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1. Self-healing behaviour of furan–maleimide poly(ionic liquid) covalent adaptable networks

   https://doi.org/10.1039/D0PY00016G  

   Lindenmeyer, Katelyn M.; Johnson, R. Daniel; Miller, Kevin M. (January 2020, Polymer Chemistry)

   Poly(ionic liquid) covalently adaptable networks containing thermoreversible furan–maleimide linkages were prepared and characterized for their thermal, mechanical and conductive properties. Self-healing behaviour was initially evaluated using oscillatory rheology where a G ′/ G ′′ crossover temperature of ∼110 °C was observed. Anhydrous conductivities, as determined by dielectric relaxation spectroscopy, were found to be on the order of 10 −8 S cm −1 at 30 °C. Recovery of >70% of the original stress and strain at break was found within 2 hours at 105 °C as determined from tensile testing experiments, with breakage occurring at a new point on the film. Recovery of conductivity was completed utilizing chronoamperometric cycling whereby >75% of the original current was recovered within two hours at 110 °C. 

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2. Eelgrass meadow response to heat stress. II. Impacts of ocean warming and marine heatwaves measured by novel metrics

   https://doi.org/10.3354/meps14588  

   Berger, AC; Berg, P; McGlathery, KJ; Aoki, LR; Kerns, K (May 2024, Marine Ecology Progress Series)

   In June 2015, a marine heatwave triggered a severe eelgrassZostera marinadie-off event at the Virginia Coast Reserve (USA), followed by a slow and spatially heterogeneous recovery. We investigated the effects of heat stress on seagrass loss and recovery. Using hourly summer water temperature measurements from 2016-2020, we developed a novel approach to quantifying the stress of ocean warming on seagrass meadows. We defined 2 metrics: cumulative heat stress (as heating degree-hours, HDHs) and heat stress relief (as cooling degree-hours, CDHs), relative to a 28.6°C eelgrass ecosystem thermal tolerance threshold previously determined at this site from aquatic eddy covariance measurements. These metrics were compared to spatiotemporal patterns of summertime eelgrass shoot density and length. We found that the healthiest parts of the meadow benefited from greater heat stress relief (2-3×) due to tidal cooling (inputs of cooler ocean water through ocean inlets) during warm periods, resulting in ~65% higher shoot densities compared to the center of the meadow, which experienced higher heat stress (2×) and less relief. We also calculated the amount of heat stress preceding the eelgrass die-off in summer 2015, and found that this event was triggered by a cumulative heat stress of ~100-200°C-hours during the peak growing season. Sulfur isotope analyses of eelgrass leaves and sediment also suggested that sulfide toxicity likely contributed to eelgrass decline. Overall, our metrics incorporate physiological heat tolerances with the duration and intensity of heat stress and relief, and thus lay the groundwork for forecasting seagrass meadow vulnerability and resilience to future warming oceans. 

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3. Resilience to Hurricanes Is High in Mangrove Blue Carbon Forests

   https://doi.org/10.1111/gcb.70124  

   Reed, David; Chavez, Selena; Castañeda‐Moya, Edward; Oberbauer, Steven_F; Troxler, Tiffany; Malone, Sparkle (March 2025, Global Change Biology)

   ABSTRACT Mangrove forests are typically considered resilient to natural disturbances, likely caused by the evolutionary adaptation of species‐specific traits. These ecosystems play a vital role in the global carbon cycle and are responsible for an outsized contribution to carbon burial and enhanced sedimentation rates. Using eddy covariance data from two coastal mangrove forests in the Florida Coastal Everglades, we evaluated the impact hurricanes have on mangrove forest structure and function by measuring recovery to pre‐disturbance conditions following Hurricane Wilma in 2005 and Hurricane Irma in 2017. We determined the “recovery debt,” the deficit in ecosystem structure and function following a disturbance, using the leaf area index (LAI) and the net ecosystem exchange (NEE) of carbon dioxide (CO₂). Calculated as the cumulative deviation from pre‐disturbance conditions, the recovery debt incorporated the recapture of all the carbon lost due to the disturbance. In Everglades mangrove forests, LAI returned to pre‐disturbance levels within a year, and ecosystem respiration and maximum photosynthetic rates took much longer, resulting in an initial recovery debt of 178 g C m⁻²at the tall forest with limited impacts at the scrub forest. At the landscape scale, the initial recovery debt was 0.40 Mt C, and in most coastal mangrove forests, all lost carbon was recovered within just 4 years. While high‐intensity storms could have prolonged impacts on the structure of subtropical forests, fast canopy recovery suggests these ecosystems will remain strong carbon sinks. 

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4. Fast and pervasive transcriptomic resilience and acclimation of extremely heat-tolerant coral holobionts from the northern Red Sea

   https://doi.org/10.1073/pnas.2023298118  

   Savary, Romain; Barshis, Daniel J.; Voolstra, Christian R.; Cárdenas, Anny; Evensen, Nicolas R.; Banc-Prandi, Guilhem; Fine, Maoz; Meibom, Anders (May 2021, Proceedings of the National Academy of Sciences)

   null (Ed.)

   Corals from the northern Red Sea and Gulf of Aqaba exhibit extreme thermal tolerance. To examine the underlying gene expression dynamics, we exposed Stylophora pistillata from the Gulf of Aqaba to short-term (hours) and long-term (weeks) heat stress with peak seawater temperatures ranging from their maximum monthly mean of 27 °C (baseline) to 29.5 °C, 32 °C, and 34.5 °C. Corals were sampled at the end of the heat stress as well as after a recovery period at baseline temperature. Changes in coral host and symbiotic algal gene expression were determined via RNA-sequencing (RNA-Seq). Shifts in coral microbiome composition were detected by complementary DNA (cDNA)-based 16S ribosomal RNA (rRNA) gene sequencing. In all experiments up to 32 °C, RNA-Seq revealed fast and pervasive changes in gene expression, primarily in the coral host, followed by a return to baseline gene expression for the majority of coral (>94%) and algal (>71%) genes during recovery. At 34.5 °C, large differences in gene expression were observed with minimal recovery, high coral mortality, and a microbiome dominated by opportunistic bacteria (including Vibrio species), indicating that a lethal temperature threshold had been crossed. Our results show that the S. pistillata holobiont can mount a rapid and pervasive gene expression response contingent on the amplitude and duration of the thermal stress. We propose that the transcriptomic resilience and transcriptomic acclimation observed are key to the extraordinary thermal tolerance of this holobiont and, by inference, of other northern Red Sea coral holobionts, up to seawater temperatures of at least 32 °C, that is, 5 °C above their current maximum monthly mean. 

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5. Mixed mechanisms of bond exchange in covalent adaptable networks: monitoring the contribution of reversible exchange and reversible addition in thiol–succinic anhydride dynamic networks

   https://doi.org/10.1039/d0py00091d  

   Podgórski, Maciej; Spurgin, Nathan; Mavila, Sudheendran; Bowman, Christopher N. (August 2020, Polymer Chemistry)

   Dynamic photopolymer networks that take advantage of the thermodynamically controlled reversibility of thiol–succinic anhydride adducts were synthesized from commercial substrates and investigated as a new class of covalent adaptable networks (CANs). Through systematic studies of the catalyst and stoichiometry effects on the exchange dynamics two distinctive exchange mechanisms were found, and then demonstrated to contribute to the overall dynamic characteristics. By varying the catalyst activity, i.e. basicity and/or nucleophilicity, control over the dynamic responsiveness through changes in the type of dynamic covalent chemistry mode (reversible addition vs. reversible exchange) was achieved in otherwise compositionally analogous materials. More specifically, the participation of the associative mechanism (thiol–thioester exchange) in the otherwise dissociative networks, and its relevance on materials properties was demonstrated by dielectric analysis (DEA) and dynamic mechanical analysis (DMA). The activation energies ( E a ) for viscous flow obtained from DMA stress relaxation experiments and from dielectric modulus and loss crossover points were shown to match well between the two techniques. The E a in stoichiometric systems was found to be 110–120 kJ mol −1 , whereas 50% excess thiol systems were characterized by E a ranging 95–105 kJ mol −1 . The thermodynamic equilibrium conversion, estimated in the temperature controlled FTIR, for a stoichiometric 3-mercaptopropionate-succinic anhydride combination was determined at 92 ± 1% at ambient temperature, and decreased to 67 ± 1% at 120 °C within one hour of equilibration time (Δ H ° = −46 ± 5 kJ mol −1 ). Such high potential for reversibility of the thioester anhydride linkages resembles maleimide-furan Diels–Alder networks but has many other attributes that make these CANs of unprecedented value in fundamental research on dynamic materials. 

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