Two Shades of Grey: Effect of Temperature on Seed Germination of the Escaping Ornamental Species Lychnis Coronaria and Stachys Byzantina

This paper describes germination and cytological variability in two popular ornamental and potentially invasive species, lamb’s ear Stachys byzantina and rose campion Lychnis coronaria. Both xerophytic species have the potential to invade natural habitats across Europe and create viable naturalised populations, with subsequent impacts on native vegetation. To assess the species’ invasiveness, seeds were collected from naturalised populations and germination rate recorded under different temperature regimes. Flow cytometry, used to record cytological variability, indicated that all populations of both species were cytologically homogeneous. Germination success, a key spreading factor in both species, was significantly influenced by temperature, with final germination of L. coronaria being extremely high at temperatures > 15/10 °C (98.5%) and extremely low at temperatures < 10/5 °C (2.9%). In comparison, final germination in S. byzantina highest at 22/15 °C (55.6%), reducing to 40.3% at 15/10 °C and just 0.3% at temperatures < 10/5 °C. No significant differences in germination rate were observed between escaping and non-escaping populations, though there were differences between particular populations. Our results indicate germination temperature limits between species consistent with sizes of primary distribution and distance between primary and secondary distribution borders. However, the observed germination rates allow for successful generative reproduction of both species over their secondary distribution areas, suggesting that these species are likely to become invasive species of European grasslands soon.

Seeds of the threatened dry rainforest tree Cadellia pentastylis (Surianaceae) are non-dormant

Cadellia pentastylis (Surianaceae) is an Australian endemic threatened rainforest tree. Irregular flowering and fruiting events coupled with high rates of infertility and insect predation has meant that seed testing has not been possible for this species. Seeds were opportunistically collected from a wild population in early 2021, which allowed for the first germination tests to be conducted. In this study, the presence of physical dormancy was examined by performing an imbibition test using scarified and non-scarified seeds. We also investigated whether a 5-min heat shock treatment at temperatures ranging from 60 to 120°C improved germination success. The presence of physiological dormancy was also examined by recording germination success following a gibberellic acid or smoke-water pre-treatment. Both scarified and non-scarified seeds readily imbibed water over a 72-h period, and several seeds had germinated in both treatments after 48 h. Final germination proportion and t50 following a heat shock, gibberellic acid or smoke-water pre-treatment did not significantly differ from the controls. We conclude that C. pentastylis seeds are non-dormant. Although a palisade cell layer has been reported in the endocarp, our results suggest that this layer may not be sufficiently formed to restrict germination. We recommend that seeds are collected from populations following dispersal and propagated shortly after or stored as conservation collections in ex situ Seedbanks.

How Does Ocean Acidification Affect the Early Life History of Zostera marina? A Series of Experiments Find Parental Carryover Can Benefit Viability or Germination

Elevated partial pressure of carbon dioxide (pCO2) as a concomitant of global climate change may facilitate the establishment of future seagrass meadows and subsequently its benefit could be incorporated into techniques to increase restoration success. In five manipulative experiments, we determined how increased CO2 affects the maturation of flowers, and the development of seeds and seedlings for the foundation species Zostera marina. Experiments tested the development from both seeds collected from non-treated flowering shoots (direct) and seeds harvested from flowering shoots after CO2 exposure (parental carryover). Flowering shoots were collected along the western coast of Sweden near the island of Skafto. The seeds produced were used in experiments conducted at Kristineberg, Sweden and Dauphin Island, AL, United States. Experiments varied in temperature (16, 18°C) and salinity (19, 33 ppt), as well as duration and magnitude of elevated CO2 exposure. Environmental conditions among experiments, such as temperature (16, 18°C) and salinity (19, 33 ppt), as well as duration and magnitude of pCO2 exposure differed. Flowering maturation, spathe number, seed production, and indicators of seed quality did not appear to be affected by 39–69 days of exposure to CO2 conditions outside of natural variability (pCO2 = 1547.2 ± 267.60 μatm; pHT = 7.53 ± 0.07). Yet, seeds produced from these flowers showed twofold greater germination success. In another experiment, flowering shoots were exposed to an extreme CO2 condition (pCO2 = 5950.7 ± 1,849.82 μatm; pHT = 6.96 ± 0.15). In this case, flowers generated seeds that demonstrated a fivefold increase in an indicator for seed viability (sinking velocity). In the latter experiment, however, germination appeared unaffected. Direct CO2 effects on germination and seedling production were not observed. Our results provide evidence of a parental CO2 effect that can benefit germination or seed viability, but early benefits may not lead to bed establishment if other environmental conditions are not well suited for seedling development. Outcomes have implications for restoration; CO2 can be supplied to flowering shoot holding tanks to bolster success when the purpose is to redistribute seeds to locations where beds are extant and water quality is adequate.

Seed Biologists Beware: Estimates of Initial Viability Based on Ungerminated Seeds at the End of an Experiment May Be Error-Prone

Seed viability is routinely measured on seeds that fail to germinate at the end of an experiment. Together with the number of germinants, this is used to estimate viability of the seeds at start of the experiment (i.e., initial viability) and provides the comparative basis on which germination success is determined. Perusal of the literature shows that sometimes (perhaps often, as the problem has yet to be recognized or reported) prolonged duration in the treatment, especially the control where little germination occurs, can lead to loss of viability. This results in underestimation of initial viability if that treatment is used. I caution against the routine use of end-of-trial germination and viability of ungerminated seeds as an estimate of initial viability in determining germination success of various treatments. I explore ways to deal with the problem but the preference is for estimates of initial viability to be undertaken on a separate sample of seeds concurrently with the experiment as this avoids the risk of seed death during the trial.

Restoring the Soils of Nauru: Plants as Tools for Ecological Recovery

<p>The restoration of Nauru’s mined areas is fundamental to the future wellbeing of the people and ecosystems of Nauru. Extensive open cast phosphate mining on Nauru over the last 100 years has led to soil losses and landscape degradation to the extent that over 70% of this South-Western Pacific island state is now uninhabitable and almost all productive land has been lost. Significant landscape degradation has occurred and as a consequence the soils that remain are insufficient in volume and quality to achieve the Government’s restoration goals which support the long-term development of Nauru and the well-being of its people. The aim of this research is to evaluate aspects of cover-crop use as a means for soil restoration in Nauru. This research evaluates biomass production, phytoremediation potential, and germination success for a range of species in Nauruan soils. Field trials exploring biomass production and cadmium phytoextraction were performed, as was an experiment assessing the effects of cadmium on germination success. It was found that, in the circumstances assessed, biomass productivity was significantly determined by species, mulch use, soil type, and to a small degree – cadmium. Phytoextraction was significantly determined by tissue type. Germination success was not determined by soil cadmium, but soil type was a significant factor.</p>

Restoring the Soils of Nauru: Plants as Tools for Ecological Recovery

<p>The restoration of Nauru’s mined areas is fundamental to the future wellbeing of the people and ecosystems of Nauru. Extensive open cast phosphate mining on Nauru over the last 100 years has led to soil losses and landscape degradation to the extent that over 70% of this South-Western Pacific island state is now uninhabitable and almost all productive land has been lost. Significant landscape degradation has occurred and as a consequence the soils that remain are insufficient in volume and quality to achieve the Government’s restoration goals which support the long-term development of Nauru and the well-being of its people. The aim of this research is to evaluate aspects of cover-crop use as a means for soil restoration in Nauru. This research evaluates biomass production, phytoremediation potential, and germination success for a range of species in Nauruan soils. Field trials exploring biomass production and cadmium phytoextraction were performed, as was an experiment assessing the effects of cadmium on germination success. It was found that, in the circumstances assessed, biomass productivity was significantly determined by species, mulch use, soil type, and to a small degree – cadmium. Phytoextraction was significantly determined by tissue type. Germination success was not determined by soil cadmium, but soil type was a significant factor.</p>

Seed Biologists Beware: Estimates of Initial Viability Based on Ungerminated Seeds at the End of an Experiment May Be Error-Prone

Seed viability is routinely measured on seeds that fail to germinate at the end of an experiment. Together with the number of germinants, this is used to estimate viability of the seeds at start of the experiment (i.e., initial viability) and provides the comparative basis on which germination success is determined. Perusal of the literature shows that sometimes (perhaps often, as the problem has yet to be recognized or reported) prolonged duration in the treatment, especially the control where little germination occurs, can lead to loss of viability. This results in underestimation of initial viability if that treatment is used. I caution against the routine use of end-of-trial germination and viability of ungerminated seeds as an estimate of initial viability in determining germination success of various treatments. I explore ways to deal with the problem but the preference is for estimates of initial viability to be undertaken on a separate sample of seeds concurrently with the experiment as this avoids the risk of seed death during the trial.

Restoration of Citropsis articulata, a Species at Risk from Medicinal Overharvesting in a Ugandan Rainforest Reserve

Citropsis articulata, the African cherry orange, is considered to be threatened in Ugandan forests as a result of its purported aphrodisiac properties. This study, part of an ongoing effort to address restoration needs of Mabira Central Forest Reserve in Uganda, demonstrates the feasibility of restoring depleted C. articulata populations using seedlings transplanted from nursery-grown seeds. Phenology of 20 Mabira forest plants was monitored with the aim of collecting seeds. One hundred and fifty-six ripe fruits were collected, and 233 of the extracted seeds were planted in pots in a nursery during January–March 2019. During November-December 2019, seedlings were planted near the sites from which fruits were collected. Seed germination success rate was 89%, and fifteen months after transplanting, in situ survival was 100%. These results suggest that depleted C. articulata populations may be restored in situ using nursery-grown seeds.

Simulated winter warming has negligible effects on germination success of Acadian Forest tree species

Dormant seeds that require long periods of cold stratification to become germinable may be most sensitive to increases in winter temperatures caused by anthropogenic climate change. In this study, we used outdoor plots with infrared heaters to simulate the effects of projected winter warming (+6°C) for Canada’s Acadian Forest Region and compared seed germination success of tree species with varying stratification requirements. We evaluated four seedlots each of balsam fir (Abies balsamea (L.) Mill.), red spruce (Picea rubens Sarg.), white pine (Pinus strobus L.), red maple (Acer rubrum L.), sugar maple (Acer saccharum Marshall) and yellow birch (Betula alleghaniensis Britton). Three central findings emerged from this study: (1) none of the tested species were significantly affected by warming; (2) the random effect of seedlot explained more variation in germination success of deciduous species than it did for conifers; and (3) balsam fir seedlots exhibited considerable differences in their response to warming, implying intraspecific variation in depth of dormancy. These results suggest seed germination success of the tested tree species may not be impeded by their individual seed characteristics under the magnitude of winter warming projected over the coming century in our study area.