Comparative Photosynthesis in Developing Leaves of Brachystegia spiciformis Benth

Photosynthesis and dark respiration were studied during andafter the spring flush in Brachystegia spiciformis Benth. Variousparameters were examined including anthocyanin and chlorophyllcontent, Hill reaction activity, and gas exchange. Total chlorophyllcontent steadily increased reaching a constant value in fullyexpanded (25-d-old) leaves, whereas anthocyanin concentrationincreased as the chlorophylls but rapidly declined after 23d. Hill reaction measurements confirmed that leaf material fromevery stage of the flush (bud burst to mature leaves) was photosyntheticallyfunctional. The activity was low in flushing leaves with highanthocyanin content and then dramatically increased as leafanthocyanin content declined. Oxygen exchange measurements showedflushing leaves to have lower photosynthetic rates but higherrespiratory activity than mature leaves (60% and 120%, respectively).Gas exchange and in vitro electron transport were also generallycorrelated; Hill reaction activity was 128% of gas exchangein mature leaves and 92% in flushing leaves. It is concludedthat although photosynthetic rates are lower and respirationrates are higher in flushing leaves than in mature, fully expandedleaves, flushing leaves are fully photosynthetically competentand apparently require no net input of carbon for growth anddevelopment. Key words: Brachystegia, Hill reaction, photosynthesis, Zimbabwe     

Compensatory responses of the fall armyworm (Spodoptera frugiperda) when fed water- and cellulose-diluted diets

Abstract Caterpillars of the noctuid moth, Spodoptera frugiperda (J. E. Smith), reared on artificial diets diluted with cellulose and water, increased fresh weight (fw) consumption 2.2–2.5-fold over those on the undiluted diet. At moderate levels of water- or cellulose-dilution, the increased consumption, combined with increased digestion and absorption of nutrients (ADNU), sufficiently compensated for the reduced nutrient intake to achieve pupal biomass equivalent to that of pupae from the undiluted diet. At higher levels of water- and cellulose-dilution, fw consumption and ADNU increased further but pupal dry weight declined on the water-diluted diets. At each level of dilution fw consumption and ADNU increased similarly on the water- and cellulose-diluted diets, but biomass gain was reduced on the water- compared with the cellulose-diluted diets. This was due in part to lowered food conversion efficiency on the water-diluted diets, possibly caused by increased costs of metabolizing the wetter diets. Our data support the hypothesis that consumption rates are regulated by a nutrient feedback mechanism. Our data also suggest that digestive enzyme activity is correlated with consumption. Furthermore, the cost of increased consumption rates on diets of reduced energetic value may constitute a substantially greater energy expenditure than previously believed. However, this cost was insufficient to reduce relative growth rates but was apparently manifested in lowered lipid accumulation.     

A comparison of the phytosociology and dynamics of three floodplain (Várzea) forests of known ages, Rio Jurua, western Brazilian Amazon

CAMPBELL, D. G., STONE, J. L. & ROSAS Jr, A., 1992. A comparison of the phytosociology and dynamics of three floodplain (Várzea) forests of known ages, Rio Juruá, western Brazilian Amazon. An unusual historic accident has resulted in three adjacent inundated (vórzea) forests of known ages (50 years old, 14–50 years old, and 14 years old), on the margin of the Rio Juruá, near the village of Rodrigues Alves in western Acre, Brazilian Amazon. One-hectare quantitative inventories (500 × 20 m) were conducted on each of the three forests. Physical characteristics of the plots, including soil particle size, soil cation levels, level of inundation and rate of soil deposition were measured. Plot 1, steeply sloping and ecotonal between várzea and terra firme, was infrequently flooded, with a mean high water mark of 0.0. Plot 2, on slightly undulating terrain, had a mean high water mark of 1.16 m. Plot 3 was level and deeply-flooded, with a mean high water mark of 4.00 m. All trees ≥ 10 cm diameter at breast height (dbh) were mapped, measured and identified to species. Plots 1, 2 and 3 contained 523, 420 and 777 trees, 106, 73 and 20 species, Shannon diversity indices of 3.60, 3.51 and 1.82, and stand basal areas of 25.46 m², 27.01 m² and 25.72 m², respectively. Alchomea triplinervia was the superior competitor on species-rich plot 1; Annona sp. strongly dominated in the limiting conditions of plot 3. On plot 2, no single species was able to achieve dominance. For the 25 species with N≥ 10, habitat specialization as a function of the level of annual inundation was demonstrated, and for five of these species that occurred on plot 1, further refinement of niche as a function of gradient was demonstrated. One-year mortality in plots 1, 2 and 3, was 1.99%, 1.56% and 1.70%, respectively. In Plot 3, 77% of the mortalities were trees that had died standing, vs 40% and 43% in plots 1 and 2.     

SITE TO SITE VARIATION IN THE SOAP CHAMBER TEST

This investigation was conducted to examine the contribution of intrasite variation on the volar forearm to the overall variation in irritation under the conditions of a soap chamber test. Six sites on each forearm of human volunteers were patched with an eight percent aqueous solution of a commercial bar soap, known to be moderately irritating. Clinical evaluations of the sites were made independently by two judges twenty-four hours after the first patch application and six hours following applications conducted over the next four consecutive days. Site to site variability was estimated to be only 3.2% of the total variance component. It is suggested that as with any biologic assay, this variance can be reduced by an increase in the number of panelists.