Soil-Seed Bank Survival in Forests of the Southern United States

We evaluated the longevity of seeds of 12 common woody species buried in fresh condition in the forest floor at three forest locations in Mississippi and Louisiana. Seed samples of each species were retrieved annually for 5 years from each location. Germination and tetrazolium chloride staining tests were conducted on the samples to determine germinative capacity. When averaged across all species, seeds remained viable longer at the Alexandria, Louisiana site than at the two sites in Mississippi. Seeds of the 12 species varied widely in their response to burial. Some species, such as American beautyberry (Callicarpa americana L.), muscadine grape (Vitis rotundifolia Michx.), and sugarberry (Celtis laevigata Willd.), had relatively high germinative capacities (from 33 to 60 percent, depending on species) even after burial in the forest floor for 5 years, whereas other species, such as flowering dogwood (Cornus florida L.) and yaupon (Ilex vomitoria Ait.), had very low germinative capacities (less than 6 percent) by the end of the first year after burial. Species were classified into five groups based on their similarity of response.     

The Current State of Solar Modeling

Data from the Global Oscillation Network Group (GONG) project and other helioseismic experiments provide a test for models of stellar interiors and for the thermodynamic and radiative properties, on which the models depend, of matter under the extreme conditions found in the sun. Current models are in agreement with the helioseismic inferences, which suggests, for example, that the disagreement between the predicted and observed fluxes of neutrinos from the sun is not caused by errors in the models. However, the GONG data reveal subtle errors in the models, such as an excess in sound speed just beneath the convection zone. These discrepancies indicate effects that have so far not been correctly accounted for; for example, it is plausible that the sound-speed differences reflect weak mixing in stellar interiors, of potential importance to the overall evolution of stars and ultimately to estimates of the age of the galaxy based on stellar evolution calculations.     

刈牧后休闲期对草地牧草生产的影响

通过不同间隔时期对多年生黑麦草、白三叶混播草地牧草产量的监测与分析,得出随着休闲期的增加,青绿物质和死亡物质均呈现上升趋势,在较低和较高草地牧草现存量下都会降低牧草生长率。     

贵州足球场草坪建植及化管理模型研究

在一定的生境和管理条件下,以修剪高度、修剪次数和施N、P、K量为因素,利用二次正交回归设计,用模糊综合评分法评定草坪质量,最佳3因子水平为:修剪高度5～7.4cm,修剪次数4～6次/月,施N量为2.5～3.7g/(m2·年),施P、K量各为L25～1.85g/(m2·年),建立了草坪质量与养护3因子间的显著相关回归模型.     

Ecology. The advantages of togetherness

What would be the advantage of unicellular organisms becoming multicellular? For organisms that feed on organic food (heterotrophs), the most efficient way to produce energy is to metabolize the food by aerobic respiration, but the fastest way is to metabolize it by fermentation. In their Perspective, Cox and Bonner discuss a mathematical model (Pfeiffer et al.), which shows that when these two kinds of organisms (respirators and fermenters) compete for a limited food source, the respirators manage best when they are grouped in clusters rather than remaining as separate cells. In this way, multicellularity could have originated.     

Cell sorting: automated separation of mammalian cells as a function of intracellular fluorescence

A system for high-speed sorting of fluorescent cells was able to sort mouse spleen cells from Chinese hamster ovarian cells after development of fluorochromasia. Highly fluorescent fractions separated after similar treatment from mouse spleen cells immunized to sheep erythrocytes were enriched in antibody-producing cells by factors of 4 to 10.     

Relative Contributions of Uranium, Thorium, and Potassium to Heat Production in the Earth

Data from a wide variety of igneous rock types show that the ratio of potassium to uranium is approximately 1 X 10(4). This suggests that the value of K/U approximately 1 X 10(4) is characteristic of terrestrial materials and is distinct from the value of 8 X 10(4) found in chondrites. In a model earth with K/U approximately 10(4), uranium and thorium are the dominant sources of radioactive heat at the present time. This will permit the average terrestrial concentrations of uranium and thorium to be 2 to 4.7 times higher than that observed in chondrites. The resulting models of the terrestrial heat production will be considerably different from those for chondritic heat production because of the longer half-life of U(238) and Th(238) compared with K(40).