Search Results - (Author, Cooperation:R. J. Mitchell)

2016-01-30

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

*Biodiversity ; *Grassland ; *Plant Development

2018-02-16

American Physical Society (APS)

1050-2947

1094-1622

Physics

Quantum information

1526-100X

Blackwell Publishing Journal Backfiles 1879-2005

Biology

Restoration of the longleaf pine ecosystems of the southeastern United States has focused interest on the regeneration and establishment of Aristida sp. (wiregrass) as a means to reestablish ecological function and structure of the ecosystem. This study examined dispersal distance from planted adults and canopy cover and density effects on establishment and reproduction. In 1994 wiregrass plugs were planted in two densities (500 seedlings/100 m2 and 49 seedlings/100 m2) and three canopy-thinning treatments (25 m2 basal area/ha, 16 m2 basal area/ha, and 8 m2 basal area/ha) were implemented in a 20-year-old longleaf plantation in southwestern Georgia. Due to the intense site preparation and the density of pines planted, virtually no understory vegetation was present. The site was burned in June 1995, which promoted seed production of the planted wiregrass. Results indicate that the 8 m2 basal area/ha treatment results in larger plants that in turn produce a greater number of seedling recruits. No seedling recruitment occurred in control plots. Dispersal distances of up to 594 cm were recorded. Natural seedling recruitment occurred at low-density transplanting (5 plants/10 m2), denoting that high-density planting similar to natural density (5 plants/m2) is not required for successful establishment or reproduction. However, overstory thinning in dense pine plantations is required for reproduction and increases the survival of individual plants due to changes in the environmental conditions at the forest floor.

Electronic Resource

1365-3040

Blackwell Publishing Journal Backfiles 1879-2005

Biology

Abstract. The effect of plant competition on spectral reflectance in the 400–2500 nm wavelength region was determined for 3-month-old and 15-month-old leaves of loblolly pine (Pinus taeda L.). Strong competition decreased water potentials and Mg concentrations, and increased K in young and old leaves. Also, competition decreased Ca and total chlorophyll in young leaves. As measured with a scanning radiometer, reflectance in young leaves at 551 nm decreased from 20 to 14% as water potentials increased from -2.2 to -0.9 MPa (r2= 0.82). For young and old leaves reflectance at 551 nm decreased from 20 to 10% with increasing total chlorophyll (r2= 0.64). Reflectance decreased slightly with increasing K in young leaves (401 nm, r2= 0.55), and with increasing Mg in old leaves (470 nm, r2= 0.57). Increased visible reflectance under strong competition may have resulted primarily from decreased water potentials. Reflectances were much greater in young versus old leaves in the 750–1300 nm range, and were greater in old rather than young leaves from 1400–2500 nm. Infrared reflectances were not, however, significantly affected by competition.

Electronic Resource

1365-3040

Blackwell Publishing Journal Backfiles 1879-2005

Biology

Abstract. A field study was conducted to determine the relationship of solar-excited chlorophyll a fluorescence to net CO2 assimilation rate in attached leaves. The Fraunhofer line-depth principle was used to measure fluorescence at 656.3 nm wavelength while leaves remained exposed to full sunlight and normal atmospheric pressures of CO2 and O2. Fluorescence induction kinetics were observed when leaves were exposed to sunlight after 10 min in darkness. Subsequently, fluorescence varied inversely with assimilation rate. In the C4Zea mays, fluorescence decreased from 2.5 to 0.8 mW m-2 nm-1 as CO2 assimilation rate increased from 1 to 8 μmol m-2 s-1 (r2= 0.520). In the C3Liquidambar styraciflua and Pinus taeda, fluorescence decreased from 6 to 2 mW m-2 nm-1 as assimilation rate increased from 2 to 5 or 0 to 2 μmol m-2 s-1 (r2= 0.44 and 0.45. respectively). The Fraunhofer line-depth principle enables the simultaneous measurement of solar-excited fluorescence and CO2 assimilation rate in individual leaves, but also at larger scales. Thus, it may contribute significantly to field studies of the relationship of fluorescence to photosynthesis.

Electronic Resource

1365-246X

Blackwell Publishing Journal Backfiles 1879-2005

Geosciences

Palaeomagnetic data have been obtained from Plio-Pleistocene rocks of the Indian Heaven volcanic field (IHVF) located in the High Cascade province in southern Washington. Alternating field demagnetization yielded well-defined directions from 56 individual lava flows (sites) from 23 volcanic units. All units sampled were normally magnetized suggesting that volcanic activity within the Indian Heaven region occurred primarily during the last 0.73 Myr and not over the last 3.75 Myr as suggested by K-Ar ages. Combining palaeomagnetically similar site mean directions from lava flows from the same volcanic unit resulted in N= 35. the mean direction calculated from this data set is I= 65.2° and D = 0.2° (095 = 3.3°; k = 56.4) while the palaeomagnetic pole [calculated using virtual geomagnetic pole (VGP) data] is located at 87.7°N, 231.4°E (or95 = 4.7; k= 27.2). This pole is not significantly different from the pole determined from all data (N= 56) or the rotational axis and is slightly near-sided with respect to the mean sampling site longitude. the between-site angular dispersion of the VGPs about the mean for N-35 and N= 56, although low, is not statistically different at the 95% confidence level from the expected value predicted by model F of McFadden & McElhinny (1984). Our data, together with other recent data from the western United States, do not confirm the presence of a persistent standing non-dipole field component in this region during the Plio-Pleistocene as suggested by Brown & Mertzman (1979). Additionally, these data suggest that VGP angular dispersion associated with the geomagnetic field has been decreasing over the last 5 Myr.

Electronic Resource

0018-7143

Biology

0018-7143

Biology

0018-7143

Biology

0018-7143

Biology

0018-7143

Biology

0018-7143

Biology

0018-7143

Biology

0018-7143

Biology

0013-8266

History

0013-8266

History

1572-946X

Springer Online Journal Archives 1860-2000

Physics

Abstract The MSSL X-ray detectors onCopernicus have been used to study a number of extragalactic objects. At least three classes of unresolved sources are found and we suggest that accretion may be the dominant mechanism. The mass of the accreting object then determines the X-ray emission properties.

Electronic Resource

1432-1203

Springer Online Journal Archives 1860-2000

Biology

Medicine

Summary Several regional series from Britain and 3 Asian series were typed for the Esterase D polymorphism. It was found that haemolysates up to 5 years old could be reliably typed when prepared from washed anticoagulated red blood cells. Lysates prepared from blood clots do not retain Esterase D activity quite as well. The Manx population has higher Esterase D 2 gene frequencies than neighbouring populations. A Nepalese population exhibits the highest Esterase D 2 gene frequency so far recorded. The other series presented supplement or confirm results already published.

Electronic Resource

1432-1939

Key words Inflorescence size  ;  Female reproductive success  ;  Pollinator visitation  ;  Pre-dispersal seed predation  ;  Compensation

Springer Online Journal Archives 1860-2000

Biology

Abstract Large floral displays should theoretically provide advantages to plants through increased pollinator visitation and resulting fruit and seed set. However empirical tests of the response of pollinators to floral display size have been limited by a lack of direct experimentation, and the results of such studies have been equivocal. In addition, other selective agents such as pre-dispersal seed predators might modulate effects of floral display on pollination. By artificially altering flower number, we examined the direct effects of floral display in the monocarpic herb, Ipomopsis aggregata (Polemoniaceae), on visitation rates by broad-tailed and rufous hummingbird pollinators, as well destruction of fruits by a pre-dispersal seed predator (Hylemya: Anthomyiidae). In addition, we quantified the ultimate effects of flower number on female reproductive success. Plants with larger floral displays were most likely to be visited first in any given foraging bout (P 〈 0.01). As expected, plants with more flowers received more total flower visits. However, we found no gain in the proportion of flowers visited for many- versus few-flowered plants, or the total number of approaches/hour. In fact, a significantly greater percentage of flowers were visited on few-flowered plants. Plants did not compensate for our reduction in flowers by increasing investment in the number or proportion of flowers that set fruit, the number of seeds/fruit, or seed weight. Pre-dispersal seed predation was greater for many- than for few-flowered plants (P 〈 0.001), but this did not offset the potential fitness gains of producing large displays. Our data support the hypothesis that large floral displays function primarily in long-distance attraction of pollinators, and enhance maternal success.

Electronic Resource

1433-7479

Springer Online Journal Archives 1860-2000

Computer Science

Abstract The recursive least-squares algorithm with a forgetting factor has been extensively applied and studied for the on-line parameter estimation of linear dynamic systems. This paper explores the use of genetic algorithms to improve the performance of the recursive least-squares algorithm in the parameter estimation of time-varying systems. Simulation results show that the hybrid recursive algorithm (GARLS), combining recursive least-squares with genetic algorithms, can achieve better results than the standard recursive least-squares algorithm using only a forgetting factor.

Electronic Resource