Five years (1998, 2000–2003) of summer records of temperature, nutrients and dissolved oxygen concentrations in the upper 400 m of the water column of the northern Gulf of Aqaba were employed to produce a simple statistical model of the relationship between temperature versus nitrate, phosphate, silicate andd issolved oxygen concentrations. Temperature profiles in the upper 400 m during summer revealeda clear thermocline in the upper 200 m. This was reflected in nutrient ando xygen concentrations as nitrate, phosphate, and silicate increasedfr om the surface to deep water while dissolved oxygen decreased. The best fit relationship between temperature versus nitrate andphosphate was inverse linear and the best fit correlation between temperature versus silicate andd issolvedo xygen was fractional. The observedn utrient concentrations were shaped by a combination of the hydrodynamics and biological factors. Deep winter mixing and high nutrient concentrations dominate during winter. Shortly after the water stratifies in spring, the nutrients are drawn down by phytoplankton during the spring bloom and remain low throughout the rest of the year. The regression equations presented here will be useful in estimating nutrient concentrations from temperature records as long as the annual natural cycle is the main driver of nutrient concentrations and external inputs are insignificant. Deviations from these relationships in the future could provide insight into modifications in the nutrient concentrations probably resulting from new nutrient sources, such as anthropogenic inputs.
Fruits of large-leaved lime dried to 10% may be stored for 16 years in sealed containers at –3°C without loosing seed viability. Dormancy of seeds, extracted from hard fruit coats, may be released after chemical scarification in concentrated sulphuric acid for 10 minutes, followed-by stratification without any medium (chilling) at the temperature of 3°C, for 20–24 weeks, i.e. until the first seeds start to germinate. After such pretreatment, during the germination test conducted at alternating temperatures 3~15°C (16 + 8 hours/day) seeds germinate near 90% in several weeks. For seedling production scarified and stratified seeds should be sown in early spring into trays under a plastic tunnel which ensures a high percentage of seedlings emergence. Sowing of the pretreated seeds in spring in a open nursery gives poor results.
Effects of several stratification variants on seed dormancy breaking were compared in Crataegus submollis Sarg. (hairy cockspur-thorn or Quebec hawthorn). Ripe seeds were collected (in October), cleaned, and dried to a moisture content of 7–12%. Seed dormancy in this species was broken most effectively by warm-cold stratification of nutlets, in a substrate or without any substrate, at 15~25°/3°C or 20~30°/3°C, i.e. with a cyclically alternating warm stage (16+8 hrs or 24+24 hrs/cycle) lasting 16–20 weeks, followed the cold stage lasting ca. 20 weeks, i.e. till the appearance of the first germinating seeds. After stratification, emergence rate is equally high (ca 50%) at cyclically alternating temperatures of 3~15°C and 3~20°C (16+8 hrs). Chemical scarification of nutlets in 96% sulphuric acid for 3 hrs, followed by warm-cold stratification at 20~30°/3°C, with a short, 4-week warm stage, also ensures a high emergence rate (58%). Seed desiccation (in nutlets) slowly to a moisture content of 10–12%, after stratification in a substrate or without any substrate as well as after scarification, results in a reduced emergence rate, especially if seeds are dried to the lower moisture content. Seed storage (in nutlets after drying to a moisture content of 10%) for 10 years at –3°C, does not decrease the emergence rate (93%) after stratification at 20~30°/3°C in a substrate, with a cyclically alternating warm stage (24+24 h) lasting 16 weeks.
The effects of stratification and scarification on seed dormancy breaking were compared in scarlet hawthorn (Crataegus pedicellata Sarg. = C. coccinea L). Ripe fruits were collected (in October) and the extracted nutlets were cleaned, and dried to a moisture content of 9–12%. Seed dormancy in this species was broken most effectively by warm-followed-by-cold stratification of nutlets, in a substrate or without any substrate, as well as at 15~25° or 20~30°C, i.e. with a cyclically alternating warm stage (16+8 hrs or 24+24 hrs/cycle) lasting 16–20 weeks, followed by the cold stage at 3°C lasting ca. 20 weeks, i.e. till the appearance of the first germinating seeds. After stratification, emergence rate is equally high (ca 76%) at cyclically alternating temperatures of 3~15°C or 3~20°C (16+8 hrs). Chemical scarification of nutlets in 96% sulphuric acid for 2 hrs, followed by warm-cold stratification at 20~30°/3°C, with a short, 4-weeks warm stage, also ensures a high emergence rate (85–93%). Seed desiccation (in nutlets) slowly to moisture content of 12–14%, after stratification in a substrate or scarification does not reduce the seedling emergence of seeds. Emergence decreased when seeds were desiccated after stratification without any substrate. Results provide new methods of breaking of dormancy and high germination and emergence of hard-coated Crataegus seeds in controlled conditions.
Thermohaline structure in the Gulf of Riga (GoR) was investigated by a multiplatform measurement campaign in summer 2015. Stratification of the water column was mainly controlled by the temperature while salinity had only a minor contribution. Buoyant salinity maxima with variable strength were observed in the intermediate layer of the Gulf of Riga. The salinity maxima were likely formed by a simultaneous upwelling—downwelling event at the two opposite sides of the Irbe strait. The inflowing salty water did not reach the deeper (> 35 m) parts of the gulf and, therefore, the near-bottom layer of the gulf remained isolated throughout the summer. Thus, the lateral water exchange regime in the near bottom layer of the Gulf of Riga is more complicated than it was thought previously. We suggest that the occurrence of this type of water exchange resulting in a buoyant inflow and lack of lateral transport into the near-bottom layers might contribute to the rapid seasonal oxygen decline in the Gulf of Riga
Common milkweed (Asclepias syriaca L.) has become an invasive weed in Central and Eastern Europe, where human-induced fires have also taken part in forming the landscape. There is growing evidence that plant-derived smoke enhances seed germination, especially for species from fire-prone ecosystems, via the mechanisms of dormancy-breaking, germination stimulation or both. Hence, we hypothesized that smoke promotes seed germination for common milkweed by either or both mechanisms. To test this, germination responses of A. syriaca to the application of aqueous smoke solution (smoke-water) were studied in laboratory. Seeds were either cold stratified ( 7°C, 16 days) in tap water (TW), smoke-water (SW) or were not stratified at all, and then were germinated with SW or with TW (encompassing 5 treatments: 0—TW, 0—SW, TW—TW, TW—SW and SW—TW, where the first abbreviation indicates stratification, the second germination condition). In line with our hypothesis, the low (5%) germination of seeds was enhanced by cold stratification with SW at a greater extent (increasing to 52%) than by cold stratification with TW (25%), indicating that SW contributed to dormancy-breaking of seeds for A. syriaca. In contrast, SW did not stimulate germination when it was applied during the germination phase. To our best knowledge, this is the first study demonstrating smokeenhanced germination for common milkweed, which mechanism may help this species to successfully colonize new habitats after fire. As fire frequency is expected to increase in Europe with recent climate change, these results might contribute to a more efficient control of A. syriaca in areas threatened by its invasion.
Experiments were done to determine the effects of cold stratification (0, 20, 40, 60, 80 or 100 days), application of gibberelic acid (GA3) (0, 250, 500, 1000 or 2000 mg/l) and the combination (GA3 + stratification) on seed germination of black mulberry. Application of 1000 mg/l GA3 proved more effective than any of the other concentrations of GA3 applied. Seeds stratified for 100 days showed 88% germination. The combined treatment of 250 mg/l GA3 and 100 days of stratification yielded 96% germination of seeds. The relationships between GA3 concentration and seed germination (r = 0.93), and between stratification duration and seed germination (r = 0.91) of black mulberry were linear.
The most advantageous time for collecting fruits of the common hawthorn (Crataegus monogyna Jacq.) falls on October, when they are fully ripe. The stones extracted from the fruits must be dried at room temperature to the moisture content of about 10%. The dormancy of the common hawthorn seeds can be overcome by their stratification in a moist medium in one of the three thermal regimes: - 25°/3°C (16 weeks at 25°C followed by 15-18 weeks at 3°C, i.e. to the time when the first seedlings start to appear) - 20~30°/3°C (16 weeks at 20~30°C (16+8 hrs/day) followed by 15-18 weeks at 3°C, i.e. to the time when first seedlings start to appear) - 20~30°/3°C (16 weeks at 20~30°C (24+24 hrs) followed by 15-18 weeks at 3°C, i.e. to the time when first seedlings start to appear) Having been stratified, the seeds germinate vigorously (in 3-5 weeks) and at a high percentage at temperatures of 3~10°, 3~15°, 3~20° and 3~25°C, (16+8 hrs/day) and the seedlings emerge at 3~20°C (16+8 hrs/day) in 4-6 weeks. Storage for one year at -3°C in the case of the seeds dried after harvest to the moisture content of 10% does not reduce their germination capacity. Stones scarification in concentrated sulphuric acid for 120 minutes followed by stratification at 3°C has an adverse effect on seed emergence at the temperature 3~20°C (16+8 hrs/day). It is recommended that stratified seeds should be sown into the still cool soil at the end of March or the beginning of April, as the increased temperature induces the secondary dormancy in seeds.