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1. Individual variation in plasticity dulls transgenerational responses to stress

   https://doi.org/10.1111/1365-2435.13409  

   Gillis, Michael K. ; Walsh, Matthew R. ; Pfrender, ed., Michael ( August 2019 , Functional Ecology)

   Much research has shown that environmental stress can induce adaptive and maladaptive phenotypic changes in organisms that persist for multiple generations. Such transgenerational phenotypic plasticity shrouds our understanding of the long‐term consequences of ongoing anthropogenic pressures.

   Here, we evaluated within‐ and transgenerational phenotypic responses to food stress in the freshwater crustacean,Daphnia. We reared 45 clones ofDaphnia pulicariaeach on high‐qualityScenedesmusand low‐quality (but also non‐toxic) cyanobacteria (generation 1). Offspring produced by generation 1 adults were then reared onScenedesmus(generation 2), and life‐history traits were measured across both generations.

   The results show thatDaphniain generation 1 exhibited reduced fitness (i.e., delayed maturation, lower reproductive output, increased clutch interval) when reared in the presence of cyanobacteria as opposed to high‐quality food. However, maternal stress had no clear influence on the fitness of offspring. That is,Daphniain the second experimental generation had similar mean trait values, irrespective of whether their mothers were reared on cyanobacteria or high‐quality food.

   Signals of transgenerational life‐history effects were obscured, in part, by extensive clonal variation amongDaphniain the direction of transgenerational responses to cyanobacteria (i.e., adaptive and maladaptive plasticity). Further analyses demonstrated that such individual variance in plasticity might be open to selection and potentially offer a means of contemporary adaptation to cyanobacteria. Taken together, our results denote a link between the overall strength of transgenerational responses to the environment and the potential for rapid evolution in populations.

   A freePlain Language Summarycan be found within the Supporting Information of this article.

    

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2. Asymmetric responses of primary productivity to precipitation extremes: A synthesis of grassland precipitation manipulation experiments

   https://doi.org/10.1111/gcb.13706  

   Wilcox, Kevin R. ; Shi, Zheng ; Gherardi, Laureano A. ; Lemoine, Nathan P. ; Koerner, Sally E. ; Hoover, David L. ; Bork, Edward ; Byrne, Kerry M. ; Cahill, Jr., James ; Collins, Scott L. ; et al ( May 2017 , Global Change Biology)

   Climatic changes are altering Earth's hydrological cycle, resulting in altered precipitation amounts, increased interannual variability of precipitation, and more frequent extreme precipitation events. These trends will likely continue into the future, having substantial impacts on net primary productivity (NPP) and associated ecosystem services such as food production and carbon sequestration. Frequently, experimental manipulations of precipitation have linked altered precipitation regimes to changes inNPP. Yet, findings have been diverse and substantial uncertainty still surrounds generalities describing patterns of ecosystem sensitivity to altered precipitation. Additionally, we do not know whether previously observed correlations betweenNPPand precipitation remain accurate when precipitation changes become extreme. We synthesized results from 83 case studies of experimental precipitation manipulations in grasslands worldwide. We used meta‐analytical techniques to search for generalities and asymmetries of abovegroundNPP(ANPP) and belowgroundNPP(BNPP) responses to both the direction and magnitude of precipitation change. Sensitivity (i.e., productivity response standardized by the amount of precipitation change) ofBNPPwas similar under precipitation additions and reductions, butANPPwas more sensitive to precipitation additions than reductions; this was especially evident in drier ecosystems. Additionally, overall relationships between the magnitude of productivity responses and the magnitude of precipitation change were saturating in form. The saturating form of this relationship was likely driven byANPPresponses to very extreme precipitation increases, although there were limited studies imposing extreme precipitation change, and there was considerable variation among experiments. This highlights the importance of incorporating gradients of manipulations, ranging from extreme drought to extreme precipitation increases into future climate change experiments. Additionally, policy and land management decisions related to global change scenarios should consider howANPPandBNPPresponses may differ, and that ecosystem responses to extreme events might not be predicted from relationships found under moderate environmental changes.

    

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3. Repetitive desiccation events weaken a salt marsh mutualism

   https://doi.org/10.1111/1365-2745.13178  

   Derksen‐Hooijberg, Marlous ; Angelini, Christine ; Hoogveld, Jasper R. H. ; Lamers, Leon P. M. ; Borst, Annieke ; Smolders, Alfons ; Harpenslager, Sarah Fay ; Govers, Laura L. ; van der Heide, Tjisse ; Randall Hughes, ed., A. ( April 2019 , Journal of Ecology)

   Salt marshes suffered large‐scale degradation in recent decades. Extreme events such as hot and dry spells contributed significantly to this, and are predicted to increase not only in intensity, but also in frequency under future climate scenarios. Such repetitive extreme events may generate cumulative effects on ecosystem resilience. It is therefore important to elucidate how marsh vegetation responds to repetitive stress, and whether changes in key species interactions can modulate vegetation resilience.

   In this study, we investigated how moderate but repetitive desiccation events, caused by the combined effects of drought and high temperatures, affect cordgrass (Spartina alterniflora), the dominant habitat‐forming grass in southeasternUSsalt marshes. In a 4‐month field experiment, we simulated four consecutive desiccation events by periodically excluding tidal flooding and rainfall, while raising temperature. We crossed this desiccation treatment with the presence/absence of ribbed mussels (Geukensia demissa) – a mutualist of cordgrass known to enhance its desiccation resilience – and with grazing pressure by the marsh periwinkle (Littoraria irrorata) that is known to suppress cordgrass’ desiccation resilience.

   We found that each subsequent desiccation event deteriorated sediment porewater conditions, resulting in high salinity (53 ppt), low pH‐levels (3.7) and increased porewater Al and Fe concentrations (≈800 μmol/L and ≈1,500 μmol/L) upon rewetting. No effects on porewater chemistry were found as a result of snail grazing, while ribbed mussels strongly mitigated desiccation effects almost to control levels and increased cordgrass biomass by approximately 128%. Importantly, although cordgrass generally appeared healthy above‐ground at the end of the experiment, we found clear negative responses of the repetitive desiccation treatment on cordgrass below‐ground biomass, on proline (osmolyte) levels in shoots and on the number of tillers (−40%), regardless of mussel and/or snail presence.

   Synthesis. Even though the mutualism with mussels strongly mitigated chemical effects in the sediment porewater throughout the experiment, mussels could not buffer the adverse ecophysiological effects observed in cordgrass tissue. Our results therefore suggest that although mussels may alleviate desiccation stress, the predicted increased frequency and intensity of hot dry spells may eventually affect saltmarsh resilience by stressing the mutualism beyond its buffering capacity.

    

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4. Restoration and resilience to sea level rise of a salt marsh affected by dieback events

   https://doi.org/10.1002/ecs2.4467  

   Rolando, J. L. ; Hodges, M. ; Garcia, K. D. ; Krueger, G. ; Williams, N. ; Carr, Jr., J. ; Robinson, J. ; George, A. ; Morris, J. ; Kostka, J. E. ( April 2023 , Ecosphere)

   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 used a 13‐year collection of remotely sensed imagery to 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, as indicated by the Palmer drought stress index. A second dieback event occurred in 2016 after a historic flood influenced by Hurricane Joaquin in 2015. Unvegetated zones reached nearly 30% of the total marsh area in 2017. We used a light detection and ranging‐derived digital elevation model to determine that most affected areas were associated with lower elevation zones in the interior of the marsh. Further, restoration by grass planting was effective, with pilot‐scale restored plots having greater aboveground biomass than reference sites after two years of transplanting. A positive outcome indicated that the stressors that caused the dieback are no longer present. Despite that, many affected areas have not recovered naturally, even though they are located within the typical elevation range of healthy marshes. A mechanistic modeling 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 year⁻¹) would persist at a moderate SLR rate of 60 cm in 100 years, whereas a nonrestored mudflat would lose all 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 that trigger irreversible marsh diebacks underestimates salt marsh vulnerability to climate change. Finally, at an elevated SLR rate of 122 cm in 100 years, which is 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.

    

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5. Vegetation response to climatic changes in western Amazonia over the last 7,600 years

   https://doi.org/10.1111/jbi.13704  

   Nascimento, Majoi N. ; Martins, Gabriel S. ; Cordeiro, Renato C. ; Turcq, Bruno ; Moreira, Luciane S. ; Bush, Mark B. ( September 2019 , Journal of Biogeography)

   Ongoing and future anthropogenic climate change poses one of the greatest threats to biodiversity, affecting species distributions and ecological interactions. In the Amazon, climatic changes are expected to induce warming, disrupt precipitation patterns and of particular concern, to increase the intensity and frequency of droughts. Yet the response of ecosystems to intense warm, dry events is not well understood. In the Andes the mid‐Holocene dry event (MHDE),c. 9,000 to 4,000 years ago, was the warmest and driest period of the last 100,000 years which coincided with changes in evaporation and precipitation that caused lake levels to drop over most of tropical South America. This event probably approximates our near‐climatic future, and a critical question is:How much did vegetation change in response to this forcing?

   Lake Pata, Brazilian Western Amazonia.

   Terrestrial and aquatic plants.

   We used pollen, charcoal, total organic carbon (TOC), total nitrogen (TN), δ¹³C and δ¹⁵N data from a new high‐resolution core that spans the lastc. 7,600 years history of Lake Pata.

   We found that in the wettest section of Amazonia changes associated with the MHDE were detected in the geochemistry analysis but that vegetation changed very little in response to drought during the Holocene. This is the first high‐resolution core without apparent hiatuses that spans most of the Holocene (last 7,600 cal yrbp) from Lake Pata, Brazil. Changes in the organic geochemistry of sediments indicated that between c. 6,500 and 3,600 cal yrbplake levels dropped. Vegetation, however, showed little change as near‐modern forests were seen throughout the record, evidencing the substantial resilience of this system. Only a few species replacements and minor fluctuations in abundance were observed in the pollen record.

   The mid‐Holocene warming and reduced precipitation had a limited impact on western Amazonian forests. We attribute much of the resilience to a lack of fire in this system, and that if human‐set fires were to be introduced, the forest destruction from that cause would override that induced by climate alone.

    

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