Diversity of active root-associated methanotrophs of three emergent plants in a eutrophic wetland in northern China

Abstract

Root-associated aerobic methanotrophs play an important role in regulating methane emissions from the wetlands. However, the influences of the plant genotype on root-associated methanotrophic structures, especially on active flora, remain poorly understood. Transcription of the pmoA gene, encoding particulate methane monooxygenase in methanotrophs, was analyzed by reverse transcription PCR (RT-PCR) of mRNA isolated from root samples of three emergent macrophytes, including Phragmites australis, Typha angustifolia, and Schoenoplectus triqueter (syn. Scirpus triqueter L.) from a eutrophic wetland. High-throughput sequencing of pmoA based on DNA and cDNA was used to analyze the methanotrophic community. Sequencing of cDNA pmoA amplicons confirmed that the structure of active methanotrophic was not always consistent with DNA. A type I methanotroph, Methylomonas, was the most active group in P. australis, whereas Methylocystis, a type II methanotroph, was the dominant group in S. triqueter. In T. angustifolia, these two types of methanotroph existed in similar proportions. However, at the DNA level, Methylomonas was predominant in the roots of all three plants. In addition, vegetation type could have a profound impact on root-associated methanotrophic community at both DNA and cDNA levels. These results indicate that members of the genera Methylomonas (type I) and Methylocystis (type II) can significantly contribute to aerobic methane oxidation in a eutrophic wetland.

Methanotrophs Contribute to Nitrogen Fixation in Emergent Macrophytes

“…The bacterial communities of different plants, including roots, stems and leaves, vary between plant species ( Bulgarelli et al, 2013 ; Pietrangelo et al, 2018 ). The same type of regulation was found in studies of root methanotrophs; the difference in plant species strongly affected the community structure ( Yoshida et al, 2014 ; Liu et al, 2020 ) and level of expression of the methanotrophs ( Cui et al, 2020 ). In this study, we compared the structure of diazotrophic communities in the roots of S. triqueter and T. angustifolia .…”

“…T. angustifolia and S. triqueter were located in shallow water (50–70 cm) and deep water (80–100 cm) areas in the Wuliangsuhai wetland (N 40°52′36″, E 108°51′16″; Figure 1 ) in the Inner Mongolia Autonomous Region, China, respectively, and three to four individual plants of each species were collected on July 15, 2017 ( Cui et al, 2020 ). The physicochemical properties of the sediments are shown in Supplementary Table 1 .…”

“…The nifH gene in cDNA samples from the roots of both plants was amplified with the primers PolF (TGCGAYCCSAARGCBGACTC; Poly et al, 2001 ) and AQER (GACGATGTAGATYTCCTG; Wartiainen et al, 2008 ). Amplification and purification were conducted as previously described ( Cui et al, 2020 ). The purified DNA fragments were linked to the pEASY-T1 vector (TransGen, Beijing, China).…”

“…In wetlands dominated by emergent plants, more than 70% of the CH 4 produced is transported through plants ( Van der Nat and Middelburg, 1998 ; Laanbroek, 2010 ), and up to 90% is oxidized by aerobic methanotrophs from the root zone ( Laanbroek, 2010 ). Aerobic methanotrophs in wetland ecosystems have been analyzed using culture-dependent and –independent approaches ( Calhoun and King, 1998 ; Yun et al, 2013 ; Cai et al, 2016 ; Cui et al, 2020 ; Liu et al, 2020 ). Most aerobic methanotrophic strains oxidize CH 4 using oxygen (O 2 ), and they can fix N 2 to ammonia (NH 4 + ; Auman et al, 2001 ).…”

“…Studies have shown that root-associated Methylomonas (Type I; Gammaproteobacteria ) is dominant in the roots of three emergent plants ( P. australis, T. angustifolia and S. triqueter ) using in situ hybridization or next-generation sequencing amplicons of pmo A, which encodes the particulate methane monooxgynase, based on their DNA ( Fausser et al, 2012 ; Liu et al, 2020 ). However, root-associated Methylocystis (Type II methanotrophs, Alphaproteobacteria ) is dominant in S. triqueter and T. angustifolia by sequencing pmo A gene amplicons based on cDNA ( Cui et al, 2020 ). Owing to rapid economic development, many wetlands or lakes in the world have become eutrophic because of the excessive application of nitrogen ( Bhagowati and Ahamad, 2018 ).…”