Low Temperature Stratification Research Articles

Transcriptome Analysis of Seed in Dormancy and Dormancy Release State of Epimedium koreanum Nakai

Epimedium koreanum is a perennial herb of the Berberidaceae family, which is a traditional tonic in Chinese medicine. Seed germination of E. koreanum is difficult. Dormancy is an intrinsic factor that affects seed germination. Elucidating the molecular mechanism of seed dormancy and the lifting process of E. koreanum is of great significance for the breeding, conservation, and utilization of E. koreanum. Previous studies have concluded that E. koreanum seed dormancy breakage requires warm-temperature stratification followed by low-temperature stratification treatments. Therefore, we performed transcriptome sequencing using freshly harvested, untreated seeds (NS), seeds that developed a cotyledonary embryo after 90 d of constant-temperature stratification at 15 °C (CS), and seeds that broke dormancy by 90 d of stratification at 15 °C and 60 d of stratification at 5 °C (ND) in order to find the responsive genes and regulatory genes that regulate dormancy. A total of 92,867 genes with differential expression were identified. GO enrichment analysis highlighted redox processes, as well as structural components of the nucleus and ribosomes. KEGG enrichment analysis revealed a significant enrichment of phytohormone signaling pathways, which play a crucial role in seed dormancy release. Additionally, protein–protein interactions (PPIs) were predicted with starch and sucrose metabolic pathways. This study introduces a novel concept for a more profound comprehension of the molecular regulatory mechanism of E. koreanum and lays a theoretical foundation for the screening of E. koreanum candidate genes.

Study on Dormant and Germination Characteristics of Chinese Olive (Canarium album) Seeds

This study aimed to determine the dormancy type of Chinese olive seeds and improve their germination rate. The water permeability and germination-inhibiting substances of Chinese olive seeds were assessed. Low-temperature stratification and soaking in a GA3 solution were implemented to measure the time lag, initial time, germination rate, and germination potential of the seeds. The findings revealed that the seed coat exhibited poor water permeability, which negatively influenced the germination rate. Additionally, Chinese olive seeds contained substances that inhibited germination. The duration of low-temperature stratification (at 4 ± 1 °C) gradually diminished the dormancy of Chinese olive seeds, resulting in early and rapid germination. The germination rate significantly increased, with the percentage of seed germination rising from 0% to 42.33% within 60 days of stratification. Furthermore, combining low-temperature stratification with different concentrations of GA3 notably enhanced the germination rate. The optimal concentrations of gibberellins for 40 and 60 days of stratification were determined to be 300 and 100 mg/L, respectively. These results indicate that Chinese olive seeds possess non-deep physiological dormancy.

Augmenting the thermal response of helical coil latent-heat storage systems with a central return tube configuration

Low-temperature stratification, high-volumetric storage capacity, and less-complicated material processing make phase-changing materials (PCMs) very suitable candidates for solar energy storage applications. However, their poor heat diffusivities and suboptimal containment designs severely limit their decent storage capabilities. In these systems, the arrangement of tubes conveying the heat transport fluid (HTF) plays a crucial role in heat communication between the PCM and HTF during phase transition. This study investigates a helical coil tube-and-shell thermal storage system integrated with a novel central return tube to enhance heat transfer effectiveness. Three-dimensional computational fluid dynamics simulations compare the proposed design against a baseline helical coil system without a return tube under equivalent conditions. Outcomes quantify the return tube's efficacy in augmenting heat transfer uniformity and accelerating phase transition. Adding the return tube markedly boosts heat storage and recovery rates, increasing charging by 88% and discharging by 56% versus the baseline. Moreover, total phase transition time reduces by 48% for melting and 36% for solidification with the return tube. The accelerated charging stems from sustained convective heat transfer inside the return tube even as the molten layer thickens. Meanwhile, enhanced solidification results from ongoing cooling of inner regions. Isotherm analysis visualizes the return tube's efficacy in maintaining thermal uniformity throughout the phase transition process. Overall, the return tube significantly improves PCM thermal response, demonstrating a novel but straightforward approach to address heat transfer limitations in latent thermal storage systems.

New insights into the molecular mechanism of low-temperature stratification on dormancy release and germination of Saposhnikovia divaricata seeds

New insights into the molecular mechanism of low-temperature stratification on dormancy release and germination of Saposhnikovia divaricata seeds

An experimental comparison of radiant wall and ceiling cooling system integrated with ground source heat pump and direct expansion fan coil system in a highly glazed office room

Hydronic radiant systems, which provide a thermal comfort environment, come to the fore in different building applications due to their energy saving potential and being integrated with renewable energy systems. The aim of this study is to present a full-scale experiment to compare the thermal comfort performances of radiant ceiling, wall and wall + ceiling systems coupled ground source heat pump and direct expansion fan coil system implemented in Yildiz Technical University Science and Technology Application and Research Center, Istanbul, Turkey. Air velocity, horizontal and vertical air temperature differences, mean radiant temperature and humidity values, which are four physical parameters that can affect the thermal satisfaction of office workers for 9 different experimental conditions, are measured for fan coil and all radiant systems. The results indicate that vertical temperature differences between ankle and head level vary from 0.9 °C to 1.4 °C for both fan coil system and all radiant system configurations in different location of the test room. Acceptable overall comfort in indoor environments Class A only showed stable performance with an average of 0.12 PMV and 5.3 % PPD when ceiling + wall radiant panels were actively cooled. The result shows that the difference between room air temperature and room operating temperature varies between 0.45 °C and 0.6 °C when cooling loads are met by radiant systems. This may not make it possible to use indoor air temperature instead of indoor operating temperature in the control of radiant systems. Moreover, the thermal environment of the radiant system are more uniform than fan coil system due to low air temperature stratification, air velocity and small differences between mean radiant temperature and indoor air temperature.

Chilling-Requirement Release of Seed and Bud Dormancy in Apricot

Dormancy shows common physiological features in buds and seeds. Specific period of chilling is usually required to release dormancy. Reproductive meristems and embryos display dormancy mechanisms in specialized structures named respectively buds and seeds that arrest the growth of perennial plants until environmental conditions are optimal for survival. Chilling requirements for breaking dormancy were studied for 3 successive years in 20 seedling apricot trees which spanned the range of flowering times in these trees. Different methods for estimating chilling requirements were evaluated and compared, and correlations between chilling requirements and flowering date were established. The trees examined showed a range of chilling requirements, chill hours (CH) between 199 CH and 274 CH, and chill units, (CU), between 612CU and 873CU. The results obtained in different years by the Utah and Dynamic models were more homogeneous with respect to the hours below 7 °C model. The apricot trees showed important differences concerning flowering date, and the results indicate a high positive correlation between chilling requirements and flowering date.Moreover, a specific low-temperature stratification treatment was required to overcome seed dormancy. 5°C cold stratification was found to be the best for breaking seed dormancy and germination. Increased seed germination percentage was recorded when the period of stratification prolonged. Apricot seeds required a cold stratification of about 12-15 days to reach maximum germination.

Impact of seed cold stratification on apricot germination and subsequent seedling growth as well as chemical constituents of seeds during stratification

Freshly harvested seeds of apricot varieties "Balady (Amar)" and "Hamawy" were found to be dormant and did not germinate at all. A specific low-temperature stratification treatment was required to overcome seed dormancy. 5°C cold stratification was found to be the best for breaking seed dormancy, germination and seedling growth. Increased seed germination percentage was recorded when the period of stratification prolonged. Seedling developed from stratified seeds had better growth than those developed from non-stratified seeds. Apricot seeds required a cold stratification of about 12-15 days for "Balady variety (Amar)" and15-18 days for "Hamawy" variety "to reach maximum germination and normal seedling growth. Chemical constituents of apricot seeds (total and reducing sugars, total free amino acids and total indoles were increased while that of free phenols and total soluble phenols were decreased) when stratification period prolonged. Therefore, it can be suggested that breaking of dormancy is coincided with several changes in different chemical constituents of seeds. Some of these materials increased and other materials which decreased at seed germinations.

THE CONTROL OF APRICOT SEED DORMANCY AND GERMINATION BY LOW TEMPERATURE TREATMENTS

Objective: Freshly harvested seeds of “Local” apricot variety were found to be dormant and did not germinate at all. A specific low-temperature stratification treatment was required to overcome seed dormancy. The most effective temperature for breaking seed dormancy, germination, and seedling growth was 5°C cold stratification (CS). Increased seed germination percentage was recorded when the period of stratification prolonged. Seedling developed from stratified seeds had better growth than those developed from non-stratified seeds.
 Methods: For stratification treatments, the seeds with removed endocarp were mixed with moistened sand. Afterward, they were subjected to a period of stratification at 5°C. Seeds were stratified in pots of 30 cm×40 cm. Stratified seeds were regularly irrigated once per week. To prevent the water loss during stratification upper surface of pots was covered by a sack. The following stratification was applied for apricot variety: CS for 0, 3, 6, 9, 12, and15 days in 1998 and 1999 years for “Local” variety.
 Results: Apricot seeds required a CS of about 15 days for “Local” variety to reach maximum germination and normal seedling growth. Moreover, when stratification period was prolonged, some of the chemical constituents of apricot seeds were increased and other was decreased. Therefore, it can be suggested that breaking of dormancy is coincided with several changes in different chemical constituents of seeds. Some of these materials increased (total, reducing and non-reducing sugars, total free amino acids, total indoles, and total and conjugated phenols) and other materials such as free phenols which decreased at seed germinations.
 Conclusion: The most effective temperature for breaking seed dormancy, germination, and seedling growth was 5°C CS. Increased seed germination percentage was recorded when the period of stratification prolonged. Seedling developed from stratified seeds had better growth than those developed from non-stratified seeds.

Germination Ecophysiology for Three Peri-urban Ephemeral Weeds from Morelia, Michoacan, Mexico

The environmental requirements leading to germination were determined by three common species found during the June-October 2009 rainy season in a peri-urban site from Morelia, Michoacan, Mexico, where the construction of a campus of the Universidad Nacional Autonoma de Mexico (UNAM) was underway. In particular, we evaluated responses in the laboratory to low-temperature stratification, day/night air temperature, and water potential for the native Onagraceae Lopezia racemosa and Ludwigia octovalvis, and the exotic Polygonaceae Rumex crispus. Low-temperature stratification had no effect on germination by L. racemosa, for which maximum germination averaging 88% was optimal at 25/15 and 30/20 ºC. Germination at 21 d was halved at –0.5 MPa and completely inhibited at –1.0 MPa. The seeds of L. octovalvis were also insensitive to low temperature stratification and their germination never exceeded 70%, with the two highest temperatures of 30/20 and 35/25 ºC being the optimum. For this species germination was maximal at 0.0 MPa, decreasing significantly under every treatment with a minimum germination of 21% for seeds incubated at –0.1 MPa. Germination for the exotic R. crispus was delayed by low-temperature stratification, although all its seeds germinated regardless of the temperature or water potential treatment. While the environmental requirements for germination of ephemeral species often match the typical climate of their growing season, the differential responses found for the species considered in the present study provide some insight into the mechanisms leading to changes in species composition for communities from disturbed environments, including the displacement of native species and the proliferation of exotic, potentially invasive plants.

Erratum to: “Stochastic approach to the theory of stratification of water and aqueous solutions: A model of twinkling hydrogen bonds”

The equations of state for liquids and liquid solutions with intermolecular hydrogen bonds were derived in the dichotomous noise model for these bonds. The analytically obtained PT and TC phase diagrams show that finite-lifetime bonds can be responsible for new experimentally found phase transitions. These are (i) stratification of solutions in a closed TC region (i.e., a region with upper and lower critical points) and in a low-concentration TC region and (ii) low-temperature stratification of monomolecular liquids into heavy and light phases.

The use of displacement and zoning ventilation in a multipurpose arena

ABSTRACTThis study investigated the performance of ventilation and indoor climate in a multipurpose arena located in Malmö, Sweden, with a seating capacity of 13,000 individuals, and in which a combination of displacement and zoning ventilation was applied. The main objective was to explore thermal conditions, indoor air quality, airflow patterns and air distribution. The measured operating conditions were ice hockey game and training situation. The measurements were conducted to observe the indoor climate and computational fluid dynamics (CFD) simulations were performed to get a generic view of the air distribution and the flow field over the whole arena indoor environment. The results show that air movement was highly case-dependent. However, the experiments indicated an upward flow along the lower seating area and a downward flow along the upper seating area. During the game, the average rise of temperature was around 2 °C in arena with low stratification while using displacement ventilation. The temperature range was 12–17 °C at the lower seating area and 15–17 °C at the upper seating area. The corresponding air-speed level was 0.06–0.36 m/s. The relative humidity was about 30%–40% where a part of the humidity was transferring into the ice sheet. The carbon dioxide concentration increased locally to near 900 ppm indicating reasonable operation of ventilation. The CFD simulations predicted well-mixed conditions in arena, thus supporting the measured low-temperature stratification. Overall, the air movement was significantly affected by supply air temperature, variable airflow rates and retractable stand position (on–off) in the arena enclosure. The results support the use of displacement and zoning ventilation in multipurpose arenas.

Screening and Expression Analysis of Temperature-responsing Proteins that Can Remove Low Temperature Stagnancy of Seeds Germination of <i>Lepidium apetalum</i>

As a kind of ephemeral plant, Lepidium apetalum Willd. in northern XinJiang shows special responsible characteristics to temperature during the germination: low temperature stratification could improve germination rate and homogeneity of L.apetalum seeds. But it could not germinate and be at stagnation stage under 4 °C , while this phenomenon could be removed by the treatment with 25 °C for 45 minutes or longer time. The mechanism why the treatment by higher temperature for a short time could remove germination stagnation under low temperature is not clear yet. In this study, the total proteins difference of seeds with three treatments were analyzed by2-DE, which the seeds were without stratification, stayed at germination stagnation stage under low temperature and removed stagnation with 25℃treatment. Screened proteins responsing to temperature which were related to remove germination stagnation under low temperature, and the corresponding genes expression were confirmed by qRT-PCR. The result showed that there was no obvious difference between the seeds without stratification and the seeds at germination stagnation stage by low temperature. But the proteins expression was quite different between the seeds treated with 25 °C for 45 minutes to remove the germination stagnation and the other two treated samples. 37 distinct protein spots were found in the 2-DE map with 14 up-regulated spots, 23 down-regulated spots. Among them, 6 up-regulated proteins of 14 spots were identified by LC-MS/MS, CDC48E , HSP17.6 and PER12 were further chosen to be confirmed expression analysis by qRT-PCR.The result showed that their relative expression levels were significantly higher in seeds removed stagnation than in seeds before breaking stagnation. In addition, their expression levels were obviously increased with the time prolonging treated by 25 °C with the highest level with the dealt for 45-55 min and then maintaining this level of expression. The result showed that the genes expression levels were positively correlated to the germination percentage treated with 25 °C from 30-60 minutes. All the above suggested that Cdc48E, Hsp17.6, and Per12 induced by 25 °C might be related to the germination stagnation removing of the seeds of L.apetalum . This conclusion provides a new clue for the study on the signal response to temperature in plants.

Formation of the well-mixed homogeneous layer in the bottom water of the Japan Sea

The deep and bottom waters of the Japan Sea (depth ≳ 1000 m) are characterized by low temperature and weak stratification. In the Japan Basin, especially, the bottom water (depth ≳ 2500 m), called the Japan Sea bottom water (JSBW), with a thickness of over 1000 m, is mostly homogeneous. Several studies in recent decades have suggested that the potential temperature of the JSBW is gradually increasing, even though the thick homogeneous vertical structure is being maintained. Although downward mixing of heat from the upper layer was believed to be responsible for this characteristic feature, our microstructure measurements found that the intensity of turbulence in the JSBW is too weak to explain the formation of the gradually warming thick homogeneous layer. By use of a one-dimensional numerical model we demonstrated that this characteristic feature of the JSBW can be reasonably explained on the basis of a combination of geothermal heating from the seabed and an appropriate horizontal supply of cold water to the bottom layer.

Salinity effects on Ruppia maritima L. seed germination and seedling survival at the Everglades-Florida Bay ecotone

Ruppia maritima L. is a cosmopolitan species that dominates in highly variable environments with respect to hydrology, salinity and water quality. This species is critical in the development of aquatic habitats which support secondary production in the Everglades-Florida Bay ecotone coastal estuaries. While R. maritima has been identified as an indicator species for successful Everglades restoration, the factors controlling its current distribution are poorly understood making it difficult to predict its future presence, abundance and ability to support secondary production. In our ongoing research, we are experimentally examining the factors controlling R. maritima early life history including seed germination and seedling survival with a focus on salinity dynamics. In the experiments presented herein, we hypothesized that the highly variable salinity at the Everglades-Florida Bay ecotone promotes R. maritima seed germination, but that seedlings are sensitive to high salinities. We conducted a series of experiments examining seed germination across a range of salinities known to occur at the ecotone (0–45psu) with and without low-temperature stratification (6–10°C). Across this range of salinity, germination rates were low and primarily restricted to salinities <25psu. However, when seeds were transferred to fresh water, significantly higher germination rates were observed in seeds previously exposed to high salinity. In fact, there was a strong positive linear relationship between prior salinity exposure level and germination rate once salinities were lowered (R2≥0.97). These results lead us to suggest that osmotic shifts from hyper- to hyposalinity promote R. maritima seed germination. This result explains a mechanism driving seed germination when annual temperatures remain higher than those previously recognized to cause seed stratification (≤6°C). Further, we found seeds germinated in relatively high temperatures (>30°C) characteristic of the subtropics and were inhibited in low temperatures (10°C), even with osmotic stratification. During seedling development, we observed that a slow rate of salinity increase allowed osmotic adjustment of seedlings and a high salinity tolerance up to 50psu. As would be expected in seed-germinated aquatic species, nutrients and moderate salinity conditions were required to promote development of tissues beyond embryonic stages. In summary, we determined that R. maritima seed germination is promoted by variable salinity, but fresh water is necessary for germination and low salinities (≤10psu) enhance seedling development.

Research on Failure Mechanism of Plastic Encapsulated Microcircuits

Plastic encapsulated microcircuit (PEM) had been invented in the 60s of the 20th century, with great advantages in size, weight, cost and performance. Nevertheless, there are still great differences between PEMs and high reliable devices and many problems cannot be ignored, such as corrosion, popcorn effect and low-temperature stratification. In this paper, common failure modes and their mechanisms of PEMs have been discussed according to some typical failure cases, which can provide an important basis for improving the process technology and enhancing the reliability of PEMs.

The influence of the Indian Ocean Dipole on interannual variations in phytoplankton size structure as revealed by Earth Observation

Using a decade of satellite ocean-colour observations and a model that links chlorophyll-a to the size of the phytoplankton cells, parameterised using pigment data from the Indian Ocean, we examine the implications of the Indian Ocean Dipole (IOD) for phytoplankton size structure. The inferred interannual anomalies in phytoplankton size structure are related to those in sea-surface temperature (SST) and sea-surface height (SSH), derived using satellite radiometry and altimetry, and stratification, derived using the Simple Ocean Data Assimilation (SODA) database. In regions influenced by the Indian Ocean Dipole, we observe a tight correlation between phytoplankton size structure and the physical variables, such that interannual variations in the physical variables accounts for up to 70% of the total variance in phytoplankton size structure. For much of the Indian Ocean, low temperature, low SSH and low stratification (indicative of a turbulent environment) are correlated with larger size classes, consistent with theories on coupling between physical–chemical processes and ecosystem structure. To the extent that phytoplankton function is related to its size structure, changes in physical forcing are likely to influence biogeochemical cycles in the region and the pelagic food web. The limitations of our approach are discussed and we highlight future challenges in satellite ocean-colour monitoring, should climate change lead to any modification in our marine ecosystem.

Karymorphological and molecular studies on seven species in Polygonoideae (Polygonaceae) in Egypt

Seven species in four genera of the Polygonoideae (Polygonaceae) in Egypt were subjected to karyomorphological and molecular studies in order to identify their chromosomal characteristics and investigate their phylogenetical relationships by the conventional staining method and the 5S rDNA PCR. Seed germination after treatment with low temperature stratification and acidification by concentrated H2SO4 was studied. Three rates of germination were obtained in response to the cold stratification and acidification: 1) High in Polygonum equisetiforme, Persicaria lanigera, Pe. lapathifolia and Pe. salicifolia; 2) low in Rumex dentatus; 3) no effect in R. pictus and Emex spinosa. Variation in the chromosome complements number, length and structure were detected for Po. equisetiforme (2n=58; new count); Pe. lanigera (2n=40; new count); Pe. lapathifolia (2n=22); Pe. salicifolia (2n=60); Emex spinosa (2n=18; a new count); Rumex dentatus (2n=40); and R. pictus (2n=18; a new count). Eighteen polymorphic bands of 5S rDNA were used to determine the similarities among the taxa with the similarity coefficient ranging between 0.2 and 0.67.

Seed dormancy in red rice. XIII: Interaction of dry-afterripening and hydration temperature

AbstractWhile red rice (Oryza sativaL.) can remain dormant and viable for many years when fully imbibed, the environmental factors that stimulate germination or induce secondary dormancy in the field have not been characterized. In this study, the interactions between the extent of dry-afterripening and germination temperature have been evaluated as possible factors. Red rice dispersal units (florets) were afterripened for 0–10 weeks at 30°C and incubated in water at 1, 5, 15, 20, 25, 30 and 35°C for 2 weeks; then, all the ungerminated florets were transferred to 30°C for two additional weeks. Germination at the end of each of the two sequential treatments was compared to define both the effect of differing temperatures on germination (first treatment), and the effect of these temperatures on subsequent germination at the optimum temperature (30°C, second treatment). In afterripening red rice, the opening of the temperature window for germination begins at 25–35°C. Fully dormant florets acquired the ability to germinate ≥ 90% at 30°C after 4 weeks of dry-afterripening. However, imbibing florets for 2 weeks at 15°C followed by 2 weeks at 30°C, yielded suboptimal germination and induced a degree of secondary dormancy, dependent upon the extent of previous dry-afterripening. Cold stratification (1°C) had a consistent promotive effect on the subsequent germination, particularly when preceded by 1–2 weeks of dry-afterripening at 30°C. To monitor the effects of germination temperature, median afterripening time was utilized as a relative dormancy index, and changes in this index have been interpreted as an overlapping of germination and the temperature-induced changes in the dormancy status. Field weather data suggested that low-temperature stratification may be a germination trigger in the field, even in southern Louisiana, and this merits further investigation in studies of soil-buried seeds.

Seed dormancy and germination of a panel of New Zealand plants suitable for re‐vegetation

Seeds of Carex trifida, Coprosma robusta, Cyperus ustulatus, Hebe stricta, Lepto‐spermum scoparium, Muehlenbeckia australis, Myrsine australis, Phormium tenax, P. tenax ’Yellow Wave’, and Sophora prostrata were assessed for germination and dormancy. Seeds of Carex trifida, Cyperus ustulatus, and Myrsine australis showed no germination in light or dark at 20°C, but a high percentage of seed of Carex and Cyperus germinated after 12 weeks of low stratification. Despite high viability, germination of Myrsine australis seeds was low and occurred only after 12 weeks of low temperature stratification. Germination was low for Muehlenbeckia australis in the light, at 20°C, but increased after 4 weeks of low temperature stratification. After 12 months, 50% of Coprosma robusta seeds germinated but germination was greater after 4 weeks or more of stratification. No seeds of Coprosma robusta or Muehlenbeckia australis germinated in the dark. Rapid germination of Hebe stricta seeds was obtained, with 100% of the seed germinating in the light but 7% in the dark. Leptospermum scoparium had rapid germination, with 100% germinating in the light but 3% in the dark. A low percentage of Phormium tenax seeds germinated in both the light and dark in the first month with no further germination, but after 8 weeks or more of low temperature stratification there was almost complete germination. There was rapid germination of Sophora prostrata seeds with 100% of the seed germinating in the light and dark.

The effect of cold stratification and light on the seed germination of temperate sedges (Carex) from various habitats and implications for regenerative strategies

The germination responses of 32 temperate Carex species were tested in light and darkness at five constant temperatures and under one fluctuating temperature regime, before and after cold-wet stratification. Using a linear logistic regression model, the probability of germination tested across all species was found to be significantly higher after stratification, in light and at the fluctuating temperature. In addition, the probability increased with temperature. Stratification increased germination in 28 species and had very little or no effect on four species. There was almost no germination in darkness prior to stratification, and the germination in light was considerably higher in all but two species compared with that in darkness. Thus, it can be concluded that the Carex species tested have broadly similar germination response patterns. The fact that Carices can be released from high levels of primary dormancy by low-temperature stratification implies that they are spring germinators. A light requirement after stratification in the major fraction of seeds and the capability of almost all investigated sedges to respond to fluctuating temperatures make it likely that persistent seed banks are formed. Additionally, sedges generally seem to have a high temperature requirement for germination which prevents them from emerging at the very beginning of the growing season. Regeneration by seed is probably largely restricted to gaps resulting from late spring disturbances where buried seeds have an opportunity to germinate and grow. Differences in germination were apparent between species occupying different habitats. Overall germination was significantly higher in wetland species than in dry-site species, probably owing to the greater capability of wetland species to respond to fluctuating temperatures. Differences in germination between forest and open-site species can be attributed to the higher capability of forest sedges to respond to low temperatures and temperature fluctuations. The influence of seed weight on germination was not significant in the 18 species adapted to wet, open habitats. There was, however, a tendency for the germination percentages to be low for large-seeded Carices. The interpretation of habitat differences is difficult due to a positive correlation between seed weight and dry habitats.