Higher Germination Success Research Articles

Interactions between the invasive treeMelia azedarach(Meliaceae) and native frugivores in South Africa

Abstract:The spread of many invasive plants is facilitated through seed dispersal by frugivorous animals. The effectiveness of various frugivores as dispersers of the seeds ofMelia azedarach, a highly invasive alien tree species, was evaluated in South Africa in savanna and bushveld vegetation. During 264 h of observation, seven bird species and one bat species were recorded foraging on fruiting trees ofM. azedarach. The most common visitors were the dark-capped bulbul (Pycnonotus barbatus) followed by Wahlberg's epauletted fruit bat (Epomophorus wahlbergi), but both species dropped nearly as many seeds as they dispersed. Knysna turaco (Tauraco corythaix) dispersed the highest number of fruits per minute, but occurred in low abundance in our study sites. Seed germination differed significantly between de-pulped fruits and untreated fruits after 2 mo, but was similar after 4 mo. Germination success did not differ between animal-handled and hand-depulped fruits. In contrast to the high germination success in the greenhouse, seedlings showed very low recruitment in the field. Thus,M. azedarachseems likely to benefit from frugivores (particularly dark-capped bulbul and Wahlberg's epauletted fruit bat) dispersing seeds to suitable microsites.

Germination of Epiphytic Bromeliads in Forests and Coffee Plantations: Microclimate and Substrate Effects

This study explores whether differences in germination ability shape habitat distributions among closely related epiphytic species, particularly in the context of the ability to colonize disturbed habitats. We compared the germination of three epiphytic bromeliad species differing in their ability to colonize secondary arboreal vegetation in natural forests, and in old and young coffee plantations. We asked if germination is related to their distribution within the canopy and between habitats, and the extent to which the substrate (branch) or microclimate affects germination success. Tillandsia viridiflora, a species that is largely restricted to closed forests, had highest germination success in natural forests, Tillandsia juncea, a pioneer species, germinated best in young coffee plantations, and Tillandsia heterophylla, an intermediate species, equally in forests and young plantations. Surprisingly germination rates of all three species were lowest in old plantations. Bryophyte cover on branches had a positive effect on germination of T. viridiflora and T. heterophylla, but T. juncea germination rates were largely independent of climate and substrate. These results show that germination can limit the ability of species to colonize disturbed habitats and also contributes to within-canopy distribution. Abstract in Spanish is available at http://www.blackwell-synergy.com/loi/btp.

Seed germination techniques of Phoenix dactylifera: A new experience from Bangladesh

A new experiment on seed germination technique for Phoenix dactylifera, an exotic species was conducted in the nursery of Forestry and Wood Technology Discipline, Khulna University, Bangladesh. The seeds imported from Saudi Arabia were collected from Nirala Central Mosque, Khulna, Bangladesh, in September 2008 and treated with four presowing treatments (control, immersion in normal water at room temperature (20–22°C) for 12 h, immersion in sun-heated water (25–35°C) for 12 h, and immersion in hot water (50°C) for 10 h) before seed germination with different germination media (well dried loamy soil, coarse sand, mixture of coarse and fine sand at a ratio of 3:1, mixture of coarse and fine sand at a ratio of 3:2, and mixture of coarse and fine sand at a ratio of 1:1). The experiment showed that presowing treatments significantly increased the germination rates of seeds compared to those in control (68%) and hot water treatment (69%). The highest germination success (84%) was found in the immersion in normal water and sunheated water for 12 h. Experiment also showed that seed germination with course sand and mixture of coarse and fine sand with a ratio of 3:1 performed better than the loamy soil. Germination started from 21 to 26 days and completed between 38–40 days of the germination period in all treatments. ANOVA showed a significant difference among the treatments in seed germination, but there was no significant difference among the media in seed germination. Normal water and sun-heated water for 12 h for pretreatment and coarse sand or mixture of coarse and fine sand at a ratio of 3:1 may be recommended for seed germination of the species in rural Bangladesh.

Spatial distribution and performance of native and invasive Ardisia (Myrsinaceae) species in Puerto Rico: the anatomy of an invasion

Comparisons between native and invasive congeners are potentially useful approaches for identifying characteristics that promote invasiveness. Those traits for which an invasive exhibits superior ecological performance are likely to contribute to its invasiveness. We tested the hypothesis that invasive tree species have better ecological performance in early life cycle stages than native species in forests where they coexist. We studied locally sympatric populations of the invasive Ardisia elliptica and the native A. obovata (Myrsinaceae) in Puerto Rico. We compared spatial distribution, herbivory and growth in seedlings, seed germination in the field and under controlled conditions, and fruit production. We found the distribution of each species was aggregated in the three categories of size (seedlings, juveniles and adults) and the populations partially overlapped. The invasive species was the most abundant species in every category of size. The two species did not differ in percentage of leaf area consumed and seedlings of both species had the same relative growth rate (RGR) in the forest. However, the invasive species had higher germination success in the field, faster mean germination time in the lab and higher fruit production. It appears that the success of A. elliptica is not through escape from pathogens or herbivores, but by a better performance in fruiting and seed germination in the forest.

Allelopathic influences of the invasive Ailanthus altissima on a native and a non-native herb1,2

As a highly aggressive non-native invasive and an allelopathic species, Ailanthus altissima (tree of heaven) has the capacity to negatively affect native plant communities by suppressing resident species and altering competitive interactions. We examined effects of A. altissima on the establishment and growth of two herbaceous species common in invaded natural areas. Soil samples were collected from six replicate A. altissima-dominated stands and six control stands (no A. altissima present) in the Appalachian Ridge and Valley province of southwestern Virginia. Two target species, Verbesina occidentalis, native to the southeastern US, and Dipsacus fullonum, non-native and invasive throughout North America, were selected for their high germination success and contrasting native vs. invasive status. Germination and growth of target species were monitored in greenhouse flats for six weeks. We found severe reductions in all measured aspects of V. occidentalis when grown in Ailanthus versus control soils, including seed germination (P = 0.002), seedling height (P = 0.001), leaf production (P < 0.001), and root∶shoot ratio (P = 0.008). In contrast, Dipsacus fullonum appeared resistant to allelopathic effects, with no significant differences in germination or growth relative to soil type (P > 0.25 for all measures). Our results support the role of allelopathy in the invasive success of A. altissima and further suggest that A. altissima may differentially affect resident native versus non-native species, potentially facilitating the spread of other non-natives in the invaded community.

Seed germination tests of the parasitic perennial Viscum album (Viscaceae) from fragmented habitats at the northern edge of its range

Background and aims - Despite being a rather common species throughout Europe, little is known about the effects of habitat change on the fitness of Viscum album. We expected to find a reduction in fitness in V. album populations growing in fragmented habitats resulting from a loss of genetic diversity through increased inbreeding. Methods - We studied seed germination as a measure of fitness among sixteen Belgian V. album popula tions varying in size and degree of isolation to investigate the fitness consequences of habitat fragmenta tion. Populations were sampled from two landscapes differing in their degree of habitat fragmentation and V. album population characteristics. We also compared germination percentages of three populations at three different temperatures (5, 20, 30?C) to examine the potential effects of climate change on V. album regeneration in northern Europe. Key results - Germination percentages (at 20?C) were high (69-100%) and we found no evidence of relationships between germination and population size, density, or area. There was no direct relationship between germination percentage and population isolation within study regions, but connectivity among populations appears to be important. Samples from the more fragmented habitat showed a negative correla tion between germination percentage and the proportion of females, suggesting reduced mate availability and pollination resulting from increased isolation of populations. There was no significant difference in mean germination percentages among the three temperature treatments, bui the high temperature samples (30?C) exhibited the highest variation in germination success. Conclusion - Our results suggest that V. album has evolved high germination success to compensate for limited success in establishing on a host plant. Successful germination under a wide range of environmental conditions is expected to increase the likelihood of establishing on host plants, possibly helping V. album respond to changes in climate.

Effects of pre-sowing treatments on seed germination of Melia azedarach

A germination experiment of pre-treated seeds of Melia azedarach was conducted in the nursery of Forestry and Wood Technology Discipline, Khulna University, Bangladesh. Matured seeds of Melia azedarach were collected from healthy trees of National Botanical Garden, Bangladesh and were treated with five pre-sowing treatments (control, immersion in cold water, immersion in hot water, scarification with sand paper, and immersion in concentrated H2SO4) on seed germination. Results revealed that the germination rates of pre-sowing treated seeds were significantly increased compared to those in control, except for cold water treatment. The highest germination success (80%) was found in scarification with sand paper, followed by 74% and 69% in immersion in H2SO4 and hot water treatment, respectively. Germination started on 8–11 days and completed on 20–21 days of the germination period in all cases. Analysis of variance showed the significance difference in germination success among the treatments but no significance difference in germination period among the treatment. Hot water treatment may be recommended on seed germination of the species in rural Bangladesh.

Coexisting Cytotypes ofArnica cordifolia: Morphological Differentiation and Local‐Scale Distribution

Habitat differentiation is thought to play a role in polyploidy establishment and coexistence. Differences in morphology and microhabitat association could play a role in cytotype distribution, but random factors could also be important. Little work has been performed to examine mechanisms affecting local‐scale cytotype spatial distribution. Multiple cytotypes of Arnica cordifolia (Asteraceae) co‐occur in populations throughout Colorado. This study tests the hypothesis that habitat differentiation (specifically disturbance) controls the local distribution of triploids and tetraploids. We used flow cytometry to determine the local distribution of cytotypes in four populations. We measured plant morphological traits and environmental characteristics of each microlocation. We performed an experiment to test for differentiation in germination behavior between cytotypes. Tetraploids had higher germination success, were larger, and had a lower stomatal area index than did triploids. Both cytotypes were found in understory and roadside locations, with no relationship between cytotype prevalence and distance from the road. Triploid locations were not significantly different from tetraploid locations for a number of environmental factors. Triploids did not show a greater tendency to germinate preferentially in the light. Although triploids and tetraploids co‐occur in most populations of A. cordifolia, there is no evidence for consistent habitat partitioning at the local scale.

Spatio‐temporal structure of multi‐storied, multi‐aged interior Douglas fir (Pseudotsuga menziesii var. glauca) stands

Summary 1. We used replicated, repeated‐measures data to examine the spatio‐temporal structure of multi‐storied, multi‐aged interior Douglas fir (Pseudotsuga menziesii var glauca (Mirb.) Franco) stands growing on dry sites under more than 50 years of fire protection. Along with the univariate and bivariate Ripley’s K and related functions, we used a random coefficients mixed model to investigate the variation in these functions over replicates and time. 2. The spatio‐temporal analyses revealed that trees greater than 1.3 m in height were clustered over space, and clustering was more evident for small trees (i.e. diameter at breast height (d.b.h.) ≤ 7.0 cm). 3. Bivariate functions indicated that small trees were spatially aggregated with large trees, indicating higher germination success and early survival near large trees. For these dry sites, moisture is more limiting than light and large trees provide moister microsites. 4. Dead trees were clustered, more commonly smaller in size and aggregated near large trees, indicating competition for moisture. 5. For the 16‐year period of the study, there was very little evidence that the spatio‐temporal patterns changed from a clustered to a more regular arrangement over time, unlike evidence from studies in other forest types. 6. Using the random coefficients mixed model approach, the majority of spatio‐temporal variation was due to differences among replicates, with little variation over time. 7. Under fire protection, interior Douglas fir stands on dry sites might be expected to have lower mortality but any increase in density will be limited by moisture availability. Since interior Douglas fir is moderately shade‐tolerant, this may result in an approach to a steady state of regeneration and death over the long term. 8. Synthesis. Spatio‐temporal analysis using replicated, repeated‐measures data, including a random coeffcieints mixed model approach, gave useful insights into mortality and recruitment in multi‐storied and multi‐aged stands. Similar patterns might be expected in other naturally occurring multi‐storied and multi‐aged stands. The use of replicated, repeated‐measures data rather than chronosequence data allows for the examination of true changes in spatial patterns over time.

Is the endangeredApium repens(Jacq.) Lag. rare because of a narrow regeneration niche?

AbstractThe conservation of rare plant species is an important aspect of global biodiversity protection, but in many cases these species and the reasons why they are rare are poorly understood. The perennial umbelliferApium repensis generally regarded to be a rare species all over its European range. We hypothesized that its rarity might be caused by a restricted regeneration niche, that is, highly specific requirements for sexual regeneration, low seed dispersal potential and low endurance capacity of seeds in the ground. We conducted several experimental investigations on its germination ecology, hydrochorous dispersal potential and soil seed bank properties.Apium repensshowed high germination success under a variety of abiotic conditions. Either light or cold‐wet stratification was necessary to stimulate germination. Seeds were able to float for more than 50 days when protected from precipitation, and soil seed bank sampling revealed that at least some seeds ofA. repenswere contained in soil depths of up to 10 cm. Overall, our findings do not support the hypothesis that the rarity ofA. repensis caused by highly specific requirements for its sexual regeneration. Nonetheless, its germination ecology should be considered when designing conservation measures for this endangered species.

REPRODUCTIVE LONGEVITY OF DRIFTING KELP MACROCYSTIS PYRIFERA (PHAEOPHYCEAE) IN MONTEREY BAY, USA1

Drifting Macrocystis pyrifera (L.) C. Agardh sporophytes have long been viewed as the primary long‐distance dispersal vector; yet, few data exist that support the ability of reproductive viable sporophytes to actually travel the presumed hundreds to thousands of kilometers. This study addressed the reproductive longevity of experimental and naturally occurring M. pyrifera drifters. Temporal variability in sporophyte size and reproduction was estimated for experimental drifting sporophytes that were tethered to surface buoys and compared with attached plants (controls). Reproductive viability was also studied for beach‐cast drifters (BCD), and naturally drifting sporophytes observed during field surveys in Monterey Bay. Detached drifting sporophytes were tracked with radio transmitters to follow drifter trajectories and to measure drifting speed. Experimental drifters (ED) experienced a 74% reduction in frond length after 35 days, a 76% reduction in average frond number after 70 days, and a reduction in average sorus area by 83% after 28 days. Although zoospore production was reduced following detachment, sporophytes remained fertile with high zoospore germination success as long as sori were present (125 days). Zoospore production and germination success for natural and BCD was similar to ED. The average displacement of radio‐tagged drifters was 7.12 km·day−1, suggesting that a sporophyte adrift for 125 days disperses viable propagules (zoospores) over 890 km (±363). Dispersal of propagules is important for population restoration, distribution, and genetic diversity. Such dispersal distances are long enough to connect potentially all Northern Hemisphere Macrocystis populations across a generational timescale and may facilitate inter‐hemispheric gene flow.

Dispersal and germination of seeds of Pisonia grandis, an Indo-Pacific tropical tree associated with insular seabird colonies

The distribution of the forest tree Pisonia grandis (Nyctaginaceae) coincides with seabird colonies on small tropical islands. Its seeds are enclosed in a calyx exuding extremely sticky resin which adheres strongly to feathers. Birds are obviously seed-dispersal vectors, but the multi-seeded infructescences frequently entangle birds, often fatally. On Cousin Island, Seychelles, I investigated the production, germination, survival, and tolerance to seawater of Pisonia seeds, and the occurrence of entanglement with birds. Fresh seeds had high germination success (62–87% in experimental trays), but seedling survival in Cousin's forests was low (0.1% of 6020 seeds survived as seedlings after 2–8 mo). Some seeds tolerated 30 min daily immersions in seawater (8–15% germination after 14–28 d treatment), but not continuous immersion in seawater (reduced germination after 5 d and none after 12 d). Inter-island dispersal is likely via living unencumbered seabirds carrying a few seeds, but not on floating carcasses. Seeds attached to carcasses did not have improved germination or survival. Intra-island propagation is almost entirely vegetative, with negligible local seed dispersal. Pisonia plants therefore do not benefit from fatal entanglements. The extreme stickiness of the seeds evidently evolved to resist removal by seabirds and so facilitate long-distance dispersal. The mortality of some potential vectors is an unfortunate consequence, but has little impact on the large populations of tree- and ground-nesting seabirds which nest in or under these trees.

Biology of common crupina and yellow starthistle, two Mediterranean winter annual invaders in western North America

Abstract This paper reviews the biology of two closely related Mediterranean annuals, yellow starthistle and common crupina, which have invaded grassland, shrub steppe, and open woodland habitats in western North America. Despite the similarity of their winter annual life cycle, the two species differ significantly in population dynamics. Common crupina has traits that favor persistence rather than rapid population growth: large, heavy achenes with an after-ripening requirement; lower fecundity but higher germination success; and reproduction regulated by vernalization and photoperiod in addition to thermal time. Persistence traits also foster invasion of undisturbed or less degraded steppe habitats. Yellow starthistle has more ruderal traits: small, light, rapidly germinating achenes; higher fecundity, with greater seedling mortality; and reproduction that is less sensitive to photoperiod and vernalization. These characteristics confer a greater adaptability for rapid spread and colonization of disturban...

Germination characteristics of naturally occurring cysts of Alexandrium tamarense (Dinophyceae) in Hiroshima Bay, Inland Sea of Japan

In order to examine temporal changes in the germination ability, time to germination and autofluorescence properties of the resting cysts of the toxic dinoflagellate Alexandrium tamarense, a long-term investigation was conducted in Hiroshima Bay. In Hiroshima Bay, a spring bloom (March to May) of A. tamarense has been observed almost every year since 1992. Approximately 50 resting cysts were isolated monthly from the bottom sediment between June 1994 and June 1997. The cysts were incubated from the day of sampling onwards under in situ bottom water temperature conditions, and germination success and the emission of autofluorescence were checked every day. High germination success rates (>50%) were observed between December and April each year (bottom water temperature = 10.0–16.5°C), with an average germination time of 10.2 days (n = 455). Resting cysts were found to start to emit red autofluorescence a few days before germination (average duration = 3.1 days, n = 449), and germination time was nearly constant within the temperature range 10–20°C. From June to November, germination success rates were considerably lower (0–40%, bottom water temperature = 14.6–23.9°C). No germination at all was observed in September (bottom temperature = 23.6–23.9°C). The relationship between the incubation temperature and the rate of germination success indicates that the resting cysts have a temperature ‘window’ (c. 10–15°C) for germination, which controls the seasonal change in germination ability. The present results indicate that the germination characteristics of A. tamarense resting cysts are well adapted to the ambient water temperature rhythm in temperate shallow coastal environments, allowing A. tamarense to seed vegetative cell populations for the spring bloom.

Two-stage dispersal of Guarea glabra and G. kunthiana (Meliaceae) in Monteverde, Costa Rica

Seed dispersal of Guarea glabra and G. kunthiana (Meliaceae) in Monteverde, Costa Rica was studied to determine how seed predation and secondary dispersal affect the distribution of seeds available for recruitment. The arillate seeds are consumed mainly by birds that regurgitate or defecate the seeds intact. After dispersal, 45.6% of G. glabra and 26.6% of G. kunthiana seeds were buried 1–3 cm in the soil, presumably by scatterhoarding rodents such as agoutis (Dasyprocta punctata). G. glabra seeds that were not cached were eaten mostly by beetles, and 33.7% of the seeds remained cached after 12 wk. The cached G. glabra seeds did not germinate, however, perhaps as a result of experimental procedures used to mark the seeds. In greenhouse experiments, G. glabra seeds buried to mimic scatterhoarding had higher germination success than seeds on the soil surface. G. kunthiana seeds not cached were eaten by peccaries (Tayassu tajacu) and other seed predators (60%) or were inviable (10%). Only nine (7.5%) viable G. kunthiana seeds remained in caches after 12 wk. Secondary dispersal resulted in a rearrangement of the seed shadow. G. glabra seeds were moved to sites with less leaf litter and lower vegetation density, while G. kunthiana seeds were moved farther from conspecific trees and closer to fallen logs during secondary dispersal. Considering the high rates of seed predation in the field for both species, the germination advantages for G. glabra in the greenhouse, and the shifts in microhabitat during scatterhoarding, it is likely that secondary dispersal by scatterhoarding rodents is an important stage in Guarea recruitment.RESUMEN. Dispersión de semillas de Guarea glabra y G. kunthiana (Meliaceae) en Monteverde, Costa Rica fureon examinadas para determinar como la predación de semillas y dispersión secundaria afectan la distribución de semillas disponibles para recrutamiento. Las semillas ariladas son consumidas principalmente por aves que regurgitan o defecan la semilla intacta. Luego de dispersión, 30–45% de las semillas fueron enterradas 1–3 cm en el suelo, posiblemente por roedores que disperan y acumulan como al agouti (Dasyprocta puncaata). Semillas de G. kunthiana que no fueron escondidas fueron comidas por pécaris (Tayassu tajacu) y otros predadores de semillas (60%) o no fueron viables (10%). Solo neuve (7.5%) semillas viables de G. kunthiana permanecieron en los escondites luego de 12 semanas. En contraste, semillas de G. glabra que no fueron escondidas fueron comidas mayormente por escarabajos que por pécaris, y 33.7% de las semillas permanecieron escondidas luego de 12 semanas. Las semillas esconditas de G. glabra enterradas para imitar dispersión y acumulión tuvieron una germinación mayor que semillas en la superficie del suelo. Dispersión secundaria resulto en un rearreglo de la sombra de semillas. Las dos especies experimentaron un leve aumento neto en la distancia promedio de conspecificos en frutos luego de dispersión y acumulación. Semillas de G. kunthiana fueron movidas cerca de troncos caidos durante dispersión secundaria, mientras semillas de G. glabra fueron movidas a lugares con menos lecho de hojas y baja densidad de vegetación. Considerando la alta proporción de predación de semillas en el campo para ambas especies, la ventaja de germinación de G. glabra en el invernáculo, y el cambio en micrambiente durante dispersión y acumulación, es posible que dispersión secundaria por roedores que dispersan y acumulan es importante in etapas de recrutamiento en Guarea.