Seagrass ecosystem multifunctionality under the rise of a flagship marine megaherbivore

Large grazers (megaherbivores) have a profound impact on ecosystem functioning. However, how ecosystem multifunctionality is affected by changes in megaherbivore populations remains poorly understood. Understanding the total impact on ecosystem multifunctionality requires an integrative ecosystem approach, which is especially challenging to obtain in marine systems. We assessed the effects of experimentally simulated grazing intensity scenarios on ecosystem functions and multifunctionality in a tropical Caribbean seagrass ecosystem. As a model, we selected a key marine megaherbivore, the green turtle, whose ecological role is rapidly unfolding in numerous foraging areas where populations are recovering through conservation after centuries of decline, with an increase in recorded overgrazing episodes. To quantify the effects, we employed a novel integrated index of seagrass ecosystem multifunctionality based upon multiple, well-recognized measures of seagrass ecosystem functions that reflect ecosystem services. Experiments revealed that intermediate turtle grazing resulted in the highest rates of nutrient cycling and carbon storage, while sediment stabilization, decomposition rates, epifauna richness, and fish biomass are highest in the absence of turtle grazing. In contrast, intense grazing resulted in disproportionally large effects on ecosystem functions and a collapse of multifunctionality. These results imply that (i) the return of a megaherbivore can exert strong effects on coastal ecosystem functions and multifunctionality, (ii) conservation efforts that are skewed toward megaherbivores, but ignore their key drivers like predators or habitat, will likely result in overgrazing-induced loss of multifunctionality, and (iii) the multifunctionality index shows great potential as a quantitative tool to assess ecosystem performance. Considerable and rapid alterations in megaherbivore abundance (both through extinction and conservation) cause an imbalance in ecosystem functioning and substantially alter or even compromise ecosystem services that help to negate global change effects. An integrative ecosystem approach in environmental management is urgently required to protect and enhance ecosystem multifunctionality.     

Short rotation coppice culture of willows and poplars as energy crops on metal contaminated agricultural soils

Phytoremediation, more precisely phytoextraction, has been placed forward as an environmental friendly remediation technique, that can gradually reduce increased soil metal concentrations, in particular the bioavailable fractions. The aim of this study was to investigate the possibilities of growing willows and poplars under short rotation coppice (SRC) on an acid, poor, sandy metal contaminated soil, to combine in this way soil remediation by phytoextraction on one hand, and production of biomass for energy purposes on the other. Above ground biomass productivities were low for poplars to moderate for willows, which was not surprising, taking into account the soil conditions that are not very favorable for growth of these trees. Calculated phytoextraction efficiency was much longer for poplars than these for willows. We calculated that for phytoextraction in this particular case it would take at least 36 years to reach the legal threshold values for cadmium, but in combination with production of feedstock for bioenergy processes, this type of land use can offer an alternative income for local farmers. Based on the data of the first growing cycle, for this particular case, SRC of willows should be recommended.     

Element profiles and growth in Zn-sensitive and Zn-resistant Suilloid fungi

Zn pollution has triggered evolution for adaptive Zn tolerance in populations of Suilloid ectomycorrhizal fungi. The objectives of this study were to determine differential physiological responses that are linked to the Zn tolerance trait and to obtain more insight in the general mechanism responsible for the differential growth in Zn-enriched medium. Therefore, we identified intrinsic growth rates and element profiles in Zn-sensitive and Zn-tolerant genotypes. Isolates from Zn-polluted and unpolluted sites were exposed in vitro to increasing Zn²⁺ stress. The Zn concentration which inhibits growth by 50% (EC₅₀) was determined, and element (Zn, Fe, Mn, Cu, Mg, Ca and P) profiles in the mycelia were analysed. The intraspecific variation in growth rate and nutrient content of the in vitro grown mycelia is great and was not reduced in Zn-tolerant populations. The Zn resistance was not correlated to the intrinsic mycelial growth rate of the isolates or to the concentrations of the elements analysed, except for Zn. At low external Zn, Zn-resistant genotypes had lower Zn concentrations than sensitive isolates. At high external Zn, the differential Zn accumulation pattern between resistant and sensitive isolates became very prominent. Zn-exclusion mechanisms are most likely involved in the naturally selected adaptive Zn resistance. Other mechanisms of Zn detoxification such as sequestration of Zn on cell wall compounds or intracellular chelation and/or compartmentation are probably active but cannot explain the differential Zn sensitivity of the isolates.     

The effects of acclimation on thermal tolerance, desiccation resistance and metabolic rate in Chirodica chalcoptera (Coleoptera: Chrysomelidae)

Despite much focus on species responses to environmental variation through space and time, many higher taxa and geographic areas remain poorly studied. We report the effects of temperature acclimation on thermal tolerance, desiccation rate and metabolic rate for adult Chirodica chalcoptera (Coleoptera: Chrysomelidae) collected from Protea nerifolia inflorescences in the Fynbos Biome in South Africa. After 7 days of acclimation at 12, 19 and 25 degrees C, critical thermal maxima (mean+/-s.e.: 41.8+/-0.2 degrees C in field-fresh beetles) showed less response (<1 degrees C change) to temperature acclimation than did the onset of the critical thermal minima (0.1+/-0.2, 1.0+/-0.2 and 2.3+/-0.2 degrees C, respectively). Freezing was lethal in C. chalcoptera (field-fresh SCP -14.6 degrees C) and these beetles also showed pre-freeze mortality. Survival of 2 h at -10.1 degrees C increased from 20% to 76% after a 2 h pre-exposure to -2 degrees C, indicating rapid cold hardening. Metabolic rate, measured at 25 degrees C and adjusted by ANCOVA for mass variation, did not differ between males and females (2.772+/-0.471 and 2.517+/-0.560 ml CO2 h(-1), respectively), but was higher in 25 degrees C-acclimated beetles relative to the field-fresh and 12 degrees C-acclimated beetles. Body water content and desiccation rate did not differ between males and females and did not respond significantly to acclimation. We place these data in the context of measured inflorescence and ambient temperatures, and predict that climate change for the region could have effects on this species, in turn possibly affecting local ecosystem functioning.     

Cadmium stress: an oxidative challenge

At the cellular level, cadmium (Cd) induces both damaging and repair processes in which the cellular redox status plays a crucial role. Being not redox-active, Cd is unable to generate reactive oxygen species (ROS) directly, but Cd-induced oxidative stress is a common phenomenon observed in multiple studies. The current review gives an overview on Cd-induced ROS production and anti-oxidative defense in organisms under different Cd regimes. Moreover, the Cd-induced oxidative challenge is discussed with a focus on damage and signaling as downstream responses. Gathering these data, it was clear that oxidative stress related responses are affected during Cd stress, but the apparent discrepancies observed in between the different studies points towards the necessity to increase our knowledge on the spatial and temporal ROS signature under Cd stress. This information is essential in order to reveal the exact role of Cd-induced oxidative stress in the modulation of downstream responses under a diverse array of conditions.     

Critical oxygen partial pressures and maximal tracheal conductances for Drosophila melanogaster reared for multiple generations in hypoxia or hyperoxia

In Drosophila melanogaster and other insects, increases in atmospheric oxygen partial pressure (aPO₂) tend to increase adult body size and decrease tracheal diameters and tracheolar proliferation. If changes in tracheal morphology allow for functional compensation for aPO₂, we would predict that higher aPO₂ would be associated with higher critical PO₂ values (CritPO₂) and lower maximal tracheal conductances (G_max). We measured CritPO₂ and G_max for adult and larval vinegar flies reared for 7-9 generations in 10, 21 or 40 kPa O₂. The CritPO₂, CO₂ emission rates and G_max values were generally independent of the rearing PO₂ these flies had experienced, suggesting that minimal functional changes in tracheal capacities occurred in response to rearing PO₂. Larvae were able to continue activity during 20 min of anoxia. The lack of multigenerational rearing PO₂ effects on tracheal function suggests that the functional compensation at the whole-body level due to tracheal morphological changes in response to aPO₂ may be minimal; alternatively the benefits of such compensation may occur in specific tissues or during processes not assessed by these methods. In larvae, the CritPO₂ and the capacity for movement in anoxia suggest adaptations for life in hypoxic organic matter.     

Neuroligin Trafficking Deficiencies Arising from Mutations in the α/β-Hydrolase Fold Protein Family

Despite great functional diversity, characterization of the α/β-hydrolase fold proteins that encompass a superfamily of hydrolases, heterophilic adhesion proteins, and chaperone domains reveals a common structural motif. By incorporating the R451C mutation found in neuroligin (NLGN) and associated with autism and the thyroglobulin G2320R (G221R in NLGN) mutation responsible for congenital hypothyroidism into NLGN3, we show that mutations in the α/β-hydrolase fold domain influence folding and biosynthetic processing of neuroligin3 as determined by in vitro susceptibility to proteases, glycosylation processing, turnover, and processing rates. We also show altered interactions of the mutant proteins with chaperones in the endoplasmic reticulum and arrest of transport along the secretory pathway with diversion to the proteasome. Time-controlled expression of a fluorescently tagged neuroligin in hippocampal neurons shows that these mutations compromise neuronal trafficking of the protein, with the R451C mutation reducing and the G221R mutation virtually abolishing the export of NLGN3 from the soma to the dendritic spines. Although the R451C mutation causes a local folding defect, the G221R mutation appears responsible for more global misfolding of the protein, reflecting their sequence positions in the structure of the protein. Our results suggest that disease-related mutations in the α/β-hydrolase fold domain share common trafficking deficiencies yet lead to discrete congenital disorders of differing severity in the endocrine and nervous systems.     

Endophytic bacterial diversity in poplar trees growing on a BTEX-contaminated site: the characterisation of isolates with potential to enhance phytoremediation

The diversity of endophytic bacteria found in association with poplar was investigated as part of a larger study to assess the possibility and practicality of using endophytic bacteria to enhance in situ phytoremediation. Endophytic bacteria were isolated from the root, stem and leaf of two cultivars of poplar tree growing on a site contaminated with BTEX compounds. They were further characterised genotypically by comparative sequence analysis of partial 16S rRNA genes and BOX-PCR genomic DNA fingerprinting, and phenotypically by their tolerance to a range of target pollutants, heavy metals and antibiotics. One hundred and 21 stable, morphologically distinct isolates were obtained, belonging to 21 genera, although six isolates could not be identified with confidence to a genus. The endophytic bacteria exhibited marked spatial compartmentalisation within the plant, suggesting there are likely to be species-specific and non-specific associations between bacteria and plants. A number of isolates demonstrated the ability to degrade BTEX compounds or to grow in the presence of TCE. This study demonstrates that within the diverse bacterial communities found in poplar several endophytic strains are present that have the potential to enhance phytoremediation strategies.