Tree architecture is an important determinant of the height extension, light capture, and mechanical stability of trees, and it allows species to exploit the vertical height gradient in the forest canopy and horizontal light gradients at the forest floor. Tropical tree species partition these gradients through variation in adult stature (Hmax) and light demand. In this study we compare 22 architectural traits for 54 Bolivian moist-forest tree species. We evaluate how architectural traits related to Hmax vary with tree size, and we present a conceptual scheme in which we combine the two axes into four different functional groups. Interspecific correlations between architecture and Hmax varied strongly from negative to positive, depending on the reference sizes used. Stem height was positively related to Hmax at larger reference diameters (14-80 cm). Species height vs. diameter curves often flattened toward their upper ends in association with reproductive maturity for species of all sizes. Thus, adult understory trees were typically shorter than similar-diameter juveniles of larger species. Crown area was negatively correlated with Hmax at small reference heights and positively correlated at larger reference heights (15-34 m). Wide crowns allow the small understory species to intercept light over a large area at the expense of a reduced height growth. Crown length was negatively correlated with Hmax at intermediate reference heights (4-14 m). A long crown enables small understory species to maximize light interception in a light-limited environment. Light-demanding species were characterized by orthotropic stems and branches, large leaves, and a monolayer leaf arrangement. They realized an efficient height growth through the formation of narrow and shallow crowns. Light demand turned out to be a much stronger predictor of tree architecture than Hmax, probably because of the relatively low, open, and semi-evergreen canopy at the research site. The existence of four functional groups (shade-tolerant, partial-shade-tolerant, and long- and short-lived pioneer) was confirmed by the principal component and discriminant analysis. Both light demand and Hmax capture the major variation in functional traits found among tropical rain forest tree species, and the two-way classification scheme provides a straightforward model to understand niche differentiation in tropical forests.

a b s t r a c tAn adaptation of fully automated gas production equipment was tested for its ability to simultaneously measure methane and total gas. The simultaneous measurement of gas production and gas composition was not possible using fully automated equipment, as the bottles should be kept closed during the incubations. A separate small opening with a screw cap and septum was made in each bottle, making it possible to take very small aliquots (10 l) from the gas in the headspace with a syringe for immediate gas analysis. As the used automatic gas production equipment was a venting system, corrections had to be made for the vented total gas and methane, as well as for the dilution of the produced methane with the gas in the headspace. To test the suitability and accuracy of the system, known amounts of methane were injected in bottles in the venting system and methane concentrations in the headspace were determined. It proved that the methane concentration in the headspace, corrected for the vented gas, coincided with the injected amount of methane. To show the potency of the adapted equipment, experiments were conducted with different feedstuffs. Total gas production and methane production were recorded and their relationships were calculated. The ability of the system to test feed additives for methane reduction was demonstrated for maize and soybean hulls as substrate (0.5 g DM), supplemented with monensin (15 mg), sodium-2-bromoethanesulphonate (BES, 15 mg), cinnemaldehyde (150 mg) and tea tannins (150 mg), additives known to effect methane synthesis. The adapted gas production equipment showed to be a powerful tool to determine rate and extent of gas production as a measure of fermentation and to simultaneously determine methane production.

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The hypothesis that propionate is a short-term feed intake-regulating agent was studied. Mature wether sheep were infused over 20 min with Na propionate into the mesenteric vein, while feed intake and feeding pattern were monitored over 1.5 h. Feed intake was reduced by infusions at 2 mmol/min, which were associated with marked increases in jugular as well as portal concentrations of insulin, glucose, and propionate. In a second experiment, animals were infused with 2 mmol/min Na propionate into the portal vein. No decrease in feed intake was observed, although there were similar increases in insulin, glucose, and propionate as found in mesenteric vein-infused animals. It is concluded that mesenteric propionate in high doses acts as a satiety factor. Possible explanations for the difference between site of infusion may be a different distribution of the infusate over the liver and/or the presence of propionate-sensitive receptors in the mesenteric/portal vein region. It seems unlikely that insulin concentrations are involved in inducing satiety in propionate-infused animals.

Sugarbeet pulp, citrus pulp, sugarbeet molasses and minerals and vitamins were mixed with different amounts of groundnut expeller, potato protein, peas or dried brewers' grains to give 6 concentrates with protein solubility from 7 to 51%. The concentrates (600 g daily) were given with rye grass (300 g daily) to 2 Texel wethers with an infusion tube into the abomasum and with cannulae in the cranial duodenum and terminal ileum. Apparent digestibility of amino acid nitrogen in the small intestine was 57.0 to 73.2% and increased with increasing amounts of protein entering the small intestine. Mean true digestibility in the small intestine was 90.3%. Apparent and true digestibilities of individual amino acids varied considerably. Of protein leaving the small intestine 75% was endogenous (non-ammonia N 321 mg/kg0.75 daily). (Abstract retrieved from CAB Abstracts by CABI’s permission)