Young adults' experiences of biographical retrogression whilst living with long COVID.

During the early years (2020-2021) of the COVID-19 pandemic, relatively little attention focused on experiences of people with long-lasting symptoms, particularly young adults who were commonly understood to be invulnerable to serious effects of the virus. Drawing on narrative interviews with 15 adults in their twenties and living in the UK when they became ill with long COVID, we explore contextual factors which made their long COVID illness experience, and the wholescale disruption to their lives, challenging. We propose that existing adaptations of the concept of biographical disruption are problematic for this group, and instead suggest that 'biographical retrogression' may more accurately reflect these young adults' experiences. For many of these young adults, their illness occurred at a crucial stage in forming or solidifying (presumed) adult trajectories. Secondly, the recency of long COVID did not allow for comparison with an existing 'grand narrative' of recovery, so the future course of their illness was not just unknown for them as individuals; there was no prognostic map against which to assess their symptoms. Thirdly, the lives of people with long COVID have been disrupted in the context of global societal disruption by the same virus, rendering their experiences both topical yet invisible.

From bottom-up to top-down control of invertebrate herbivores in a retrogressive chronosequence.

In the long-term absence of disturbance, ecosystems often enter a decline or retrogressive phase which leads to reductions in primary productivity, plant biomass, nutrient cycling and foliar quality. However, the consequences of ecosystem retrogression for higher trophic levels such as herbivores and predators, are less clear. Using a post-fire forested island-chronosequence across which retrogression occurs, we provide evidence that nutrient availability strongly controls invertebrate herbivore biomass when predators are few, but that there is a switch from bottom-up to top-down control when predators are common. This trophic flip in herbivore control probably arises because invertebrate predators respond to alternative energy channels from the adjacent aquatic matrix, which were independent of terrestrial plant biomass. Our results suggest that effects of nutrient limitation resulting from ecosystem retrogression on trophic cascades are modified by nutrient-independent variation in predator abundance, and this calls for a more holistic approach to trophic ecology to better understand herbivore effects on plant communities.

Isotopic constraints on plant nitrogen acquisition strategies during ecosystem retrogression.

Plant root associations with microbes such as mycorrhizal fungi or N-fixing bacteria enable ecosystems to tap pools of nitrogen (N) that might otherwise be inaccessible, including atmospheric N or N in large soil organic molecules. Such microbially assisted N-foraging strategies may be particularly important in late-successional retrogressive ecosystems where productivity is low and soil nutrients are scarce. Here, we use natural N-stable isotopic composition to constrain pathways of N supplies to different plant functional groups across a well-studied natural soil fertility gradient that includes a highly retrogressive stage. We demonstrate that ectomycorrhizal fungi, ericoid mycorrhizal fungi, and N-fixing bacteria support forest N supplies at all stages of ecosystem succession, from relatively young, N-rich/phosphorus (P)-rich sites, to ancient sites (ca. 500 ky) where both N supplies and P supplies are exceedingly low. Microbially mediated N sources are most important in older ecosystems with very low soil nutrient availability, accounting for 75-96% of foliar N at the oldest, least fertile sites. These isotopically ground findings point to the key role of plant-microbe associations in shaping ecosystem processes and functioning, particularly in retrogressive-phase forest ecosystems.

Evolutionary perspectives on ageing.

From an evolutionary perspective, ageing is a decrease in fitness with chronological age - expressed by an increase in mortality risk and/or decline in reproductive success and mediated by deterioration of functional performance. While this makes ageing intuitively paradoxical - detrimental to individual fitness - evolutionary theory offers answers as to why ageing has evolved. In this review, I first briefly examine the classic evolutionary theories of ageing and their empirical tests, and highlight recent findings that have advanced our understanding of the evolution of ageing (condition-dependent survival, positive pleiotropy). I then provide an overview of recent theoretical extensions and modifications that accommodate those new discoveries. I discuss the role of indeterminate (asymptotic) growth for lifetime increases in fecundity and ageing trajectories. I outline alternative views that challenge a universal existence of senescence - namely the lack of a germ-soma distinction and the ability of tissue replacement and retrogression to younger developmental stages in modular organisms. I argue that rejuvenation at the organismal level is plausible, but includes a return to a simple developmental stage. This may exempt a particular genotype from somatic defects but, correspondingly, removes any information acquired during development. A resolution of the question of whether a rejuvenated individual is the same entity is central to the recognition of whether current evolutionary theories of ageing, with their extensions and modifications, can explain the patterns of ageing across the Tree of Life.

Saprotrophic and ectomycorrhizal fungal sporocarp stoichiometry (C†:†N†:†P) across temperate rainforests as evidence of shared nutrient constraints among symbionts.

Quantifying nutritional dynamics of free-living saprotrophs and symbiotic ectomycorrhizal fungi in the field is challenging, but the stoichiometry of fruiting bodies (sporocarps) may be an effective methodology for this purpose. Carbon (C), nitrogen (N) and phosphorus (P) concentrations of soils, foliage and 146 sporocarp collections were analyzed from 14 Pseudotsuga menziesii var. menziesii stands across a podzolization gradient on Vancouver Island (Canada). N and P concentrations were considerably higher in saprotrophic fungi. Fungal N% increased with soil N content at a greater rate for saprotrophs than ectomycorrhizal fungi, while fungal P% of saprotrophs was more constrained. Fungal N : P was more responsive to soil N : P for ectomycorrhizal fungi (homeostatic regulation coefficient 'H' = 2.9) than saprotrophs (H = 5.9), while N : P of ectomycorrhizal fungi and host tree foliage scaled almost identically. Results underscore the role of ectomycorrhizal fungi as nutrient conduits, supporting host trees, whereas saprotrophs maintain a greater degree of nutritional homeostasis. Site nutrient constraints were shared in equal measure between ectomycorrhizal fungi and host trees, particularly for P, suggesting neither partner benefits from enhanced nutrition at the expense of the other. Sporocarp stoichiometry provides new insights into mycorrhizal relationships and illustrates pervasive P deficiencies across temperate rainforests of the Pacific Northwest.

Symmetric assembly and disassembly processes in an ecological network.

The processes whereby ecological networks emerge, persist and decay throughout ecosystem development are largely unknown. Here we study networks of plant and arbuscular mycorrhizal fungal (AMF) communities along a 120 000 year soil chronosequence, as they undergo assembly (progression) and then disassembly (retrogression). We found that network assembly and disassembly were symmetrical, self-reinforcing processes that together were capable of generating key attributes of network architecture. Plant and AMF species that had short indirect paths to others in the community (i.e. high centrality), rather than many direct interaction partners (i.e. high degree), were best able to attract new interaction partners and, in the case of AMF species, also to retain existing interactions with plants during retrogression. We then show using simulations that these non-random patterns of attachment and detachment promote nestedness of the network. These results have implications for predicting extinction sequences, identifying focal points for invasions and suggesting trajectories for restoration.

Soil fertility shapes belowground food webs across a regional climate gradient.

Changes in soil fertility during pedogenesis affect the quantity and quality of resources entering the belowground subsystem. Climate governs pedogenesis, yet how climate modulates responses of soil food webs to soil ageing remains unexplored because of the paucity of appropriate model systems. We characterised soil food webs along each of four retrogressive soil chronosequences situated across a strong regional climate gradient to show that belowground communities are predominantly shaped by changes in fertility rather than climate. Basal consumers showed hump-shaped responses to soil ageing, which were propagated to higher-order consumers. There was a shift in dominance from bacterial to fungal energy channels with increasing soil age, while the root energy channel was most important in intermediate-aged soils. Our study highlights the overarching importance of soil fertility in regulating soil food webs, and indicates that belowground food webs will respond more strongly to shifts in soil resources than climate change.

Host identity is a dominant driver of mycorrhizal fungal community composition during ecosystem development.

Little is known about the response of arbuscular mycorrhizal fungal communities to ecosystem development. We use a long-term soil chronosequence that includes ecosystem progression and retrogression to quantify the importance of host plant identity as a factor driving fungal community composition during ecosystem development. We identified arbuscular mycorrhizal fungi and plant species from 50 individual roots from each of 10 sites spanning 5-120 000 yr of ecosystem age using terminal restriction fragment length polymorphism (T-RFLP), Sanger sequencing and pyrosequencing. Arbuscular mycorrhizal fungal communities were highly structured by ecosystem age. There was strong niche differentiation, with different groups of operational taxonomic units (OTUs) being characteristic of early succession, ecosystem progression and ecosystem retrogression. Fungal alpha diversity decreased with ecosystem age, whereas beta diversity was high at early stages and lower in subsequent stages. A total of 39% of the variance in fungal communities was explained by host plant and site age, 29% of which was attributed to host and the interaction between host and site (24% and 5%, respectively). The strong response of arbuscular mycorrhizal fungi to ecosystem development appears to be largely driven by plant host identity, supporting the concept that plant and fungal communities are tightly coupled rather than independently responding to habitat.

Effect of Retrogression with Different Cooling Ways on the Microstructure and Properties of T'/η' Strengthened Al-Zn-Mg-Cu Alloys.

Retrogression and re-aging (RRA) treatment has been proven to effectively overcome the trade-off between strength and corrosion resistance. Current research focuses on the heating rate, temperature, and holding time of retrogression treatment while ignoring the retrogression cooling ways. In this paper, the effects of RRA treatment with different retrogression cooling ways on the microstructure and properties of newly developed T'/η' strengthened Al-Zn-Mg-Cu alloys were investigated by performing tests on mechanical properties, intergranular corrosion (IGC) resistance, and electrochemical corrosion behavior. The results show that the mechanical properties of samples subject to RRA treatment with water-quenching retrogression (ultimate tensile strength, yield strength, and elongation of 419.2 MPa, 370.2 MPa, and 15.9, respectively) are better than those of air-cooled and furnace-cooled samples. The corrosion resistance of water-quenching (IGC depth of 162.2 µm, corrosion current density of 0.833 × 10-5 A/cm2) and furnace-cooled samples (IGC depth of 123.7 µm, corrosion current density of 0.712 × 10-5 A/cm2) is better than that of air-cooled samples. Microstructure characterization reveals that the effect of the retrogression cooling rate on mechanical properties is related to the size of T'/η' precipitates with grains as well as the proportion of T' and η', while the difference in corrosion resistance depends on the continuity of grain boundary precipitates (GBPs). With mechanical properties, corrosion resistance, and time cost taken into consideration, it is appropriate to select water quenching for retrogression. These findings offer valuable insights for further design to achieve superior performance in various applications.

Influence of Retrogression Time on the Fatigue Crack Growth Behavior of a Modified AA7475 Aluminum Alloy.

This paper investigates the effect of retrogression time on the fatigue crack growth of a modified AA7475 aluminum alloy. Tests including tensile strength, fracture toughness, and fatigue limits were performed to understand the changes in properties with different retrogression procedures at 180 °C. The microstructure was characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The findings indicated that as the retrogression time increased, the yield strength decreased from 508 MPa to 461 MPa, whereas the fracture toughness increased from 48 MPa√m to 63.5 MPa√m. The highest fracture toughness of 63.5 MPa√m was seen after 5 h of retrogression. The measured diameter of η' precipitates increased from 6.13 nm at the retrogression 1 h condition to 6.50 nm at the retrogression 5 h condition. Prolonged retrogression also increased the chance of crack initiation, with slower crack growth rate in the long transverse direction compared to the longitudinal direction. An empirical relationship was established between fracture toughness and the volume fraction of age-hardening precipitates, with increasing number density of precipitates seen with increasing retrogression time.

Influence of Nanoclay Content on Cement Matrix for Oil Wells Subjected to Cyclic Steam Injection.

High-temperature conditions drastically compromise the physical properties of cement, especially, its strengths. In this work, the influence of adding nanoclay (NC) particles to Saudi class G oil well cement (OWC) strength retrogression resistance under high-temperature condition (300 °C) is evaluated. Six cement slurries with different concentrations of silica flour (SF) and NC were prepared and tested under conditions of 38 °C and 300 °C for different time periods (7 and 28 days) of curing. The changes in the cement matrix compressive and tensile strengths, permeability, loss in the absorbed water, and the cement slurry rheology were evaluated as a function of NC content and temperature, the changes in the structure of the cement surfaces were investigated through the optical microscope. The results revealed that the use of NC (up to 3% by weight of cement (BWOC)) can prevent the OWC deterioration under extremely high-temperature conditions. Incorporating more than 3% of NC severely damaged the cement matrix microstructure due to the agglomeration of the nanoparticles. Incorporation of NC particles increased all the cement slurry rheological properties.

Displacement of a landslide retaining wall and application of an enhanced failure forecasting approach.

The 10-mile Slide is contained within an ancient earthflow located in British Columbia, Canada. The landslide has been moving slowly for over 40 years, requiring regular maintenance work along where a highway and a railway track cross the sliding mass. Since 2013, the landslide has shown signs of retrogression. Monitoring prisms were installed on a retaining wall immediately downslope from the railway alignment to monitor the evolution of the retrogression. As of September 2016, cumulative displacements in the horizontal direction approached 4.5 m in the central section of the railway retaining wall. After an initial phase of acceleration, horizontal velocities showed a steadier trend between 3 and 9 mm/day, which was then followed by a second acceleration phase. This paper presents an analysis of the characteristics of the surface displacement vectors measured at the monitoring prisms. Critical insight on the behavior and kinematics of the 10-mile Slide retrogression was gained. An advanced analysis of the trends of inverse velocity plots was also performed to assess the potential for a slope collapse at the 10-mile Slide and to obtain further knowledge on the nature of the sliding surface.

Plant succession as an integrator of contrasting ecological time scales.

Ecologists have studied plant succession for over a hundred years, yet our understanding of the nature of this process is incomplete, particularly in relation to its response to new human perturbations and the need to manipulate it during ecological restoration. We demonstrate how plant succession can be understood better when it is placed in the broadest possible temporal context. We further show how plant succession can be central to the development of a framework that integrates a spectrum of ecological processes, which occur over time scales ranging from seconds to millions of years. This novel framework helps us understand the impacts of human perturbations on successional trajectories, ecosystem recovery, and global environmental change.