Robin J. Probert

SEED GERMINATION RESPONSES TO SOME ENVIRONMENTAL FACTORS IN THE SEAGRASS ZOSTERA CAPRICORNI FROM EASTERN AUSTRALIA

Abstract The germination requirements of Zostera capricorni Aschers. were studied in relation to temperature, salinity and oxygen potential. In treatments maintained at 16°C (corresponding to winter mean water temperature) and a salinity of 15‰ (half that of normal seawater), the cumulative percentage germination in both aerobic and anaerobic treatments was over 80%. However, seed germination was much faster under anaerobic conditions than aerobic conditions (cf. mean time-to-germinate (MTG) of 136 days, respectively). Under anaerobic conditions, at a constant 16°C, salinity level did not affect germination which was high (>80%) and rapid (MTG 82 days) and the cumulative percentage germination did not exceed 40%. The effects of temperature on germination were more marked under anaerobic conditions than aerobic conditions. When Z . capricorni seeds were transferred to 16°C, after 24 days at 26°C (where germination rate was very slow), rapid germination followed in the anaerobic treatments. In contrast, when seeds were similarly transferred from 16°C to 26°C, the germination rate decreased to a negligible level following a 1-week lag period immediately after transfer when they continued to germinate rapidly. After 5 months cold stratification in artificial seawater at 6°C, both final germination and germination rate under anaerobic conditions were broadly similar to that recorded in unstratified seeds. In contrast, under aerobic conditions despite the fact that final germination at both salinity levels did not exceed 60%, stratified seeds germinated much quicker than unstratified seeds (average MTG value across both salinity levels, 51.2 and 148 days, respectively) indicating a reduction in the conditional dormancy originally maintained by aerobic conditions.

Climate warming could shift the timing of seed germination in alpine plants.

BACKGROUND AND AIMS Despite the considerable number of studies on the impacts of climate change on alpine plants, there have been few attempts to investigate its effect on regeneration. Recruitment from seeds is a key event in the life-history of plants, affecting their spread and evolution and seasonal changes in climate will inevitably affect recruitment success. Here, an investigation was made of how climate change will affect the timing and the level of germination in eight alpine species of the glacier foreland. METHODS Using a novel approach which considered the altitudinal variation of temperature as a surrogate for future climate scenarios, seeds were exposed to 12 different cycles of simulated seasonal temperatures in the laboratory, derived from measurements at the soil surface at the study site. KEY RESULTS Under present climatic conditions, germination occurred in spring, in all but one species, after seeds had experienced autumn and winter seasons. However, autumn warming resulted in a significant increase in germination in all but two species. In contrast, seed germination was less sensitive to changes in spring and/or winter temperatures, which affected only three species. CONCLUSIONS Climate warming will lead to a shift from spring to autumn emergence but the extent of this change across species will be driven by seed dormancy status. Ungerminated seeds at the end of autumn will be exposed to shorter winter seasons and lower spring temperatures in a future, warmer climate, but these changes will only have a minor impact on germination. The extent to which climate change will be detrimental to regeneration from seed is less likely to be due to a significant negative effect on germination per se, but rather to seedling emergence in seasons that the species are not adapted to experience. Emergence in autumn could have major implications for species currently adapted to emerge in spring.

Advances in seed conservation of wild plant species: a review of recent research

The importance of wild plant diversity for future food security, human health and ecosystem function and repair is generally accepted. Seed banking is widely used to safeguard wild species and research into the complexity of seed behaviour has led to changes in how seeds of wild species are handled in genebanks.

Seed Persistence in the Field May Be Predicted by Laboratory-Controlled Aging

Abstract Weed management is complicated by the presence of soil seed banks. The complexity of soil–seed interactions means that seed persistence in the field is often difficult to measure, let alone predict. Field trials, although accurate in their context, are time-consuming and expensive to conduct for individual species. Some ex situ techniques for estimating seed life expectancy have been proposed, but these fail to simulate the environmental complexity of the field. Also, it has been questioned whether techniques such as the controlled aging test (CAT) are useful indicators of field persistence. This study aimed to test the validity of the standard CAT (seed aging at 45 C and 60% relative humidity) in use at the Royal Botanic Gardens, Kew, U.K., for predicting field seed-persistence. Comparison of seed persistence and CAT data for 27 northwest European species suggested a significant positive correlation of 0.31. Subsequently, 13 species of emerging and common weeds of Queensland were assessed for their seed longevity using the CAT. The seed longevity data of these species in the CAT were linked with field seed-persistence data according to three broad seed-persistence categories: < 1 yr, 1 to 3 yr, and > 3 yr. We discuss the scope for using the CAT as a tool for rapid assignment of species to these categories. There is a need for further studies that compare predictions of seed persistence based on the CAT with seed persistence in the field for a larger range of species and environments.

Seeds of alpine plants are short lived: implications for long-term conservation

BACKGROUND AND AIMS Alpine plants are considered one of the groups of species most sensitive to the direct and indirect threats to ecosystems caused by land use and climate change. Collecting and banking seeds of plant species is recognized as an effective tool for providing propagating material to re-establish wild plant populations and for habitat repair. However, seeds from cold wet environments have been shown to be relatively short lived in storage, and therefore successful long-term seed conservation for alpine plants may be difficult. Here, the life spans of 69 seed lots representing 63 related species from alpine and lowland locations from northern Italy are compared. METHODS Seeds were placed into experimental storage at 45 °C and 60 % relative humidity (RH) and regularly sampled for germination. The time taken in storage for viability to fall to 50 % (p(50)) was determined using probit analysis and used as a measure of relative seed longevity between seed lots. KEY RESULTS Across species, p(50) at 45 °C and 60 % RH varied from 4·7 to 95·5 d. Seed lots from alpine populations/species had significantly lower p(50) values compared with those from lowland populations/species; the lowland seed lots showed a slower rate of loss of germinability, higher initial seed viability, or both. Seeds were progressively longer lived with increased temperature and decreased rainfall at the collecting site. CONCLUSIONS Seeds of alpine plants are short lived in storage compared with those from lowland populations/related taxa. The lower resistance to ageing in seeds of alpine plants may arise from low selection pressure for seed resistance to ageing and/or damage incurred during seed development due to the cool wet conditions of the alpine climate. Long-term seed conservation of several alpine species using conventional seed banking methods will be problematic.

Habitat-correlated seed germination behaviour in populations of wood anemone ( Anemone nemorosa L.) from northern Italy

Although various aspects of the biology of Anemone nemorosa have been examined, few studies present data on seed germination, and even then information tends to be rather contradictory. A. nemorosa L. is a spring-flowering, woodland geophyte, widely distributed across much of Europe. Germination phenology, including embryo development and radicle and shoot emergence, were investigated in one mountain and three lowland populations from northern Italy. Immediately after harvest, seeds were either sown on agar in the laboratory under simulated seasonal temperatures, or placed in nylon mesh sachets and buried in the wild. Embryos, undifferentiated at the time of dispersal, grew under summer conditions in the laboratory and in the wild. However, seeds did not germinate under continuous summer conditions. Radicle emergence in the field was first recorded at the beginning of autumn, when soil temperatures had dropped to c. 15°C in the case of the three lowland populations, and to c. 10°C at the mountain site. Shoot emergence was delayed under natural conditions until late autumn/early winter, when soil temperatures had dropped to c. 10°C in the lowlands and c. 6°C at the mountain site. In the laboratory, a period of cold stratification was required for shoot emergence, and this requirement was more pronounced in the mountain population. Seeds of the mountain population completed embryo development, radicle emergence and shoot emergence at cooler temperatures compared with the lowland populations. These results suggest that germination in A. nemorosa is highly adapted and finely tuned to local climate. We conclude that seeds of A. nemorosa display deep, simple epicotyl, morphophysiogical dormancy, and this is the first report of such dormancy for the genus Anemone . However, the continuous development and growth of embryos from the time of natural dispersal, and the lack of evidence of developmental arrest under natural conditions, suggests that radicles are non-dormant.

Seed quality for conservation is critically affected by pre-storage factors

The quality of seed-conservation collections, and hence their value for species reintroduction or restoration, is critically dependent on factors operating in the period between the point of collection and arrival at environmentally controlled processing and storage facilities. The timing of the acquisition of desiccation tolerance and seed longevity in air-dry storage, in relation to mass maturity and the time of natural seed dispersal, varies across species. In some wild plant species, seed quality continues to improve up to, and possibly beyond, the point of dispersal. Holding immature berries of Solanum dulcamara L. and capsules of Digitalis purpurea L. under natural conditions enabled comparison of seed quality between seeds stored under natural conditions and those dried rapidly under seedbank dry-room conditions. While seeds from fully ripe (post-mature) capsules of D. purpurea were insensitive to different post-harvest drying treatments, seed quality declined when mature berries of S. dulcamara were held under natural conditions. These results emphasise that the selection of post-harvest treatment will not only depend on the maturity of collected seeds but also may vary across species depending on the fruit type. Except for subtropical and tropical coastal locations, ambient daytime conditions during the main seed-collecting season (November–February) across Australia can be expected to result in tolerable rates of seed deterioration for the duration of seed-collecting missions. However, because seed moisture levels can be considerably higher than when equilibrated with ambient relative humidity, post-harvest handling decisions should ideally be informed by measurements of seed moisture at the time of collection, and subsequently seed moisture should be monitored during transit.

The effect of environmental factors on field and laboratory germination in a population of Zostera marina L. from southern England

The effects of temperature, oxygen availability and salinity on seed germination in a population of Zostera marina L. from the Fleet, a tidal lagoon in southern England, were investigated in the laboratory. The fate of seeds under natural conditions was also monitored throughout the year from core samples and from seed samples buried in the sediment layer in nylon sachets. Supported with temperature, salinity and oxygen level measurements at the study site, field data confirmed that following seed dispersal in September/October, the majority of seeds germinated in the Fleet during the winter and early spring. In the laboratory, seeds germinated more rapidly and to a higher final percentage under anaerobic conditions compared to aerobic conditions. Under anaerobic conditions, rapid, near complete germination was possible at full salinity (30 g l -1 ) or when the salinity was reduced by 50%(15 g l -1 ). Under aerobic conditions, seeds germinated more rapidly at lower salinity. The effects of temperature were strongly dependent on the presence or absence of oxygen. Under anaerobic conditions, there was a pronounced optimum constant temperature for germination around 6°C, corresponding closely to the average water temperature recorded during the period mid-October to the end of March. On the other hand, under aerobic conditions, very low levels of germination were recorded at low temperatures. These findings support previously published evidence that seeds of Z. marina are well adapted to germinate in anaerobic sediments and that water temperature is the key environmental variable that determines the timing of germination under natural conditions. Previous misuse of dormancy terms to describe seed populations of Z. marina is discussed.

The effects of priming on seed longevity in Ranunculus sceleratus L.

Priming in polyethylene glycol (PEG, −1.5 MPa) for 7 d followed by drying, led to a 4–5 fold increase in mean longevity when achenes (seeds) of Ranunculus sceleratus L. were subsequently stored at 35°C and 9.2% moisture content on a fresh weight basis (67.1% equilibrium relative humidity). The increase in longevity was due to an increase in the standard deviation of the frequency distribution of individual seed lifespans (decrease in the slope of transformed survival curves) and to a lesser extent to an increase in the intercept of survival curves. Priming for 1 d resulted in a smaller but significant increase in longevity independent of whether seeds were primed in PEG, distilled water or a saturated atmosphere (100% RH). The effects of priming were not due to the prevention of imbibition injury, and there was no evidence that the water relations of whole achenes was affected by priming. The effects of a 7 d priming treatment were dependent on the temperature and nature of the priming medium. However, no differences were recorded between corresponding treatments which were primed in PEG or distilled water. Moreover, the survival and responsivity to priming of R. sceleratus seeds was not related to dormancy status. The effects of priming on the longevity of R. sceleratus seeds are apparently unrelated to seed quality as the response of seeds previously aged for 8 d at 35°C and 7.9% moisture content was similar to that for unaged seeds. Priming followed by drying did not increase seed longevity in the related species R. acris L. The promotive effects of priming on seed survival appear to be species specific and may be related to ecological factors.

Parental effects modulate seed longevity: exploring parental and offspring phenotypes to elucidate pre-zygotic environmental influences

• Seed longevity, which is essential for germplasm conservation and survival of many land plant species, can vary considerably within species and cultivars. Here, we explore the relationship between parental and offspring phenotypes to elucidate how pre-zygotic environment affects seed longevity. • Plants of the wild species Plantago cunninghamii were exposed to wet or dry soil within a warm or cool glasshouse until flowering and then moved to a common environment. Seeds subsequently produced were collected at maturity, and longevity was assessed by controlled ageing at 45°C, 60% relative humidity. Multivariate analysis was used to examine relationships between the parental and offspring phenotypes. • The pre-zygotic environment resulted in a highly plastic parental response which was passed on to offspring seeds and changed their longevity (p(50)) by more than a factor of 2. Seed longevity is a function of the seed populations distribution of deaths in time (σ) and quality (K(i)); σ was associated with plant size, and K(i) with reproductive plant traits. • The pre-zygotic growth environment modulated seed longevity via a parental effect. Reproductive performance and seed quality (K(i)) were highly correlated with each other and unrelated to the maternal plant phenotype. Hence seed quality may be associated with the paternal plant response to the environment.