Morphological and physiological adjustment to N and P fertilization in nutrient-limited Metrosideros polymorpha canopy trees in Hawaii

Leaf-level studies of Metrosideros polymorpha Gaud. (Myrtaceae) canopy trees at both ends of a substrate age gradient in the Hawaiian Islands pointed to differential patterns of adjustment to both nutrient limitation and removal of this limitation by long-term (8-14 years) nitrogen (N), phosphorus (P) and N + P fertilizations. The two study sites were located at the same elevation, had similar annual precipitation, and supported forests dominated by M. polymorpha, but differed in the age of the underlying volcanic substrate, and in soil nutrient availability, with relatively low N at the young site (300 years, Thurston, Hawaii) and relatively low P at the oldest site (4,100,000 years, Kokee, Kauai). Within each site, responses to N and P fertilization were similar, regardless of the difference in soil N and P availability between sites. At the young substrate site, nutrient addition led to a larger mean leaf size (about 7.4 versus 4.8 cm2), resulting in a larger canopy leaf surface area. Differences in foliar N and P content, chlorophyll concentrations and carboxylation capacity between the fertilized and control plots were small. At the old substrate site, nutrient addition led to an increase in photosynthetic rate per unit leaf surface area from 4.5 to 7.6 micromol m(-2) s(-1), without a concomitant change in leaf size. At this site, leaves had substantially greater nutrient concentrations, chlorophyll content and carboxylation capacity in the fertilized plots than in the control plots. These contrasting acclimation responses to fertilization at the young and old sites led to significant increases in total carbon gain of M. polymorpha canopy trees at both sites. At the young substrate site, acclimation to fertilization was morphological, resulting in larger leaves, whereas at the old substrate site, physiological acclimation resulted in higher leaf carboxylation capacity and chlorophyll content.     

Carbon dioxide and water vapor exchange by young and old ponderosa pine ecosystems during a dry summer

We investigated key factors controlling mass and energy exchange by a young (6-year-old) ponderosa pine (Pinus ponderosa Laws.) plantation on the west side of the Sierra Nevada Mountains and an old-growth ponderosa pine forest (mix of 45- and 250-year-old trees) on the east side of the Cascade Mountains, from June through September 1997. At both sites, we operated eddy covariance systems above the canopy to measure net ecosystem exchange of carbon dioxide and water vapor, and made concurrent meteorological and ecophysiological measurements. Our objective was to understand and compare the controls on ecosystem processes in these two forests. Precipitation is much higher in the young plantation than in the old-growth forest (1660 versus 550 mm year-1), although both forests experienced decreasing soil water availability and increasing vapor pressure deficits (D) as the summer of 1997 progressed. As a result, drought stress increased at both sites during this period, and changes in D strongly influenced ecosystem conductance and net carbon uptake. Ecosystem conductance for a given D was higher in the young pine plantation than in the old-growth forest, but decreased dramatically following several days of high D in late summer, possibly because of xylem cavitation. Net CO2 exchange generally decreased with conductance at both sites, although values were roughly twice as high at the young site. Simulations with the 3-PG model, which included the effect of tree age on fluxes, suggest that, during the fall through spring period, milder temperatures and ample water availability at the young site provide better conditions for photosynthesis than at the old pine site. Thus, over the long-term, the young site can carry more leaf area, and the climatic conditions between fall and spring offset the more severe limitations imposed by summer drought.     

Transpiration and forest structure in relation to soil waterlogging in a Hawaiian montane cloud forest

Transpiration, leaf characteristics and forest structure in Metrosideros polymorpha Gaud. stands growing in East Maui, Hawaii were investigated to assess physiological limitations associated with flooding as a mechanism of reduced canopy leaf area in waterlogged sites. Whole-tree sap flow, stomatal conductance, microclimate, soil oxidation-reduction potential, stand basal area and leaf area index (LAI) were measured on moderately sloped, drained sites with closed canopies (90%) and on level, waterlogged sites with open canopies (50-60%). The LAI was measured with a new technique based on enlarged photographs of individual tree crowns and allometric relationships. Sap flow was scaled to the stand level by multiplying basal area-normalized sap flow by stand basal area. Level sites had lower soil redox potentials, lower mean stand basal area, lower LAI, and a higher degree of soil avoidance by roots than sloped sites. Foliar nutrients and leaf mass per area (LMA) in M. polymorpha were similar between level and sloped sites. Stomatal conductance was similar for M. polymorpha saplings on both sites, but decreased with increasing tree height (r(2) = 0.72; P < 0.001). Stand transpiration estimates ranged from 79 to 89% of potential evapotranspiration (PET) for sloped sites and from 28 to 51% of PET for level sites. Stand transpiration estimates were strongly correlated with LAI (r(2) = 0.96; P < 0.001). Whole-tree transpiration was lower at level sites with waterlogged soils, but was similar or higher for trees on level sites when normalized by leaf area. Trees on level sites had a smaller leaf area per stem diameter than trees on sloped sites, suggesting that soil oxygen deficiency may reduce leaf area. However, transpiration per unit leaf area did not vary substantially, so leaf-level physiological behavior was conserved, regardless of differences in tree leaf area.     

Use of formulated diets as replacements for Artemia in the rearing of juvenile American lobsters (Homarus americanus)

American lobsters, Homarus americanus, have been successfully reared in hatchery operations for over a century, yet formulated diets have never been commercially produced. In recent years, commercial Artemia replacement (CAR) diets have been developed and marketed for use in aquaculture production of marine shrimp. Three separate experiments assessed the utility of rearing American lobsters on these shrimp CAR diets. First, survival and growth of stage IV American lobsters fed one of three CAR diets (Artemac 5, CAR1; Economac 4, CAR2; and Progression 3, CAR3) were compared to those of animals fed frozen adult n-3 fatty acid enriched Artemia. Survival to 3 months was highest for animals fed CAR3 (85%), while animals fed Artemia had the greatest weight gain (> 6 % day^− 1). A cost / benefit ratio analysis showed that CAR2 was the most cost efficient for juvenile production because of its low overall purchase cost. Second, stage IV lobsters were fed either CAR2 or frozen adult n-3 fatty acid enriched Artemia exclusively, or in combination (2 : 5, and 5 : 2). Again, CAR2 was a cost effective feed to use, even as a partial replacement for Artemia. Survival was higher in diets that included CAR2, and feeding it two days per week compensated for low quality Artemia. Finally, 1.5 year old lobsters fed a gelatin-bound mix of 80% CAR2 and 20% frozen Artemia for five months survived and grew equally well compared to lobsters fed gelatin-bound frozen adult Artemia, and better than a custom formulated maintenance diet. The benefits of incorporating formulated feeds into American lobster rearing programs to increase the effectiveness of enhancement programs is discussed.     

Are Primary Cultures of Trout (<Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>) Ventricular Cardiomyocytes Metabolically Viable?

The objectives of this study were to establish a protocol for the isolation of metabolically viable ventricular cardiomyocytes from the rainbow trout and to determine which measures may best reflect viability 24 h after isolation. Cardiomyocytes were isolated by enzymatic digestion and maintained in cell suspension. Viability was assessed using Trypan blue dye exclusion, ATP content, oxygen consumption and lactate dehydrogenase (LDH) leakage into the medium. Viability, assessed by these measures did not significantly change over the time period of this study. ATP content did correlate significantly with oxygen consumption but not with Trypan blue exclusion. We conclude that primary cultured cardiomyocytes remain metabolically viable for at least 24 h after isolation. Also, it appears that ATP content and oxygen consumption most adequately reflect metabolic cell viability. To be confident with a culture, however, a combination of viability measures is necessary when isolating cardiomyocytes from fish.     

Bluefin tuna (Thunnus thynnus) distribution in relation to sea surface temperature fronts in the Gulf of Maine (1994–96)

Fishery‐linked aerial surveys for bluefin tuna (Thunnus thynnus) were conducted in the Gulf of Maine (GOM) from July through October, 1994–96. Each year, from 507 to 890 surface schools were detected and their locations examined in relation to oceanographic conditions. Correlations between bluefin tuna presence and environmental variables were explored for sea surface temperature (SST), distance to a SST front, frontal density (relative density of all SST fronts seen in a given 1 km area for 2 weeks prior to each tuna sighting), and bottom depth and slope. Mean SST associated with bluefin schools was 18.1°C (±2.8). Schools were located at a mean distance of 19.7 km (±19.6) from SST fronts, and in water masses with an average frontal density of 28.2 m km^?2 (±35.7). Mean bottom depth of detected schools was 139.0 m (±70.3), and mean bottom slope was 0.7% rise (±0.7). A binomial generalized linear model fit to these variables indicated that bluefin are seen closer to fronts than locations in which no tuna were seen. Using simple and partial Mantel tests, we investigated the spatial correlation between bluefin tuna presence and the environmental variables, controlling for spatial autocorrelation. For each day that schools were sighted, we performed 24 Mantel tests, on a combination of response and predictor variables. The spatial relationship between bluefin tuna and SST fronts was inconsistent. Our analysis identified significant spatial structure in the bluefin school locations that had no significant correlation with any of the measured environmental features, suggesting that other untested features, such as prey density, may be important predictors of bluefin distribution in the GOM.     

Group B erythrocytes enzymatically converted to group O survive normally in A, B, and O individuals

With an alpha-galactosidase, B erythrocytes can be converted to blood group O under conditions that neither impair their viability in vitro nor affect their ability to survive normally after transfusion to individuals of groups O, A, and B. Such an approach has the potential for producing enzymatically converted group O cells for use in transfusion therapy. It should also be possible to convert A cells to group O by using the appropriate alpha-N-acetylgalactosaminidase.     

Mercury: Surface Features Observed during Radar Studies

Radar studies of Mercury have shown the presence of several large, rough surface features and of one smooth area.