Uroporphyria development in cultured chick embryo fibroblasts long-term treated with chloramphenicol and ethidium bromide

In brain cortex, low concentrations of GTP or Gpp(NH)p activated the membrane-bound low Km cyclic AMP phosphodiesterase while higher concentrations of GTP, but not of Gpp(NH)p, reversed this activation. The adenosine analog N6-phenylisopropyladenosine (N6-PIA) elicited biphasic effect on this enzyme (activation up to 10(-8) M, complete reversion at 10(-5) M), provided that GTP was present. N6-PIA activation was reduced in the presence of Gpp(NH)p and blocked by sodium (80 mM). In contrast, the soluble low Km cyclic AMP phosphodiesterase was insensitive to GTP or N6-PIA. This study suggests that guanine nucleotides and N6-PIA exert their effects on the membrane-bound enzyme through guanine nucleotide regulatory proteins.     

Differential environmental response of plant functional types in hedgerow habitats

Classifying species into functional groups reacting similar to multiple environmental factors based on shared biological characteristics forms a major challenge faced by present-day ecologists. Based on data of a hedgerow plant community, this study uses a multivariate approach to analyse if trait-based emergent species groups have real functional significance, i.e. if these groups are characterised by specific response profiles to a wide range of environmental factors. First, the influence of explanatory variable groups (abiotic environmental conditions, management variables, structural aspects, historical background and spatial configuration of the hedgerow network) on distribution patterns of individual plant species was analysed with partial logistic regression. Significant relationships were found between the ecological characteristics of a species and the relative importance of variable groups affecting the distribution of that species within a hedgerow network landscape. Next, a trait-based classification of hedgerow plant species was constructed using a hierarchical clustering procedure. Woody species segregated into two distinct groups, with differences predominantly associated with generative traits, herbaceous species in four groups differing mainly in vegetative traits and habitat preferences. Clear differences in response to multiple environmental factors between the emergent species groups demonstrated the functional significance of the constructed classification. Relationships between the trait- and response profile were examined and their ecological relevance discussed. With respect to the woody species groups, zoochorous species were affected more strongly by hedgerow structure and landscape context than anemochorous species. For the herbaceous species clustering, a relatively strong impact was found, amongst others, of historical variables on species with woodland preference in comparison with other species groups.

Zusammenfassung

Die Klassifizierung von Arten in funktionelle Gruppen, die aufgrund von gemeinsamen biologischen Eigenschaften in gleicher Weise auf multiple Umweltfaktoren reagieren, ist eine große Herausforderung, vor der heutige Ökologen stehen. Auf der Grundlage von Daten einer Heckenpflanzen-Lebensgemeinschaft folgt diese Untersuchung einer multivariaten Vorgehensweise, um zu analysieren, ob die auftretenden Artengruppen auf der Basis von Merkmalen eine wirkliche funktionelle Bedeutung haben, d. h. ob diese Gruppen durch spezifische Antwortprofile auf eine große Auswahl von Umweltfaktoren charakterisiert sind. Zuerst wurde der Einfluss von Gruppen erklärender Variablen (abiotische Umweltbedingungen, Managementvariablen, strukturelle Aspekte, geschichtlicher Hintergrund und räumliche Anordnung des Heckennetzes) auf die Verteilungsmuster einzelner Pflanzenarten mit partiellen logistischen Regressionen analysiert. Signifikante Beziehungen wurden zwischen den ökologischen Eigenschaften einer Art und der relativen Wichtigkeit von Variablengruppen gefunden, die die Verbreitung der Art innerhalb der Heckennetzlandschaft beeinflussen. Im Anschluss wurde eine merkmalsbasierte Klassifikation der Heckenpflanzenarten unter der Verwendung einer hierarchischen Gruppierungsprozedur konstruiert. Aufgrund von Unterschieden, die vor allem mit den Fortpflanzungsmerkmalen einhergingen, trennten sich die holzigen Arten in zwei verschiedene Gruppen auf. Krautige Arten trennten sich in vier Gruppen auf, die sich vor allem in den vegetativen Merkmalen und Habitatpräferenzen unterschieden. Klare Unterschiede in den Reaktionen auf multiple Umweltfaktoren zwischen den entstandenen Artengruppen demonstrierten die funktionelle Bedeutung der konstruierten Klassifikation. Die Beziehungen zwischen den Merkmals- und Antwortprofilen wurden untersucht und ihre ökologische Relevanz diskutiert. In Bezug auf die holzigen Artengruppen waren die zoochoren Arten stärker von der Heckenstruktur und dem Landschaftskontext beeinflusst als anemochore Arten. Für die krautigen Artencluster wurde unter anderem ein relativ starker Einfluss von historischen Variablen auf die Arten mit Waldpräferenz im Vergleich zu anderen Artengruppen gefunden.     

The economics and greenhouse gas balance of land conversion to Jatropha: the case of Tanzania

Due to higher oil prices, abundance of labor and suitable land and its stable political climate, Tanzania attracted many investments in Jatropha. Although several studies on Jatropha's economic potential are available, its true economics are still uncertain. This paper aims to add to the growing body of knowledge on the socio‐economic performance of the Jatropha system by (i) studying the economic potential (net present value – NPV) of the current most prevailing Jatropha system for Tanzanian farmers and its regional differences, by (ii) making a greenhouse gas (GHG) balance and its economic value of the Jatropha activities on regional level, and by (iii) calculating break‐even thresholds for yield and seed price. Therefore, regional yield modeling, regional life‐cycle assessment, and NPV calculations based on Monte Carlo simulations, each with its set of assumptions, are combined. This study shows positive economic potential of Jatropha cultivation in most of the Tanzanian regions. However, the results also show that 13 of 20 Tanzanian regions will not attain a net positive GHG balance within 10 years. This indicates that the environmental impacts might be more restrictive for Jatropha's sustainability potential in Tanzania than the socio‐economic potential. These results are based on the combination of three models, which consists of strong interdisciplinary modeling work. However, this modeling also contains simplifications (e.g., no opportunity cost for ‘marginal’ land) and uncertainties (e.g., using globally modeled potential yield estimations), which have to be considered in the interpretation of the results.     

The potential of small exclosures in assisting regeneration of coffee shade trees in South‐Western Ethiopian coffee forests

Ethiopian Afromontane moist forests where coffee grows as understorey shrub are traditionally managed by the local communities for coffee production through thinning of the shade tree canopy and slashing of competing undergrowth. This management practice has a negative impact on the coffee shrubs, because the removal of shade tree saplings and seedlings reduces the succession potential of the shade tree canopy, which threatens the very existence of the shade coffee production system. We assessed the functionality of small exclosures to initiate coffee shade tree canopy restoration through natural regeneration. Our results show that small exclosures have a strong restoration potential for the coffee shade trees preferred by farmers (Albizia schimperiana, A. gummifera and Millettia ferruginea), as evidenced from their seedling abundance, survival and growth. The regeneration of late‐successional tree species of the moist Afromontane forest was not successful in the small exclosures, most probably due to the low abundance or absence of adult trees as seed sources for regeneration. Therefore, temporary establishment of small exclosures in degraded coffee forest fragments where shade trees are getting old or dying is recommended for sustainable shade coffee production.     

Invasiveness risk of the tropical biofuel crop Jatropha curcas L. into adjacent land use systems: from the rumors to the experimental facts

Jatropha curcas L. produces seeds rich in non‐edible oil suitable for biodiesel but it has been categorized as invasive. Although not scientifically verified, this allegation has resulted in a cultivation ban in several countries. In this article we report an integrated series of observations and experimental findings from invasiveness research in Zambia. We studied the impacts of J. curcas plantations on adjacent land use systems focusing on spontaneous occurrence of seedlings, seed dispersal mechanisms, seed predation by animals, and germination success of dispersed seeds. No spontaneous regeneration was observed in land use systems adjacent to J. curcas plantations. Primary seed dispersal was limited, predominantly under the canopy of the mother plant. Rodents and shrews dispersed and predated J. curcas seeds and fruits. They transported the seeds up to 23 m from the sources and repositioned them in their burrows up to 0.7 m deep, but none of these seeds could establish. Germination experiments in adjacent land use systems revealed 4% germination success at the soil surface, and 65% if buried artificially at 1–2 cm depth, yet the latter is unlikely to occur under natural conditions. These findings show that J. curcas seeds may be dispersed by animals to adjacent land use systems, but no natural recruitment was observed given low germination on the surface and none in burrows. Altogether these results suggest that the plant currently does not show an elevated risk of invasion to adjacent land use systems, at least in the investigated case study. But more long‐term studies, also in other growing areas are needed to corroborate these results.     

How do trees respond to species mixing in experimental compared to observational studies?

For decades, ecologists have investigated the effects of tree species diversity on tree productivity at different scales and with different approaches ranging from observational to experimental study designs. Using data from five European national forest inventories (16,773 plots), six tree species diversity experiments (584 plots), and six networks of comparative plots (169 plots), we tested whether tree species growth responses to species mixing are consistent and therefore transferrable between those different research approaches. Our results confirm the general positive effect of tree species mixing on species growth (16% on average) but we found no consistency in species‐specific responses to mixing between any of the three approaches, even after restricting comparisons to only those plots that shared similar mixtures compositions and forest types. These findings highlight the necessity to consider results from different research approaches when selecting species mixtures that should maximize positive forest biodiversity and functioning relationships.