Climate warming and atmospheric deposition affect seed viability of common juniper (<Emphasis Type="Italic">Juniperus communis</Emphasis>) via their impact on the nutrient status of the plant

Global environmental change is increasingly affecting species worldwide. One of the emblematic casualties among plants in several European countries is common juniper (Juniperus communis). Many populations of common juniper throughout its distribution range are declining. The relative lack of viable seed production, resulting in low probabilities for successful natural regeneration, is one of the main reasons for this decline. Climate warming and elevated atmospheric depositions have been shown to negatively affect seed viability of common juniper, but our understanding of the underlying mechanisms remains scarce. One possible pathway is via changes in the plant nutrient status that, in turn, may affect seed viability. Here we took advantage of large-scale gradients in climate and atmospheric depositions between central Sweden and northern Spain, and analysed foliar nutrient concentrations and stoichiometry and seed viability in 20 juniper populations spread across Europe. Our results show that increasing temperatures can negatively affect needle N and P concentrations while enhanced potentially acidifying depositions resulted in lower foliar N and Ca concentrations. Needle C:N ratios increased with higher temperature, acidifying depositions and precipitation. By linking these patterns to seed viability, we found that low needle P, Ca and Mg concentrations were related to low seed viability. Thus, a shortage of these key elements during seed development and seed nutrient storage, can lead to anomalies and seed abortion. These findings help to explain the low seed viability of juniper in Europe and may help to assist land managers to take urgently needed conservation actions.     

How tree species identity and diversity affect light transmittance to the understory in mature temperate forests

Light is a key resource for plant growth and is of particular importance in forest ecosystems, because of the strong vertical structure leading to successive light interception from canopy to forest floor. Tree species differ in the quantity and heterogeneity of light they transmit. We expect decreases in both the quantity and spatial heterogeneity of light transmittance in mixed stands relative to monocultures, due to complementarity effects and niche filling. We tested the degree to which tree species identity and diversity affected, via differences in tree and shrub cover, the spatiotemporal variation in light availability before, during, and after leaf expansion. Plots with different combinations of three tree species with contrasting light transmittance were selected to obtain a diversity gradient from monocultures to three species mixtures. Light transmittance to the forest floor was measured with hemispherical photography. Increased tree diversity led to increased canopy packing and decreased spatial light heterogeneity at the forest floor in all of the time periods. During leaf expansion, light transmittance did differ between the different tree species and timing of leaf expansion might thus be an important source of variation in light regimes for understory plant species. Although light transmittance at the canopy level after leaf expansion was not measured directly, it most likely differed between tree species and decreased in mixtures due to canopy packing. A complementary shrub layer led, however, to similar light levels at the forest floor in all species combinations in our plots. Synthesis. We find that a complementary shrub layer exploits the higher light availability in particular tree species combinations. Resources at the forest floor are thus ultimately determined by the combined effect of the tree and shrub layer. Mixing species led to less heterogeneity in the amount of light, reducing abiotic niche variability.     

Non-dermatophytic moulds: onychomycosis in four patients infected with the human immunodeficiency virus

Patients infected with human immunodeficiency virus (HIV) are a risk group for onychomycosis, fungal infections caused mainly by dermatophytes and yeast. However, non-dermatohytic moulds are becoming common agents for nail infections in this population of patients. We report four cases of onychomycosis caused by non-dermatophytic moulds (Aspergillus niger, Scytalidium hyalinum, Scytalidium dimidiatum and Fusarium solani) in patients infected with HIV from Recife, Pernambuco, Brazil. Onychomicosis by non-dermatophytic species in HIV-positive patients requires special attention in the clinical and the laboratory. A proper diagnosis is necessary to establish the specific and adequate treatment, preventing fungal invasion.     

Disentangling relationships between habitat conditions, disturbance history, plant diversity, and American black cherry (Prunus serotina Ehrh.) invasion in a European temperate forest

Whether non-native plant invasions are causes, consequences, or independent of the low species diversity in recipient ecosystems remains a debated question. We tried to test these three hypotheses in the special case of the American black cherry ( Prunus serotina Ehrh.), a gap-dependent tree species, which is invading European temperate forests. We compared plant communities, soil properties, and disturbance history between P. serotina -invaded and uninvaded paired-stands in a managed mixed forest. Relationships between invasion, disturbances, plant communities, and environmental conditions were investigated using redundancy analyses with variation partitioning. Several soil characteristics differed between paired stands, but were rather components of stand invasibility than invasion effects, except for topsoil available phosphorus. The disturbance history was similar among paired stands except for the amount of storm-induced tree falls, which correlated with the invader's density. Wild boar-disturbed soil areas were more important beneath P. serotina canopies, suggesting a positive feedback on its own establishment. Overall, species assemblages in invaded and uninvaded stands were similar; their ecological inconsistency suggested a management-sustained non-equilibrium. Habitat conditions and disturbances explained most of the variation in both plant diversity and P. serotina density, the last two factors exhibiting a weak direct association. We conclude that in managed forest ecosystems where plant communities are mainly driven by non-interactive factors and immigration processes, non-native plant species can naturalize without being directly influenced by measured features of the plant community in the receiving environment on the short term.     

Long‐term seed bank dynamics in a temperate forest under conversion from coppice‐with‐standards to high forest management

Questions: How do changes in forest management, i.e. in disturbance type and frequency, influence species diversity, abundance and composition of the seed bank? How does the relationship between seed bank and vegetation change? What are the implications for seed bank dynamics? Location: An ancient Quercus petraea — Carpinus betulus forest in conversion from coppice‐with‐standards to regular Quercus high forest near Montargis, France. Methods: Seed bank and vegetation were sampled in six replicated stand types, forming a chronosequence along the conversion pathway. The stand types represented mid‐successional stages of stands in transition from coppice‐with‐standards (to high forest (16 plots) and early‐ and mid‐successional high forest stands (32 plots). Results: Seed bank density and species richness decreased with time since last disturbance. Adjusting for seed density effects obscured species richness differences between stand types, but species of later seres were nested subsets of earlier seres, implying concomitant shifts in species richness and composition with time since disturbance. Later seres were characterized by species with low seed weight and high seed longevity. Seed banks of early seres were more similar to vegetation than to later seres. Conclusions: Abandonment of the coppice‐with‐standards regime altered the seed bank characteristics, as well as its relationship with vegetation. Longer management cycles under high forest yield impoverished seed banks. For their persistence, seed bank species will increasingly rely on management of permanently open areas in the forest landscape. Thus, revegetation at the beginning of new high‐forest cycles may increasingly depend on inflow from seed sources.     

Depletion of high energy phosphates implicates post-exercise mortality in carp and trout; an in vivo 31P-NMR study.

As in vivo 31P-Nuclear Magnetic Resonance spectroscopy is currently the state of the art method to measure continuously intracellular pH (pH(i)) and energy status of muscle tissue, we used this method to study the recovery from exhaustive exercise. The biochemical changes during recovery are not well understood and it was suggested that post-exercise mortality could be caused by low pH(i); other studies however indicate that energy depletion might be more important. To analyse the mechanism of post-exercise recovery pH(i), ATP, P(i), and PCr must be measured at the same time, which is possible using in vivo 31P-NMR. Common carp and rainbow trout of about 100 g were exercised to exhaustion in a swim tunnel. After swimming 10 h at 1.5 body lengths (BL)/s (aerobic control), 50% of the fish were forced to swim at 6 BL/s until exhaustion. Recovery of energy rich phosphates was found to be faster in carp (1.2-1.9 h) than in trout (1.5-2.3 h). The same applied for the recovery from acidosis, which took 1.75 h in carp and 5.75 h in trout. In parallel experiments the energy phosphates and lactate levels were measured in liver, red muscle, and white muscle. Exhaustion caused a significant drop in the energy status of red and white muscle tissue of trout and carp (corroborates NMR data), while no change at all was observed in liver tissue. The lactate levels were increased in the muscle but not in liver and blood. While all experimental animals looked healthy after exhaustion, 40-50% of the carp as well as trout died during the recovery phase. The energy status of those individuals measured by 31P-NMR was much lower than that of the survivors, while in contrast there was no difference in pH(i). Thus, it appears that not acidosis but depletion of high energy phosphates disabled muscle function and therefore may have been the cause of death of the non-survivors.     

Drosophila nemo promotes eye specification directed by the retinal determination gene network

Drosophila nemo (nmo) is the founding member of the Nemo-like kinase (Nlk) family of serine-threonine kinases. Previous work has characterized nmo's role in planar cell polarity during ommatidial patterning. Here we examine an earlier role for nmo in eye formation through interactions with the retinal determination gene network (RDGN). nmo is dynamically expressed in second and third instar eye imaginal discs, suggesting additional roles in patterning of the eyes, ocelli, and antennae. We utilized genetic approaches to investigate Nmo's role in determining eye fate. nmo genetically interacts with the retinal determination factors Eyeless (Ey), Eyes Absent (Eya), and Dachshund (Dac). Loss of nmo rescues ey and eya mutant phenotypes, and heterozygosity for eya modifies the nmo eye phenotype. Reducing nmo also rescues small-eye defects induced by misexpression of ey and eya in early eye development. nmo can potentiate RDGN-mediated eye formation in ectopic eye induction assays. Moreover, elevated Nmo alone can respecify presumptive head cells to an eye fate by inducing ectopic expression of dac and eya. Together, our genetic analyses reveal that nmo promotes normal and ectopic eye development directed by the RDGN.     

Conservation units based on mitochondrial and nuclear DNA variation among European bullhead populations (Cottus gobio L., 1758) from Flanders, Belgium

In this study, we aimed to delineateevolutionarily significant units (ESUs) andmanagement units (MUs) for the Europeanbullhead in Flanders (Belgium). Therefore, wedetermined the genetic interrelationshipsbetween 11 bullhead populations, using lengthvariation at 7 polymorphic microsatellite lociand sequence variation in the d-loop of themitochondrial DNA (mtDNA). Despite therelatively small geographical scale of ourstudy, the analysis of the d-loop sequencesshows that the Flemish bullhead populationscontain 3 haplotype groups, which can beassigned to 3 previously described EuropeanmtDNA clades. Because of the importantdifferences between these clades, they may bedefined as evolutionarily significant units,which should be managed separately. Analysis ofmicrosatellite data reveals very high degreesof isolation between populations, with theexception of 3 pairwise comparisons whichinvolved adjacent populations. Our data suggestthat the 3 haplotype groups probably qualify asESUs, as they show phylogeographicdifferentiation for mtDNA variants as well assignificant divergence of allele frequencies atnuclear loci. However, one of these units,limited to a single population, may be ofCentral European origin. All populations of theScheldt basin meet the criteria for MUrecognition, since significantly differentmicrosatellite allele frequencies as well asprivate alleles are found. In contrast, geneticdifferentiation among the 3 populations of theMeuse basin is very low.     

Discovery of a new RNA-containing nuclear structure in UVC-induced apoptotic cells by integrated laser electron microscopy

Background information. Treatment of cells with UVC radiation leads to the formation of DNA cross‐links which, if not repaired, can lead to apoptosis. γ‐H2AX and cleaved caspase 3 are proteins formed during UVC‐induced DNA damage and apoptosis respectively. The present study sets out to identify early morphological markers of apoptosis using a new method of correlative microscopy, ILEM (integrated laser electron microscopy). Cleaved caspase 3 and γ‐H2AX were immunofluorescently labelled to mark the cells of interest. These cells were subsequently searched in the fluorescence mode of the ILEM and further analysed at high resolution with TEM (transmission electron microscopy). Results. Following the treatment of HUVECs (human umbilical vein endothelial cells) with UVC radiation, in the majority of the cells γ‐H2AX was formed, whereas only in a subset of cells caspase 3 was activated. In severely damaged cells with high levels of γ‐H2AX a round, electron‐dense nuclear structure was found, which was hitherto not identified in UV‐stressed cells. This structure exists only in nuclei of cells containing cleaved caspase 3 and is present during all stages of the apoptotic process. Energy‐loss imaging showed that the nuclear structure accumulates phosphorus, indicating that it is rich in nucleic acids. Because the nuclear structure did not label for DNA and was not affected by regressive EDTA treatment, it is suggested that the UV‐induced nuclear structure contains a high amount of RNA. Conclusions. Because the UV‐induced nuclear structure was only found in cells labelled for cleaved caspase 3 it is proposed as an electron microscopic marker for all stages of apoptosis. Such a marker will especially facilitate the screening for early apoptotic cells, which lack the well‐known hallmarks of apoptosis within a cell population. It also raises new questions on the mechanisms involved in the UV‐induced apoptotic pathway.