Sexual reproduction of common juniper (Juniperus communis) in the face of global change

With a distribution range that covers most of the northern hemisphere, common juniper (Juniperus communis L.) has one of the largest distribution ranges of all plant species on earth. The last decades, however, multiple studies are reporting a significantly declining size and plummeting number of common juniper populations in many regions, including in the western European lowlands and the Mediterranean mountain regions. Failing recruitment is one of the main reasons for this decline. In many of the remaining European juniper populations, the percentage of viable seeds is extremely low, thereby limiting the chances for successful regeneration. However, also other reasons, such as the absence of microclimate suitable for germination and seedling establishment, can be responsible for the lack of recruitment. It was suggested that climate warming as well as enhanced atmospheric depositions can negatively affect juniper’s seed viability. However, the mechanisms behind these effects remain unclear. The aim of this thesis was to further our understanding of the effects of climate change (changing temperature and precipitation) and air pollution (atmospheric depositions of nitrogen and sulphur) on different phases of the sexual reproductive phase of common juniper. We focussed on three crucial seed phases: (seed phase 1, SP1) the early gametophyte development and pollination; (seed phase 2, SP2) further development of the gametophytes, fertilization and early embryo development; (seed phase 3, SP3) late embryo development. The seed viability of populations with and without recruitment was compared. Only after SP3, we found significant differences in seed viability between populations with and populations without recruitment. Hence, this made us conclude that late embryo development is the most crucial phase during seed development. However, anomalies during SP2 can have a delayed effect on embryo development. Therefore, both seed phases were retained for further research. With both observational and experimental research we studied the effects of global environmental changes on seed viability. Overall, we found viability of SP2- and SP3-seedsto decrease with temperature. Enhanced atmospheric depositions were only negatively correlated with SP3-seed viability. There are different pathways through which these global-change drivers possibly elaborate their negative effects. For example, increasing temperatures can negatively affect the development and growth of the female gamethophyte and the pollen tube, the male-female synchrony in the pre-fertilization phases, the development of the megagametophyte and the nutrition and growth of the embryo. On the other hand, both atmospheric depositions and warming can cause nutrient imbalances. Although the ripening of the embryo (SP3) was identified as the most vulnerable phase, we found strong indications that the actual reasons for low seed viability should be searched in the preceding processes. For example, our transplant experiment along a latitudinal gradient clearly showed that significant differences in seed viability between the temperature treatments only occurred if the seeds also experienced higher temperatures during SP2. Hence, it is plausible that anomalies, induced by warming or enhanced atmospheric deposition, occur during the development of the female gametophyte (SP2). However, their effects only manifested themselves in SP3, for example, by leading to a malfunctioning megagametophyte that will not be able to nourish the developing embryo. In addition, with a germination experiment, we assessed ideal microclimatic soil conditions for germination and seedling establishment. We found that it is highly important that juniper seeds are in contact with mineral soil, with a sufficient amount of loam or organic matter, for successful germination. For example, sod cutting can create these conditions. To conclude, our findings highlight that common juniper, arguably one of the most iconic threatened tree species of Europe, is becoming a victim of global change. Successful recruitment in common juniper will only occur if the following conditions are met: enough viable seed must be available (e.g. during a colder period of several years) and enough microsites suitable for establishment must be present. The probability that microsites exist where these conditions (viable seeds and chances for establishment) occur at the same time increases in larger areas where the management is already suited for common juniper. Concerning the low seed viability, attention should be focused on locations where the microclimate is expected to be colder (e.g. northerly oriented slopes or the vicinity of small rivers) and where atmospheric depositions are lower (e.g. not too close to busy roads and/or farms). This work is also an extra call for policy makers to increase their efforts in reducing the emissions of greenhouse gases and reactive nitrogen

Genetic structure and seed-mediated dispersal rates of an endangered shrub in a fragmented landscape: a case study for Juniperus communis in northwestern Europe

<p>Abstract</p> <p>Background</p> <p>Population extinction risk in a fragmented landscape is related to the differential ability of the species to spread its genes across the landscape. The impact of landscape fragmentation on plant population dynamics will therefore vary across different spatial scales. We quantified successful seed-mediated dispersal of the dioecious shrub <it>Juniperus communis </it>in a fragmented landscape across northwestern Europe by using amplified fragment length polymorphism (AFLP) markers. Furthermore we investigated the genetic diversity and structure on two spatial scales: across northwestern Europe and across Flanders (northern Belgium). We also studied whether seed viability and populations size were correlated with genetic diversity.</p> <p>Results</p> <p>Unexpectedly, estimated seed-mediated dispersal rates were quite high and ranged between 3% and 14%. No population differentiation and no spatial genetic structure were detected on the local, Flemish scale. A significant low to moderate genetic differentiation between populations was detected at the regional, northwest European scale (PhiPT = 0.10). In general, geographically nearby populations were also genetically related. High levels of within-population genetic diversity were detected but no correlation was found between any genetic diversity parameter and population size or seed viability.</p> <p>Conclusions</p> <p>In northwestern Europe, landscape fragmentation has lead to a weak isolation-by-distance pattern but not to genetic impoverishment of common juniper. Substantial rates of successful migration by seed-mediated gene flow indicate a high dispersal ability which could enable <it>Juniperus communis </it>to naturally colonize suitable habitats. However, it is not clear whether the observed levels of migration will suffice to counterbalance the effects of genetic drift in small populations on the long run.</p

Effects of heathland management on seedling recruitment of common juniper (Juniperus communis)

Background and aims: Common juniper (Juniperus communis L.) is one of the most widespread woody species on the planet. Over recent decades, however, common juniper populations are decreasing in size and number in different regions. Lack of recruitment, caused by extremely low seed viability and the absence of suitable microsites for recruitment, is the key reason for this decline. For successful germination, the seeds need gaps in the existing vegetation and a soil with a relatively high base saturation. The aim of this study was therefore to assess how management actions such as sod cutting, rotavation and liming (alone or in various combinations) influence soil characteristics, seed germination and seedling survival of common juniper. Methods: We installed a sowing experiment across 104 1-m2 plots in four different sites in Belgium and the Netherlands using treatments with different combinations of fencing, sod cutting, rotavation, litter addition and liming. We determined how these treatments affected soil characteristics and how they influenced seed germination and seedling survival. Key results and conclusions: Across the whole experiment, germination rates of juniper seeds were very low (almost always < 1%). Our results confirm that bare ground promotes the germination of juniper seeds. Secondly, higher silt and lutum (clay) proportions in the soil and higher soil organic matter content seemed to have a positive impact on recruitment, possibly due to drought reduction. Management actions that negatively affect those soil characteristics, such as deep sod cutting, should thus be avoided in heathlands on sandy soils. Our results reveal a complex relationship between seedling recruitment success, soil conditions and management of common juniper populations. Overall, combinations of fencing, (superficial) sod cutting and liming or rotavation were most successful

The European TeleCheck-AF project on remote app-based management of atrial fibrillation during the COVID-19 pandemic: Centre and patient experiences

Aims: TeleCheck-AF is a multicentre international project initiated to maintain care delivery for patients with atrial fibrillation (AF) during COVID-19 through teleconsultations supported by an on-demand photoplethysmography-based heart rate and rhythm monitoring app (FibriCheck® ). We describe the characteristics, inclusion rates and experiences from participating centres according the TeleCheck-AF infrastructure as well as characteristics and experiences from recruited patients.Methods: Three surveys exploring centre characteristics (n=25), centre experiences (n=23) and patient experiences (n=826) were completed. Self-reported patient characteristics were obtained from the app.Results: Most centres were academic (64%) and specialized public cardiology/district hospitals (36%). Majority of centres had AF outpatient clinics (64%) and only 36% had AF ablation clinics. The time required to start patient inclusion and total number of included patients in the project was comparable for centres experienced (56%) or inexperienced in mHealth use. Within 28 weeks, 1930 AF patients were recruited, mainly for remote AF control (31% of patients) and AF ablation follow-up (42%). Average inclusion rate was highest during the lockdown restrictions and reached a steady state at a lower level after easing the restrictions (188 vs 52 weekly recruited patients). Majority (>80%) of the centres reported no problems during the implementation of the TeleCheck-AF approach. Recruited patients (median age 64 [55-71], 62% male) agreed that the FibriCheck® app was easy to use (94%).Conclusions: Despite different health care settings and mHealth experiences, the TeleCheck-AF approach could be set up within an extremely short time and easily used in different European centres during COVID-19

Welke toekomst voor de jeneverbes in Vlaanderen : een evaluatie aan de hand van beheerscenario's

The latest decennia Common Juniper populations show a strong decline in Flanders (northern Belgium). It is necessary that the remaining 72 populations get a targeted management. By means of a simple model we tried to examine how state of Common Juniper during the next two decades will be influenced by three management actions: (1) clearing of competing vegetation to prevent out-shading, (2) creating bare ground to promote natural regeneration and (3) altering the number of individuals in a population by planting new bushes. We also studied the effect of policy choices that will determine the management that will be applied in each of the remaining populations on the base of their characteristics (e.g. type of habitat, type of owner and EU Habitat Directive). We found that, because of the problematic recruitment, the first two management actions will have practically no influence on the state of Common Juniper in Flanders in comparison with a business as usual scenario (in which the present management was continued). So, as long as natural recruitment stays out, the planting of new individuals will be the only action that generates any results. We also concluded that the overall status of Common Juniper in Flanders will strongly decline if the planting is only performed in populations that are situated in EU Habitat Directive areas. Therefore it is recommended to apply appropriate management in populations that aren’t located in these areas or to create new populations in suitable habitats within the EU Habitat Directive areas

Critical phases in the seed development of common juniper (Juniperus communis)

Common juniper (Juniperus communis L.) populations in northwest European lowlands are currently declining in size and number. An important cause of this decline is a lack of natural regeneration. Low seed viability seems to be one of the main bottlenecks in this process. Previous research revealed a negative relation between seed viability and both temperature and nitrogen deposition. Additionally, the seeds of common juniper have a variable ripening time, which possibly influences seed viability. However, the underlying mechanisms remain unresolved. In order to elucidate this puzzle, it is important to understand in which phases of seed production the main defects are situated, together with the influence of ripening time. In this study, we compared seed viability of populations with and without successful recruitment. We examined three seed phases: (i) gamete development; (ii) fertilisation and early-embryo development; and (iii) late-embryo development. After the first two phases, we found no difference in the percentage viable seeds between populations with or without recruitment. After late-embryo development, populations without recruitment showed a significantly lower percentage of viable seeds. These results suggest that late-embryo development is a bottleneck in seed development. However, the complex interaction between seed viability and ripening time suggest that the causes should be in the second seed phase, as the accelerated development of male and female gametophytes may disturb the malefemale synchrony for successful mating