Germination Phenology Research Articles

Heteromorphic seeds of wheat wild relatives show germination niche differentiation.

Crop wild relatives are fundamental genetic resources for crop improvement. Wheat wild relatives often produce heteromorphic seeds that differ in morphological and physiological traits. Several Aegilops and Triticum species possess, within the same spikelet, a dimorphic seed pair, with one seed being larger than the other. A comprehensive analysis is needed to understand which traits are involved in seed dimorphism and if these aspects of variation in dimorphic pairs are functionally related. To this end, dispersal units of Triticum urartu and five Aegilops species were X-rayed and the different seed morphs weighed. Germination tests were carried out on seeds, both dehulled and left in their dispersal units. Controlled ageing tests were performed to detect differences in seed longevity among seed morphs, and the antioxidant profile was assessed in terms of antioxidant compounds equipment and expression of selected antioxidant genes. We used PCA to group seed morphs sharing similar patterns of germination traits, longevity estimates and antioxidant profile. Different seed morphs differed significantly in terms of mass, final germination, germination timing, longevity estimates and antioxidant profile in most of the tested species. Small seeds germinated slower, had lower germination when left in their dispersal units, a higher antioxidant potential and were longer-lived than large seeds. The antioxidant gene expression varied between morphs, with different patterns across species but not clearly reflecting the phenotypic observations. The results highlight different trait trade-offs in dimorphic seeds of Aegilops and T.urartu, affecting their germination phenology and longevity, thereby resulting in recruitment niche differentiation.

Climate change shifts natural selection and the adaptive potential of the perennial forb Boechera stricta in the Rocky Mountains.

Heritable genetic variation is necessary for populations to evolve in response to anthropogenic climate change. However, antagonistic genetic correlations among traits may constrain the rate of adaptation, even if substantial genetic variation exists. We examine potential genetic responses to selection by comparing multivariate genetic variance-covariances of traits and fitness (multivariate Robertson-Price identities) across different environments in a reciprocal transplant experiment of the forb Boechera stricta in the Rocky Mountains. By transplanting populations into four common gardens arrayed along an elevational gradient, and exposing populations to control and snow removal treatments, we simulated future and current climates and snowmelt regimes. Genetic variation in flowering and germination phenology declined in plants moved downslope to warmer, drier sites, suggesting that these traits may have a limited ability to evolve under future climates. Simulated climate change via snow removal altered the strength of selection on flowering traits, but we found little evidence that genetic correlations among traits are likely to affect the rate of adaptation to climate change. Overall, our results suggest that climate change may alter the evolutionary potential of B. stricta, but reduced expression of genetic variation may be a larger impediment to adaptation than constraints imposed by antagonistic genetic correlations.

Spatio-Temporal Metabolite and Elemental Profiling of Salt Stressed Barley Seeds During Initial Stages of Germination by MALDI-MSI and µ-XRF Spectrometry.

Seed germination is the essential first step in crop establishment, and can be severely affected by salinity stress which can inhibit essential metabolic processes during the germination process. Salt stress during seed germination can trigger lipid-dependent signalling cascades that activate plant adaptation processes, lead to changes in membrane fluidity to help resist the stress, and cause secondary metabolite responses due to increased oxidative stress. In germinating barley (Hordeum vulgare), knowledge of the changes in spatial distribution of lipids and other small molecules at a cellular level in response to salt stress is limited. In this study, mass spectrometry imaging (MSI), liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QToF-MS), inductively coupled plasma mass spectrometry (ICP-MS), and X-ray fluorescence (XRF) were used to determine the spatial distribution of metabolites, lipids and a range of elements, such as K+ and Na+, in seeds of two barley genotypes with contrasting germination phenology (Australian barley varieties Mundah and Keel). We detected and tentatively identified more than 200 lipid species belonging to seven major lipid classes (fatty acyls, glycerolipids, glycerophospholipids, sphingolipids, prenol lipids, sterol lipids, and polyketides) that differed in their spatial distribution based on genotype (Mundah or Keel), time post-imbibition (0 to 72 h), or treatment (control or salt). We found a tentative flavonoid was discriminant in post-imbibed Mundah embryos under saline conditions, and a delayed flavonoid response in Keel relative to Mundah. We further employed MSI-MS/MS and LC-QToF-MS/MS to explore the identity of the discriminant flavonoid and study the temporal pattern in five additional barley genotypes. ICP-MS was used to quantify the elemental composition of both Mundah and Keel seeds, showing a significant increase in Na+ in salt treated samples. Spatial mapping of elements using µ-XRF localized the elements within the seeds. This study integrates data obtained from three mass spectrometry platforms together with µ-XRF to yield information on the localization of lipids, metabolites and elements improving our understanding of the germination process under salt stress at a molecular level.

Germination niche breadth and potential response to climate change differ among three North American perennials

Responses of species to environmental change are largely dependent on their niche breadth. To investigate the relationship between germination niche breadth and sensitivity to climate change, we selected three North American perennials: Physalis longifolia, Asclepias syriaca and Penstemon digitalis. Dormancy loss and germination requirements were determined for seeds from populations along a Midwest US latitudinal gradient. Fresh seeds were incubated at 1, 5, 9, 15/6, 20/10, 25/15 and 30/15°C, and seeds cold stratified at 1, 5 and 9°C for 4–12 weeks were incubated at 15/6, 20/10, 25/15 and 30/15°C. Germination niche breadth (Levins’ Bn) was calculated from final germination proportion. In addition, a sequence of temperatures evaluated the effect of future warming on germination phenology. Germination differed significantly among populations and collection latitudes (P < 0.001), but variation did not have a latitudinal pattern. Niche breadth was widest for Physalis and Asclepias and narrowest for Penstemon (P ≤ 0.05), with implications for germination phenology. Germination shifted to autumn for Physalis and Asclepias under future warming in northern collection regions, and shifted earlier in spring for Penstemon regardless of region. Due to limited stratification and germination requirements, resulting in the narrowest niche breadth, we initially predicted Penstemon to be most at-risk, as future warming would fall outside its stratification envelope. However, species with wide niche breadths (Physalis and Asclepias) may be more vulnerable to climate change due to maladaptive shifts in germination phenology.

Non-deep simple morphophysiological dormancy in seeds of Angelica keiskei (Apiaceae)

Angelica keiskei is a vegetable and medicinal plant with high economic value. Growing demands for market and unprecedented anthropogenic damage to forests has caused severe degeneration of its populations. Moreover, the germination protocol for seeds of A. keiskei is complex, leading to a high cost of propagation and seed wastage. The primary aim of present study was to determine the requirements for seed dormancy break and germination and to characterize the class of seed dormancy in A. keiskei. The effects of temperature, light, cold stratification, dry storage, gibberellic acid (GA3) on dormancy break and germination were tested combined with move-along experiments and a germination phenology study. The results showed that seeds of A. keiskei had embryos that were differentiated but underdeveloped (small) and had physiological dormancy (PD) at maturity in autumn. Before the emergence of radicles, the embryo/seed length ratio increased from 0.20 to 0.85, a 425% increase. Germination of A. keiskei gradually increased following increased amounts of cold stratification. After 8 weeks of cold stratification, seeds germinated to 75, 78, 63 and 14% at 5/15, 10/20, 15/25 and 20/30 °C, respectively, in light. GA3 substituted for cold stratification. After 8 weeks of cold stratification, > 80% of seeds treated with ≥10 mg·L-1 GA3 germinated across the temperature range. In the move-along experiments, little or no embryo growth and germination occurred at 5 °C. However, after breaking PD by cold stratification at 5 °C, the rate of embryo growth increased rapidly at warm temperatures (5/15 °C) and reached the critical length for germination within 2 weeks of incubation. We identified that seeds of A. keiskei exhibited non-deep simple morphophysiological dormancy. Natural cold stratification broke PD during winter and allowed the germination of seeds and the production of seedlings at the start of the growing season.

Exposure of coastal dune vegetation to plastic bag leachates: A neglected impact of plastic litter

The presence of plastic bags on coastal dunes worldwide is well documented. Plastic bags contain additives that during rainfall events can leach out from bags into sand dune and be absorbed by seeds and roots of plants. Dune plants play a fundamental role in dune system formation, yet the possible impact of bag leaching on their establishment and development has been neglected. We assessed in laboratory whether (i) not biodegradable bags (high-density polyethylene, PE) and new generation of compostable bags (Mater-bi®, MB) would influence via leaching water chemical/physical properties and (ii) leachates would affect germination and seedling growth using Thinopyrum junceum and Glaucium flavum as models. Leachates were obtained from different amounts of not-exposed and bags exposed to beach or marine conditions simulating various pollution degrees (none, low, intermediate and high pollution). All water variables were affected by leaching. The magnitude of these alterations depended on bag type and environmental exposure. Seeds of T. junceum treated with the high concentration of marine-exposed MB bag leachate germinated later than controls while those of G. flavum treated with the remaining leachates germinated earlier. For both species, leachates from the low concentration of PE and MB marine-exposed bags increased seed germinability. A short radicle was observed in T. junceum seedlings treated with not-exposed MB bag leachates. Glaucium flavum seedlings treated with beach- and marine-exposed PE bags and not-exposed MB bags leachates showed a greater below-aboveground length ratio and those grown with the low concentration of not-exposed PE bag leachate had a longer hypocotyl compared to controls. Leachates from the high concentration of PE and MB bag caused seedling anomalies in both species. These findings indicate that not biodegradable and compostable bags may interact with abiotic/biotic factors and affect via leaching germination phenology, seedling establishment and plant interactions with consequences on dune community structure.

Radicle emergence with increased temperatures following summer dispersal in Trillium camschatcense: A species with deep simple double morphophysiological dormancy in seeds

AbstractSeeds with deep simple double morphophysiological dormancy (MPD) need cold stratification during the first winter after dispersal for radicle emergence, followed by the summer for root and bud development and finally a second winter for shoot emergence. In a previous study, we demonstrated that Trillium camschatcense seeds have this type of dormancy with radicles emerging from most seeds after the first winter. However, radicles also emerged from a few seeds in autumn during the same year as dispersal. We thought that temperatures after seed dispersal played a role in radicle emergence before the first winter. To confirm our idea, we investigated germination phenology outdoors, relationships between temperatures after seed dispersal and radicle emergence in the first year outdoors, radicle emergence in the first winter under varied temperatures using incubators, and shoot emergence from seeds with an emerged radicle in the first year outdoors. Our phenology study confirmed that T. camschatcense seeds have deep simple double MPD. Over 7 years, 0.2–7.5% of radicles emerged in the first year before winter and these percentages were moderately positively correlated with temperatures, especially minimum temperatures. Increasing August and September temperatures increased radicle emergence in the laboratory. Shoots emerged from seeds with an emerged radicle in the first year after the first winter. With increased autumn temperatures in warmer regions or with global warming, we predict that germination phenology may shift: increased radicle emergence in the first year and shoot emergence following the first (and not second) winter.

Seed heteromorphy influences seed longevity in Aegilops

AbstractThe genus Aegilops belongs to the secondary gene pool of wheat and has great importance for wheat cultivar improvement. As a genus with only annual species, regeneration from seeds in Aegilops is crucial. In several species in Aegilops, spikes produce different seed morphs, both in size and germination patterns. However, little is known about the ecology of seed germination, nor about the seed longevity in this genus. Here we investigated the germination phenology of Ae. neglecta under laboratory and field conditions and assessed longevity of different seed morphs of five additional Aegilops species using controlled ageing tests. Large seeds were short-lived and germinated faster than small seeds in most of the species. Field experiments with Ae. neglecta showed that large seeds of the dimorphic pair germinated 3 months after dispersal in contrast to 14 months for smaller seeds. Differences in longevity were detected not only in dimorphic seed pairs, but also among seeds from different positions on the spike. Our results indicate that different longevities in seed morphs of Aegilops may reflect a different soil seed bank persistence, with smaller seeds able to maintain a higher viability after dispersal than larger ones, thereby spreading seedling emergence over two years. Differences of seed germination and longevities between seed morphs in Aegilops may have important implications for ex situ seed conservation and reinforce the hypothesis of a bet-hedging strategy in the germination ecology of this genus.

Hydrothermal thresholds for seed germination in winter annual forbs from old-field Mediterranean landscapes.

Under Mediterranean climates with dry-hot summers and cool-wet winters, many forbs with potential for habitat restoration are winter annuals, but there is little information about their germination. We performed laboratory germination experiments on 13 ruderal dicots native to Andalusia (southern Spain). We measured the germination of recently harvested seeds from natural populations across nine temperature treatments (from 5 to 35°C, constant and alternate); two storage periods; and eight water stress treatments (from 0 to -1.0MPa). We then calculated the hydrothermal thresholds for seed germination. Final germination ranged from 0-100% and results were mixed in response to temperature. Base temperature was below 6°C, optimal temperature was around 14°C and the ceiling temperature around 23°C. For five species, 10months of storage improved total germination, indicating a dormancy-breaking effect, but the other species did not respond or had their germination reduced. All species were relatively tolerant to water stress, with base water potential ranging from -0.8 to -1.8MPa. Our results suggest that hydrothermal germination thresholds, rather than physiological dormancy, are the main drivers of germination phenology in annual forbs from Mediterranean semi-dry environments. The variation in germination responses of these forb species differs from winter annual grasses, but their seeds are all suitable for being stored before restoration.

SEED GERMINATION ECOLOGY AND SEEDLING EMERGENCE OF SIXTEEN TREE SPECIES AUTUMN SOWN

In nature, the regeneration and the seed germination ecology of tree species is varied due to divers’ environmental factors and evolution process. As a consequence, understanding the factors controlling the seed germination and seedling emergence in the time and the space. In most nurseries, tree seeds are usually sown in spring or rarely in autumn and, they are often pretreated to increase the seed germination where the germination timing is selective sieve that a plant experiences throughout its life history. However, in most nursery of Kurdistan region, the managers have not a good knowledge about the seeds sowing timing and seedling emergency of native tree species. Therefore, the main aim of this study is to investigate seed germination phenology with providing new data and determine optimal ways of seed sowing time that will permit a best seedling establishment of sixteen native and introduced tree species. The results showed, the seed sowing timing and seedling emergence of these tree species. In addition, these species exhibit significant divergence in term sowing timing and seedling establishment. Thereby, our results have a high value for managers of Kurdistan governmental and private nurseries as a suggestion which exact time is better for sowing seeds and which seeds need pre-treatment before sowing in order to obtain better regeneration.

Timing of seed dispersal and seed dormancy in Brazilian savanna: two solutions to face seasonality.

The relationship between fruiting phenology and seed dispersal syndrome is widely recognized; however, the interaction of dormancy classes and plant life-history traits in relation to fruiting phenology and seed dispersal is understudied. Here we examined the relationship between fruiting season and seed dormancy and how this relationship is modulated by dormancy classes, dispersal syndromes, seed mass and seed moisture content in a Brazilian savanna (cerrado). Dormancy classes (non-dormancy and physical, morphological, morphophysiological, physiological and physiophysical dormancy) of 34 cerrado species were experimentally determined. Their seed dispersal syndrome (autochory, anemochory, zoochory), dispersal season (rainy, dry, rainy-to-dry and dry-to-rainy transitions), seed mass and moisture contents, and the estimated germination date were also determined. Log-linear models were used to evaluate how dormancy and dormancy classes are related to dispersal season and syndrome. The proportions of dormant and non-dormant species were similar in cerrado. The community-estimated germination date was seasonal, occurring at the onset of rainy season. Overall, anemochorous non-dormant species released seeds during the dry-to-rainy transition; autochorous physically dormant species dispersed seeds during the dry season and rainy-to-dry transition; zoochorous species dispersed non-dormant seeds during the dry and rainy seasons, while species with morphological, morphophysiological or physiological dormancy dispersed seeds in the transitional seasons. Seed mass differed among dispersal seasons and dormancy classes, but seed moisture content did not vary with dispersal syndrome, season or dormancy class. The beginning of the rainy season was the most favourable period for seed germination in cerrado, and the germination phenology was controlled by both the timing of seed dispersal and seed dormancy. Dormancy class was influenced by dispersal syndrome and season. Moreover, dormancy avoided seed germination during the rainy-to-dry transition, independently of dispersal syndrome. The variability of dormancy classes with dispersal syndrome allowed animal-dispersed species to fruit all year round, but seeds germinated only during the rainy season. Conversely, seasonally restricted wind-dispersal species dispersed and germinated their non-dormant seeds only in the rainy season.

Between invaders and a risky place: Exotic grasses alter demographic tradeoffs of native forb germination timing

AbstractPriority effects are hypothesized to play an important role in community assembly and may promote suppression of native by exotic species. Work in a range of grassland systems has proved valuable for testing these effects, demonstrating that earlier germination by some exotic annual grasses contributes to their competitive dominance over natives. Yet few studies have measured native forb germination phenology under field conditions, and the demographic consequences of emergence timing for competitive interactions and native fitness are not well understood. We focused on three native annual species in a southern California grassland dominated by exotic Bromus spp. over three years, measuring (1) seedling emergence rates, for both early (October) and later (November and December) germinators; (2) effects of exotic grasses on native survival and reproduction, through a grass removal experiment; and (3) interactions between emergence timing and grass competitive effects on native mortality, survival, and flowering. We quantified tradeoffs of emergence timing, by estimating mortality experienced by early germinants until the late cohort emerged (early survival), and then for both cohorts from the time of late emergence to flowering (spring survival). The two most common focal natives, Amsinckia intermedia and Phacelia distans, varied substantially in germination phenology but primarily emerged early. The less abundant Clarkia purpurea germinated late. Late emergence reduced spring survival in control plots but not those where exotic grasses were reduced experimentally, supporting the importance of priority effects and benefits of early germination in competition with grasses. However, early emergence entailed a high cost of initial mortality risk in some years. We found no effect of emergence timing on size at flowering. Estimates of net survivorship to flowering suggest that late emergence consistently was associated with the highest survival when exotic grasses were reduced experimentally. Early emergence was more favored in control than in exotic grass reduction plots, but the survival tradeoffs differed substantially between years. These results suggest that priority effects contribute to suppression of native forbs, but may not consistently promote higher fitness for earlier germinators. Instead, exotic invasion may increase yearly variation in the fitness consequences of native germination phenology, with potential implications for bet hedging strategies.

Role of indehiscent pericarp in formation of soil seed bank in five cold desert Brassicaceae species

The dispersal and germination unit of some Brassicaceae species is the fruit, and we hypothesized that it could affect germination phenology and promote formation of a soil seed bank. We determined the effects of the indehiscent pericarp on germination and longevity of buried seeds of five Brassicaceae species native to cold deserts of central Asia. Germination phenology (seedling emergence) was monitored for intact dispersal units and isolated seeds of Chorispora sibirica, Goldbachia laevigata, Spirorrhynchus sabulosus, Tauscheria lasiocarpa (annuals), and Sterigmostemum fuhaiense (perennial) at natural temperatures in watered and non-watered (natural precipitation) soil. Intact dispersal units and isolated seeds were buried under natural conditions and exhumed at regular intervals for 35 months to monitor germination, viability and moisture content of isolated seeds, seeds in dispersal units, and seeds removed from dispersal units after burial. Isolated seeds of Goldbachia, Spirorrhynchus, and Tauscheria germinated only the first autumn and those of Chorispora and Sterigmostemum the first autumn and first spring, with higher germination percentages in all species in watered than in non-watered soil. A high percentage of seeds in buried dispersal units of Chorispora, Goldbachia, and Sterigmostemum was viable after 35 months, and seeds exhibited a 6-month dormancy cycle, being non-dormant only in autumn and spring. Seeds in buried dispersal units of Spirorrhynchus and Tauscheria germinated when exhumed in the first spring, but all non-germinated seeds were dead after 1 year. Thus, the presence of the pericarp allows Chorispora, Goldbachia, and Sterigmostemum to form a persistent seed bank but not Spirorrhynchus and Tauscheria.

Germination phenology determines the propensity for facilitation and competition.

A single plant can interact both positively and negatively with its neighbors through the processes of facilitation and competition, respectively. Much of the variation in the balance of facilitation and competition that individuals experience can be explained by the degree of physical stress and the sizes or ages of plants during the interaction. Germination phenology partly controls both of these factors, but its role in defining the facilitation-competition balance has not been explicitly considered. I performed an experiment in a population of the winter annual Arabidopsis thaliana (Brassicaceae) to test whether germinating during physically stressful periods leads to facilitation while germinating during periods that promote growth and reproduction leads to competition. I manipulated germination and neighbor presence across two years in order to quantify the effects of the local plant community on survival, fecundity, and total fitness as a function of germination phenology. Neighbors increased survival when germination occurred under conditions that were unsuitable for survival, but they reduced fecundity in germinants that were otherwise the most fecund. Later germination was associated with facilitation in the first year but competition in the second year. These episodes of facilitation and competition opposed each other, leading to no net effect of neighbors when averaged over all cohorts. These results indicate that variation in germination timing can explain some of the variation in the facilitation-competition balance in plant communities.

Reproductive Phenology and Germination Behavior of Some Important Tree Species of Northeast India

The reproductive phenology and germination behavior of 15 important tree species (Acer laevigatum, Adinandra griffithii, Citrus latipes, Elaeocarpus prunifolius, Engelhardtia spicata, Ilex embelioides, Ilex khasiana, Ilex venulosa, Illicium griffithii, Magnolia lanuginosa, Magnolia punduana, Photinia cuspidata, Photinia integrifolia, Quercus glauca and Schima khasiana) were monitored at monthly intervals for two calendar years in subtropical broad-leaved humid forests of Northeast India. These species are either endemic or threatened to the region. The investigated species showed peak flowering during the spring- while fruiting peak was observed in the autumn-season. Of the fruit types, drupes and follicles were produced by many of these species. Majority of the species adopted zoochoric mode of dispersal. The germination phenology revealed that most of the species (Acer laevigatum, Elaeocarpus prunifolius, Illicium griffithii, Magnolia lanuginosa, Magnolia punduana and Quercus glauca) undergo a period of dormancy during winter season (December–February) and germination collides with the onset of rain indicating that moisture aids in germination. The prevailing environmental condition coupled with human disturbance seems to be of potential importance in influencing the recruitment of the selected species. Such studies would help in formulating effective strategies for conservation of these species.

Timing is everything: does early and late germination favor invasions by herbaceous alien plants?

Plant invasions represent a unique opportunity to study the mechanisms underlying community assembly rules and species distribution patterns. While a superior competitive ability has often been proposed as a major driver of successful plant invasions, its significance depends crucially on the timing of any competitive interaction. We assess whether a mismatch in germination phenology can favor the establishment of alien species, allowing them to exploit vacant niches where competition is low. As well as having important effects on the survival, growth and fitness of a species, asymmetric competition and potential soil legacies resulting from early or late germination can also impact on species recruitment. However, early or late germination comes at a cost, increases the risks of exposure to unfavorable conditions and requires an enhanced abiotic resistance if it is to lead to successful establishment. While there are several anecdotal accounts of early and late germination for invasive species, there are limited comparative data with resident species growing under natural conditions. Available evidence from grassland communities indicates that a short-term germination advantage or priority (few days/weeks) provides invasive species with a strong competitive advantage over native species and is a critical factor in many invasions. While the exploitation of periods of low competition is a plausible mechanism for the successful establishment of many invasive plants, direct evidence for this strategy is still scarce. This is particularly true with regard to the exploitation of late germination niches. Consequently, long-term comparative monitoring of the germination phenology of invasive and native plants in situ is needed to assess its significance in a range of ecosystems and its impact on community dynamics.

Delayed dehiscence of the pericarp: role in germination and retention of viability of seeds of two cold desert annual Brassicaceae species.

Considerable variation occurs in post-maturity timing of dehiscence in fruits of Brassicaceae species, and several studies have shown that the pericarp plays an important role in seed germination and retention of viability in species with indehiscent fruits. However, little is known about the significance to seed biology of delay in pericarp dehiscence for <1year in the field. Thus, we determined the role of the pericarps of Leptaleum filifolium and Neotorularia korolkovii, which open in <1year after fruit maturity and dispersal, in seed germination and retention of seed viability. We compared dormancy-break via after-ripening in the laboratory and germination phenology and retention of seed viability in intact siliques and isolated seeds buried in an experimental garden. Seeds of both species have Type 6 non-deep physiological dormancy, which is enhanced by the pericarp. Seeds of both species after-ripened during summer 2013, and some of them germinated in autumn and some in the following spring in watered and non-watered soil. Germination percentages of seeds in siliques increased in soil in spring 2014, after the pericarps had opened. Most isolated seeds of L.filifolium and N.korolkovii had germinated or were dead by spring 2014 and summer 2015, respectively, whereas 60% of the seeds of both species in the (opened) pericarps were viable after 24months. Thus, although the pericarp opened 9-10months after burial, its presence had a significant effect on seed dormancy, germination phenology and retention of viability of seeds of L.filifolium and N.korolkovii.

Why are native annual abundances low in invaded grasslands? Testing the effects of competition and seed limitation

Competitive suppression of native species has long been considered among the most important mechanisms allowing exotic plants to dominate some communities, but recent work has focused attention on the potential role of native seed limitation. We tested effects of competition from exotic annual grasses and seed limitation on the abundances of four native annual plants in invaded southern California grassland for two different years. Both initial responses and effects still present 1–3 years later were measured. In the wetter year of 2006, all four native species (Amsinckia menziesii var. intermedia, Phacelia distans, Camissonia bistorta and Clarkia purpurea ssp. quadrivulnera) increased in abundance with exotic grass removal, and two (Clarkia and Camissonia) responded significantly to seed addition. We observed limited treatment effects during the much drier growing season of 2007. By 2008–2009, any initial effects of exotic grass removal had disappeared. However, for both the 2006 and 2007 experiments seeding significantly increased native cover in 2009, independent of initial grass removal. Abundances of both Amsinckia and Phacelia, but not Camissonia or Clarkia, were significantly higher in seeded plots during 2008–2009. These delayed responses may have resulted from seed dormancy. Our results support the importance of both competition with exotics and seed limitation in determining native annual community composition of California grasslands. An interesting future question is whether traits related to resource use or germination phenology may predict differences in native species interactions with exotic grasses.

A re-examination of the Salicornias (Amaranthaceae) of Saudi Arabia and their polymorphs.

During the period from 1964 to 1999 Saudi Arabian species of Salicornia were wrongly treated under the European species, S. europaea L. Recent explorations proved that there are two separate allopatric species of Salicornia in Saudi Arabia, one inhabiting the inland salt-marshes of the Najd (highlands) and the other inhabiting the Arabian Gulf Coast (lowlands). Morphological, ecological and exploratory studies confirm that they are two distinct species. The two species differ in features of bark, axillary spikes, basal vegetative segment(s) of spike, fertile segments, colour of senescent plants, and flowering, fruiting and germination phenology. As both the species have been described earlier from Iran, they are now new records for Saudi Arabia. The species are, S. persica ssp. iranica (Akhani) Kadereit & Piirainen and S. sinus-persica Akhani. S. sinus-persica, of which the status was thought doubtful has been confirmed. Both the species have been described and illustrated. Each species comprises a number of polymorphs. As leaves and flowers are rudimentary, confusing species circumscriptions, a proliferation of binomials has resulted in the taxonomy of Salicornia. To mitigate such confusion, the full range of variability of the Saudi Arabian species has been documented.

Forest management options for adaptation to climate change: a case study of tall, wet eucalypt forests in Victoria’s Central Highlands region

ABSTRACTAustralia has a highly diverse and variable climate and its forests are well-adapted to climatic variation. However, human-induced changes in climate could exceed historical ranges of variability and have effects on forests well beyond the experience of forest managers. These conditions will require implementation of management practices appropriate to a changing climate but there has been little analysis of potential management options for Australian native forests. The paper analyses potential management options for the tall, wet eucalypt forests in Victoria’s Central Highlands. This region has already experienced a strong drying and warming trend and a high incidence of severe bushfires over the last 15 years. Future changes are likely to include rising CO2, increasing temperatures and an overall decrease and changing seasonal patterns in rainfall. This is likely to result in higher fire danger weather conditions, changes in phenology of flowering, seeding and germination and shifts in forest composition and productivity. A range of different management options were considered and analysed in terms of current practice, costs and implementation feasibility. Many management actions identified to support adaptation to climate change were assessed as currently being implemented as part of sustainable forest management arrangements. Options that are not generally currently implemented include developing gene management programs and off-site gene banks, ex-situ conservation and increasing cooperation in species management, increasing stand and regional species diversity, identification and deployment of more drought- or disturbance-tolerant species or genotypes, planning to reduce disease losses through monitoring and sanitation harvests, managing stand structure to reduce impacts on water availability and implementing silvicultural techniques to promote stand vigour, as practised elsewhere in Australia. The likelihood of more intense rainfall events will require changes to infrastructure, such as forest road design and construction specifications. Implementing adaptation will require new approaches to forest management, potentially involving significant human intervention, new ecological, environmental and social research, new modes of communication with the public, new policies and revised regulations and management prescriptions.