Vegetation Effects on Bacteria and Denitrifier Abundance in the Soils of Two Tidal Freshwater Wetlands in Virginia

Joseph C Morina,Ember M Morrissey,Rima B Franklin

doi:10.1155/2018/4727258

Abstract

This study examined the abundance of bacteria and nirS-type denitrifiers associated with the rhizospheres of three emergent macrophyte species (Juncus effusus, Typha latifolia, and Peltandra virginica) to gain a greater understanding of plant-microbe interactions in wetland soils. Sampling of plant and soil properties was performed during the growing season (June) and following plant senescence (November) at two tidal freshwater wetlands. Quantitative polymerase chain reaction was used to determine the abundance of bacteria (16S rRNA) and nirS-type denitrifier genes from the rhizosphere and rhizoplane of each plant species and from nearby unvegetated soils. For bacteria, there was a positive rhizosphere effect that did not differ significantly across plant species. In contrast, significant differences in the abundance of nirS-type denitrifiers were observed across the plant species. Rhizosphere abundance was ∼2-fold greater in Peltandra virginica and 4-fold greater in Typha latifolia compared to Juncus effusus. For both bacteria and nirS-type denitrifiers, plant effects were greater during the growing season, and abundance was highly correlated with soil pH, moisture, and organic matter content. Overall, these results demonstrate plant effects on the rhizosphere microbial community can be species‐specific and that there is a synergistic relationship between plant species and environmental conditions.

Highlights

Wetlands are ecosystems of intense biogeochemical transformations, especially in regard to nitrogen cycling. ey are estimated to remove nearly 20% of anthropogenic nitrogen inputs worldwide [1, 2]
A preliminary analysis using a subset of samples indicated nirK abundance was very low (101–103 copies per g dry weight of soil) and showed no significant plant or site effects; our analyses focused on nirS. ose quantitative polymerase chain reaction (qPCR) were performed using nirS-specific primers cd3aF and R3cd [26] and genomic DNA from Paracoccus denitrificans (ATCC Strain #17741) for the standard curve
We found the effect to differ based on site, which is consistent with prior research that there is a synergistic relationship between plant species and soil type that shapes microbial abundance in the rhizosphere [5, 44,45,46]. e physical-chemical properties of the native soil can be important directly via their impact on the microbial community or indirectly via the selective pressure they exert that determines which plants are successful in certain areas [47, 48]

Summary

Introduction

Wetlands are ecosystems of intense biogeochemical transformations, especially in regard to nitrogen cycling. ey are estimated to remove nearly 20% of anthropogenic nitrogen inputs worldwide [1, 2]. Rates of nitrogen removal have been linked with broad-scale changes in the size and composition of wetland plant communities [3,4,5,6]. Most prior efforts to disentangle this relationship have focused on how plant communities, sediment properties, and hydrology interact, and considerably less is known about the small-scale interactions that take place in the rhizosphere and rhizoplane of individual plants. Such information is essential if we are to develop a predictive understanding of ecosystem nitrogen dynamics based on plant functional characteristics and plant community composition [7]. Microbial communities may respond to changes in redox conditions and oxygen availability that arise from differences in radial

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Conclusion