Photosynthesis and respiration in bladelets of Ecklonia cava Kjellman (Laminariales, Phaeophyta) in two localities with different temperature conditions

Characteristics of photosynthesis and respiration of bladelets were compared between Ecklonia cava Kjellman sporophytes growing in a warmer temperate locality (Tei, Kochi Pref., southern Japan) and in a cooler temperate locality (Nabeta, Shizuoka Pref., central Japan). Photosynthesis and respiration were measured with a differential gas-volumeter (Productmeter). In photosynthesis-light curves at 20°C, the rate of net photosynthesis was almost the same at light intensities lower than 25 μmol m⁻² s⁻¹ and the light-saturation occurred at 200–400 μmol m⁻²s⁻¹ in plants of both localities. The light-saturated net photosynthetic rates were higher in winter and spring than in summer and autumn in both plants. The optimum temperature for net photosynthesis at 400 μmol m⁻²s⁻¹ was 27°C throughout the year in the Tei plant and 25–27°C in the Nabeta plant. The decrease of net photosynthetic rates in the supraoptimal temperature range up to 29°C was sharper in winter and spring than in summer and autumn in both plants, being smaller in the Tei plant than in the Nabeta plant in all seasons. The dark respiration rate always increased with water temperature rise in both plants. No clear differences were found in the dark respiration rate between Tei and Nabeta plants except that when measured against dry weight, the Tei plant showed a slightly lower rate as compared with the Nabeta plant.     

Growth of Ecklonia cava (Laminariales, Phaeophyta) sporophytes transplanted to a locality with different temperature conditions

Transplanting experiments were carried out to determine whether the small type sporophytes with short stipe of Ecklonia cava Kjellman (Laminariales, Phaeophyta) growing in a locality with warm temperatures, change into larger type with a long stipe when transplanted to a locality with cooler temperatures. Juvenile E. cava sporophytes, having a stipe shorter than 5 cm long were collected from Tei in Tosa Bay (southern Japan) (seawater temperature 15–29°C) and transplanted to Nabeta Bay (central Japan) (seawater temperature 13–25°C), where larger type E. cava sporophytes characterized by long stipe (ca 1 m) grow. They were attached to artificial reefs at the sea bottom (9 m depth) in Nabeta Bay to monitor their growth. For comparison, juvenile E. cava sporophytes of almost similar size growing in Nabeta Bay were also transplanted in the same way to the same experimental site. Observations of growth of sporophytes from Tei and Nabeta were carried out monthly for 2 years from November 1995 to October 1997. The transplanted Tei and Nabeta sporophytes showed an increase in stipe length and diameter from winter to spring, whereas almost no increase was observed during summer and autumn. At the end of the study period, the stipe of Nabeta sporophytes reached 25.6 cm in length and 17.0 mm in diameter, whereas that of Tei sporophytes reached 11.1 cm in length and 11.2 mm in diameter. The primary blade length was 16.0 cm in Nabeta sporophytes, whereas it was 5.5 cm in Tei sporophytes. Thus, Tei sporophytes still remained smaller than Nabeta sporophytes even under the same environmental conditions.     

Morphometric study of Ecklonia cava (Laminariales, Phaeophyta) sporophytes in two localities with different temperature conditions

Sporophytes of Ecklonia cava Kjellman (Laminariales, Phaeophyta) were collected seasonally from within 3–4 replicate, 1‐m² quadrates, haphazardly placed in dense assemblages at 6–9 m depth in Tei, Tosa Bay (southern Japan; water temperature 15–29°C) from 1995 to 1996, and in Nabeta Bay, Shimoda (central Japan; water temperature 13–25°C) from 1996 to 1997. Growth rings were checked for all samples and mean values of each biometric parameter of sporophytes 1‐year‐old and over were compared. The plant length (stipe length + primary blade length) was always shorter in Tei sporophytes (24–52 cm) than Nabeta sporophytes (70–100 cm), the difference being mainly owing to the shorter stipe length in Tei sporophytes (7–14 cm) than in Nabeta sporophytes (54–83 cm). However, the primary blade length was sometimes longer in Tei sporophytes (12–38 cm) than in Nabeta sporophytes (14–21 cm). Stipe diameter, longest bladelet length and primary blade width were mostly less in Tei sporophytes (8.6–12.4 mm, 5.5–7.0 cm and 23.4–38.0 cm, respectively) than Nabeta sporophytes (16.4–20.2 mm, 9.2–12.0 cm and 43.0–52.6 cm, respectively). Nevertheless, the number of bladelets of sporophytes from Tei (15–28) and Nabeta (18–29) were within the same range. At Tei, 32–43% of the sporophytes had wrinkled blades in summer and autumn, whereas wrinkled primary blades or bladelets were not observed in Nabeta sporophytes throughout the experimental period. These morphometric differences of E. cava between the two localities are suggested to be dependent on environmental factors, especially seawater temperature.     

The life cycle of Laminaria abyssalis (Laminariales,Phaeophyta) in culture

Laminaria abyssalis occurs in deep water in tropical latitudes of the Brazilian coast (19° 23 S, 38° 28 W to 22° 54 S, 42° 13 09 W). Its life cycle has been completed in the laboratory in seven months using different conditions of light and temperature. The gametophytic stage required for growth the low photon flux density of 1.2 ± 0.3 µmol m^–2 s^–1 and 18 °C, while the juvenile and adult sporophytes needed 15 µmol m^–2 s^–1 and 18 °C. The sporophytes became fertile at 23 °C. Our results showed that light and temperature are the main factors regulating the growth and life history of this species under the culture conditions tested.     

Growth and survival rates of large-type sporophytes of Ecklonia cava transplanted to a growth environment with small-type sporophytes

Stipe lengths of sporophytes of Ecklonia cava Kjellman have been reported to be longer along the southeast than southwest coast of the Izu Peninsula, central Japan. Two bays in this region that have natural populations of E. cava, but with different stipe lengths, were chosen for transplant experiments to examine if stipe length was an environmentally controlled trait. Transplant experiments were carried out in order to determine whether large-type sporophytes of E. cava with long stipes growing in Nabeta Bay (southeast Izu Peninsula, Japan) would turn into small-type sporophytes with short stipes when transplanted to Nakagi Bay (southwest Izu Peninsula). Ten juvenile sporophytes of E. cava (stipe length < 5 cm) were collected from Nabeta Bay (large-type habitat) and transplanted to Nakagi Bay (short-type habitat) in December 1995. As a transplant control, ten juvenile sporophytes of E. cava growing in Nakagi Bay were also transplanted to the same artificial reefs. Growth and survival rates of the sporophytes were monitored monthly for 3 y until December 1998. The transplanted sporophytes showed an increase in their stipe length and diameter from winter to spring, whereas almost no increase was observed from summer to autumn. However, the elongation was greater in Nabeta sporophytes than in Nakagi sporophytes. The primary blade length increased mainly from winter to early spring and decreased largely in autumn. Average primary blade lengths were similar in both Nabeta and Nakagi sporophytes from the end of the first year of transplanting. Although ca. 70% of both Nabeta and Nakagi sporophytes survived during the first 2 y after transplantation, no Nakagi sporophytes and only two Nabeta sporophytes survived to the end of the 3 y study period. Despite transplantation to Nakagi Bay, where short sitpes are naturally present, the sporophytes from Nabeta Bay persisted in having longer stipes, which suggests that stipe length is genetically, rather than environmentally, controlled.     

Phenology and photosynthetic activity in sterile and fertile sporophytes of Dryopteris filix-mas (L.) Schott

Summary This study describes the phenology of sporophytes of the fern Dryopteris filix-mas in relation to whole plant development. Sterile and fertile potted sporophytes were set out at an exposed site and the seasonal development of the fronds was measured from the commencement of unfolding, through the phase of increasing length, up to discoloration. The physiological activity of the fronds was determined by measuring photosynthetic gas exchange. The fronds of sterile sporophytes unfolded in April, about a week earlier than those of fertile plants, but the colour had already begun to turn in September and their life span was 1–2 months shorter. However, between mid-June and the end of August the sterile sporophytes put out several sets of new fronds: these overwintered without changing color and were still photosynthetically active in the following spring. All types of fronds were fully expanded 1–2 months from the beginning of unfolding and, with a natural supply of CO₂, had similar maximum net photosynthetic rates of 8–9 mol/m² · s. The decline in photosynthetic performance began before symptoms of senescence were visible and was due to decreased efficiency of the mesophyll. It is concluded that the phenology of D. filix-mas changes with transition from the sterile to the fertile phase. Whereas fertile sporophytes are genuinely summergreen, the sterile sporophytes with their summer fronds remain green throughout the winter and should therefore be termed semi-evergreen. The formation of overwintering summer shoots clearly extends the period of photosynthetic productivity of sterile sporophytes.     

SelectingRhizobium phaseoli strains for use with beans (Phaseolus vulgaris L.) in Kenya: Tolerance of high temperature and antibiotic resistance

Forty one strains ofRhizobium phaseoli were screened for the ability to multiply at high temperatures on yeast extract-mannitol agar. Most strains were tolerant of 30°C, eight strains were tolerant of 45°C and two of 47°C although the rate of multiplication was reduced at 45–47°C. The high temperature-tolerant strains were isolated from Kenyan soils and were fast-growing. Seven of the eight strains tolerant of 45–47°C lost their infectiveness after incubation at high temperature but four strains tolerant of 40°C remained infective after incubation at that temperature.Thirty six strains were resistant to 200 g ml^–1 streptomycin sulphate and 29 strains to 200 g ml^–1 spectinomycin dihydrochloride. Eight strains were resistant to both antibiotics each at 200 g ml^–1. Two of the double-labelled antibiotic-resistant mutants lost their infectiveness onPhaseolus vulgaris. The response to acidity was unaltered and two of the mutants showed a decrease in temperature tolerance. The doublelabelled mutants were recoverable from two Kenyan soils.     

Growth responses ofPterocladiella capillacea(Rhodophyta) in laboratory and outdoor cultivation

The growth and photosynthetic responses ofPterocladiella capillaceato NH₄, PO₄, CO₂-enrichment, pH, irradiance and temperature were evaluated for winter or summer plants cultivated under laboratory and outdoor settings. In the laboratory, using a gradient table, optimal growth temperature and irradiance for winter plants occurred at 10–20 °C and 100 mol photon m^–2s^–1, averaging 24.3% per week. The optimal growth conditions found for summer plants were 10–20 °C and 20 mol photon m^–2s^–1, averaging 29.0% per week. In a pH-stat cultivation system photosynthetic rates and growth rates were largely unaffected by pH in the range 6.5–8.5, however, they both decreased significantly above 8.5. In outdoor settings, using 40 L tanks,P. capillaceawas more responsive to the frequency the algae were fed with NH₄and PO₄rather than the relative concentrations of these nutrients. The average growth rates during winter were 28.3% and 12.5% per week when NH₄and PO₄were included once and twice a week for 24-h periods, respectively, while summer plants grew 15.0% and 25.3% per week at these nutrient regimes. Algae grown in seawater (containing 13.8 ± 1.8 M CO₂) or CO₂-enriched seawater (averaging 33.7 ± 13.2 M CO₂) had similar growth rates or even reduced productivity under CO₂-enrichment during winter. Concentrations of chlorophyllawere in average significantly higher in winter as compared to summer especially when nutrients were included twice a week. Phycoerythrin levels were also higher for plants fed with nutrients twice a week particularly during summer time. Although agar yields were limited and not seasonally dependent, this study shows high growth capacity forP. capillaceaas compared to previous investigations. Future mariculture prospective using current tank cultivation techniques for this species will likely depend on market demands for high quality agar.     

Growth and reproductive responses of Laminaria longicruris (Laminariales,Phaeophyta) to nutrient enrichment

A series of comparative culture experiments were conducted in order to determine responses of Laminaria longicruris male and female gametophytes and juvenile sporophytes to several temperatures (5, 10, 15, 20 °C), light levels (10, 35, 75 µmol m^–2 s^–1) and media nitrogen concentrations (0, 20, 100 µM ammonium-nitrogen). Responses were measured as numbers of male and female gametophytes producing gametangia and number of sporophytes produced following fertilization. Both male and female gametogenesis was reduced at 5 and 20 °C versus 10 and 15 °C. At 20 °C gametogenesis inhibition was greater with higher levels of ammonium-nitrogen concentration (100 µM). Sporophyte production was more sensitive to light, temperature and nitrogen concentration than gametogenesis. Production of sporophytes was inhibited completely at 20 °C. At lower temperatures, increasingly higher nutrient concentrations produced greater inhibition of production of sporophytes.     

Influence of krummholz mat microclimate on needle physiology and survival

Summary Microclimate and photosynthesis of krummholz mat growth forms of Picea engelmanii (Parry) and Abies lasiocarpa [Hook.] Nutt. were investigated to determine structural features which may aid survival in alpine environments. The structure of krummholz mats was described in terms of the vertical distribution of leaf area index and leaf area density, which exceeded 50 m^-1 (based on total leaf surface area) near the canopy surface and approached zero below 30 cm from the surface in both species. Photosynthetic photon flux density (PPFD, 0.4–0.7 m wavelengths) and wind decreased by an average of 6 and 50-fold, respectively, between 1 m above and 10 cm below mat surfaces in both species. Needle temperatures on a P. engelmannii krummholz mat during July averaged about 2°C above air temperature during the day, with a maximum overtemperature of greater than 20°C above T _air during one sunlit period. At night, needle temperatures averaged 3–4°C below T _air.Net photosynthesis in year-old P. engelmannii shoots reached a maximum at 15–20°C during July and August. Surface shoots were light saturated at near 1200 moles m^-2s^-1 PPFD, and had higher photosynthetic rates than subsurface, predominantly shaded shoots above 800 moles m^-2s^-1. Shade shoots had higher photosynthetic rates when PPFD was below 600 moles m^-2s^-1, and at 250 moles m^-2s^-1 shade shoots maintained about 50% of the net photosynthetic rate of sun shoots at light saturation. Shade shoots appeared capable of benefitting photosynthetically from elevated temperatures within krummholz mats despite relatively low light levels. Especially rapid photosynthesis may occur when canopy needles are illuminated by sunflecks and needle temperatures rise by 10° C or more.Snow cover appears crucial for the survival of needles during winter. Snow accumulated within krummholz needle canopies before the sub-canopy zone of unfoliated branches became filled. The concentrated needle growth in the krummholz canopy captured snow in early autumn without support from ground-level snowpack. Early snow cover in both species prevented cuticle abrasion and resulted in high winter needle water contents and viabilities for subsurface compared to surface needles which became abraded, severely dehydrated, and had high mortality between December and February, especially on windward sides of shoots.Extremely high concentrations of needles within krummholz mat canopies created an aerodynamic structure which elevated needle temperatures to more optimal photosynthetic levels in summer and resulted in more efficient snow accumulation in winter. These factors appear crucial for winter needle survival. Thus, krummholz mats appear to be an important adaptation in growth form which provides survival benefits in both summer and winter.     

Seasonal Dynamics of the Diatoms of the Genus Chaetoceros Ehrenberg in Amursky Bay (Sea of Japan)

The qualitative and quantitative composition of the Chaetoceros Ehr. species was studied in Amursky Bay (Sea of Japan) from January 1996 until May 1998. In all, 30 species, 1 variety, and 1 form of this genus were registered. The species Chaetoceros occurred in plankton throughout the year at a water temperature of –1.8–25°C and a salinity of 11–35. The numbers of Chaetoceros species varied between 100 and 1071000 cells/l, and the biomass varied between 0.9 × 10^–3 and 3.3 g/m³. The numbers were maximum in summer and minimum in the beginning of spring. The Chaetoceros species comprised 45–70 and 5–18% (winter), 68–98 and 65–95% (spring), 50% (summer), and 20% (autumn) of the total phytoplankton numbers and biomass. Six dominant species and 1 variety of Chaetoceros were found. Seasonal complexes formed by the Chaetoceros species were identified and described.     

The effect of seasonality on oxidative metabolism in Nacella (Patinigera) magellanica

We studied the seasonal variation on aerobic metabolism and the response of oxidative stress parameters in the digestive glands of the subpolar limpet Nacella (P.) magellanica. Sampling was carried out from July (winter) 2002 to July 2003 in Beagle Channel, Tierra del Fuego, Argentina. Whole animal respiration rates increased in early spring as the animals spawned and remained elevated throughout summer and fall (winter: 0.09 ± 0.02 μmol O₂ h^− 1 g^− 1; summer: 0.31 ± 0.06 μmol O₂ h^− 1 g^− 1). Oxidative stress was assessed at the hydrophilic level as the ascorbyl radical content / ascorbate content ratio (A / AH⁻). The A / AH⁻ ratio showed minimum values in winter (3.7 ± 0.2 10^− 5 AU) and increased in summer (18 ± 5 10^− 5 AU). A similar pattern was observed for lipid radical content (122 ± 29 pmol mg^− 1 fresh mass [FW] in winter and 314 ± 45 pmol mg^− 1 FW in summer), iron content (0.99 ± 0.07 and 2.7 ± 0.6 nmol mg^− 1 FW in winter and summer, respectively) and catalase activity (2.9 ± 0.2 and 7 ± 1 U mg^− 1 FW in winter and summer, respectively). Since nitrogen derived radicals are thought to be critically involved in oxidative metabolism in cells, nitric oxide content was measured and a significant difference in the content of the Fe–MGD–NO adduct in digestive glands from winter and summer animals was observed. Together, the data indicate that both oxygen and nitrogen radical generation rates in N. (P.) magellanica are strongly dependent on season.     

Seasonal variations in the immune system of the tench,Tinca tinca (Cyprinidae): proliferative response of lymphocytes induced by mitogens

The proliferation of tench lymphocytes induced by mitogens was studied during the four seasons of the year. Fish were maintained under natural conditions of photoperiod and temperature (mean ± SD: 12±2°C in winter, 22±3°C in spring, 30±3°C in summer and 21±3°C in autumn). Cultures were performed in vitro at 22°C in all seasons and the results were compared. Subsequently, in seasons with extreme water temperatures, cultures in vitro were performed at the same temperature as that of the water (12°C in winter and 30°C in summer) and the results were compared seasonally at the seasonal temperature, i.e. at 22°C in spring, 30°C in summer, 22°C in autumn and 12°C in winter. Phytohemagglutinin, concanavalin A, lipolisaccharide from E. coli and pokeweed mitogen were used as mitogens. Studies performed at 22°C as assay temperature in all seasons showed profound seasonal changes: while in spring, summer and autumn the mitogenic response of lymphocytes to phytohemagglutinin, concanavalin A, lipolisaccharide from E. coli and pokeweed mitogen was very low, during winter the results obtained were significantly higher. However, when the assays were performed at the corresponding seasonal temperature the differences were not as pronounced between the different seasons, and the mitogenic responses of lymphocytes were found to be the lowest during the winter and the highest during the summer with all mitogens used. This fact suggests that immunosuppression occurs in winter and an immunostimulation occurs in summer. However, the higher response found in winter when assaying at 22°C suggests that this property of lymphocytes needs an assay temperature higher than the in vivo temperature in order to observe accurate mitogenic responses.Abbreviations Con A concanavalin A - cpm counts per minute - LPS E. coli lipolisaccharide - MS222 tricainemethane sulphonate - PBS phosphate-buffered saline - PHA phytohemagglutinin - PWM pokeweed mitogen - SI stimulation index     

Life history and growth in culture of the endemic New Zealand kelp <Emphasis Type="Italic">Lessonia variegata</Emphasis> J. Agardh in response to differing regimes of temperature,photoperiod and light

Lessonia variegata J. Agardh (Laminariales, Phaeophyta) is endemic to New Zealand, where it occurs in subtidal kelp forests on wave exposed coasts in the North, South and Stewart Islands. This is the first account of the growth in culture and life history of L. variegata. Microscopic gametophytes alternate with macroscopic sporophytes, characteristic of members of the order Laminariales. The life history was completed in culture within 14 days under growth conditions of 12 °C, 12:12 (L:D) and 15 °C, 15:9 (L:D). Maximum growth of sporophytes occurred at 15 °C, 15:9, and slowest growth at 10 °C, 9:15. Under low light conditions (8–9 μmol photon m⁻² s⁻¹) filamentous growth of gametophytes predominated, and both the proportion of gametogenesis and the growth of sporophytes after 30 days was much reduced from equivalent cultures grown under conditions of higher light (16–17.5 μmol photon m⁻² s⁻¹). Interest in this species relates both to its potential for commercial utilisation as well as in the role it plays in coastal rocky reef ecosystems.     

Climatic adaptability of populations ofDiplotaxis erucoides D.C. (Brassicaceae) from Sicily,based on leaf morphology,leaf anatomy and δ13 C studies

The morphological and anatomical variability ofDiplotaxis erucoides populations from Sicily was investigated. Populations growing during the summer months exhibit distinct xeromorphic features. Leaf area is strongly reduced and leaf thickness is increased when compared with winter populations. Cell size, as well as cell arrangement and mesophyll cell surface area differ significantly between summer and winter populations. Leaf thickness is almost three times higher in summer populations andA (cell)/A, i.e. the mesophyll cell surface area per unit leaf area changes from about 16 for winter populations to almost 52 for summer populations. These differences are partly due to differences in intercellular volume and partly due to alterations in mesophyll cell sizes. The organic materal of the summer populations exhibits ¹³C values in the order of –27%. to –28%., while the corresponding values for the winter populations are in the order of –31%. to –33%.. Analysis ofD. erucoides populations from the transition period revealed intermediate ¹³C values. Anatomical variations such as reductions or increases ofA (cells)/A and changes of intercellular volume correlate with the corresponding ¹³C data. The ¹³C data are discussed in conjunction with the differences in leaf anatomy.     

Photosynthesis and growth rates of Laurencia brongniartii J. Agardh (Rhodophyta, Ceramiales) in preparation for cultivation

Laurencia brongniartii is usually found at depths below 4 m, but can be found in shallow subtidal areas in crevices and on the walls of a coral reef in Amami Oshima Island, Kagoshima Prefecture, Japan, where irradiances were significantly lower than those at similar depths in open water. In preparation for the possible cultivation of this species for its antibiotic compounds, the effects of temperature and irradiance on photosynthesis and growth were measured. Photosynthesis and growth rates of L. brongniartii explants were highest at 26 and 28 °C, which closely corresponded to temperatures found during August to late December when it was most abundant. The estimated maximum photosynthesis rate (P _max) was 4.41 mol photon m^–2 s^–1 at 26 °C and 4.07 mol photon m^–2 s^–1 at 28 °C. Saturating irradiance occurred at 95 mol photon m^–2 s^–1 at 26 °C and 65 mol photon m^–2 s^–1 at 28 °C. In contrast, growth experiments at 41.7 mol photon m^–2 s^–1 caused bleaching of explants and the maximum growth rate observed during the study was 3.02 ± 0.75% day^–1 at 28 °C and 25 mol photon m^–2 s^–1. The difference in the saturating irradiance for photosynthesis and the irradiance that caused bleaching in growth experiments suggests that long-term exposure to high irradiance was detrimental and should be addressed before the initiation of large scale cultivation.     

Year-class strength regulation in plaice (Pleuronectes platessa L.) on the Swedish west coast

Year-class strength of plaice (Pleuronectes platessa) has been studied over periods of 10 and 35 years, respectively, in two shallow sandy areas on the Swedish west coast. In one area, Gullmar Bay (N 58 ° 19 – W 11 ° 33), 0-group plaice were sampled quantitatively with a drop trap at 0–0.7 m depth and densities between 0.2 and 3.8 ind./m² were recorded in early summer. In the other area, Laholm Bay (N 56 ° 30 – W 12 ° 55), 0-group plaice were sampled semi-quantitatively in August with young-fish trawl at 1.5 m depths. Densities between 0.001 and 0.28 ind./m² were assessed.The effects of temperature and wind (in the winter and early spring) and predation (in early summer), on the recruitment of 0-group plaice were investigated. In Gullmar Bay high recruitment occurred after severe winters and in years when on-shore winds dominated during spring. No such correlations were found in Laholm Bay. In Gullmar Bay a significant inverse relationship was found between the density of O-group plaice in early summer and the biomass of brown shrimp (Crangon crangon) and the shore crab (Carcinus maenas), the main predators in the nursery area.The importance of physical and biological factors regulating recruitment in plaice are discussed.     

Contribution of fern gametophytes to the growth of produced sporophytes on the basis of carbon gain

Sporophytes appeared on most gametophytes of Thelypteris palustris (Salisb.) Schott that reached a certain size, which is interpreted to be a critical size of gametophytes for the production of sporophytes. After sporophytes were produced, attached gametophytes ceased dry weight growth, but the gametophytes which did not produce sporophytes grew successively. It was hypothesized that matter produced by gametophytes was being supplied to young sporophytes. Photosynthesis and respiration of gametophytes with attached sporophytes were not significantly different from that of gametophytes without sporophytes. Photosynthetic activity of gametophytes dropped from 0.18 to 0.03 mol CO₂ g^–1 s^–1 during the growth period. The higher photosynthetic rates of gametophytes in the early growth stage were important for reaching the critical size for sporophyte production in a short time. Sporophytes in the one leaf stage averaged 0.14 mol CO₂ g^–1 s^–1 of photosynthetic activity. The results show that sporophytes that had expanded the first leaf grow by their own photosynthetic production. Gametophytes allocated the photosynthate for sporophytes and it was an important aid before the one-leaf stage. The supportive role of gametophytes ended at that stage.     

Coexistence of Tetranychus urticae (Acarina: Tetranychidae) with different capacities for diapause: comparative life-history traits

Summary Individuals of the two-spotted spider mite, Tetranychus urticae Koch (Acarina: Tetranychidae), with and without a capacity for diapause, coexist in central Japan. Diapause appears to be adaptive because females in diapause suffered less mortality than non-diapausing individuals when frozen at –24°C for more than 4 h. However non-diapausing females showed good survival up to 4 h of freezing. Active non-diapausing mites survived on rose leaves in Kyoto (35°N) throughout the winters of 1988–1989 and 1989–1990. Cultures of mites with low (LD) and high (HD) diapause capacities at 18°C and 9L-15D photoperiod were successfully selected from the rose population and from a population on chrysanthemum in Nara (34.4°N). Their life-history traits at 15, 20, 25 and 30°C were characterized. HD and LD mites from both populations were of similar ages at first reproduction at 15–30° C. However, at temperatures 20° C, HD individuals produced more eggs than LD individuals, resulting in higher fecundity and intrinsic rate of natural increase. These traits allow HD individuals, which stop breeding between October and April, to increase faster in summer than LD individuals. This provides a mechanism, together with climatic fluctuations, in maintaining the coexistence of diapausing and non-diapausing T. urticae in Kyoto where winter conditions are rarely lethal to the non-diapausing individuals.     

Effects of pre-storage conditions on storage of in vitro cultures of Nephrolepis exaltata (L.) Schott and Cordyline fruticosa (L.) A. Chev.

In vitro cultures of Nephrolepis exaltata and Cordyline fruticosa were stored at 5°, 9° or 13°C, at a low irradiance (3–5 mol m^–2 s^–1) or in darkness. Prior to storage the cultures were subjected to 18°, 21°, 24° or 27°C and 15, 30 or 45 mol m^–2 s^–1 in a factorial combination.The optimal storage conditions for Nephrolepis were 9°C in complete darkness. These cultures were still transferable to a peat/perlite mixture at the end of the experimental period of 36 months.The optimal storage conditions for Cordyline were 13°C and a low light level (±3–5 mol m^-2 s^-1). When the pre-storage conditions were normal growth room conditions (24°C and 30 mol m^-2 s^-1), in vitro cultures could be stored for 18 months. With the most favourable pre-storage treatment (18°C and 15 mol m^-2 s^-1) some cultures still had green shoots after 36 months of storage, but did not survive transfer to peat/perlite.Pre-conditioning before storage was most favourable for Nephrolepis, and not that important, but still favourable, for Cordyline. There was an interaction between pre-storage temperature and pre-storage irradiance. For both species a high irradiance level was less favourable than a low irradiance level when combined with high growth room temperatures.Abbreviations BA 6-benzyladenine - IAA indole-3-acetic acid - NOA 2-naphthoxyacetic acid