Dataset Information

Silica uptake by Spartina-evidence of multiple modes of accumulation from salt marshes around the world.

ABSTRACT: Silicon (Si) plays a critical role in plant functional ecology, protecting plants from multiple environmental stressors. While all terrestrial plants contain some Si, wetland grasses are frequently found to have the highest concentrations, although the mechanisms driving Si accumulation in wetland grasses remain in large part uncertain. For example, active Si accumulation is often assumed to be responsible for elevated Si concentrations found in wetland grasses. However, life stage and differences in Si availability in the surrounding environment also appear to be important variables controlling the Si concentrations of wetland grasses. Here we used original data from five North American salt marshes, as well as all known published literature values, to examine the primary drivers of Si accumulation in Spartina, a genus of prolific salt marsh grasses found worldwide. We found evidence of multiple modes of Si accumulation in Spartina, with passive accumulation observed in non-degraded marshes where Spartina was native, while rejective accumulation was found in regions where Spartina was invasive. Evidence of active accumulation was found in only one marsh where Spartina was native, but was also subjected to nutrient over-enrichment. We developed a conceptual model which hypothesizes that the mode of Si uptake by Spartina is dependent on local environmental factors and genetic origin, supporting the idea that plant species should be placed along a spectrum of Si accumulation. We hypothesize that Spartina exhibits previously unrecognized phenotypic plasticity with regard to Si accumulation, allowing these plants to respond to changes in marsh condition. These results provide new insight regarding how salt marsh ecosystems regulate Si exchange at the land-sea interface.

SUBMITTER: Carey JC

PROVIDER: S-EPMC4033131 | biostudies-literature | 2014

REPOSITORIES: biostudies-literature

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Silica uptake by Spartina-evidence of multiple modes of accumulation from salt marshes around the world.

Carey Joanna C JC Fulweiler Robinson W RW

Frontiers in plant science 20140520

Silicon (Si) plays a critical role in plant functional ecology, protecting plants from multiple environmental stressors. While all terrestrial plants contain some Si, wetland grasses are frequently found to have the highest concentrations, although the mechanisms driving Si accumulation in wetland grasses remain in large part uncertain. For example, active Si accumulation is often assumed to be responsible for elevated Si concentrations found in wetland grasses. However, life stage and differenc ...[more]

PMID: 24904599

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Project description:BackgroundSalt marshes are dominated by the smooth cordgrass Spartina alterniflora on the US Atlantic and Gulf of Mexico coastlines. Although soil microorganisms are well known to mediate important biogeochemical cycles in salt marshes, little is known about the role of root microbiomes in supporting the health and productivity of marsh plant hosts. Leveraging in situ gradients in aboveground plant biomass as a natural laboratory, we investigated the relationships between S. alterniflora primary productivity, sediment redox potential, and the physiological ecology of bulk sediment, rhizosphere, and root microbial communities at two Georgia barrier islands over two growing seasons.ResultsA marked decrease in prokaryotic alpha diversity with high abundance and increased phylogenetic dispersion was found in the S. alterniflora root microbiome. Significantly higher rates of enzymatic organic matter decomposition, as well as the relative abundances of putative sulfur (S)-oxidizing, sulfate-reducing, and nitrifying prokaryotes correlated with plant productivity. Moreover, these functional guilds were overrepresented in the S. alterniflora rhizosphere and root core microbiomes. Core microbiome bacteria from the Candidatus Thiodiazotropha genus, with the metabolic potential to couple S oxidation with C and N fixation, were shown to be highly abundant in the root and rhizosphere of S. alterniflora.ConclusionsThe S. alterniflora root microbiome is dominated by highly active and competitive species taking advantage of available carbon substrates in the oxidized root zone. Two microbially mediated mechanisms are proposed to stimulate S. alterniflora primary productivity: (i) enhanced microbial activity replenishes nutrients and terminal electron acceptors in higher biomass stands, and (ii) coupling of chemolithotrophic S oxidation with carbon (C) and nitrogen (N) fixation by root- and rhizosphere-associated prokaryotes detoxifies sulfide in the root zone while potentially transferring fixed C and N to the host plant. Video Abstract.

Project description:As a symptom of accelerated sea level rise and historic impacts to tidal hydrology from agricultural and mosquito control activities, coastal marshes in the Northeastern U.S. are experiencing conversion to open water through edge loss, widening and headward erosion of tidal channels, and the formation and expansion of interior ponds. These interior ponds often form in high elevation marsh, confounding the notion applied in predictive modeling that salt marshes convert to open water when elevation falls below a critical surface inundation threshold. The installation of tidal channel extension features, or runnels, is a technique that has been implemented to reduce water levels and permit vegetation reestablishment in drowning coastal marshes, although there are limited data available to recommend its advisability. We report on 5 years of vegetation and hydrologic monitoring of two locations where a total of 600-m of shallow (0.15-0.30-m in diameter and depth) runnels were installed in 2015 and 2016 to enhance drainage, in the Pettaquamscutt River Estuary, in southern Rhode Island, United States. Results from this Before-After Control-Impact (BACI) designed study found that runnel installation successfully promoted plant recolonization, although runnels did not consistently promote increases in high marsh species presence or diversity. Runnels reduced the groundwater table (by 0.07-0.12 m), and at one location, the groundwater table experienced a 2-fold increase in the fraction of the in-channel tidal range that was observed in the marsh water table. We suggest that restoration of tidal hydrology through runnel installation holds promise as a tool to encourage revegetation and extend the lifespan of drowning coastal marshes where interior ponds are expanding. In addition, our study highlights the importance of considering the rising groundwater table as an important factor in marsh drowning due to expanding interior ponds found on the marsh platform.

Project description:Salt marsh hydrology presents many difficulties from a measurement and modeling standpoint: bi-directional flows of tidal waters, variable water densities due to mixing of fresh and salt water, significant influences from vegetation, and complex stream morphologies. Because of these difficulties, there is still much room for development of a truly mechanistic model of salt marsh groundwater and surface-water hydrology. This in turn creates an obstacle for simulating other marsh processes, such as nutrient cycling, that rely heavily on hydrology as a biogeochemical control and as a mode of nutrient transport. As a solution, we have used water level data collected from a well transect in Winant Slough, a mesotidal salt marsh on the Oregon coast, to create and calibrate a simple, empirical dynamic marsh hydrology model with few parameters. The model predicts the response of a marsh's water table level to tides and precipitation as a function of surface elevation and distance from tidal channel. Validation was conducted using additional well data from a separate transect in Winant Slough (achieving a standard error of 2.5 cm) and from two other mesotidal marshes in Tillamook Bay, Oregon (achieving standard errors of 3.1 cm and 3.6 cm). Inundation frequencies of the top 10 cm of soil were estimated from model outputs to be 18.3 % of a 14.8-day tidal cycle for the area closest to the tidal creek and 59.3 % for the area furthest from the creek. Model outputs were also used to predict the amount of soil pore space available to receive incoming tide water in Winant Slough, finding the volume available to range from 12.5 % to 24.7 % of the incoming marsh tidal prism volume, depending on the maximum tide height. Incrementally increasing sea level rise scenarios ranging from 15 cm to 75 cm predicted an exponential decrease in soil pore space available to receive incoming tidal water and an approximately linear increase in inundation frequency of the top 10 cm of soil; this substantial change in hydrology would impact the marsh's ability to process incoming water and could alter the zonation of vegetation. The model is relatively easy to apply to salt marshes and can provide informative hydrology predictions to land managers, ecologists, and biogeochemists who may not have the time or expertise required to apply more complex models.

Dataset Information

Silica uptake by Spartina-evidence of multiple modes of accumulation from salt marshes around the world.

Publications

Silica uptake by Spartina-evidence of multiple modes of accumulation from salt marshes around the world.

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