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91.
Christopher I Keeling Macaire MS Yuen Nancy Y Liao T Roderick Docking Simon K Chan Greg A Taylor Diana L Palmquist Shaun D Jackman Anh Nguyen Maria Li Hannah Henderson Jasmine K Janes Yongjun Zhao Pawan Pandoh Richard Moore Felix AH Sperling Dezene P W Huber Inanc Birol Steven JM Jones Joerg Bohlmann 《Genome biology》2013,14(3):R27
92.
Nancy Shackelford Michael Renton Michael P. Perring Kristine Brooks Richard J. Hobbs 《Journal of Plant Ecology》2015,8(1):17
Aims Understanding the relationships among disturbance, invasion and species change is essential for effective management of many systems. We investigated relationships among fire history, invasion by a native tree species, Allocasuarina huegeliana, and diversity change to understand the potential drivers of plant community alteration in a complex and biodiverse system.Methods We used plant species surveys from 1983 and 2011 to quantify species loss/gain and thence compositional changes. Additionally, we surveyed population densities of the invasive species and collated long-term fire history data for each site. General linear models and non-parametric models were used to assess the strength of relationships between the three variables of interest.Important findings Within the last 30 years, ~11% of the plant species richness was lost from the reserve. At an individual site level, we found only a 4% average decrease in overall plant species richness, but large species losses and gains that imply considerable compositional shifts. Though such shifts might be expected over 30 years, many of the gained species were common, potentially opportunistic species, while those lost were often locally rare woody perennials. In addition, gained species tended to be expanding their recorded range westward suggesting that they may be responding to the regional drying climate. The relationship between invasion density and species loss was strong over all spatial scales. We identified a potential state change to dominance by the native invasive particularly as high densities prevented species gain at the site scale. In these extreme cases of high invasive density and high biodiversity loss, we argue that there may be a need to directly address the expanding native population. 相似文献
93.
A full-length Picea abies cDNA clone Pa18, encoding a protein with the characteristics of plant lipid transfer proteins, has been isolated and characterized. The size of the deduced 173 amino acid (aa) long protein is around 18 kDa. The first 100–120 aa show similarity to angiosperm lipid transfer proteins in amino acid sequence as well as in predicted secondary structure. The Pa18 gene is constitutively expressed in embryogenic cultures of Picea abies representing different stages of development as well as in non-embryogenic callus and seedlings. The Pa18 gene product has an antimicrobial activity. In situ hybridization showed that the Pa18 gene is equally expressed in all embryonic cells of proliferating embryogenic cultures but during embryo maturation the expression of the gene in maturing and mature somatic as well as in mature zygotic embryos is stronger in the outer cell layer than in other tissues. Southern blot analysis at different stringencies was consistent with a single gene with one or two copies rather than a gene family. Twenty independent transgenic sublines over- and under-expressing the Pa18 gene under the Zea mays ubiquitin promoter were established. There was a high yield of mature somatic embryos with a smooth surface only in untransformed, control cultures. Irrespective of the expression level of Pa18, the somatic embryos started to mature when given a maturation treatment. However, in the transgenic sublines, the outer cells in the maturing embryos frequently became elongated and vacuolated instead of remaining small and uniform. One explanation for this was that the expression of Pa18 was not restricted to the outer cell layer in transformed sublines. Angiosperms and gymnosperms separated about 300 million years ago and the embryo genesis is different in the two groups. The outer cell layer (protoderm), the first tissue to differentiate, is less clearly delineated in gymnosperms. For normal embryo development in angiosperms, expression of the LTP gene must be restricted to the protodermal cells. In this work we show that the expression of the Pa18 gene must be restricted to the putative protodermal cells of the gymnosperm. 相似文献
94.
95.
A. Ramarosandratana L. Harvengt A. Bouvet R. Calvayrac M. Pâques 《In vitro cellular & developmental biology. Plant》2001,37(1):29-34
Summary The influence of carbon sources and polyethylene glycol combined with 0.45 and 0.9% (w/v) of gellan gum on the maturation
of maritime pine somatic embryos was tested. The effect of the carbon source and polyethylene glycol varied widely between
lines. One out of the five lines tested showed a striking response to polyethylene glycol (PEG) treatment; the addition of
this osmoticum limited the embryonal-suspensor mass (ESM) proliferation while it enhanced the maturation rate. Conversely,
the ESM proliferation was stimulated by PEG in the other lines without subsequent improvement of the maturation rate. The
use of a high concentration of gellan gum (0.9%) improved the maturation of the five ESM lines. It was concluded that the
most efficient culture medium to recover cotyledonary embryos from all lines is one supplemented with sucrose at 6% (w/v)
and gellan gum at 0.9% (w/v) without PEG. The determining factor in the maturation of maritime pine somatic embryos is the
genotype and/or the quality of ESM. The possible relationship between maturation performances and ESM morphology, particularly
the suspensor organization, is discussed. 相似文献
96.
97.
98.
Joseph B. Yavitt 《Geomicrobiology journal》2013,30(1):8-16
Following a summer drought, intact cores of peat soil from two cool temperate peatlands (a rain-fed bog and a groundwater-fed swamp) were exposed experimentally to three different water table levels. The goal was to examine recovery of anaerobic methanogenesis and to evaluate peat soil decomposition to methane (CH4), carbon dioxide (CO2), and dissolved organic carbon (DOC) upon rewetting. Methane emission from soils to the atmosphere was greatest (mean = 80 μmol m?2 s?1) when the entire peat core was rewetted quickly; emission was negligible at low water level and when peat cores were rewetted gradually. Rates of CO2 emission (mean = 1.0 μmol m?2 s?1) were relatively insensitive to water level. Concentrations of CH4 in soil air spaces suggest that onset of methanogenesis induces, but later represses, aerobic oxidation of CH4 above the water table. Concentrations of CO2 suggest production at the soil surface of swamp peat versus at greater depths in bog peat. Portions of peat soil incubated in vitro without oxygen (O2) exhibited a lag before the onset of methanogenesis, and the lag time was less in peat from the cores rewetted quickly. The inhibition of methanogenesis by the selective inhibitor 2-bromoethanesulfonic acid (BES) decreased CO2 production by 20 to 30% but resulted in an increase in concentrations of DOC by 2 to 5 times. The results show that methanogens in peat soils tolerate moderate drought, and recovery varies among different peat types. In peat soils, the inhibition of methanogenesis might enhance DOC availability. 相似文献
99.
Vulnerability of stem xylem to cavitation was measured in 10 species of conifers using high pressure air to induce xylem embolism. Mean values of air pressure required to induce a 50% loss in hydraulic conductivity (φ50 ) varied enormously between species, ranging from a maximum of 14.2±0.6 MPa (corresponding to a xylem water potential of −14.2 MPa) in the semi-arid species Actinostrobus acuminatus to a minimum of 2.3±0.2 MPa in the rainforest species Dacrycarpus dacrydioides . Mean φ50 was significantly correlated with the mean rainfall of the driest quarter within the distribution of each species. The value of φ50 was also compared with leaf drought tolerance data for these species in order to determine whether xylem dysfunction during drought dictated drought response at the leaf level. Previous data describing the maximum depletion of internal CO2 concentration (ci ) in the leaves of these species during artificial drought was strongly correlated with φ50 suggesting a primary role of xylem in effecting leaf drought response. The possibility of a trade-off between xylem conductivity and xylem vulnerability was tested in a sub-sample of four species, but no evidence of an inverse relationship between φ50 and either stem-area specific (Ka ) or leaf-area specific conductivity (K1 ) was found. 相似文献
100.
Estelle Arbellay Markus Stoffel Elaine K. Sutherland Kevin T. Smith Donald A. Falk 《Annals of botany》2014,114(5):973-980