 2016a). Swine wastewater contains a high concentration of ammonia nitrogen (NH₄⁺) (Ye et al., 2010, Huang et al., 2016), which cannot be effectively removed at a large scale without the use of wastewater disposal technology (Xu et al., 2015). Constructed wetlands (CWs) are widely regarded as a low cost, low energy, simple operation and high efficiency technology for treating various wastewater (Vymazal, 2009, Filali et al., 2017, Hernandez-Crespo et al., 2017). Plants are important components of CWs for nitrogen (N) and phosphorus (P) removal due to their strong absorption capacity (Li et al., 2009, Zhang et al., 2011). In addition, plant root exudates and secreted oxygen strongly influence rhizosphere microbes (Bever et al., 2010). The rhizosphere often has higher microbial activity than non-rhizosphere soil and these microbes are involved in the processing of organics and nutrients (Wang et al., 2008). Some researchers have reported that rhizosphere microbes play an essential role in reducing the concentrations of pollutants (Marschner et al., 2011, Bell et al., 2014). Rhizosphere microbial community structure often varies with plant species (Bell et al., 2015).

Myriophyllum elatinoides is one of the best floating plants for removing high concentrations of N and P from swine wastewater due to its tolerance of high nutrient conditions and ability to improve sediment microbial activity (Li et al., 2018, Li et al., 2019). However, the responses of M. elatinoides rhizosphere microbes to different N concentrations, and the effect on N removal from swine wastewater, are still unclear. Moreover, patterns of M. elatinoides growth and the dynamics of N distribution in the plant’s organs under varying N concentrations are not known. Understanding the growth characteristics of M. elatinoides and mechanisms of microbial N removal can inform the management and application of M. elatinoides in treating swine wastewater.

In this study, surface flow constructed wetlands (SFCWs) planted with M. elatinoides were created to treat swine wastewater with five different levels of N concentration. The aims of this study were 1) to examine M. elatinoides growth characteristics and biomass under different N concentrations in swine wastewater; 2) to investigate the community structure of rhizosphere microbes; 3) to determine the N removal mechanisms and understand the interactions between environmental factors and rhizosphere microbes. These results will increase the understanding of the N removal mechanism for treatment different N concentrations swine wastewater in M. elatinoides SFCWs and provide a plant management strategy for M. elatinoide.

Section snippets

Experimental set-up

SFCWs were constructed at the Changsha Research Station for Agricultural and Environmental Monitoring, Hunan Province, China (28°30′N, 113°18′E). The study was conducted from September 1 to November 3, 2017. During the experimental period, average temperature and average precipitation were 26 °C and 23.6 mm, respectively. Fifteen concrete ponds (0.8 m long by 0.5 m wide by 0.4 m deep) were used as SFCWs, and filled to about 0.1 m depth with paddy soil. An inlet was placed at the surface of the

Plant growth under different N concentrations

Fig. 1 shows the fitted growth curve for M. elatinoides under different N concentrations (R² > 0.94) (Table 1), which shows the variation in biomass over 63 days. Myriophyllum elatinoides growth tended to stabilize at 49 days in all treatments, suggesting that M. elatinoides could be harvested for nutrient removal at this time. Some studies have reported that harvesting plants at regular intervals can improve overall nutrient removal in CWs (Wang et al., 2015, Zheng et al., 2015). The biomass

Conclusions

M. elatinoides SFCWs were studied to determine plant growth and factors driving rhizosphere bacterial community structure under different N concentrations. High N concentrations lead to decreases in biomass and RGR. N concentrations in the roots, stems, and leaves were higher in T2 than those in other treatments. Sequencing showed that the highest bacterial diversity was found in treatment T3. Bacterial community structure changed under different N concentrations. pH was a key factor in shaping

Author contribution

Xi Li design and performed the experiment, analyze the experimental data, and write this manuscript.

Yuyuan Li, Yong Li and Jinshui Wu guide the experiment and revise this manuscript.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This study was financially supported by the National Key Research and Development Program of China (2018YFD0800100), the Key Science and Technology Project of Henan Province, China (161100310600), and the Natural Science Foundation of Hunan Province, China (2018JJ3581). We thank Public Service Technology Center, Institute of Subtropical Agriculture, and the Chinese Academy of Sciences for providing experimental platform.

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Myriophyllum elatinoides growth and rhizosphere bacterial community structure under different nitrogen concentrations in swine wastewater

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Experimental set-up

Plant growth under different N concentrations

Conclusions

Author contribution

Declaration of Competing Interest

Acknowledgements

Sci. Total Environ.

Desalination

Environ. Exp. Bot.

Soil Biol. Biochem.

Trends Ecol. Evol.

Ecol. Eng.

Ecol. Eng.

Bioresour. Technol.

Ecol. Eng.

Plant Sci.

Ecol. Eng.

Sci. Total Environ.

Sci. Total Environ.

J. Clean. Prod.

Water Res.

Bioresour. Technol.

Bioresour. Technol.

J. Environ. Manage.

Soil Biol. Biochem.

Bioresour. Technol.

Chem. Eng. J.

Ecol. Eng.

China. Sci. Total Environ.

Ecol. Eng.