Search

Background and aims: Over-grazing have significantly altered above- and belowground functions in terrestrial ecosystem. However, the influence of grazing intensity on plant-soil stoichiometric relations in alpine ecosystems remains unclear. Methods: We investigated the responses of plant-soil nutrient stoichiometric relationships to four grazing intensities (un-grazing (UG), light grazing (LG), moderate grazing (MG) and heavy grazing (HG)) in an alpine meadow on the eastern Tibetan Plateau. We measured carbon (C), nitrogen (N), phosphorus (P) and potassium (K) concentrations and their ratios in plants and soils in the peak growing season after three years of yak-grazing. Results: Compared to UG and LG plots, heavier grazing intensity at community levels and taxonomic groups decreased plant C and K concentrations by 7.6–10.5% and 17.6–21.3%, respectively, while grazing did not significantly influence plant N and P concentrations. Grazing intensity altered plant C:N and C:P ratios but not C:K and N:P ratios. By contrast, grazing intensity had no significant effects on soil nutrients and stoichiometry. Thus, the differential responses of plant and soil nutrients to grazing intensity caused that plants were more sensitive to grazing than soils. Conclusions: Our results confirm that grazing intensity has differential effects on plant and soil nutrients, implying that plant nutrients do not covary with soil nutrients under changing grazing intensity and challenging the past positive relations between plant and soil nutrients. Further long-term grazing experiments are required to understand the drivers of grazing effect on plant-soil nutrient interactions. [ABSTRACT FROM AUTHOR]

Subnival glasshouse plants provide a text-book example of high-altitude adaptation with reproductive organs enclosed in specialized semi-translucent bracts, monocarpic reproduction and continuous survival under stress. Here, we present genomic, transcriptomic and metabolomic analyses for one such plant, the Noble rhubarb (Rheum nobile). Comparative genomic analyses show that an expanded number of genes and retained genes from two recent whole-genome duplication events are both relevant to subnival adaptation of this species. Most photosynthesis genes are downregulated within bracts compared to within leaves, and indeed bracts exhibit a sharp reduction in photosynthetic pigments, indicating that the bracts no longer perform photosynthesis. Contrastingly, genes related to flavonol synthesis are upregulated, providing enhanced defense against UV irradiation damage. Additionally, anatomically abnormal mesophyll combined with the downregulation of genes related to mesophyll differentiation in bracts illustrates the innovation and specification of the glass-like bracts. We further detect substantial accumulation of antifreeze proteins (e.g. AFPs, LEAs) and various metabolites (e.g. Proline, Protective sugars, procyanidins) in over-wintering roots. These findings provide new insights into subnival adaptation and the evolution of glasshouse alpine plants. A chromosome-level genome assembly for the glasshouse plant Rheum nobile (noble rhubarb) combined with phylogenetic, transcriptomic, and metabolomic analyses provides insight into how alpine plants have adapted to growth in extreme environments. [ABSTRACT FROM AUTHOR]

Semiconductor quantum dots (QDs) are among the most promising emerging fluorescent labels for cellular imaging. However, it is unclear whether QDs, which are nanoparticles rather than small molecules, can specifically and effectively label molecular targets at a subcellular level. Here we have used QDs linked to immunoglobulin G (IgG) and streptavidin to label the breast cancer marker Her2 on the surface of fixed and live cancer cells, to stain actin and microtubule fibers in the cytoplasm, and to detect nuclear antigens inside the nucleus. All labeling signals are specific for the intended targets and are brighter and considerably more photostable than comparable organic dyes. Using QDs with different emission spectra conjugated to IgG and streptavidin, we simultaneously detected two cellular targets with one excitation wavelength. The results indicate that QD-based probes can be very effective in cellular imaging and offer substantial advantages over organic dyes in multiplex target detection. [ABSTRACT FROM AUTHOR]

Introgression frequently occurs between closely related plant species when there is incomplete reproductive isolation. However, few studies have been designed to examine the extent and direction of introgression from all three genomes, especially when they have different rates of gene flow. Conifers, in which chloroplast (cp), mitochondrial (mt) and nuclear (nr) genomes show contrasting rates of gene flow, provide a good model in which to carry out such a case study. Here we use data on sequence variation in 18 DNAs from three genomes for 311 individuals of 31 populations to investigate the extent and direction of introgressions between three spruce species in areas where they are sympatrically distributed. We found that one species seem to have introgressions derived from the other two species in areas of sympatric distribution; there were more introgressions from the maternally inherited mtDNA, which has the lowest rate of gene flow, and fewer introgressions from the bi-parentally inherited nrDNA. Further coalescent analysis of nrDNA population genetic data suggested that the species containing introgressions had experienced range expansion in the recent past while there was no such indication for the other two species. Our results support the hypotheses that introgressions occurred more frequently at genetic markers with lower rates of gene flow and that they usually took place from local species towards invading species that had undergone recent demographic expansion. [ABSTRACT FROM AUTHOR]

Elucidating the evolutionary history of current species diversity, especially trees with large effective population sizes and long generation times, is a complicated exercise confounded by gene flow and incomplete lineage sorting. In the present study, we aim to determine the origin and speciation of Picea schrenkiana and Picea smithiana using population genetic data from chloroplast (cp), mitochondrial (mt), and nuclear (nr) genomes. These two species occur in the Central Asian Highlands and Himalayas, respectively, where they are isolated from other Asian congeneric species by the Qinghai-Tibet Plateau (QTP) or adjacent deserts. Previous studies based on both morphological and molecular evidence suggest that they have contrasting phylogenetic relationships with Picea likiangensis or Picea wilsonii which are closely related and both located in the QTP. We examined genetic variation among 16 loci of three genomes from 30 populations of these four species. At both cpDNA loci and mtDNA loci, P. schrenkiana appeared to be closely related to P. likiangensis, although statistical support for this was weak. However, phylogenetic analyses and speciation tests based on the nuclear data from 11 loci provided evidence that P. schrenkiana and P. smithiana are sister species. These two species diverged around five million years ago (Mya) while the divergence between them and the P. likiangensis- P. wilsonii clade occurred about 18.4 Mya. We also detected gene flow accompanying these speciation events. Our results highlight the complex speciation histories of these alpine conifers due to interspecific gene flow and/or incomplete lineage sorting, and the importance of the early QTP uplifts in promoting the origin of these important conifer species in the Asian highlands. [ABSTRACT FROM AUTHOR]

Polyploidization has contributed greatly to current plant diversity. Allopolyploid speciation, which can rapidly overcome meiosis abnormalities, is a common and repeated process in numerous genera. However, most polyploids within a single morphological/taxonomic species have been considered autopolyploids, which were assumed to arise through spontaneous genome doubling and/or following the fusion of unreduced diploid gametes. It remains untested whether these intraspecific polyploids may also be the result of 'allopolyploid' hybridizations between differentiated diploid populations and whether such speciation has also occurred repeatedly. In this study, we examined the diploid-tetraploid species Allium przewalskianum on the Qinghai-Tibet Plateau (QTP) to test this cryptic speciation hypothesis under morphological stasis, based on three sets of nuclear genetic data (AFLP, ITS, and CHS) and niche modeling. Our analyses of the three datasets together revealed that the diploid populations across the northeastern to southeastern QTP exhibit strong geographical differentiation. Based on the shared nuclear lineages fixed in the different diploids, three tetraploid groups in the northern, southern, and eastern QTP were identified as having originated independently, through 'allopolyploid' hybridization between the differentiated diploids. Ecological niche modeling based on ecological variables suggested distinct niche differentiation between two tetraploid groups in the northern and southern QTP and also between these and the diploid populations. Furthermore, they also differed in their responses to past climate changes. These findings together suggested that at least two tetraploid groups had originated independently through hybridizations between the differentiated diploid populations. Our results highlight the cryptic allopolyploid speciation underlying a single morphological species, which mirrors well the repeated allopolyploid speciations within the genus. This allopolyploid speciation may prevail within the diploid-polyploid species complex that is classified as a single morphological species; indeed, the underlying cryptic speciation and evolutionary dynamics are certainly more complex than previously assumed. [ABSTRACT FROM AUTHOR]

Species delimitation has been a major research focus in evolutionary biology. However, the genetic delimitation of recently diverged species varies depending on the markers examined. In this study, we aimed to examine genetic differentiation and delimitations between only two species of Pugionium Gaertn (Brassicaceae)- Pugionium cornutum (L.) Gaertn and Pugionium dolabratum Maxim-that occur in the desert habitats of central Asia and have parapatric distributions. We genotyped 169 individuals from 25 populations, using two chloroplast (cp) DNA fragments ( trnV- trnM and trnS- trnfM), seven simple repeated sequence (SSR) loci and the nuclear ribosomal internal transcribed spacer (ITS). Four cp haplotypes were identified, three of which commonly occur in the two species, suggesting incomplete species-specific lineage sorting. Between-species cpDNA differentiation ( F) was low, even lower than among populations of the same species. However, we found higher than average SSR F values, and both Bayesian clustering of SSR variables and maximum-likelihood genetic analyses divided all sampled individuals into two groups, agreeing well with morphological separation, although gene flow between species was obvious according to the SSR loci data. However, two types of ITS sequences were highly consistent with the morphological delimitation of the two species in all sampled individuals. These results together suggest that these two species shared numerous ancestral cpDNA polymorphisms and point to the importance of nuclear DNA (ITS or genetic accumulation at multiple loci) in delimiting recently diverged species. [ABSTRACT FROM AUTHOR]

The Kobresia pastures of the Tibetan Plateau represent the world's largest alpine grassland ecosystem. These pastures remained stable during the last millennia of nomadic animal husbandry. However, strongly increased herds' density has promoted overgrazing, with unclear consequences for vegetation and soils, particularly for cycles of carbon (C), nutrients and water. Vegetation-free patches of dead root-mat covered by blue-green algae and crustose lichens (crusts) are common in overgrazed Kobresia pastures, but their effect on C turnover processes is completely unknown. We tested the hypothesis that the crusts strongly affect the C cycle by examining: (i) the long-term C stock measured as soil organic matter content; (ii) medium-term C stock as dead roots; (iii) recent C fluxes analyzed as living roots and CO efflux; and (iv) fast decomposition of root exudates. Up to 7.5 times less aboveground and 1.9 times less belowground living biomass were found in crust patches, reflecting a much smaller C input to soil as compared with the non-crust Kobresia patches. A lower C input initially changed the long-term C stock under crusts in the upper root-mat horizon. Linear regression between living roots and CO efflux showed that roots contributed 23% to total CO under non-crust areas (mean July-August 5.4 g C m day) and 18% under crusts (5.1 g C m day). To identify differences in the fast turnover processes in soil, we added C labeled glucose, glycine and acetic acid, representing the three main groups of root exudates. The decomposition rates of glucose (0.7 day), glycine (1.5 day) and acetic acid (1.2 day) did not differ under crusts and non-crusts. More C, however, remained in soil under crusts, reflecting less complete decomposition of exudates and less root uptake. This shows that the crust patches decrease the rates of medium-term C turnover in response to the much lower C input. Very high C amounts recovered in plants from non-crust areas as well as the two times lower uptake by roots under crusts indicate that very dense roots are efficient competitors with microorganisms for soluble organics. In conclusion, the altered C cycle in the overgrazing-induced crustose lichens and blue-green algae crusts is connected with strongly decreased C input and reduced medium-term C turnover. [ABSTRACT FROM AUTHOR]

The purpose of this study was to examine the repairing ability of nano-hydroxyapatite (nano-HA) artificial bone with different pore sizes. Animal models of bone defects were created in both radii of 60 New Zealand white rabbits. The bone defects in A, B, and C groups were repaired with nano-HA artificial bone with three different pore sizes while those in group D were left unrepaired. The repairing ability of material was evaluated by gross observation, histopathological study, X-ray examination, scanning electron microscope (SEM), and biomechanical analysis in the fourth, eighth, and 12th weeks. Group B stimulated more bone formation than the other groups. Nano-HA artificial bone is capable of good bone formation and biocompatibility. The ability of bone formation of nano-HA artificial bone may be affected significantly by the pore size. The material with pore size in the range of 100 -250 μm has a greater ability to form bone. [ABSTRACT FROM AUTHOR]

This paper provides information about the distribution, structure, and ecology of the world's largest alpine ecosystem, the Kobresia pygmaea pastures in the southeastern Tibetan plateau. The environmental importance of these Cyperaceae mats derives from the extremely firm turf, which protects large surfaces against erosion, including the headwaters of the Huang He, Yangtze, Mekong, Salween, and Brahmaputra. The emphasis of the present article is on the climate-driven evolution and recent dynamics of these mats under the grazing impact of small mammals and livestock. Considering pedological analyses, radiocarbon datings, and results from exclosure experiments, we hypothesize that the majority of K. pygmaea mats are human-induced and replace forests, scrub, and taller grasslands. At present, the carrying capacity is increasingly exceeded, and reinforced settlement of nomads threatens this ecosystem especially in its drier part, where small mammals become strong competitors with livestock and the removal of the turf is irreversible. Examples of rehabilitation measures are given. [ABSTRACT FROM AUTHOR]

Presents a corrected version of the article `Immunofluorescent labeling of cancer marker Her2 and other cellular targets with semiconductor quantum dots,' by Xingyong Wu et al, published in the Number 21, 2003 issue of the `Nature Biotechnology' journal.

Introgression may act as an important source of new genetic variation to facilitate the adaptation of organisms to new environments, yet how introgression might enable tree species to adapt to higher latitudes and elevations remains unclear. Applying whole-transcriptome sequencing and population genetic analyses, we present an example of ancient introgression from a cypress species (Cupressus gigantea) that occurs at higher latitude and elevation on the Qinghai-Tibet Plateau into a related species (C. duclouxiana), which has likely aided the latter species to extend its range by colonizing cooler and drier mountain habitats during postglacial periods. We show that 16 introgressed candidate adaptive loci could have played pivotal roles in response to diverse stresses experienced in a high-elevation environment. Our findings provide new insights into the evolutionary history of Qinghai-Tibet Plateau plants and the importance of introgression in the adaptation of species to climate change. Yazhen Ma et al. find evidence of an ancient introgression from cypress into a related species from the Qinghai-Tibet Plateau, which aided in the colonization of cooler and drier mountain habitats. They identify 16 introgressed loci that may provide protection against high-elevation stressors. [ABSTRACT FROM AUTHOR]

Wood, which consists mainly of plant cell walls, is an extremely important resource in daily lives. Genes whose products participate in the processes of cell wall and wood formation are therefore major subjects of plant science research. The Wood-Formation Related Genes database (WFRGdb, http://me.lzu.edu.cn/woodformation/) serves as a data resource center for genes involved in wood formation. To create this database, we collected plant genome data published in other online databases and predicted all cell wall and wood formation related genes using BLAST and HMMER. To date, 47 gene families and 33 transcription factors from 57 genomes (28 herbaceous, 22 woody and 7 non-vascular plants) have been covered and more than 122,000 genes have been checked and recorded. To provide easy access to these data, we have developed several search methods, which make it easy to download targeted genes or groups of genes free of charge in FASTA format. Sequence and phylogenetic analyses are also available online. WFRGdb brings together cell wall and wood formation related genes from all available plant genomes, and provides an integrative platform for gene inquiry, downloading and analysis. This database will therefore be extremely useful for those who focuses on cell wall and wood research. [ABSTRACT FROM AUTHOR]