Elsevier

Applied Soil Ecology

Volumes 117–118, September 2017, Pages 129-136
Applied Soil Ecology

Original Communication
Elevated CO2 and nitrogen addition affect the microbial abundance but not the community structure in salt marsh ecosystem

https://doi.org/10.1016/j.apsoil.2017.04.004Get rights and content

Highlights

  • Elevated CO2 and/or N affected the microbial abundance but not structure significantly.

  • The responses of bacterial, archaeal, and fungal communities varied with each group.

  • The plant C3/C4 composition was important in structuring the microbial communities.

  • The archaeal and fungal communities responded to eCO2 and/or N more strongly.

Abstract

With unique and important characteristics, salt marsh ecosystems are expected to be affected by elevated CO2 and N enrichment. Although various studies have assessed the effects of those changes on the vegetation of salt marshes, little information is available about their impact on microbes. In this study, we comprehensively analyzed the microbial community structure of soils responding to elevated CO2 (eCO2) and N addition (N) over 3 years in salt marsh ecosystem. We employed pyrosequencing, T-RFLP analysis, and quantitative PCR to study the bacterial, archaeal, and fungal communities. The overall results indicated that 1) eCO2 and N affected the microbial abundance but not community structure significantly in salt marsh system, 2) due to their different ecophysiology, the responses of the three different microbial communities to eCO2 and/or N addition varied with each group, 3) the composition (C3/C4 or diversity) of the plant community was important in structuring the microbial community of salt marsh ecosystems, which generally have low plant diversity, 4) the archaeal and fungal communities responded more strongly to eCO2 and/or N addition than the bacterial community. This study represents the first comprehensive report of the effects of eCO2 and/or N addition on the diverse microbial community structures of tidal marsh systems. It suggests that single or combined effect of eCO2 and N on microbial abundance in salt marsh was obvious, and that the key groups playing an important role in the biogeochemical process can be shifted.

Introduction

Coastal wetlands including salt marshes often exhibit extremely high productivity and have been found to sequester carbon at a much faster rate than forest ecosystems (Barbier et al., 2011). As many coastal wetlands are exposed to the sea level rise but can maintain a constant elevation depending on the carbon and mineral accumulation rates, the possible modification of the primary production and elevation changes in coastal wetlands in future climate conditions has been drawing much attention (Langely et al., 2008, Gedan et al., 2009, Kirwan and Mudd, 2012, Kirwan et al., 2014). The rise of atmospheric CO2 concentration and the anthropogenic nitrogen input are among the most important factors influencing the structure and function of ecosystems. In addition, as soil microorganisms play important roles in mediating ecological processes, understanding the response of soil microbial communities to environmental factors is critical to fully assessing the impact of environmental factors on ecosystem functioning and stability and predicting future climate changes. As such, there are lots of studies dealing with the effects of elevated CO2 (eCO2) and/or N on primary production (Taub, 2010, Barnaby and Ziska, 2012) or microbial communities in various ecosystems (Blagodatskaya et al., 2012, Bragazza et al., 2012, Dunbar et al., 2012, Eisenhauer et al., 2012, He et al., 2012, Lesaulnier et al., 2008, Ramirez et al., 2012, Weber et al., 2011). However, while the impacts of eCO2 and/or N enrichment on the plant and soil properties of coastal marshes have been relatively well-documented, there is little information about the effect of global change, in particular multiple climate change factors, on microbial composition in salt marsh system (Bowen et al., 2009a, Bowen et al., 2009b). Salt marsh ecosystem also harbors a diverse bacteria, fungi, and archaea (Bowen et al., 2012, Seyler et al., 2014, Weber et al., 2011) and it was reported that microbial composition would directly affect functional processes in estuarine sediments (Reed and Martiny, 2013). In addition, to achieve a broader and better prediction of the interactive effects of environmental changes, studies considering the combined effects of more than two climate change components should be conducted.

In this study, we addressed the effects of multiple climate change factors such as eCO2 and N addition on three major microbial communities (bacteria, fungi, and archaea communities) in salt marsh simultaneously. Through the investigating the microbial communities of which niche and ecophysiology are different each other, it would be possible to fully understand the impact of global change on microbial communities in salt marsh ecosystem. The specific questions are follows: 1) whether eCO2 and/or N affect the overall microbial communities, ii) whether the multiple effects of eCO2 and N are synergistic or not, iii) whether bacteria, fungi, and archaea communities respond to eCO2 and/or N differently, iv) what are specific microbial groups strongly responding to eCO2 and/or N, and finally v) whether other environmental variables significantly affecting the response pattern of microbial groups are present. For addressing these questions, we analyzed the bacterial, archaeal, and fungal community structures of salt marsh system subjected to eCO2 and N addition over 3 years with molecular techniques including pyrosequencing, terminal restriction fragment length polymorphism (T-RFLP) analysis, and quantitative polymerase chain reaction (PCR) concurrently to maximize our understanding of soil microbes and to overcome the limitations of each method.

Section snippets

Study site and sampling

This study was performed at brackish marsh system located on the Rhode River, a sub-estuary of Chesapeake Bay (lat. 38° 53′N, long. 76°33′W). The site was dominated by a C3 sedge, Scheonoplectus americanus, and C4 grasses, Spartina patens and Distichlis spicata. In this study, we selected 3.3 m2 spots with homogeneous vegetation composition and established open top chambers at those spots. We located 20 plots randomly in marsh area and all plots were equally distributed with one C3 and two C4

Analysis of bacteria and archaea pyrosequencing data

After subsampling the original sequence data, we obtained standardized sequences and OTUs for each sample (Table S1 and S2). Based on these data, we analyzed the effect of each treatment on bacterial and archaeal communities. For Bacteria, N treatment significantly affected the Shannon diversity index (Table 1). Most dominant phylum was Proteobacteria, followed by Chloroflexi, Chlorobi, Bacteroidetes, Firmicutes, Actinobacteria, Spriochaetes, and Acidobacteria (Table 1). At the phylum level, 3

Discussion

As described previously, initial vegetation before the manipulation experiment was homogeneous (Langley et al., 2009) and a previous study performed with this experimental set reported distinctively different responses of C3 and C4 plants to eCO2 and N (Langley and Megonigal, 2010). They found that N addition strongly promoted the growth of C4 plant species and distribution of plant was shifted, which ultimately suppressed the CO2-stimulation of plant productivity by the third and fourth years (

Acknowledgements

This study was supported by ERC (No. 2011-0030040) and SGER (2016R1D1A1A02937049).

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    Current address: Department of Biology, Villanova University, PA19085, USA.

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