Variable seed bed microsite conditions and light influence germination in Australian winter annuals

Environmentally cued germination may play an important role in promoting coexistence in Mediterranean annual plant systems if it causes niche differentiation across heterogeneous microsite conditions. In this study, we tested how microsite conditions experienced by seeds in the field and light conditions in the laboratory influenced germination in 12 common annual plant species occurring in the understorey of the York gum-jam woodlands in southwest Western Australia. Specifically, we hypothesized that if germination promotes spatial niche differentiation, then we should observe species-specific germination responses to light. In addition, we hypothesized that species’ laboratory germination response may depend on the microsite conditions experienced by seeds while buried. We tested the laboratory germination response of seeds under diurnally fluctuating light and complete darkness, which were collected from microsites spanning local-scale environmental gradients known to influence community structure in this system. We found that seeds of 6 out of the 12 focal species exhibited significant positive germination responses to light, but that the magnitude of these responses varied greatly with the relative light requirement for germination ranging from 0.51 to 0.86 for these species. In addition, germination increased significantly across a gradient of canopy cover for two species, but we found little evidence to suggest that species’ relative light requirement for germination varied depending on seed bank microsite conditions. Our results suggest that variability in light availability may promote coexistence in this system and that the microsite conditions seeds experience in the intra-growing season period can further nuance species germination behaviour.

Effects of Light and Autotoxicity on the Reproduction of Bidens pilosa L.: From Laboratory to the Field

In Taiwan, the good agricultural practices for Bidens pilosa L. (Cobbler’s pegs) had been established due to its pharmacology application. However, the reproduction of this species that may cause phytotoxicity to the subsequent crops has not been investigated extensively. We hypothesized that both the phytotoxicity and canopy shading conditions that were altered by agricultural practices might affect its seed reproduction. Three experiments from laboratory, pot and field were conducted under different light treatments and residue application rates to evaluate the light requirement and phytotoxicity on the germination of Cobbler’s pegs. The results showed that the germination in the laboratory, dark treatments was higher than that of light treatment while it was inhibited in the darkness in the pot experiments (24% of the light treatments). Moreover, some seeds in the pot experiments germinated in the far-red light (FR) pretreated dark treatments. This observation indicated that the germination response of the investigated plant might be a very low fluence response (VLFR). Results also showed that the autotoxicity enhanced the germination reduction in the FR pretreated dark treatment while increasing the residues buried in the field. Accordingly, both autotoxicity and canopy shading may inhibit the reproduction of Cobbler’s pegs, but the application method needs further study.

Germination and emergence of common beggar’s-tick (Bidens alba) seeds at two different stages of afterripening as affected by environmental factors

Experiments were conducted to determine the effect of various environmental factors and burial depth on germination and seedling emergence of common beggar’s-tick [Bidens alba (L.) DC.] seeds at two different stages of afterripening. Mature B. alba seeds were stored at 4 C for 3 to 5 mo (new seed lot) and 13 to 15 mo (old seed lot) until experiment initiation. Germination exponentially decreased with increasing moisture stress. Germination rate decreased from 87 ± 2.9% to 13 ± 6.1% as osmotic potential decreased from 0 to −0.5 MPa and was completely inhibited at osmotic potentials below −0.83 MPa. A large portion of the new seeds tested positively photoblastic, but seeds that had afterripened for 1 additional year were partially desensitized to the light requirement. New and old seeds still germinated to a greater percentage in the presence of light than under continuous dark at temperatures ranging from 15 to 35 C. Both new and old seeds germinated over a range of temperatures from 5 to 35 C, but the optimum temperatures for germination was 15 to 30 C in the presence of light. Regardless of seed lot, seedling emergence was the greatest when seeds were sown at the soil surface. Seedling emergence was abruptly reduced when burial depth was 1 cm or greater. Based on these results, we conclude that shallow cultivation could effectively suppress this population of B. alba from emerging when incorporated into an integrated control strategy. The information obtained in this research identifies some important factors that facilitate the widespread presence of B. alba in Florida and may contribute to weed management programs.

Germination ecology of the perennial herb Xyris longiscapa: inter-annual variation in seed germination and seasonal dormancy cycles

Germination ecology was investigated in a natural population of Xyris longiscapa, a perennial herbaceous species endemic to the Brazilian campo rupestre. Seeds were collected over four consecutive years (2014 to 2017) to evaluate germination responses to a range of temperatures (from 15 to 30°C). The light requirement was evaluated in seeds collected in 2014. Seeds collected in 2014 were also buried in soil in the natural habitat of the species to evaluate changes in germinability at different temperatures over the time. Seeds showed an absolute light requirement for germination. Seed germination was affected by temperature, collection year and the interaction between these two factors. Seeds collected in 2014 showed a narrower temperature range for germination (15–20°C), compared with the seeds collected in 2015, 2016 and 2017 that germinated in a temperature range of 15–25°C. Buried seeds remained viable in soil for at least 14 months and exhibited seasonal dormancy cycling. Secondary dormancy was induced during the rainy season and alleviated during the dry season, following a conditional dormancy/dormancy cycle. The degree of primary dormancy appeared to be influenced by the environmental conditions experienced by seeds during maturation. Primary dormancy (when present), seed persistence in soil and seasonal dormancy cycles are strategies of X. longiscapa to enhance regeneration success in the harsh environment of the Brazilian campo rupestre.

Dry after-ripening, light, cold stratification and temperature effects on seed germination of Primula poissonii from Yunnan, China

Primula poissonii, an attractive wild plant growing in the subalpine/alpine region of southwest China, has low seed germination in cultivation. This study attempted to improve seed germination by testing the effect of several treatments including dry after-ripening (DAR), light, cold stratification (CS) and temperature gradient treatments. DAR increased germination at 15/5 and 25/15°C, as compared with fresh seeds. DAR seeds germinated significantly better (> 80%) at higher temperatures (20-28°C) than at lower (10°C, < 20%; 15°C, < 30%) and extreme high temperatures (30°C, < 55%; 32°C, 0%). Incubation at alternating temperature (25/15°C) did not significantly improve germination; whereas at 15/5°C germination increased significantly, compared with the corresponding constant temperature (20 and 10°C, respectively). DAR seeds had a strict light requirement at all temperatures. As DAR and CS are sufficient to break seed dormancy, the seeds of P. poissonii appear to have non-deep PD. For non-dormant cold-stratified seeds, the estimated Tb and thermal time (θ50) were 2.3°C and 74.1°Cd, respectively.

Effect of light Intensity and photoperiod on growth of Chlorella pyrenoidosa and CO2 Biofixation

Microalgae have been viewed as one of potential solution for CO2 biofixation or CO2 sequestration. However, many factors need to be evaluated to support development of CO2 biofixation. One important environmental factor for the growth of micro algae is related with light requirement. The aim of this study was to evaluate the effect of light intensity and photoperiod on growth of Chlorellapyrenoidosa (C.pyrenoidosa) and CO2 biofixation. Experiments were carried out in 1000 mL semi batch photo bioreactors, purged continuously with air (0.034% CO2). An Experiment of Factorial Design was employed in which the light intensity was evaluated 4 level at 2000, 4000, 6000 and 8000 lux with 3 level of photo period at L/D (light /dark) 8 hours/16 hours; L/D 12 hours/12 hours and L/D 16 hours/8 hours. The result indicated that both light intensity and photo period had significant effect (p< 0.05) on growth of C. pyrenoidosa. However, the photo period showed stronger effect relative to light intensity on growth of C.pyrenoidosa within the range reviewed. The interaction between the two factors was indicative but statistically not significant. Best growth profile sustained at combination of L/D 16 hours/8 hours of photoperiod and light intensity of 8000 lux with the highest average biomass observed at 0.516 ± 0.069gr/L. An increase in CO2biofixation rate of around 2 times was also observed between highest setting (8000 lux; L/D 16/12 hours) relative to that of lowest setting (2000 lux; L/D 8/12 hours).

Respuesta germinativa y crecimiento de plántulas de Mammillaria magnimamma (Cactaceae) bajo diferentes condiciones ambientales

Germination response and seedling growth of Mammillaria magnimamma were analyzed. Germination percentage and germination velocity of seeds under different conditions were quantified. Treatments included light/ dark conditions, acidity pretreatments and different temperatures. Seeds are photoblastic positive and show a high viability (86%); light requirement decreases as seeds age. Different temperatures during germination resulted in different germination velocities. Pretreatments with chlorhidric acid did not affect seed viability. Seedling growth in greenhouse conditions was studied using a factorial design which included two levels of light intensity, two levels of nutrient availability and two levels of watering frequency. Seedlings are slow growing (between 0.014 and 0.027 g g-1 d-1) and respond positively to an increase in nutrient availability and light intensity.

Germination ecology of the endangered species Asterolasia buxifolia (Rutaceae): smoke response depends on season and light

In fire-prone regions, many plant species rely on persistent seed banks for post-fire recovery. Understanding dormancy and germination cues is, therefore, important to predict population response. However, the germination ecology of species with physiologically dormant seeds in fire-prone regions is complex. We used the endangered species Asterolasia buxifolia, from riparian habitat in fire-prone south-eastern Australia, to investigate physiologically dormant seeds and their response to fire. We assessed whether fire cues alone promoted germination, or whether seasonal factors and light also played a role. Additionally, we tested the resilience of seeds to heat-shock temperatures produced in soil during fire, so as to identify potential factors that restrict such species to fire refugia. Seeds germinated only at winter seasonal temperatures, and had an obligate smoke and light requirement. Heat-shock treatments above 80°C slowed the germination rate. Smoke-related germination and the tolerance of A. buxifolia seeds to high fire-related temperatures demonstrated that recruitment dynamics can be driven by fire; however, germination is restricted to winter temperatures. This highlights the potential that changes to fire season may have on population persistence. The slow germination rate caused by heat, and a light requirement, may contribute to restricting this species to riparian habitat.