绿绒蒿属一新变种

报道了绿绒蒿属一新变种,即椭圆叶红花绿绒蒿(MeconopsispuniceaMaxim.var.ellipticaZ.J.Cui etY.Sh.Lian)。     

Response to Chilling of Zea mays, Tripsacum dactyloides and their Hybrid

Maize (Zea mays ssp. mays) and eastern gamagrass (Tripsacum dactyloides) are known for their susceptibility to chilling injuries. Their hybrid (Z. mays × T. dactyloides) showed higher tolerance to low temperatures (–2 °C) in the field than its parents. Exposure to 5 °C for 2 or 3 d reduced the variable to maximal chlorophyll fluorescence ratio (F_V/F_M), an indicator of the maximum photochemical efficiency of the photosystem 2, and the variable to minimal fluorescence ratio (F_V/F₀) more in maize and eastern gamagrass than in hybrid plants. Chlorophyll contents for rewarming plants (25 °C for 3 d) were lower than before chilling in both parents while values for hybrid plants were similar. Electrolyte leakage was higher in chilled than control plants but it did not show significant differences among genotypes. Our data suggest that hybrid plants have higher capacity to recover from chilling injury in controlled conditions than their parents.     

Potential Changes in Tree Species Richness and Forest Community Types following Climate Change

Potential changes in tree species richness and forest community types were evaluated for the eastern United States according to five scenarios of future climate change resulting from a doubling of atmospheric carbon dioxide (CO₂). DISTRIB, an empirical model that uses a regression tree analysis approach, was used to generate suitable habitat, or potential future distributions, of 80 common tree species for each scenario. The model assumes that the vegetation and climate are in equilibrium with no barriers to species migration. Combinations of the individual species model outcomes allowed estimates of species richness (from among the 80 species) and forest type (from simple rules) for each of 2100 counties in the eastern United States. Average species richness across all counties may increase slightly with climatic change. This increase tends to be larger as the average temperature of the climate change scenario increases. Dramatic changes in the distribution of potential forest types were modeled. All five scenarios project the extirpation of the spruce–fir forest types from New England. Outputs from only the two least severe scenarios retain aspen–birch, and they are largely reduced. Maple–beech–birch also shows a large reduction in area under all scenarios. By contrast, oak–hickory and oak–pine types were modeled to increase by 34% and 290%, respectively, averaged over the five scenarios. Although many assumptions are made, these modeled outcomes substantially agree with a limited number of predictions from researchers using paleoecological data or other models. Received 12 May 2000; accepted 20 October 2000.     

Influence of temperature and nutrients on species richness of deep water corals from the western coast of the Americas

Studies on biogeography of stony corals from the eastern Pacific have been conducted in detail only for reef species, and to date there have been no attempts to explain the differences of regional species richness on the basis of oceanographic conditions. The objective of this work was to determine the relationship between deep-water (<200 m) scleractinian species richness along the western coast of the Americas, and four oceanographic variables (temperature, nitrates, phosphates and silicates), and the feasibility to use this information to model effects of global warming on those associations. Data on coral distribution were gathered from bibliography and museum collections, while information on oceanographic conditions from 200 to 2000 m depth was obtained from NOAA atlases. Species richness, estimated for intervals of 5 degrees of latitude, was correlated with abiotic factors using the Spearman rank coefficient. In the Northern Hemisphere, total species richness was positively influenced by temperature, but negatively by nutrients. In contrast, there was no effect of those factors on coral diversity in the Southern Hemisphere. At the family level, high temperatures favored species richness of Caryophylliidae and Dendrophylliidae north of the Equator, but diversity was reduced in areas of high concentration of silicates. In the Southern Hemisphere, temperature was not associated with deep-water coral richness, but correlated negatively with diversity of Caryophylliidae. Nutrients also showed an inverse relationship with richness of the latter family. In the rest of the families analyzed, there was no apparent effect of oceanic conditions on species richness in the Southern Hemisphere. The results indicated that richness may be influenced by changes in oceanographic factors (especially temperature and silicate concentration). Then, it is feasible to develop numerical models to predict possible changes in deep-water coral diversity on the basis of scenarios from global warming models.     

西北地区志留纪温洛克世晚期-罗德洛世早期的一些笔石

记述西北地区志留纪温洛克世晚期－罗德洛世早期笔石5属,11种,进一步肯定罗德洛世早期nilssoni带的地层在陕西紫阳,甘肃迭部和内蒙古额济纳旗的存在,首次确认陕西紫阳和内蒙古额济纳旗发育温洛克世侯默中晚期含笔石地层,大致为parvus带或稍高。     

Discriminating Tsuga canadensis Hemlock Forest Defoliation Using Remotely Sensed Change Detection

The eastern hemlock (Tsuga Canadensis) is declining in health and vigor in eastern North America due to infestation by an introduced insect, the hemlock woolly adelgid (Adelges isugue). Adelgid feeding activity results in the defoliation of hemlock forest canopy over several years. We investigated the application of Landsat satellite imagery and change-detection techniques to monitor the health of hemlock forest stands in northern New Jersey. We described methods used to correct effects due to atmospheric conditions and monitor the health status of hemlock stands over time. As hemlocks defoliate, changes occur in the spectral reflectance of the canopy in near infrared and red wavelengths—changes captured in the Normalized Difference Vegetation Index. By relating the differences in this index over time to hemlock defoliation on the ground, four classes of hemlock forest health were predicted across spatially heterogeneous landscapes with 82% accuracy. Using a time series of images, we are investigating temporal and spatial patterns in hemlock defoliation across the study area over the past decade. Based on the success of this methodology, we are no expanding out study to monitor hemlock health across the entire Mid-Atlantic region.     

Optimized somatic embryogenesis in Pinus strobus L.

Summary Somatic embryogenesis (SE) initiation in Pinus strobus was optimized by the manipulation of plant growth regulator (PGR) concentrations in the culture medium. Modified Litvay medium (MLV) of Litvay et al. (1985) supplemented with lower than routinely used PGR concentration increased initiation of established embryogenic cultures from approximately 20 to 53%. The original developmental stage of zygotic embryos had a pronounced effect on the SE response. The optimum stage was the pre- to shortly post-cleavage stage. A substantial genetic influence on initiation of SE was indicated by a significant variance component due to families. Genotype X collection date and genotype X media interactions had large effects on initiation of SE. The PGR levels in the culture medium prior to maturation had a significant effect on subsequent production of mature somatic embryos. Embryogenic tissue initiated and proliferated on medium with a low level of PGR consistently produced a high number of somatic embryos, indicating that optimized initiation protocol also enhanced somatic embryo production. Somatic embryos of 93 embryogenic lines (representing five families) that were initiated on media with different PGR concentrations were converted to plants at an overall frequency of 76%, and grown in the greenhouse. With these improved protocols, application of P. strobus SE in commercial clonal forestry is feasible as an alternative to traditional breeding and reforestation.