ABSTRACT
Community‐level seed dormancy studies are important in understanding the dynamics of plant communities and adaptations of species to their habitat. Our aim was to develop a seed dormancy ...profile for tropical montane forests of Sri Lanka, which are a global biodiversity hotspot, and compare it to the profile made using a world database for this vegetation type.
Germination, imbibition and embryo length : seed length ratio of seeds were determined for 80 Sri Lankan montane forest species.
Seeds of 31 species were fast‐germinating with a median length of germination (MLG) <30 days and the remaining 49 were slow‐germinating with MLG >30 days. Embryos of six fast‐germinating species grew prior to radicle emergence, indicating morphological dormancy (MD). The other 25 fast‐germinating species had non‐dormant (ND) seeds. Manually scarified seeds of two species imbibed significantly more water than non‐scarified seeds, revealing physical dormancy (PY). Embryos of 20 slow‐germinating species grew prior to radicle emergence, confirming morpho‐physiological dormancy (MPD). The remaining slow‐germinating species had a fully developed embryo and thus physiological dormancy (PD). The percentage of species with ND seeds and with MD, MDP, PD and PY was 31, 7.5, 25, 34 and 2.5, respectively.
Species with dormant seeds (70%) dominate the Sri Lankan montane forest community similar to the world database, with 85% dormant seeds. Seed dormancy may be an adaptation that prevents seeds from germinating during the Sri Lankan dry season from December to March when conditions are unfavourable for seedling growth due to low water availability.
Tropical montane forests in Sri Lanka are dominated by dormant seed‐producing species.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
This study investigated seed germination of Cardiospermum halicacabum, a medicinally important invasive species.
We compared mass, moisture content (MC), dormancy and dormancy‐breaking treatments and ...imbibition and germination of scarified and non‐scarified seeds of C. halicacabum from a low‐elevation dry zone (DZ), low‐elevation wet zone (WZ1) and mid‐elevation wet zone (WZ2) in Sri Lanka to test the hypothesis that the percentage of seeds with water‐impermeable seed coats (physical dormancy, PY) decreases with increased precipitation.
Seed mass was higher in WZ2 than in DZ and WZ1, while seed MC did not vary among the zones. All scarified DZ, WZ1 and WZ2 and non‐scarified DZ and WZ1 seeds imbibed water, but only a few non‐scarified WZ2 seeds did so. When DZ and WZ1 seeds were desiccated, MC and percentage imbibition decreased, showing that these seeds have the ability to develop PY. GA3 promoted germination of embryos excised from fresh DZ and WZ1 seeds and of scarified WZ2 seeds.
At maturity, seeds from DZ and WZ1 had only physiological dormancy (PD), while those from WZ2 had combinational dormancy (PY+PD). Thus, our hypothesis was not supported. Since a high percentage of excised embryos developed into normal seedlings; this is a low‐cost method to produce C. halicacabum plants for medicinal and ornamental purposes.
Variation in the precipitation causes differences in the seed dormancy classes in Cardiospermum halicacabum populations.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
We aimed to determine seed germination responses and flood tolerance of Ludwigia hyssopifolia and L. perennis that grow in rice fields in Rajgir, India. Freshly-matured seeds were incubated in 12 hr .../ 12 hr light / dark and complete darkness at constant 25 ℃ and natural daily fluctuating temperatures. Seeds exposed to different light durations were then incubated in complete darkness. Seeds exposed to different flooding durations were incubated in continuous flooded or non-flooded environments. Seeds of both species germinated within four days in light/dark but failed to germinate in complete darkness, revealing their nondormant and positive photoblastic behavior. Some seeds of both species (10 - 20 %) germinated in complete darkness after exposure to light for 24h. Seeds failed to produce normal seedlings in a continuously flooded environment. Seeds of the two studied species tolerate at least one week of flood. Seeds of L. perennis have a higher tolerance to flooding than those of L. hyssopifolia, which survived four weeks in a flooded environment. The two species have the same germination behaviour but differ in ability to tolerate flooding. Since seeds of both species are nondormant, positively photoblastic, and have different degrees of flood tolerance, a flooding regime of rice fields will not be sufficient to control these weeds.
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FFLJ, NUK, ODKLJ, UL, UM, UPUK
Abstract
Argyreia is the most recently evolved genus in the Convolvulaceae, and available information suggests that most species in this family produce seeds with physical dormancy (PY). Our aim was ...to understand the evolution of seed dormancy in this family via an investigation of dormancy, storage behaviour, morphology and anatomy of seeds of five Argyreia species from Sri Lanka. Imbibition, germination and dye tracking of fresh intact and manually scarified seeds were studied. Scanning electron micrographs and hand sections of the hilar area and the seed coat away from the hilar area were compared. Scarified and intact seeds of A. kleiniana, A. hirsuta and A. zeylanica imbibed water and germinated to a high percentage, but only scarified seeds of A. nervosa and A. osyrensis did so. Thus, seeds of the three former species are non-dormant (ND), while those of the latter two have physical dormancy (PY); this result was confirmed by dye-tracking experiments. Since > 90 % of A. kleiniana, A. hirsuta and A. zeylanica seeds survived desiccation to 10 % moisture content (MC) and > 90 % of A. nervosa and A. osyrensis seeds with a dispersal MC of ~ 12 % were viable, seeds of the five species were desiccation-tolerant. A. nervosa and A. osyrensis have a wide geographical distribution and PY, while A. kleiniana, A. hirsuta and A. zeylanica have a restricted distribution and ND. Although seeds of A. kleiniana are ND, their seed coat anatomy is similar to that of A. osyrensis with PY. These observations suggest that the ND of A. kleiniana, A. hirsuta and A. zeylanica seeds is the result of an evolutionary reversal from PY and that ND may be an adaptation of these species to the environmental conditions of their wet aseasonal habitats.
Seeds of legumes are generally considered to have physical dormancy and to be orthodox, but most seed biologists are unaware of the various kinds and combinations of dormancy and storage behaviour in ...seeds of this family. The aim of our study was to document the dormancy and storage behaviour of seeds of 100 native and introduced tropical Fabaceae species in Sri Lanka and classify them into germination/storage behaviour categories. Moisture content (MC) was < 16% for fresh seeds of 94 species and >29% for those of six. Seeds of these six species had low tolerance for desiccation and for low temperatures. Thus, seeds of six species are non-orthodox and 94 species orthodox. Nine of the 100 species were non-dormant, and 2, 3 and 86 had physiological, physiological epicotyl and physical dormancy, respectively. Six germination/storage behaviour categories were identified among the 100 species. However, as in extratropical regions of the world, orthodox storage behaviour and physical dormancy are characteristic of seeds of the majority of species of Fabaceae in tropical Sri Lanka.
Tropical lowland rainforests are considered to be ecologically important refugia of national and global significance, yet wide‐scale deforestation and degradation of tropical lowland rainforests lead ...to losses in biodiversity. Seed storage behavior information is required for the effective restoration of these forests. Here, we studied the seed storage behavior of 42 selected tropical lowland rainforest tree species from Sri Lanka with the aim to test the reliability of current experimental methods and predictive models to predict the desiccation sensitivity of seeds. Seed storage behavior was experimentally determined through the 100 seed method and the results were compared with three predictive models; thousand seed weight–moisture content (TSW–MC), seed coat ratio–seed mass (SCR–SM), and phylogenetic affiliation models. Based on the 100 seed method, 28 species were identified as desiccation sensitive and 14 species were identified as desiccation tolerant. Compared to the 100 seed method, the predictability of the SCR–SM model was 70%, whereas the TSW–MC and phylogenetic affiliation models showed 52% and 58% predictability, respectively. Due to its higher predictability, the SCR–SM model has a high potential to be an effective predictive tool of seed storage behavior. This study revealed that tropical lowland rainforests are dominated by trees producing desiccation‐sensitive seeds. Further, species dispersing seeds in the peak rainy season have desiccation‐sensitive seeds, while those dispersing seeds in the normal wet season have desiccation‐tolerant seeds. Another key finding was that 100% of the subcanopy species produce nonorthodox, that is, desiccation‐sensitive seeds, which gradually decrease from subcanopy to understory.
This study has determined the storage behavior of 42 tropical lowland rainforest trees in Sri Lanka that have not been evaluated previously. The study found that most of the study species have desiccation‐sensitive seeds. Further, seeds dispersed in the peak rainy season were desiccation sensitive, while those dispersed in the normal wet season were desiccation tolerant.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
BACKGROUND AND AIMS: Dormancy in seeds of Cuscuta (Convolvulaceae, tribe Cuscuteae) is due to a water-impermeable seed coat (physical dormancy). In nondormant seeds of several species of this family, ...bulges adjacent to the micropyle have been identified as the initial route of water entry into seeds (water gap). However, there are claims that water enters seeds of Cuscuta spp. via the entire seed coat. Although several studies have been done on seed coat anatomy of Cuscuta, none has identified and/or characterized the morphology/anatomy of a water gap. Thus, the primary aim of this research was to identify and describe the morphology and anatomy of the water gap in seeds of Cuscuta australis. It was also determined if sensitivity cycling to dormancy-breaking treatments occurs in seeds of this species. METHODS: Light microscopy, scanning electron microscopy, tissue-sectioning and dye-tracking and blocking experiments were used to investigate the morphology and anatomy of the water gap. Treatments simulating natural conditions were used to break seed dormancy. Storage of seeds at different temperatures was tested for their effect on sensitivity to dormancy-breaking treatment. KEY RESULTS: Dormancy-breaking treatments caused the tightly closed hilar fissure to open. Staining was observed in cells below the hilum area but not in those below the seed coat away from the hilum. Sensitivity to dormancy-breaking treatment was induced by storing seeds dry and reduced by storing them wet. CONCLUSIONS: Whereas bulges adjacent to the micropyle act as the water gap in other species of Convolvulaceae with physical dormancy, the hilar fissure serves this function in Cuscuta. Cuscuta australis can cycle between insensitivity leftright arrow sensitivity to dormancy-breaking treatments.
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• Background and Aims Convolvulaceae is the most advanced plant family (asterid clade) that produces seeds with physical dormancy (water-impermeable seed coat). There are several different opinions ...about the nature of the specialized structure ('water gap') in the seed coat through which water initially enters seeds of Convolvulaceae, but none of them has been documented clearly. The primary aim of the study was to identify the water gap in seeds of Ipomoea lacunosa (Convolvulaceae) and to describe its morphology, anatomy and function. • Methods Light microscopy, scanning electron microscopy, tissue-sectioning, dye-tracking and blocking experiments were used to describe the morphology, anatomy and function of the water gap in seeds of I. lacunosa. • Key Results Dormancy-breaking treatments caused slits to form around the two bulges on the seed coat adjacent to the hilum, and dye entered the seed only via the disrupted bulges. Bulge anatomy differs from that of the rest of the seed coat. Sclereid cells of the bulges are more compacted and elongated than those in the hilum pad and in the rest of the seed coat away from the bulges. • Conclusions The transition area between elongated and square-shaped sclereid cells is the place where the water gap opens. Morphology/anatomy of the water gap in Convolvulaceae differs from that of taxa in the other 11 angiosperm plant families that produce seeds with physical dormancy for which it has been described.
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Weeds associated with rice fields cause severe yield reduction and many other problems. Effective weed management strategy depends on knowledge of weed seed biology. This study aimed to determine ...basic seed biology information of seven rice field weeds in Sri Lanka. Seeds were collected from at least five individuals from each species. Dormancy classes of seeds were determined using germination and imbibition experiments. Effect of light, dry storage, temperature and salinity on dormancy and germination was studied. Experiments were conducted with three replicates of 25 seeds. Among the tested species, seeds of Eclipta prostrata and Ludwigia peruviana were non-dormant where the non-treated fresh seeds germinated ＞ 60 %. Seeds of Aeschynomene indica and Melochia corchorifolia are physically dormant as only scarified seeds imbibed and germinated. Fimbristylis miliacea, Cyperus pilosus and L. decurrens seeds germinated only on GA_3. Thus, they have physiological dormancy. E. prostrata and L. peruviana seeds required light for germination. Five month- dry storage reduced the viability of E. prostrata seeds. In contrast, dry storage increased the sensitivity to the dormancy breaking treatment of A. indica, M. corchorifolia, C. pilosus and L. decurrens seeds and decreased the sensitivity of F. miliacea seeds. Germination of E. prostrata and L. peruviana seeds decreased with decreasing osmotic potential. Although, dormancy and dormancy breaking requirements vary among study species, keeping the rice field dry during the intercropping period could induce the seed germination of most of the above species and could be used as a mechanism to reduce the soil seed bank.
Although the level of seed desiccation sensitivity (LSDS) may have an impact on plant species conservation, information is available for <10% of tropical angiosperms. A study was conducted to assess ...the LSDS of 28 tropical montane species in Sri Lanka. Seeds were extracted from freshly collected fruits. Initial weight was recorded, and thousand seed weight (TSW) was calculated. Seed moisture content (MC) was determined. LSDS was determined using seed desiccation experiments and predicted using the TSW–MC criterion. Seed storage behaviour was predicted using LSDS and storage data and using a model based on phylogenetic affiliation. The relationship between LSDS and seed dormancy, life form and forest strata was evaluated. Fresh seeds of only 12 species germinated to >80%. Although seeds of the other species had >80% viability, only 0–70% germinated due to dormancy. Seeds of five species had MC <15%, indicating desiccation tolerance (DT). Seeds of 12 species lost viability after desiccation, indicating desiccation sensitivity (DS). Seeds of Ardisia missionis, Psychotria gartneri and Psychotria nigra remained viable after desiccation, showing DT. Seeds of 17 species were DS and those of 11 species DT. The TSW of four species was >500 g. Thus, seeds of other species were predicted to be DT by the TSW–MC criterion. A relationship was identified between LSDS and the forest strata of the species. More canopy species produced DS than DT seeds. Since seeds of most of the studied species were DS, these species may be threatened due to prolonged droughts predicted for the region due to climate change.
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