In situ nitrogen enrichment experiments in two Idaho (U.S.A.) streams

We conducted a series ofin situ experimental nutrient additions in two Idaho streams: Deep Creek, a desert stream located in Southeastern Idaho, and Big Wood River, situated in a mountainous region of Central Idaho. In both streams, a homogeneous reach was partitioned into almost identical channels. This allowed us to vary nutrient levels and measure algal response in experiments uncomplicated by differences in other factors.Ammonium nitrate was added to the treatment channels in Deep Creek. After nine days,Cladophora glomerata still predominated in both the control and treatment channels and algal biomass was not statistically different between the two. In the Big Wood River experiment significant differences in chlorophylla concentrations were not detected among three treatments of differing nitrogen enrichment and the control for both natural and artificial substrates. Also chlorophylla levels were not correlated with nitrogen concentrations, and the composition of algal communities remained similar among all treatments.We conclude that macronutrient enrichment of streams does not necessarily result in an increase in algal density or a change in algal community structure so long as other factors, which may limit the use of nutrients by algae, remain unaltered. Our results suggest that light, current velocity, and macroinvertebrate grazing may account for the failure of the periphyton to respond toin situ additions of nitrogen (and phosphorus) in our study streams.     

Physicochemical characteristics of animal and municipal wastes decomposed in arid soils

The application of anaerobically processed animal manure to maintain adequate levels of organic matter in arid soils is becoming a common practice. The purpose of this study was to characterize two farm manure products as compared with municipal waste compost (MWC). The anaerobic processing to obtain a biogas manure (BM) product was much faster (25 d) than the aerobic composting of farmyard manure (FYM) (90 d). Drying by three different methods (solar-drying, vacuum-drying at 45 degrees C, and freeze-drying) did not affect the quality of BM. Based on the chemical characteristics, FYM and BM products were comparable, and, containing less ash (30%) and heavy metals (50 mg Pb kg(-1)), seemed superior to MWC that contained 65% ash and 108 mg Pb kg(-1). On the other hand, MWC had higher C content (69.9%), lower acidity (15.04 mol kg(-1)), and higher exothermic peaks (300-460 degrees C) than BM and FYM (50% C, 20 mol kg(-1), and 275-450 degrees C, respectively), thus showing a greater extent of humification. Also, when the organic materials were incubated with arid soils and monitored for mean residence times (MRT), MWC was slightly more resistant to decomposition (MRT 175-180 d) than BM or FYM (MRT 161-166 d). The observed differences, however, were too small to dismiss any of the products as a valuable material for land applications to improve soil quality. In view of the results obtained, MWC may be considered an adequate substitute for BM or FYM, whenever the latter are in short supply.     

Computer und chemische Synthese

Numerous computer programs have gained entry into drug research; some of them are already used as a matter of routine, whereas others are still being tested. The special advantages of the use of computer programs are shown for the two fields “computer-assisted synthesis planning” and “quantitative structure-activity relationships”. Several aspects of cooperation between man and computer are briefly discussed.     

Evidence of dispersal limitation in soil microorganisms: isolation reduces species richness on mycorrhizal tree islands

Dispersal limitation plays an important role in a number of equilibrium and nonequilibrium theories about community ecology. In this study we use the framework of island biogeography to look for evidence of dispersal limitation in ectomycorrhizal fungal assemblages on "tree islands," patches of host trees located in a non-host vegetation matrix. Because of the potentially strong effects of island area on species richness and immigration, we chose to control island size by sampling tree islands consisting of a single host individual. Richness on tree islands was high, with estimates ranging up to 42 species of ectomycorrhizal fungi associating with a single host individual. Species richness decreased significantly with increasing isolation of tree islands, with our regression predicting a 50% decrease in species richness when tree islands are located distances of approximately 1 km from large patches of contiguous forests. Despite the fact that fungal fruit bodies produce large numbers of spores with high potential for long-distance travel, these results suggest that dispersal limitation is significant in ectomycorrhizal assemblages. There were no discernible effects of isolation or environment on the species identity of tree island fungal colonists. In contrast to the highly predictable patterns of tree island colonization we observed in a previous study on early successional forests, we suggest that over longer time periods the community assembly process becomes more dominated by stochastic immigration and local extinction events.