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Responses of soil nitrogen fixation to Spartina alterniflora invasion and nitrogen addition in a Chinese salt marsh.

ABSTRACT: Biological nitrogen fixation (BNF) is the major natural process of nitrogen (N) input to ecosystems. To understand how plant invasion and N enrichment affect BNF, we compared soil N-fixation rates and N-fixing microbes (NFM) of an invasive Spartina alterniflora community and a native Phragmites australis community in the Yangtze River estuary, with and without N addition. Our results indicated that plant invasion relative to N enrichment had a greater influence on BNF. At each N level, the S. alterniflora community had a higher soil N-fixation rate but a lower diversity of the nifH gene in comparison with the native community. The S. alterniflora community with N addition had the highest soil N-fixation rate and the nifH gene abundance across all treatments. Our results suggest that S. alterniflora invasion can increase soil N fixation in the high N-loading estuarine ecosystem, and thus may further mediate soil N availability.

SUBMITTER: Huang J

PROVIDER: S-EPMC4751540 | biostudies-literature | 2016 Feb

REPOSITORIES: biostudies-literature

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Responses of soil nitrogen fixation to Spartina alterniflora invasion and nitrogen addition in a Chinese salt marsh.

Huang Jingxin J Xu Xiao X Wang Min M Nie Ming M Qiu Shiyun S Wang Qing Q Quan Zhexue Z Xiao Ming M Li Bo B

Scientific reports 20160212

Biological nitrogen fixation (BNF) is the major natural process of nitrogen (N) input to ecosystems. To understand how plant invasion and N enrichment affect BNF, we compared soil N-fixation rates and N-fixing microbes (NFM) of an invasive Spartina alterniflora community and a native Phragmites australis community in the Yangtze River estuary, with and without N addition. Our results indicated that plant invasion relative to N enrichment had a greater influence on BNF. At each N level, the S. al ...[more]

PMID: 26869197

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Project description:Nitrogen fixation (NF) and phosphorus solubilization (PS) play a key role in maintaining the stability of mangrove ecosystems. In China, the invasion of Spartina alterniflora has brought a serious threat to the mangrove ecosystem. However, systematic research on NF and PS in mangrove sediments has not been conducted, and limited studies have focused on the response of NF and PS to S. alterniflora invasion, particularly at different sediment depths. In the present study, shotgun metagenomics and quantitative PCR were used to study the 0- to 100-cm sediment profile of the mangrove ecosystem in the Beibu Gulf of China. Results showed that the PS potential of mangrove sediments was primarily caused by enzymes encoded by phoA, phoD, ppx, ppa, and gcd genes. S. alterniflora changed environmental factors, such as total nitrogen, total phosphorus, and total organic carbon, and enhanced the potential of NF and PS in sediments. Moreover, most microorganisms involved in NF or PS (NFOPSMs) responded positively to the invasion of S. alterniflora. Cd, available iron, and salinity were the key environmental factors that affected the distribution of NF and PS genes (NFPSGs) and NFOPSMs. A strong coupling effect was observed between NF and PS in the mangrove ecosystem. S. alterniflora invasion enhanced the coupling of NF and PS and the interaction of microorganisms involved in NF and PS (NFAPSM), thereby promoting the turnover of NP and improving sediment quality. Finally, 108 metagenome-assembled genomes involved in NF or PS were reconstructed to further evaluate NFOPSMs. IMPORTANCE This study revealed the efficient nutrient cycling mechanism of mangroves. Positive coupling effects were observed in sediment quality, NF and PS processes, and NFOPSMs with the invasion of S. alterniflora. This research contributed to the understanding of the effects of S. alterniflora invasion on the subtropical mangrove ecosystem and provided theoretical guidance for mangrove protection, restoration, and soil management. Additionally, novel NFOPSMs provided a reference for the development of marine biological fertilizers.

Project description:Background and aimsEcosystem-based flood defence including salt-marsh as a key component is increasingly applied worldwide due to its multifunctionality and cost-effectiveness. While numerous experiments have explored the wave-attenuation effects of salt-marsh plants critical to flood protection, little is known about the physiological and biochemical responses of these species to continuous wave exposure.MethodsTo address this knowledge gap, we developed a shallow-water wave simulator to expose individual Spartina alterniflora plants to waves in a greenhouse for 8 weeks. S. alterniflora individuals were partially submerged and experienced horizontal sinusoidal motion to mimic plant exposure to shallow water waves. A factorial experiment was used to test the effects of three wave heights (4.1 cm, 5.5 cm and a no-wave control) and two wave periods (2 s and 3 s) on the following key physiological and biochemical plant parameters: plant growth, antioxidant defence and photosynthetic capacity.Key resultsComparison of wave treatment and control groups supported our hypotheses that wave exposure leads to oxidative stress in plants and suppresses plant photosynthetic capacity and thereby growth. In response, the wave-exposed plants exhibited activated antioxidant enzymes. Comparison between the different wave treatment groups suggested the wave effects to be generally correlated positively with wave height and negatively with wave period, i.e. waves with greater height and frequency imposed more stress on plants. In addition, wave-exposed plants tended to allocate more biomass to their roots. Such allocation is favourable because it enhances root anchorage against the wave impact.ConclusionsSimulated wave exposure systems such as the one used here are an effective tool for studying the response of salt-marsh plants to long-term wave exposure, and so help inform ecosystem-based flood defence projects in terms of plant selection, suitable transplantation locations and timing, etc. Given the projected variability of the global wave environment due to climate change, understanding plant response to long-term wave exposure has important implications for salt-marsh conservation and its central role in natural flood defence.

Project description:The effect of plant invasion on the microorganisms of soil sediments is very important for estuary ecology. The community structures of methanogens and sulfate-reducing bacteria (SRB) as a function of Spartina alterniflora invasion in Phragmites australis-vegetated sediments of the Dongtan wetland in the Yangtze River estuary, China, were investigated using 454 pyrosequencing and quantitative real-time PCR (qPCR) of the methyl coenzyme M reductase A (mcrA) and dissimilatory sulfite-reductase (dsrB) genes. Sediment samples were collected from two replicate locations, and each location included three sampling stands each covered by monocultures of P. australis, S. alterniflora and both plants (transition stands), respectively. qPCR analysis revealed higher copy numbers of mcrA genes in sediments from S. alterniflora stands than P. australis stands (5- and 7.5-fold more in the spring and summer, respectively), which is consistent with the higher methane flux rates measured in the S. alterniflora stands (up to 8.01 ± 5.61 mg m(-2) h(-1)). Similar trends were observed for SRB, and they were up to two orders of magnitude higher than the methanogens. Diversity indices indicated a lower diversity of methanogens in the S. alterniflora stands than the P. australis stands. In contrast, insignificant variations were observed in the diversity of SRB with the invasion. Although Methanomicrobiales and Methanococcales, the hydrogenotrophic methanogens, dominated in the salt marsh, Methanomicrobiales displayed a slight increase with the invasion and growth of S. alterniflora, whereas the later responded differently. Methanosarcina, the metabolically diverse methanogens, did not vary with the invasion of, but Methanosaeta, the exclusive acetate utilizers, appeared to increase with S. alterniflora invasion. In SRB, sequences closely related to the families Desulfobacteraceae and Desulfobulbaceae dominated in the salt marsh, although they displayed minimal changes with the S. alterniflora invasion. Approximately 11.3 ± 5.1% of the dsrB gene sequences formed a novel cluster that was reduced upon the invasion. The results showed that in the sediments of tidal salt marsh where S. alterniflora displaced P. australis, the abundances of methanogens and SRB increased, but the community composition of methanogens appeared to be influenced more than did the SRB.

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Responses of soil nitrogen fixation to Spartina alterniflora invasion and nitrogen addition in a Chinese salt marsh.

Publications

Responses of soil nitrogen fixation to Spartina alterniflora invasion and nitrogen addition in a Chinese salt marsh.

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