Soil organic matter rather than ectomycorrhizal diversity is related to urban tree health.

Urban trees provide many ecosystem services, including carbon sequestration, air quality improvement, storm water attenuation and energy conservation, to people living in cities. Provisioning of ecosystem services by urban trees, however, may be jeopardized by the typically poor quality of the soils in urban areas. Given their well-known multifunctional role in forest ecosystems, ectomycorrhizal fungi (EcM) may also contribute to urban tree health and thus ecosystem service provisioning. Yet, no studies so far have directly related in situ EcM community composition to urban tree health indicators. Here, two previously collected datasets were combined: i) tree health data of 175 Tilia tomentosa trees from three European cities (Leuven, Strasbourg and Porto) estimated using a range of reflectance, chlorophyll fluorescence and physical leaf indicators, and ii) ectomycorrhizal diversity of these trees as characterized by next-generation sequencing. Tree health indicators were related to soil characteristics and EcM diversity using canonical redundancy analysis. Soil organic matter significantly explained variation in tree health indicators whereas no significant relation between mycorrhizal diversity variables and the tree health indicators was found. We conclude that mainly soil organic matter, through promoting soil aggregate formation and porosity, and thus indirectly tree water availability, positively affects the health of trees in urban areas. Our results suggest that urban planners should not overlook the importance of soil quality and its water holding capacity for the health of urban trees and potentially also for the ecosystem services they deliver. Further research should also study other soil microbiota which may independently, or in interaction with ectomycorrhiza, mediate tree performance in urban settings.

Vegetation reflectance spectroscopy for biomonitoring of heavy metal pollution in urban soils.

Heavy metals in urban soils may impose a threat to public health and may negatively affect urban tree viability. Vegetation spectroscopy techniques applied to bio-indicators bring new opportunities to characterize heavy metal contamination, without being constrained by laborious soil sampling and lab-based sample processing. Here we used Tilia tomentosa trees, sampled across three European cities, as bio-indicators i) to investigate the impacts of elevated concentrations of cadmium (Cd) and lead (Pb) on leaf mass per area (LMA), total chlorophyll content (Chl), chlorophyll a to b ratio (Chla:Chlb) and the maximal PSII photochemical efficiency (Fv/Fm); and ii) to evaluate the feasibility of detecting Cd and Pb contamination using leaf reflectance spectra. For the latter, we used a partial-least-squares discriminant analysis (PLS-DA) to train spectral-based models for the classification of Cd and/or Pb contamination. We show that elevated soil Pb concentrations induced a significant decrease in the LMA and Chla:Chlb, with no decrease in Chl. We did not observe pronounced reductions of Fv/Fm due to Cd and Pb contamination. Elevated Cd and Pb concentrations induced contrasting spectral changes in the red-edge (690-740 nm) region, which might be associated with the proportional changes in leaf pigments. PLS-DA models allowed for the classifications of Cd and Pb contamination, with a classification accuracy of 86% (Kappa = 0.48) and 83% (Kappa = 0.66), respectively. PLS-DA models also allowed for the detection of a collective elevation of soil Cd and Pb, with an accuracy of 66% (Kappa = 0.49). This study demonstrates the potential of using reflectance spectroscopy for biomonitoring of heavy metal contamination in urban soils.

Variation in ectomycorrhizal fungal communities associated with Silver linden (Tilia tomentosa) within and across urban areas.

Trees in urban areas face harsh environmental conditions. Ectomycorrhizal fungi (EcM) form a symbiosis with many tree species and provide a range of benefits to their host through their extraradical hyphal network. Although our understanding of the environmental drivers and large scale geographical variation of EcM communities in natural ecosystems is growing, our knowledge of EcM communities within and across urban areas is still limited. Here, we characterized EcM communities using Illumina miseq sequencing on 175 root samples of the urban tree Tilia tomentosa from three European cities, namely Leuven (Belgium), Strasbourg (France) and Porto (Portugal). We found strong differences in EcM richness and community composition between cities. Soil acidity, organic matter and moisture content were significantly associated with EcM community composition. In agreement, the explained variability in EcM communities was mostly attributed to general soil characteristics, whereas very little variation was explained by city and heavy metal pollution. Overall, our results suggest that EcM communities in urban areas are significantly associated with soil characteristics, while heavy metal pollution and biogeography had little or no impact. These findings deliver new insights into EcM distribution patterns in urban areas and contribute to specific inoculation strategies to improve urban tree vitality.

Ketamine induction of p53-dependent apoptosis and oxidative stress in zebrafish (Danio rerio) embryos.

Ketamine is a widely used pharmaceutical that has been detected in water sources worldwide. Zebrafish embryos were used in this study to investigate the oxidative stress and apoptotic signals following a 24h exposure to different ketamine concentrations (0, 50, 70 and 90 mg L-1). Early blastula embryos (∼2 h post fertilisation-hpf) were exposed for 24 h and analysed at 8 and 26 hpf. Reactive oxygen species and apoptotic cells were identified in vivo, at 26 hpf. Enzymatic activities (superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), lactate dehydrogenase (LDH) and acetylcholinesterase (AChE)), glutathione levels (oxidised (GSSG) and reduced (GSH)), oxidative damage (lipid peroxidation (LPO) and protein carbonyls (CO)) as well as oxidative stress (gclc, gstp1, sod1 and cat), apoptosis (casp3a, casp6, casp8, casp9, aifm1 and tp53) and cell proliferation (pcna) related-genes were evaluated at 8 and 26 hpf. Caspase (3 and 9) activity was also determined at both time-points by colorimetric methods. Superoxide dismutase (SOD), catalase (CAT), glutathione levels (GSSG), caspase-9 and reactive oxygen species (ROS) were shown to be affected by ketamine exposure while in vivo analysis showed no difference in ROS. A significant up-regulation of superoxide dismutase (sod1) and catalase (cat) genes expression was also perceived. Ketamine-induced apoptosis was observed in vivo and confirmed by the apoptotic-related genes up-regulation. The overall results suggest that ketamine induced oxidative stress and apoptosis through the involvement of p53-dependent pathways in zebrafish embryos which could be important for the evaluation of the overall risk of ketamine in aquatic environments.

Apoptosis-related genes induced in response to ketamine during early life stages of zebrafish.

Increasing evidence supports that ketamine, a widely used anaesthetic, potentiates apoptosis during development through the mitochondrial pathway of apoptosis. Defects in the apoptotic machinery can cause or contribute to the developmental abnormalities previously described in ketamine-exposed zebrafish. The involvement of the apoptotic machinery in ketamine-induced teratogenicity was addressed by assessing the apoptotic signals at 8 and 24 hpf following 20min exposure to ketamine at three stages of early zebrafish embryo development (256 cell, 50% epiboly and 1-4 somites stages). Exposure at the 256-cell stage to ketamine induced an up-regulation of casp8 and pcna at 8 hpf while changes in pcna at the mRNA level were observed at 24 hpf. After the 50% epiboly stage exposure, the mRNA levels of casp9 were increased at 8 and 24 hpf while aifm1 was affected at 24 hpf. Both tp53 and pcna expressions were increased at 8 hpf. After exposure during the 1-4 somites stage, no meaningful changes on transcript levels were observed. The distribution of apoptotic cells and the caspase-like enzymatic activities of caspase-3 and -9 were not affected by ketamine exposure. It is proposed that ketamine exposure at the 256-cell stage induced a cooperative mechanism between proliferation and cellular death while following exposure at the 50% epiboly, a p53-dependent and -independent caspase activation may occur. Finally, at the 1-4 somites stage, the defence mechanisms are already fully in place to protect against ketamine-insult. Thus, ketamine teratogenicity seems to be dependent on the functional mechanisms present in each developmental stage.

Morphological and behavioral responses of zebrafish after 24h of ketamine embryonic exposure.

Ketamine, one anesthetic used as an illicit drug, has been detected both in freshwater and marine ecosystems. However, knowledge of its impact on aquatic life is still limited. This study aimed to test its effects in zebrafish embryos by analyzing its time- and dose-dependent developmental toxicity and long-term behavioral changes. The 24h-LC50 was calculated from percent survival using probit analysis. Based on the 24h-LC50 (94.4mgL-1), embryos (2hour post-fertilization - hpf) were divided into four groups, including control, and exposed for 24h to ketamine concentrations of 50, 70 or 90mgL-1. Developmental parameters were evaluated on the course of the experimental period, and anatomical abnormalities and locomotor deficits were analyzed at 144hpf. Although the portion of ketamine transferred into the embryo was higher in the lowest exposed group (about 0.056±0.020pmol per embryo), the results showed that endpoints such as increased mortality, edema, heart rate alterations, malformation and abnormal growth rates were significantly affected. At 144hpf, the developmental abnormalities included thoracic and trunk abnormalities in the groups exposed to 70 and 90mgL-1. Defects in cartilage (alcian blue) and bone (calcein) elements also corroborated the craniofacial anomalies observed. A significant up-regulation of the development-related gene nog3 was detected by qRT-PCR at 8 hpf. Early exposure to ketamine also resulted in long-term behavioral changes, such as an increase in thigmotaxis and disruption of avoidance behavior at 144 hpf. Altogether, this study provides new evidence on the ketamine teratogenic potential, indicating a possible pharmacological impact of ketamine in aquatic environments.

Embryonic Stage-Dependent Teratogenicity of Ketamine in Zebrafish (Danio rerio).

Ketamine, a widely used anesthetic, has been shown to have NMDA receptor dependent and independent actions during zebrafish (Danio rerio) embryogenesis. Notwithstanding, the effects of developmental toxicity and the mechanisms of ketamine action on fish embryos are still not well understood, and its implications for early vertebrate development remains to be clarified. In this work, zebrafish embryos were exposed to ketamine (0.2, 0.4, and 0.8 mg mL(-1)) in order to study the stage-developmental toxicity of this pharmaceutical. During 256-cell (2.5 h post-fertilization, hpf), 50% epiboly (5.5 hpf) and 1-4 somites (10.5 hpf), embryos were exposed to the referred ketamine concentrations for a period of 20 min and were allowed to grow until 144 hpf. Both lethal and nonlethal parameters were evaluated. Skeletal development was assessed by alcian blue and calcein staining. Additionally, the expression of the developmental genes sonic hedgehog a (shh a) and noggin 3 (nog3) was evaluated. Similar to our previous work, bone and cartilage malformations were observed after 256-cell exposure. During 50% epiboly, ketamine exposure induced concentration-dependent mortality and malformations, such as lordosis and/or kyphosis and microcephaly, namely, at higher concentrations. Conversely, exposure during 1-4 somites showed the induction of nonspecific effects with no rise in mortality. The quantitative real-time polymerase chain reaction (qRT-PCR) analysis showed differences in shh a and nog3 expressions comparatively to the control group. Overall, this study shows that the ketamine toxic profile is developmental phase-dependent with 256-cell being the most susceptible phase. The effects observed may result from ketamine interaction with cellular signaling pathways that merits further investigation.