Autumn growth of three perennial weeds at high latitude benefits from climate change

In autumn, agricultural perennial weeds prepare for winter and can store reserves into creeping roots or rhizomes. Little is known about influence of climate change in this period. We tested the effect of simulated climate change in autumn on three widespread and noxious perennial weeds, Elymus repens (L.) Gould, Cirsium arvense (L.) Scop. and Sonchus arvensis L. We divided and combined simulated climate change components into elevated CO₂ concentration (525 ppm), elevated temperatures (+2–2.5°C), treatments in open‐top chambers. In addition, a control in the open‐top chamber without any increase in CO₂ and temperature, and a field control outside the chambers were included. Two geographically different origins and three pre‐growth periods prior to the exposure to climate change factors were included for each species. All species increased leaf area under elevated temperature, close to doubling in E. repens and quadrupling in the dicot species. E. repens kept leaves green later in autumn. C. arvense did not benefit in below‐ground growth from more leaf area or leaf dry mass. S. arvensis had low levels of leaf area throughout the experiment and withered earlier than the two other species. Below‐ground plant parts of S. arvensis were significantly increased by elevated temperature. Except for root:shoot ratio of C. arvense, the effects of pure elevated CO₂ were not significant for any variables compared to the open‐top chamber control. There was an additive, but no synergistic, effect of enhanced temperature and CO₂. The length of pre‐growth period was highly important for autumn plant growth, while origin had minor effect. We conclude that the small transfer of enhanced above‐ground growth into below‐ground growth under climate change in autumn does not favour creeping perennial plants per se, but more leaf area may offer more plant biomass to be tackled by chemical or physical weed control.     

Photoacclimatory and photoprotective responses to cold versus heat stress in high latitude reef corals

Corals at the world's southernmost coral reef of Lord Howe Island (LHI) experience large temperature and light fluctuations and need to deal with periods of cold temperature (<18°C), but few studies have investigated how corals are able to cope with these conditions. Our study characterized the response of key photophysiological parameters, as well as photoacclimatory and photoprotective pigments (chlorophylls, xanthophylls, and β‐carotene), to short‐term (5‐d) cold stress (~15°C; 7°C below control) in three LHI coral species hosting distinct Symbiodinium ITS2 types, and compared the coral–symbiont response to that under elevated temperature (~29°C; 7°C above control). Under cold stress, Stylophora sp. hosting Symbiodinium C118 showed the strongest effects with regard to losses of photochemical performance and symbionts. Pocillopora damicornis hosting Symbiodinium C100/C118 showed less severe bleaching responses to reduced temperature than to elevated temperature, while Porites heronensis hosting Symbiodinium C111* withstood both reduced and elevated temperature. Under cold stress, photoprotection in the form of xanthophyll de‐epoxidation increased in unbleached P. heronensis (by 178%) and bleached Stylophora sp. (by 225%), while under heat stress this parameter increased in unbleached P. heronensis (by 182%) and in bleached P. damicornis (by 286%). The xanthophyll pool size was stable in all species at all temperatures. Our comparative study demonstrates high variability in the bleaching vulnerability of these coral species to low and high thermal extremes and shows that this variability is not solely determined by the ability to activate xanthophyll de‐epoxidation.     

High‐resolution insight into recombination events at the SD1 locus in rice

Recombination during meiosis plays an important role in genome evolution by reshuffling existing genetic variations into fresh combinations with the possibility of recovery of lost ancestral genotypes. While crossover (CO) events have been well studied, gene conversion events (GCs), which represent non‐reciprocal information transfer between chromosomes, are poorly documented and difficult to detect due to their relatively small converted tract size. Here, we document these GC events and their phenotypic effects at an important locus in rice containing the SD1 gene, where multiple defective alleles contributed to the semi‐dwarf phenotype of rice in the ‘Green Revolution’ of the 1960s. Here, physical separation of two defects allows recombination to generate the wild‐type SD1 gene, for which plant height can then be used as a reporter. By screening 18 000 F₂ progeny from a cross between two semi‐dwarf cultivars that carry these different defective alleles, we detected 24 GC events, indicating a conversion rate of ~3.3 × 10^?4 per marker per generation in a single meiotic cycle in rice. Furthermore, our data show that indels and single‐nucleotide polymorphisms (SNPs) do not differ significantly in GC rates, at least at the SD1 locus. Our results provide strong evidence that GC by itself can regain an ancestral phenotype that was lost through mutation. This GC detection approach is likely to be broadly applicable to natural or artificial alleles of other phenotype‐related functional genes, which are abundant in other plant genomes.     

Net ecosystem exchange of CO2 with rapidly changing high Arctic landscapes

High Arctic landscapes are expansive and changing rapidly. However, our understanding of their functional responses and potential to mitigate or enhance anthropogenic climate change is limited by few measurements. We collected eddy covariance measurements to quantify the net ecosystem exchange (NEE) of CO₂ with polar semidesert and meadow wetland landscapes at the highest latitude location measured to date (82°N). We coupled these rare data with ground and satellite vegetation production measurements (Normalized Difference Vegetation Index; NDVI) to evaluate the effectiveness of upscaling local to regional NEE. During the growing season, the dry polar semidesert landscape was a near‐zero sink of atmospheric CO₂ (NEE: ?0.3 ± 13.5 g C m^?2). A nearby meadow wetland accumulated over 300 times more carbon (NEE: ?79.3 ± 20.0 g C m^?2) than the polar semidesert landscape, and was similar to meadow wetland NEE at much more southerly latitudes. Polar semidesert NEE was most influenced by moisture, with wetter surface soils resulting in greater soil respiration and CO₂ emissions. At the meadow wetland, soil heating enhanced plant growth, which in turn increased CO₂ uptake. Our upscaling assessment found that polar semidesert NDVI measured on‐site was low (mean: 0.120–0.157) and similar to satellite measurements (mean: 0.155–0.163). However, weak plant growth resulted in poor satellite NDVI–NEE relationships and created challenges for remotely detecting changes in the cycling of carbon on the polar semidesert landscape. The meadow wetland appeared more suitable to assess plant production and NEE via remote sensing; however, high Arctic wetland extent is constrained by topography to small areas that may be difficult to resolve with large satellite pixels. We predict that until summer precipitation and humidity increases enough to offset poor soil moisture retention, climate‐related changes to productivity on polar semideserts may be restricted.     

Aphid–willow interactions in a high Arctic ecosystem: responses to raised temperature and goose disturbance

Recently, there have been several studies using open top chambers (OTCs) or cloches to examine the response of Arctic plant communities to artificially elevated temperatures. Few, however, have investigated multitrophic systems, or the effects of both temperature and vertebrate grazing treatments on invertebrates. This study investigated trophic interactions between an herbivorous insect (Sitobion calvulum, Aphididae), a woody perennial host plant (Salix polaris) and a selective vertebrate grazer (barnacle geese, Branta leucopsis). In a factorial experiment, the responses of the insect and its host to elevated temperatures using open top chambers (OTCs) and to three levels of goose grazing pressure were assessed over two summer growing seasons (2004 and 2005). OTCs significantly enhanced the leaf phenology of Salix in both years and there was a significant OTC by goose presence interaction in 2004. Salix leaf number was unaffected by treatments in both years, but OTCs increased leaf size and mass in 2005. Salix reproduction and the phenology of flowers were unaffected by both treatments. Aphid densities were increased by OTCs but unaffected by goose presence in both years. While goose presence had little effect on aphid density or host plant phenology in this system, the OTC effects provide interesting insights into the possibility of phenological synchrony disruption. The advanced phenology of Salix effectively lengthens the growing season for the plant, but despite a close association with leaf maturity, the population dynamics of the aphid appeared to lack a similar phenological response, except for the increased population observed.     

Increased water‐use efficiency translates into contrasting growth patterns of Scots pine and sessile oak at their southern distribution limits

In forests, the increase in atmospheric CO₂ concentrations (C_a) has been related to enhanced tree growth and intrinsic water‐use efficiency (iWUE). However, in drought‐prone areas such as the Mediterranean Basin, it is not yet clear to what extent this “fertilizing” effect may compensate for drought‐induced growth reduction. We investigated tree growth and physiological responses at five Scots pine (Pinus sylvestris L.) and five sessile oak (Quercus petraea (Matt.) Liebl.) sites located at their southernmost distribution limits in Europe for the period 1960–2012 using annually resolved tree‐ring width and δ¹³C data to track ecophysiological processes. Results indicated that all 10 natural stands significantly increased their leaf intercellular CO₂ concentration (C_i), and consequently iWUE. Different trends in the theoretical gas‐exchange scenarios as a response to increasing C_a were found: generally, C_i tended to increase proportionally to C_a, except for trees at the driest sites in which C_i remained constant. C_i from the oak sites displaying higher water availability tended to increase at a comparable rate to C_a. Multiple linear models fitted at site level to predict basal area increment (BAI) using iWUE and climatic variables better explained tree growth in pines (31.9%–71.4%) than in oak stands (15.8%–46.8%). iWUE was negatively linked to pine growth, whereas its effect on growth of oak differed across sites. Tree growth in the western and central oak stands was negatively related to iWUE, whereas BAI from the easternmost stand was positively associated with iWUE. Thus, some Q. petraea stands might have partially benefited from the “fertilizing” effect of rising C_a, whereas P. sylvestris stands due to their strict closure of stomata did not profit from increased iWUE and consequently showed in general growth reductions across sites. Additionally, the inter‐annual variability of BAI and iWUE displayed a geographical polarity in the Mediterranean.     

Molecular insight into cotton leaf curl geminivirus disease resistance in cultivated cotton (Gossypium hirsutum)

Cultivated cotton (Gossypium hirsutum) is the most important fibre crop in the world. Cotton leaf curl disease (CLCuD) is the major limiting factor and a threat to textile industry in India and Pakistan. All the local cotton cultivars exhibit moderate to no resistance against CLCuD. In this study, we evaluated an exotic cotton accession Mac7 as a resistance source to CLCuD by challenging it with viruliferous whiteflies and performing qPCR to evaluate the presence/absence and relative titre of CLCuD‐associated geminiviruses/betasatellites. The results indicated that replication of pathogenicity determinant betasatellite is significantly attenuated in Mac7 and probably responsible for resistance phenotype. Afterwards, to decipher the genetic basis of CLCuD resistance in Mac7, we performed RNA sequencing on CLCuD‐infested Mac7 and validated RNA‐Seq data with qPCR on 24 independent genes. We performed co‐expression network and pathway analysis for regulation of geminivirus/betasatellite‐interacting genes. We identified nine novel modules with 52 hubs of highly connected genes in network topology within the co‐expression network. Analysis of these hubs indicated the differential regulation of auxin stimulus and cellular localization pathways in response to CLCuD. We also analysed the differential regulation of geminivirus/betasatellite‐interacting genes in Mac7. We further performed the functional validation of selected candidate genes via virus‐induced gene silencing (VIGS). Finally, we evaluated the genomic context of resistance responsive genes and found that these genes are not specific to A or D sub‐genomes of G. hirsutum. These results have important implications in understanding CLCuD resistance mechanism and developing a durable resistance in cultivated cotton.     

The Chimonanthus salicifolius genome provides insight into magnoliid evolution and flavonoid biosynthesis

Chimonanthus salicifolius, a member of the Calycanthaceae of magnoliids, is one of the most famous medicinal plants in Eastern China. Here, we report a chromosome‐level genome assembly of C. salicifolius, comprising 820.1 Mb of genomic sequence with a contig N50 of 2.3 Mb and containing 36 651 annotated protein‐coding genes. Phylogenetic analyses revealed that magnoliids were sister to the eudicots. Two rounds of ancient whole‐genome duplication were inferred in the C. salicifolious genome. One is shared by Calycanthaceae after its divergence with Lauraceae, and the other is in the ancestry of Magnoliales and Laurales. Notably, long genes with > 20 kb in length were much more prevalent in the magnoliid genomes compared with other angiosperms, which could be caused by the length expansion of introns inserted by transposon elements. Homologous genes within the flavonoid pathway for C. salicifolius were identified, and correlation of the gene expression and the contents of flavonoid metabolites revealed potential critical genes involved in flavonoids biosynthesis. This study not only provides an additional whole‐genome sequence from the magnoliids, but also opens the door to functional genomic research and molecular breeding of C. salicifolius.     

Human‐mediated dispersals do not explain tortoise distribution on the Indian Ocean's islands

Origins of giant tortoises on the Indian Ocean's islands have been debated, and most recently attributed to human translocation (see Wilmé, Patrick, & Ganzhorn, 2017). To resolve the issue, we analyse all available molecular sequences from extinct and extant Indian Ocean's giant tortoises, along with major clades of the family Testudinidae using phylogenetic methods, Bayesian inference and maximum likelihood, and a relaxed time calibration approach. Our results most strongly support giant tortoises of the genus Cylindraspis evolving in situ in the Mascarene Islands since the early mid‐Miocence, and Aldabra tortoises diverging from a Madagascan lineage in the early Oligocene. The geologic time‐scale of these speciation events and the resulting island endemism for each lineage do not support human translocation, but rather demonstrate the impressive ability of giant tortoises to disperse long distances across oceans.     

Interactions among shrub cover and the soil microclimate may determine future Arctic carbon budgets

Arctic and Boreal terrestrial ecosystems are important components of the climate system because they contain vast amounts of soil carbon (C). Evidence suggests that deciduous shrubs are increasing in abundance, but the implications for ecosystem C budgets remain uncertain. Using midsummer CO₂ flux data from 21 sites spanning 16° of latitude in the Arctic and Boreal biomes, we show that air temperature explains c. one‐half of the variation in ecosystem respiration (ER) and that ER drives the pattern in net ecosystem CO₂ exchange across ecosystems. Woody sites were slightly stronger C sinks compared with herbaceous communities. However, woody sites with warm soils (> 10 °C) were net sources of CO₂, whereas woody sites with cold soils (< 10 °C) were strong sinks. Our results indicate that transition to a shrub‐dominated Arctic will increase the rate of C cycling, and may lead to net C loss if soil temperatures rise.     

Dispersal barriers and climate determine the geographic distribution of the helicopter damselfly Mecistogaster modesta

相似文献   

Mass spectrometry analysis of human P2X1 receptors; insight into phosphorylation,modelling and conformational changes

Recombinant FlagHis₆ tagged Human P2X1 receptors expressed in HEK293 cells were purified, digested with trypsin and analysed by mass spectroscopy (96% coverage following de‐glycosylation and reduction). The receptor was basally phosphorylated at residues S387, S388 and T389 in the carboxyl terminus, a triple alanine mutant of these residues had a modest ~ 25% increase in current amplitude and recovery from desensitization. Chemical modification showed that intracellular lysine residues close to the transmembrane domains and the membrane stabilization motif are accessible to the aqueous environment. The membrane‐impermeant cross‐linking reagent 3,3′‐Dithiobis (sulfosuccinimidylpropionate) (DTSSP) reduced agonist binding and P2X1 receptor currents by > 90%, and modified lysine residues were identified by mass spectroscopy. Mutation to remove reactive lysine residues around the ATP‐binding pocket had no effect on inhibtion of agonist evoked currents following DTSSP. However, agonist evoked currents were ~ 10‐fold higher than for wild type following DTSSP treatment for mutants K199R, K221R and K199R‐K221R. These mutations remove reactive residues distant from the agonist binding pocket that are close enough to cross‐link adjacent subunits. These results suggest that conformational change in the P2X1 receptor is required for co‐ordination of ATP action.     

Invasion,establishment, and range expansion of two parasitic nematodes in the Canadian Arctic

Climate warming is occurring at an unprecedented rate in the Arctic and is having profound effects on host‐parasite interactions, including range expansion. Recently, two species of protostrongylid nematodes have emerged for the first time in muskoxen and caribou on Victoria Island in the western Canadian Arctic Archipelago. Umingmakstrongylus pallikuukensis, the muskox lungworm, was detected for the first time in 2008 in muskoxen at a community hunt on the southwest corner of the island and by 2012, it was found several hundred kilometers east in commercially harvested muskoxen near the town of Ikaluktutiak. In 2010, Varestrongylus sp., a recently discovered lungworm of caribou and muskoxen was found in muskoxen near Ikaluktutiak and has been found annually in this area since then. Whereas invasion of the island by U. pallikuukensis appears to have been mediated by stochastic movement of muskoxen from the mainland to the southwest corner of the island, Varestrongylus has likely been introduced at several times and locations by the seasonal migration of caribou between the island and the mainland. A newly permissive climate, now suitable for completion of the parasite life cycles in a single summer, likely facilitated the initial establishment and now drives range expansion for both parasites.     

Onset and establishment of diazotrophs and other bacterial associates in the early life history stages of the coral Acropora millepora

Early establishment of coral–microbial symbioses is fundamental to the fitness of corals, but comparatively little is known about the onset and succession of bacterial communities in their early life history stages. In this study, bacterial associates of the coral Acropora millepora were characterized throughout the first year of life, from larvae and 1‐week‐old juveniles reared in laboratory conditions in the absence of the dinoflagellate endosymbiont Symbiodinium to field‐outplanted juveniles with established Symbiodinium symbioses, and sampled at 2 weeks and at 3, 6 and 12 months. Using an amplicon pyrosequencing approach, the diversity of both nitrogen‐fixing bacteria and of bacterial communities overall was assessed through analysis of nifH and 16S rRNA genes, respectively. The consistent presence of sequences affiliated with diazotrophs of the order Rhizobiales (23–58% of retrieved nifH sequences; 2–12% of 16S rRNA sequences), across all samples from larvae to 12‐month‐old coral juveniles, highlights the likely functional importance of this nitrogen‐fixing order to the coral holobiont. Dominance of Roseobacter‐affiliated sequences (>55% of retrieved 16S rRNA sequences) in larvae and 1‐week‐old juveniles, and the consistent presence of sequences related to Oceanospirillales and Altermonadales throughout all early life history stages, signifies their potential importance as coral associates. Increased diversity of bacterial communities once juveniles were transferred to the field, particularly of Cyanobacteria and Deltaproteobacteria, demonstrates horizontal (environmental) uptake of coral‐associated bacterial communities. Although overall bacterial communities were dynamic, bacteria with likely important functional roles remain stable throughout early life stages of Acropora millepora.     

SIRT1 regulates MAPK pathways in vitiligo skin: insight into the molecular pathways of cell survival

Vitiligo is an acquired and progressive hypomelanotic disease that manifests as circumscribed depigmented patches on the skin. The aetiology of vitiligo remains unclear, but recent experimental data underline the interactions between melanocytes and other typical skin cells, particularly keratinocytes. Our previous results indicate that keratinocytes from perilesional skin show the features of damaged cells. Sirtuins (silent mating type information regulation 2 homolog) 1, well‐known modulators of lifespan in many species, have a role in gene repression, metabolic control, apoptosis and cell survival, DNA repair, development, inflammation, neuroprotection and healthy ageing. In the literature there is no evidence for SIRT1 signalling in vitiligo and its possible involvement in disease progression. Here, biopsies were taken from the perilesional skin of 16 patients suffering from non‐segmental vitiligo and SIRT1 signalling was investigated in these cells. For the first time, a new SIRT1/Akt, also known as Protein Kinase B (PKB)/mitogen‐activated protein kinase (MAPK) signalling has been revealed in vitiligo. SIRT1 regulates MAPK pathway via Akt‐apoptosis signal‐regulating kinase‐1 and down‐regulates pro‐apoptotic molecules, leading to decreased oxidative stress and apoptotic cell death in perilesional vitiligo keratinocytes. We therefore propose SIRT1 activation as a novel way of protecting perilesional vitiligo keratinocytes from damage.     

Anticipating changes to future connectivity within a network of marine protected areas

Continental boundary currents are projected to be altered under future scenarios of climate change. As these currents often influence dispersal and connectivity among populations of many marine organisms, changes to boundary currents may have dramatic implications for population persistence. Networks of marine protected areas (MPAs) often aim to maintain connectivity, but anticipation of the scale and extent of climatic impacts on connectivity are required to achieve this critical conservation goal in a future of climate change. For two key marine species (kelp and sea urchins), we use oceanographic modelling to predict how continental boundary currents are likely to change connectivity among a network of MPAs spanning over 1000 km of coastline off the coast of eastern Australia. Overall change in predicted connectivity among pairs of MPAs within the network did not change significantly over and above temporal variation within climatic scenarios, highlighting the need for future studies to incorporate temporal variation in dispersal to robustly anticipate likely change. However, the intricacies of connectivity between different pairs of MPAs were noteworthy. For kelp, poleward connectivity among pairs of MPAs tended to increase in the future, whereas equatorward connectivity tended to decrease. In contrast, for sea urchins, connectivity among pairs of MPAs generally decreased in both directions. Self‐seeding within higher‐latitude MPAs tended to increase, and the role of low‐latitude MPAs as a sink for urchins changed significantly in contrasting ways. These projected changes have the potential to alter important genetic parameters with implications for adaptation and ecosystem vulnerability to climate change. Considering such changes, in the context of managing and designing MPA networks, may ensure that conservation goals are achieved into the future.     

Spatial genetic analysis of two polyploid macrophytes reveals high connectivity in a modified wetland

相似文献   

Redrawing the map: mtDNA provides new insight into the distribution and diversity of short‐finned pilot whales in the Pacific Ocean

Correlations between morphological and genetic data provide evidence to delineate species or evolutionarily significant units, which then become the units to conserve in management plans. Here, we examine the distribution and genetic differentiation of two morphotypes of short‐finned pilot whale (Globicephala macrorhynchus) in the Pacific Ocean. Mitochondrial control region sequences from 333 samples were combined with 152 previously published sequences to describe genetic variability globally and population structure in the Pacific. Although genetic variability is low, we found strong differentiation at both broad and local levels across the Pacific. Based on genetics, two types are distributed throughout the Pacific, one predominantly in the eastern Pacific and the other in the western and central Pacific. In the eastern Pacific Ocean, no correlation was found between distribution and sea surface temperature. The two types have broad latitudinal ranges, suggesting their distributions are likely driven by more complex factors, such as prey distribution, rather than sea surface temperature.     

Methane emissions from Amazonian Rivers and their contribution to the global methane budget

Methane (CH₄) fluxes from world rivers are still poorly constrained, with measurements restricted mainly to temperate climates. Additional river flux measurements, including spatio‐temporal studies, are important to refine extrapolations. Here we assess the spatio‐temporal variability of CH₄ fluxes from the Amazon and its main tributaries, the Negro, Solimões, Madeira, Tapajós, Xingu, and Pará Rivers, based on direct measurements using floating chambers. Sixteen of 34 sites were measured during low and high water seasons. Significant differences were observed within sites in the same river and among different rivers, types of rivers, and seasons. Ebullition contributed to more than 50% of total emissions for some rivers. Considering only river channels, our data indicate that large rivers in the Amazon Basin release between 0.40 and 0.58 Tg CH₄ yr^?1. Thus, our estimates of CH₄ flux from all tropical rivers and rivers globally were, respectively, 19–51% to 31–84% higher than previous estimates, with large rivers of the Amazon accounting for 22–28% of global river CH₄ emissions.