Mimosa diplotricha (creeping sensitive plant).

M. diplotricha (syn. M. invisa) is a small, often scrambling, neotropical shrub that has invaded many countries in the old tropics and many oceanic islands. In recent decades it has spread to new regions and has the potential to invade more tropical areas. It forms impenetrable spiny thickets that invade highly disturbed sites, but agricultural systems in particular. The shrub produces large quantities of seeds at an early age and has a persistent seed bank. It is extremely difficult to control effectively using mechanical or chemical means, however, biological control programmes have had a large degree of success.

“Active” Weed Seed Bank: Soil Texture and Seed Weight as Key Factors of Burial-Depth Inhibition

The ability of weeds to survive over time is highly dependent on an ecological strategy that ensures a high level of viable seed remains in the soil. Seed bank persistence occurs because of the specific characteristics of seed dormancy and longevity and the hypoxic microenvironment, which surrounds the buried seeds. These experiments investigate the role of soil texture, burial depth, and seed weight in seed bank dynamics. Seeds of twelve weed species are sown at increasing depths in various soil textures, and emergence data are used to detect the burial depth at which 50% and 95% inhibition is induced, using appropriate regressions. Clay soil is found to increase the depth-mediated inhibition, while it is reduced by sandy particles. In each soil texture, the highest level of inhibition is found for the smallest seeds. Seed weight is found to be closely related to the maximum hypocotyl elongation measured in vitro, and consequently, the seedlings are unable to reach the soil surface beyond a certain depth threshold. However, the threshold of emergence depth is always lower than the potential hypocotyl elongation. The depth-mediated inhibition of buried seeds is even more pronounced in clay soil, highlighting that the small size of clay particles constitutes a greater obstacle during pre-emergence growth. Finally, the role of soil texture and weed seed size are discussed not only in terms of evaluating the layer of “active” seed bank (soil surface thickness capable of giving rise to germination and emergence), but also in terms of developing a consistent and persistent seed bank. Finally, the role of soil texture and weed seed size are discussed, and the layer of “active” seed bank (the soil surface thickness that enables germination and emergence) is assessed with the aim of developing a consistent and persistent seed bank. Assessing seed bank performance when buried under different soil textures can help increase the reliability of the forecast models of emergence dynamics, thus ensuring more rational and sustainable weed management.

Fire can promote germination, recruitment and seed bank accumulation of the threatened annual grass Arthraxon hispidus

Disturbance plays an important role in plant life history strategies and has been documented as both enhancing and threatening populations of the vulnerable grass Arthraxon hispidus (Thunb.) Makino (hairy jointgrass) on the NSW north coast. Mechanical disturbance (slashing) is often used in A. hispidus conservation management, but many Australian plants are adapted to fire-based disturbance regimes. In this study we undertook a field burning experiment, along with soil seed bank sampling and germination trials, to explore how fire influences A. hispidus population dynamics in terms of plant recruitment and seed bank fluctuations. We found that winter burning strongly promoted A. hispidus spring germination without entirely depleting the residual seedbank. Although drought affected our field study population, burning also led to increased adult cover and substantial seed bank replenishment the following autumn. Exposure to a smoke treatment almost doubled the germination rate of A. hispidus seeds in nursery trials. Our study suggests that appropriate burning regimes can help to maintain this species in the landscape, by both structural and chemical mechanisms, by enhancing plant recruitment and facilitating seed bank accumulation. However, some A. hispidus plants also successfully germinated, established, and reproduced in unburnt plots during our study, suggesting that populations of this species can persist without disturbance in some habitats, such as native wetland communities. We found that A. hispidus has a multi-year seed longevity and a persistent seed bank, providing the species a degree of resilience in the event of unpredictable disturbance regimes and climatic anomalies.

Dormancy, germination, and sensitivity to salinity stress in five species of Potentilla (Rosaceae)

Laboratory and greenhouse experiments were conducted to determine the effect of environmental factors on the germination and emergence of five species of Potentilla L. All of the species we studied differed in their germination requirements, and these could be related to their habitat/ecology. For all species, completion of germination was the highest at 25/15 °C with a 14 h photoperiod. Seeds of Potentilla argentea L. and P. inclinata Vill. completed germination immediately after ripening while seeds of P. aurea Borkh., P. incana P.Gaertn., B.Mey. & Scherb., and P. reptans L. needed a 16-week period of cold stratification to break dormancy. GA3 treatment did not substitute for cold stratification. The seeds of all species did not complete germination in darkness and showed maximal emergence on the soil surface, which suggests the formation of a persistent seed bank. Completion of germination was inhibited by decreasing osmotic potential and increasing salt concentration. The seeds of all species we studied can complete germination in both acidic and alkaline soils. These results suggest that under field conditions, if moisture and (or) salinity are not limiting factors and a seed is located on the soil surface, completion of germination of nondormant species (P. argentea and P. inclinata) is possible any month of the growing season.

Seed bank dynamics of blowout penstemon in relation to local patterns of sand movement on the Ferris Dunes, south-central Wyoming

Plants restricted to active sand dunes possess traits that enable both survival in a harsh environment and local migration in response to a shifting habitat mosaic. We examined seed bank dynamics of Penstemon haydenii S. Watson (blowout penstemon) in relation to local sand movement. We measured within-year sand movement along a 400 m transect and examined plant density, seed production, and seed density in relation to this movement. Plant densities were highest in areas of moderate sand movement. Annual seed rain averaged 13 seeds·m−2, whereas persistent seed bank density (0–10 cm depth) averaged only 0.1 seeds·m−2. A laboratory burial experiment with nondormant (chilled) seeds showed that most deeply buried seeds (>6 cm) were held in enforced dormancy under spring conditions, while seeds at intermediate depths (4–6 cm) were induced into secondary dormancy that was broken by subsequent drying and re-chilling, thus promoting seed carryover until the following spring. Most near-surface seeds produced seedlings. Enforced and secondary dormancy provide mechanisms for maintaining a persistent seed bank of more deeply buried seeds that could become part of the active seed bank as sand movement re-exposes them near the surface. This could facilitate both population persistence and migration as previously occupied habitat becomes unsuitable.

Seed dormancy in Camellia sinensis L. (Theaceae): effects of cold-stratification and exogenous gibberellic acid application on germination

There are several different opinions regarding dormancy in tea (Camellia sinensis L.), but there is no strong evidence available to conclude whether or not these seeds are dormant. Freshly matured tea seeds collected from Hangzhou, China, at the natural dispersal time did not germinate in light at daily alternative temperature regimes of 10/15, 15/20, 20/25, or 25/35 °C, or at a constant temperature of 25 °C. Seeds were permeable to water and the embryos did not grow prior to radicle emergence, thus, the seeds have no physical, morphological, or morphophysiological dormancy. When cold-stratified at 4 °C for 1, 2, and 3 months, 64%, 88%, and 93% of the seeds germinated, respectively. Intact fresh seeds failed to germinate after treatment with 0, 10, 500, and 1000 ppm GA3, whereas 3%, 4%, 61%, and 86% of cracked seeds germinated, respectively. Thus, the seeds have nondeep and intermediate physiological dormancy. Seeds cold-stratified for 2 months that were buried at soil depths of 0, 1, and 5 cm in pots showed that seeds at 1 cm depth established significantly higher number of seedlings (P < 0.05) than at other two depths. Because tea seeds are susceptible to summer temperature drying, these seeds do not establish a persistent seed bank.