Biology subjects

Rolando, J. L.

Publications and source records attributed to Rolando, J. L..

3 recordsLinked to original sources

bioRxiv2023

Sulfur oxidation and reduction are coupled to nitrogen fixation in the roots of a salt marsh foundation plant species

Symbiotic root microbiota are crucial for plant growth as they assist their hosts in nutrient acquisition. In the roots of coastal marine plants, heterotrophic activity in the rhizosphere by sulfate-reducing microorganisms has been linked to nitrogen fixation. In this study, we recovered 239 high-quality metagenome-assembled genomes (MAGs) from a salt marsh dominated by the foundation plant Spartina alterniflora, including diazotrophic sulfate-reducing and sulfur-oxidizing bacteria thriving in the root compartment. Here we show for the first time that highly-abundant sulfur-oxidizing bacteria in the roots of a coastal macrophyte encode and highly express genes for nitrogen fixation (nifHDK). Further, we leveraged a S. alterniflora biomass gradient to gain a mechanistic understanding on how root-microbe interactions respond to abiotic stress from anoxia and elevated sulfide concentration. We observed that the roots of the stressed S. alterniflora phenotype exhibited the highest rates of nitrogen fixation and expression levels of both the oxidative and reductive forms of the dissimilatory sulfite reductase gene (dsrAB). Approximately 25% and 15% of all sulfur-oxidizing dsrA and nitrogen-fixing nifK transcripts, respectively, were associated with novel MAGs of the Candidatus Thiodiazotropha genus in the roots of the stressed S. alterniflora phenotype. We conclude that the rapid cycling of sulfur in the dynamic S. alterniflora root zone is coupled to nitrogen fixation during both reductive and oxidative sulfur reactions, and that the S. alterniflora - Ca. Thiodiazotropha symbiosis is an adaptive response to anoxic and sulfidic sediment conditions, whereby the plants benefit from reduced sulfide toxicity and potential nitrogen acquisition.

microbiology↗

bioRxiv2022

Severe drought events trigger long-term salt marsh dieback in the Southeastern and Gulf of Mexico USA

The frequency of salt marsh dieback events has increased over the last 25 years with unknown consequences to the resilience of the ecosystem to accelerated sea level rise (SLR). Salt marsh ecosystems impacted by sudden vegetation dieback events were previously thought to recover naturally within a few months to years. In this study, we provide evidence that approximately 14% of total marsh area has not revegetated 10-years after a dieback event in Charleston, SC. Dieback onset coincided with a severe drought in 2012, and a second dieback event occurred in 2016 after a historic flood influenced by Hurricane Joaquin in October of 2015, with unvegetated zones reaching nearly 30% of total marsh area in 2017. Most affected areas were associated with lower elevation zones in the interior of the marsh (midmarsh). During the 2013 dieback event, we estimate that unvegetated midmarsh area expanded by 300%. Grass planting was shown to be an effective restoration practice, with restored plants having greater aboveground biomass than relict sites after two years of transplanting. A positive restoration outcome indicated that the stressors that caused the initial dieback are no longer present. Despite that, many dieback areas have not recovered naturally even as they are located within the typical elevation range of a healthy vegetated marsh. A mechanistic modelling approach was used to assess the effects of vegetation dieback on salt marsh resilience to SLR. Predictions indicate that a highly productive restored marsh (2000 g m-2 y-1) would persist at a moderate SLR rate of 60 cm 100 y-1, whereas a non- restored mudflat would lose all of its elevation capital after 100 years. Thus, rapid restoration of marsh dieback is critical to avoid further degradation. Also, failure to incorporate the increasing frequency and intensity of extreme climatic events which trigger irreversible marsh diebacks underestimates salt marsh vulnerability to climate change. At an elevated SLR rate of 122 cm 100 y-1, most likely an extreme climate change scenario, even highly productive ecosystems augmented by sediment placement would not keep pace with SLR. Thus, climate change mitigation actions are also urgently needed to preserve present-day marsh ecosystems.

ecology↗

bioRxiv2021

The core root microbiome of Spartina alterniflora is predominated by sulfur-oxidizing and sulfate-reducing bacteria in Georgia salt marshes, USA

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 detoxify sulfide in the root zone while potentially transferring fixed C and N to the host plant.

microbiology↗