Roman Asshoff

Growth in epiphytic bromeliads: response to the relative supply of phosphorus and nitrogen

Insufficient nitrogen (N) and phosphorus (P) frequently limit primary production. Although most nutrient studies on vascular epiphytes have focused on N uptake, circumstantial evidence suggests that P rather than N is the most limiting element for growth in this plant group. We directly tested this by subjecting a total of 162 small individuals of three bromeliad species (Guzmania monostachia, Tillandsia elongata, Werauhia sanguinolenta) to three N and three P levels using a full-factorial experimental design, and determined relative growth rates (RGR) and nutrient acquisition over a period of 11 weeks. Both N and P supply had a significant effect on RGR, but only tissue P concentrations were correlated with growth. Uptake rates of N and P, in contrast, were not correlated with RGR. Increased nutrient supply led to an up to sevenfold increase in tissue P concentration compared to natural conditions, while concentrations of N hardly changed or even decreased. All treatment combinations, even at the lowest experimental P supply, led to decreased N:P ratios. We conclude that P is at least as limiting as N for vegetative function under natural conditions in these epiphytic bromeliads. This conclusion is in line with the general notion of the prevalence of P limitation for the functioning of terrestrial vegetation in the tropics.

Changes in needle quality and larch bud moth performance in response to CO2 enrichment and defoliation of treeline larches

Abstract.  1. It is hypothesised that the larch bud moth cycle is controlled by host‐tree foliage quality. In a Free Air CO2 Enrichment (FACE) experiment at the Swiss alpine treeline (2180 m a.s.l.), the effects of elevated CO2 and previous year defoliation on needle quality of larch and the performance of the larch bud moth were investigated.

Students’ conceptions of the carbon cycle: identifying and interrelating components of the carbon cycle and tracing carbon atoms across the levels of biological organisation

Abstract This study investigates students’ conceptions of the carbon cycle with regard to the components they believe to be relevant to the carbon cycle, how they interrelate these components, the ways in which they trace carbon atoms, and the different levels of biological organisation they consider when doing so. A total of 142 students aged 13–16 years (grades 8–10) participated in the study. A total of 130 students completed the diagnostic task, and an additional 12 students completed both the diagnostic task and were interviewed. The primary results show that the students identified few components of the carbon cycle, tended to trace carbon atoms exclusively at the level of the organism, and had difficulties identifying organic carbon compounds, especially during processes in which carbon compounds are transformed. Considering the main educational implications, we recommend using an instructional strategy that traces carbon atoms across the different levels of biological organisation whilst connecting fragmented knowledge by integrating knowledge from physiology, biochemistry and ecology when teaching the carbon cycle.

Discussing the Need of Experimental Replication with 5th Grade Students Conducting a Mealworm Experiment

ABSTRACT Scientific inquiry requires the replication of results in experimental studies. Recent studies draw a severe picture on the need of replication and the difficulties in replicating already published studies. As replicated confirmation of results is the basis of scientific and medical research, there may be a need to introduce the topic of replication to students. In an experiment, 5th grade students tested the effect of yeast addition on biomass increase in mealworm larvae. Each student took care of one larva on flour and one larva on flour + yeast (in total n = 30 larvae per treatment) in separate small boxes. After the experiment, students discussed the results of their two larvae. Subsequent pooling of the data in class showed a high degree of variation. When asked why replication in this experiment was important, students revealed a generally good epistemic understanding of the issue of replication and offered several explanations for why replication matters in experimentation.

Stammbäume lesen und verstehen

„Das groste Wunder unseres Planeten ist die ungeheure Vielfalt der Lebensformen“, so beginnt Edward O. Wilson, Biologieprofessor am Museum of Comparative Zoology der Harvard Universitat, das Vorwort des von ihm herausgegebenen Buchs „Ende der biologischen Vielfalt?“. Nach heutigem Kenntnisstand sind bislang ca. 1,75 Millionen Arten von Lebewesen – Bakterien, Einzeller, Pilze, Pflanzen und Tiere – wissenschaftlich beschrieben worden und es gibt Grund zu der Annahme, dass diese nur einen Bruchteil der tatsachlich vorhandenen Artenfulle auf unserem Planeten darstellen. Fur Wissenschaftler besteht kein Zweifel an der Tatsache, dass sich diese verbluffende Organismenvielfalt im Laufe der Evolution durch zahlreiche Artaufspaltungen aus einem allen Lebewesen gemeinsamen Vorfahren entwickelt hat.