Explore the vast range of titles available.

Isoprene synthase converts dimethylallyl diphosphate to isoprene and appears to be necessary and sufficient to allow plants to emit isoprene at significant rates. Isoprene can protect plants from abiotic stress but is not produced naturally by all plants; for example, Arabidopsis (Arabidopsis thaliana) and tobacco (Nicotiana tabacum) do not produce isoprene. It is typically present at very low concentrations, suggesting a role as a signaling molecule; however, its exact physiological role and mechanism of action are not fully understood. We transformed Arabidopsis with a Eucalyptus globulus isoprene synthase. The regulatory mechanisms of photosynthesis and isoprene emission were similar to those of native emitters, indicating that regulation of isoprene emission is not specific to isoprene-emitting species. Leaf chlorophyll and carotenoid contents were enhanced by isoprene, which also had a marked positive effect on hypocotyl, cotyledon, leaf, and inflorescence growth in Arabidopsis. By contrast, leaf and stem growth was reduced in tobacco engineered to emit isoprene. Expression of genes belonging to signaling networks or associated with specific growth regulators (e.g. gibberellic acid that promotes growth and jasmonic acid that promotes defense) and genes that lead to stress tolerance was altered by isoprene emission. Isoprene likely executes its effects on growth and stress tolerance through direct regulation of gene expression. Enhancement of jasmonic acid-mediated defense signaling by isoprene may trigger a growth-defense tradeoff leading to variations in the growth response. Our data support a role for isoprene as a signaling molecule.

The abundance and distribution of surface water at high latitudes is shifting rapidly in response to both climate change and permafrost thaw. In particular, the expansion and drainage of lakes and ponds is widespread but spatially variable, and more research is needed to understand factors driving these processes. In this study we used medium resolution (30 m) remote sensing data to analyse changes in lake area in permafrost-rich lowland regions across northwestern Canada. First, we used the Global Surface Water Dataset developed by the GLAD research group to map the absolute area of different land–water transitions across a 1.4 million km 2 study domain. Next, we selected six regional study areas representing a range of climatic, geologic and hydrologic conditions. Within these regional study areas, we used the Landsat satellite archive to map annual trends in the area of 27 755 lakes between 1985 and 2020. We trained a random forests model to classify lakes exhibiting significant increasing or decreasing trends in area, and assessed the relative importance of climate, disturbance and environmental variables in determining the direction of change. Our analysis shows that significant increases in lake area were 5.6 times more frequent than decreases during the study period. Wildfire and ground ice abundance were the most important predictors of the direction of change. Greater ground ice content was associated with regions that experienced increases in lake area, while wildfire was associated with regions that experienced decreases in lake area. The effects of climate, including trends in mean annual temperature and total annual precipitation were smaller than disturbance and environmental factors, indicating that climate has likely had indirect effects on lake area changes over our period of study.

Climate change at high latitudes is expected to increase the cover of woody vegetation across the forest-tundra ecotone. However, there is still uncertainty concerning the nature and magnitude of these changes. In this study, we used open access satellite remote sensing data from ICESat-2 and Landsat to model change in vegetation structure across 183 million hectares of the Canadian forest-tundra ecotone from 1985 to 2021. We used Random Forests models to predict canopy presence and height across six time periods at 30 m spatial resolution. Change between time periods was used to classify nine stable and transitional vegetation types. We used these data to map advance and retreat in the northernmost forest limit and linked change types to disturbance history. Over the study period, the extent of forested area increased by 0.9% and the forest limit warmed by 1.08 °C, receiving 25 mm more annual precipitation. However, large parts of the forest limit remained stable over time despite favorable climate conditions. Our mapping also revealed divergent patterns in forest and shrub expansion across the ecotone, with shrubs exhibiting more widespread and diffuse expansion above the forest limit. Increasing vegetation structure across the ecotone was strongly associated with fire history as 80% of mapped vegetation changes occurred in disturbed areas. The majority of forest growth and new forest expansion occurred in fires that burned over 40 years ago. These findings highlight the importance of disturbance-recovery dynamics in structural vegetation change over decadal time periods.

Global socioeconomic and ecological changes strongly impact Indigenous communities by affecting food security, physical health, and overall wellbeing. Throughout the 1900s, residents of the Mackenzie Delta in Canada's western Arctic relied heavily on the muskrat (Ondatra zibethicus) for food, fur, and culture, but recent changes to ecological and economic conditions have altered the nature of this relationship. We investigated the role of muskrats in the cultural traditions and land-based livelihoods of the Gwich'in and Inuvialuit residents of the Mackenzie Delta through interviews and meetings with over 70 community members. Although the role of muskrats has changed over the last 100 years, muskrat harvesting continues to offer Delta residents a meaningful way to remain engaged in, perpetuate, and strengthen their cultural identity and land-based traditions among generations, and ultimately, to foster individual and community wellbeing.

Recent research using repeat photography, long-term ecological monitoring and dendrochronology has documented shrub expansion in arctic, high-latitude and alpine tundra ecosystems. Here, we (1) synthesize these findings, (2) present a conceptual framework that identifies mechanisms and constraints on shrub increase, (3) explore causes, feedbacks and implications of the increased shrub cover in tundra ecosystems, and (4) address potential lines of investigation for future research. Satellite observations from around the circumpolar Arctic, showing increased productivity, measured as changes in 'greenness', have coincided with a general rise in high-latitude air temperatures and have been partly attributed to increases in shrub cover. Studies indicate that warming temperatures, changes in snow cover, altered disturbance regimes as a result of permafrost thaw, tundra fires, and anthropogenic activities or changes in herbivory intensity are all contributing to observed changes in shrub abundance. A large-scale increase in shrub cover will change the structure of tundra ecosystems and alter energy fluxes, regional climate, soil–atmosphere exchange of water, carbon and nutrients, and ecological interactions between species. In order to project future rates of shrub expansion and understand the feedbacks to ecosystem and climate processes, future research should investigate the species or trait-specific responses of shrubs to climate change including: (1) the temperature sensitivity of shrub growth, (2) factors controlling the recruitment of new individuals, and (3) the relative influence of the positive and negative feedbacks involved in shrub expansion.

Isoprene is one of the most abundant volatile organic compounds produced by some, though not all, plant species. It confers stress tolerance in both emitting and non-emitting species and has large impacts on gene regulation as well as on atmospheric chemistry. Understanding the control of isoprene emission from plants is important to understanding plant responses to future atmospheric conditions. In this study we determined that suppression of isoprene emission from plants by high CO2 concentrations is reduced but not eliminated by high temperature. We tested whether the CO2 suppression is caused by the reduction in ATP or NADPH availability caused by triose phosphate utilization (TPU) limitation of photosynthesis at high CO2. We measured CO2 assimilation as well as several photosynthetic electron transport parameters under multiple atmospheric conditions in four plant species grown at ambient CO2. While CO2 sensitivity of isoprene emission was somewhat correlated with TPU in some species, in other species it was not. Poplar exhibited significant CO2 suppression of isoprene emission but no evidence for TPU so we investigated further, measuring the electrochromic shift that gives information on ATP synthesis and photosystem I oxidation state. In all cases photosynthetic parameters were unchanged while isoprene emission dropped in response to increasing CO2. Non-photorespiratory conditions (2% O2) led to an increase in isoprene emission at low CO2 but did not alleviate suppression by high CO2. In all measured species the combination of higher temperature along with higher CO2 concentrations led to a net increase of isoprene emission in response to a moderate scenario for temperature and CO2 concentration in 2100 in the upper Midwest.

Climate change is altering northern vegetation structure and below-ground carbon storage. Expanding forest and shrub cover has decreased soil organic carbon (SOC) storage in some parts of the forest-tundra ecotone. In this study, we linked measurements of SOC with terrain and vegetation structure derived from drone imagery across treelines underlain by continuous permafrost in the Northwest Territories, Canada. We classified sites into three treeline types representing differences in vegetation productivity and topography. Between treeline types, we observed differences in C:N ratios and organic matter depth related to the rate of soil carbon turnover and SOC storage. Overall, SOC showed small positive relationships with tree stem density and average canopy height. We did not find evidence that expanding tree- and shrublines would result in losses of SOC storage in our study area. Instead, topography and landscape drainage patterns, rather than vegetation structure may be more important predictors of SOC storage. We used medium resolution satellite data to extend predictions of treeline type across our study area. The majority of predicted treelines (82%) showed positive relationships between vegetation height and SOC storage. Our findings highlight the value of integrating vegetation structure and landscape features in understanding carbon dynamics in the forest-tundra ecotone.

An apparently exindusiate filicalean fern with radial sori, sporangia with a vertical annulus, and monolete spores occurs in Paleocene sediments ca. 57 million years old of central Alberta, Canada. Specimens are preserved as coalified compressions and show features of frond morphology and venation, sporangium morphology and dehiscence mechanism, number of spores per sporangium, and spore fine structure. Fronds have a deltoid blade region and are pinnate + pinnatifid, with fertile pinnules ranging to slightly smaller than vegetative pinnules and with simpler venation. Venation is open, with each lobe of the pinnatifid pinnule having a midvein from which laterals diverge in an alternate pattern. Laterals of vegetative pinnule lobes fork once and terminate at the margin, whereas those of fertile pinnule lobes are unbranched. Sori are round with numerous sporangia and are positioned under a vein. Each sporangium has a vertical annulus that is not interrupted by the stalk and produces ca. 64 spores. Spores are bean shaped and monolete, measuring 26-36 µm long, with exospore that is dense and sculptured by minute scabrae. Perispore is not preserved. This fern, named Speirseopteris orbiculata gen. et sp. nov., displays characters that are diagnostic of the highly derived filicalean families and is assigned to the Thelypteridaceae. To a lesser extent, it also resembles the Dryopteridaceae, emphasizing that modern fern genera existed among many extinct genera during the late Cretaceous and Paleogene. [PUBLICATION ABSTRACT]

The majority of variation in six traits critical to the growth, survival and reproduction of plant species is thought to be organised along just two dimensions, corresponding to strategies of plant size and resource acquisition. However, it is unknown whether global plant trait rela­tionships extend to climatic extremes, and if these interspecific relationships are confounded by trait variation within species. We test whether trait relationships extend to the cold extremes of life on Earth using the largest database of tundra plant traits yet compiled. We show that tundra plants demonstrate remarkably similar resource economic traits, but not size traits, compared to global distributions, and exhibit the same two dimensions of trait variation. Three quarters of trait variation occurs among species, mirroring global estimates of interspecific trait variation. Plant trait relationships are thus generalizable to the edge of global trait-space, informing prediction of plant community change in a warming world.

A permineralized tree fern from the Lower Cretaceous (Aptian) near Cottonwood, California is described as Conantiopteris schuchmanii gen. et sp. nov. The specimen, 23.2 cm long and 11.7 cm wide, shows helically arranged persistent frond bases embedded in adventitious roots, and is clothed by multicellular trichomes. A parenchymatous pith with mucilaginous cells and sclerotic nests is surrounded by an amphiphloic distyostele, parenchymatous inner cortex, and outer sclerenchymatous cortex. Sclerenchyma also surrounds the cauline vasculature and leaf traces. Medullary and cortical bundles are absent. Phloem contains both axially elongated and tangential sieve elements. Frond bases are oval in outline with three vascular bundles, including an undulating abaxial arc and an adaxial pair. Protoxylem of the stipe is endarch and is associated with cavity parenchyma. These characters are indicative of tree fern affinities. A cladistic analysis using trunk characters of both living and fossil tree ferns was conducted to help establish relationships of the new species and other fossil ferns, and to test hypotheses of general tree fern relationships. Additional analyses of living taxa only were also performed. Results from the analysis using both living and fossil taxa compare favorably with those that included only living species when either morphological characters or molecular sequences of the chloroplast gene rbcL are utilized. Although there are variations in the topologies of the various trees, results indicate that the new genus is nested among a paraphyletic assemblage of dicksoniaceous, lophosoriaceous, and metaxyaceous species that subtend a monophyletic Cyatheaceae s.s