Leaf senescence and grain filling affected by post-anthesis high temperatures in two different wheat cultivars

High temperature is a major factor affecting grain yield and plant senescence in wheat growing regions of central and east China. In this study, two different wheat cultivars, Yangmai 9 with low-grain protein concentration and Xuzhou 26 with high-grain protein concentration, were exposed to different temperature regimes in growth chambers during grain filling. Four day/night temperature regimes of 34°C/22°C, 32°C/24°C, 26°C/14°C, and 24°C/16°C were established to obtain two daily temperatures of 28 and 20°C, and two diurnal day/night temperature differences of 12 and 8°C. Concentration of a lipid peroxidation product malondialdehyde (MDA), activities of the antioxidants superoxide dismutase (SOD) and catalase (CAT), chlorophyll concentration (SPAD) in flag leaves and kernel weight were determined. Results show that activities of SOD and CAT in leaves increased markedly on 14 days after anthesis (DAA) for the high-temperature treatment (34°C/22°C) and then declined. As a result, MDA concentration in leaves increased significantly under high temperature (34°C/22°C and 32°C/24°C). Compared with optimum temperature treatment, high temperature reduced the concentration of soluble protein and SPAD values in flag leaves. Grain-filling rate increased slightly initially, but decreased significantly during late grain filling under high temperature. As a result, final grain weight was reduced markedly under high temperature. Decreases in the activities of SOD and CAT and increases in MDA concentration in leaves were more pronounced with a 12°C of day/night temperature difference when under high temperatures. Kernel weight was higher under 12°C of day/night temperature difference under optimum temperatures (24°C/16°C and 26°C/14°C). The responses to high-temperature regimes appeared to differ between the two wheat cultivars with different grain protein concentrations. It is concluded that a larger diurnal temperature difference hastened the senescence of flag leaves under high-temperature conditions, but retarded senescence under optimum temperature treatments of 26°C/14°C and 24°C/16°C.     

Recruitment and growth of the sea urchin Strongylocentrotus droebachiensis (Muller) following mass mortalities off Nova Scotia,Canada

Recruitment of Strongylocentrotus droebachiensis (Muller) was monitored for four successive years following a mass mortality of this species on a subtidal boulder bottom in St. Margaret's Bay, Nova Scotia. Recently recruited juveniles (1–2 mm diameter) were observed in the fall (September–November) between (1982) and (1984), but not in (1985). Juveniles grew to 6–8 mm diameter at 1-yr post-settlement and 19 mm diameter ((1983) cohort) at 2-yr post-settlement. Individuals > 18 mm diameter had macroscopic gonads in the spring of their third year and spawning probably occurred at 2.75-yr post-settlement. The growth rate of juveniles (3–6 mm initial diameter) maintained in cages with coralline-covered rocks was similar to that of the natural population. Growth and gonad index increased significantly when kelp (Laminaria longicruris (Pylaie)) was added to cages, suggesting that juveniles were food limited in St. Margaret's Bay. Despite an abundance of kelp and other fleshy algae, they remained cryptic under rocks and were not observed grazing on attached plants. The effects of temperature and food supply on juvenile growth and survival were examined in laboratory experiments using factorial designs. Recently-metamorphosed juveniles (from laboratory cultures), maintained at three temperature regimes (5°C, ambient, 16 °C) and two feeding regimes (no added food, coralline algae added), had similar growth rates (over 9 mth) among treatment combinations. However, growth was asymptotic at 16 °C and ambient temperatures, suggesting food limitation. Survival of these juveniles was higher in treatments with coralline algae, but survival was not affected by temperature. Field-collected juveniles (3–6 mm diameter), maintained at three temperature regimes (5°C, ambient, 16 °C) and three feeding regimes (no added food, coralline algae added, and kelp and coralline algae added), grew only in treatments with kelp added as food. In these treatments, growth rates increased with temperature. However, the growth curve at variable ambient temperature regimes was linear, suggesting seasonal acclimation. Survival of the field-collected juveniles was highest in treatments at 5 °C and/or with added kelp.     

The effect of temperature on leaf appearance and canopy establishment in fibre hemp (Cannabis sativa L.)

The effects of temperature on the development and growth of hemp (Cannabis sativa L.) have never been quantified. Therefore, to establish the effect of temperature on leaf appearance and canopy establishment of fibre hemp under controlled and field conditions, plants were grown in growth chambers at 11 regimes with average temperatures between 10°C and 28°C, and three cultivars were sown in the field in March, April and May in 1990, 1991 and 1992. In the field, thermal time (base 0°C) between sowing and emergence ranged from 68°Cd to 109.5°Cd (average 88.3°Cd). Rates of leaf appearance and stem elongation increased linearly with temperature between 10°C and 28°C. The base temperature for leaf appearance was 5.7°C from the growth chamber experiments and 1°C from the field experiments. In the field, the base temperature for the relationship between light interception by the canopy and thermal time was 2.5°C, and thermal time, calculated at the appropriate base temperature, accounted for about 98% of the variance in the number of leaves and for 98.6% of the variance in the proportion of light intercepted by the canopy. Days from emergence accounted for less of the variance in both parameters than thermal time. Interception of 90% of light was attained on average at 465°Cd (base 0°C) after emergence. It is concluded that thermal time is a simple and accurate tool to describe leaf appearance and light interception in fibre hemp.     

Daily Temperature Amplitude Affects the Vegetative Growth and Carbon Metabolism of Orange Trees in a Rootstock-Dependent Manner

Both instantaneous and average growth temperatures affect plant metabolism, and the physiological importance of daily variations in temperature is frequently underestimated. To improve our understanding of the environmental regulation of citrus trees, we hypothesized that vegetative growth would be stimulated in orange plants subjected to large daily temperature variations, even without changes in the average daily air temperature or the amount of energy given by degree-days. This hypothesis was tested with orange plants grafted onto Rangpur lime or Swingle citrumelo rootstocks and grown for 20?days under thermal regimes (day/night) of 25/25°C or 32.5/17.5°C. Such regimes imposed growth conditions with daily temperature variations of 0 and 15°C. Plant growth, photosynthesis, respiration, and carbohydrate availability in leaves, stems, and roots were measured under both thermal conditions. The daily temperature variation affected the carbon metabolism of young citrus trees; plants grown under daily variation of 15°C used more of the carbon stored in mature leaves and roots and the energy generated by respiration for the biosynthesis of vegetative structures, such as leaves and branches. Thus, there was a significant increase in the leaf area of plants subjected to high daily temperature variation. Current photosynthesis was similar in the two thermal regimes; however, the photosynthetic rates increased under the 15°C variation when measurements were normalized to 25°C. In addition to the stimulatory effect of the source?Csink relationship on photosynthesis, we suggest a probable involvement of hormonal regulation of plant growth through gibberellin metabolism. The rootstock affected the response of the canopy to daily temperature amplitude, with the Rangpur lime improving plant growth through higher carbohydrate availability in roots. This is the first report that highlights the importance of daily temperature variations for citrus growth and physiology under nonlimiting conditions.     

Alternating temperatures affect life table parameters of Phytoseiulus persimilis, Neoseiulus californicus (Acari: Phytoseiidae) and their prey Tetranychus urticae (Acari: Tetranychidae)

Increasing energy costs force glasshouse growers to switch to energy saving strategies. In the temperature integration approach, considerable daily temperature variations are allowed, which not only have an important influence on plant growth but also on the development rate of arthropods in the crop. Therefore, we examined the influence of two constant temperature regimes (15 °C/15 °C and 20 °C/20 °C) and one alternating temperature regime (20 °C/5 °C, with an average of 15 °C) on life table parameters of Phytoseiulus persimilis and Neoseiulus californicus and their target pest, the two-spotted spider mite Tetranychus urticae at a 16:8 (L:D) h photoperiod and 65 ± 5 % RH. For females of both predatory mites the alternating temperature regime resulted in a 25–30 % shorter developmental time as compared to the corresponding mean constant temperature regime of 15 °C/15 °C. The immature development of female spider mites was prolonged for 7 days at 15 °C/15 °C as compared to 20 °C/5 °C. With a daytime temperature of 20 °C, no differences in lifetime fecundity were observed between a nighttime temperature of 20 and 5 °C for P. persimilis and T. urticae. The two latter species did show a higher lifetime fecundity at 20 °C/5 °C than at 15 °C/15 °C, and their daily fecundity at the alternating regime was about 30 % higher than at the corresponding mean constant temperature. P. persimilis and T. urticae showed no differences in sex ratio between the three temperature regimes, whereas the proportion of N. californicus females at 15 °C/15 °C (54.2 %) was significantly lower than that at 20 °C/5 °C (69.4 %) and 20 °C/20 °C (67.2 %). Intrinsic rates of increase were higher at the alternating temperature than at the corresponding mean constant temperature for both pest and predators. Our results indicate that thermal responses of the studied phytoseiid predators to alternating temperature regimes used in energy saving strategies in glasshouse crops may have consequences for their efficacy in biological control programs.     

Low-temperature conditioning of the ice nucleation active bacterium,Erwinia herbicola

Rapid “low-temperature conditioning” and “solute conditioning” of the ice nucleation active bacterium Erwinia herbicola No. 26 are described. Conditioning is the process by which the ability to initiate ice at high temperatures is gained in these bacteria. The cumulative ice nucleator concentration, N[T], was used to measure the number of ice nucleators present in the bacterial systems. N[T] was determined at temperatures from −2 ° to −10 °C and was measured under varying conditioning temperature, time, and solute regimes. Values of N[T] increased rapidly on cooling samples from 30 to 5 °C. The optimum low temperature for conditioning was 5 °C. The conditioning process followed first-order reaction kinetics and time constants (1/rate constant) were between 43 and 62 min at 5 °C. Individual ice nucleators were isolated in droplets and were stable for at least 2 hr. Low-temperature conditioning did not occur when protein synthesis was inhibited by eliminating amino acids in the low-temperature conditioning media or by using the protein synthesis inhibitors chloramphenicol and streptomycin. Analysis of low-temperature conditioning, using heterogeneous ice nucleation theory predicted that ice nucleators are large and have diameters ranging from 80 Å (active at −8 °C) to 300 Å (active at −3 °C). In conclusion, it was predicted that conditioning resulted from growth of the nucleator from about 80 to 300 Å, from a change in the surface properties of 300 Å nucleator making it more similar to ice, or from a combination of these.     

Seed germination and seedling growth of Zostera marina L. (eelgrass) in the chesapeake bay

Seed germination and seedling growth of Zostera marina L. were monitored in the Chesapeake Bay in 1979 and 1980. Harvested seeds were placed in small acrylic tubes at several sites representing the salinity range of Z. marina distribution. Seed germination was observed first in late September and continued through May, with peaks in the fall and spring. The majority of seeds that germinated (66%) did so between December and March when water temperatures ranged from 0–10°C. There was no correlation between sites (different salinity regimes) and frequency of germination rates, indicating that salinity was not a major factor in the germination process in this study. Additional information on seed germination was available for seeds collected in 1977 and 1980 and subsequently monitored for germination at only one site. These data were similar to germination frequency recorded in 1979–1980.Seedling growth was measured from individuals collected from an existing Zostera marina bed. Seedlings were collected from November through May, at which time we could no longer distinguish seedlings from existing vegetative stock. Growth was characterized by the increased length of the primary shoot, number of leaves per shoot and numbers of shoots per plant. Seedling growth was slow during the winter months (water temperature ? 10°C) but rapidly increased in the spring (temperatures > 10°C). The size range of the harvested seedlings indicated that seed germination in the field probably occurred from October through April, corroborating evidence from the seed germination experiments.     

Influence of temperature and ethephon concentration on growth and composition of Cabernet Sauvignon grapevines

Potted Cabernet Sauvignon grapevines were acclimated to two different temperature regimes (25°C/15°C and 35°C/25°C day/night temperatures, respectively) until 100% bloom, when the vines were treated with either 0, 250, 500, or 750 ppm ethephon (Ethrel^®). Three days after ethephon application all vines were combined and held at 25°C/15°C in a phytotron room for 15 weeks. Growth was suppressed by a greater range of ethephon concentrations at the cool temperature, but effects were shorter-lived than at the high temperature. Generally, the 500 ppm treatment reduced vigor most effectively. The degree to which ethephon influences vine growth is mediated by temperature. Ethephon and temperature treatments caused significant differences in the concentrations of potassium, calcium, and magnesium in leaves.     

The temperature acclimation of photosynthetic responses to CO2 in Zea mays and its relationship to the activities of photosynthetic enzymes and the CO2-concentrating mechanism of C4 photosynthesis

Abstract Associations between photosynthetic responses to CO₂ at rate-saturating light and photosynthetic enzyme activities were compared for leaves of maize grown under constant air temperatures of 19, 25 and 31°C. Key photosynthetic enzymes analysed were ribulose bisphosphatc (RuBP) carboxylase, phosphoenolpyruvate (PEP) carboxylase, NADP-malic enzyme and pyruvate, P_i dikinasc. Rates of CO₂-saturated photosynthesis were similar in leaves developed at 19°C and 25°C but were decreased significantly by growth at 31°C. In contrast, carboxylation efficiency differed significantly between all three temperature regimes. Carboxylation efficiency was greatest in leaves developed at 19°C and decreased with increasing temperature during growth. The changes of carboxylation efficiency were highly correlated with changes in the activity of pyruvate, P_i dikinase (r= 0.95), but not with other photosynthetic enzyme activities. The activities of these latter enzymes, including that of RuBP carboxylase, were relatively insensitive to temperature during growth. The sensitivity of quantum yield to O₂ concentration was lower in leaves grown at 19°C than in leaves grown at 31°C. These observations support the novel hypothesis that variation in the capacity for CO₂ delivery to the bundle sheath by the C₄ cycle, relative to the capacity for net assimilation by the C₂ cycle, can be a principal determinant of C₄ photosynthetic responses to CO₂.     

Effects of constant and variable temperatures on development and reproduction of the two-spotted spider mite Tetranychus urticae (Acari: Tetranychidae)

We focused on the influence of different temperature amplitudes on development and reproduction of the two-spotted spider mite, Tetranychus urticae Koch, at a 16:8 (L:D) h photoperiod and 60–95 % RH. The temperature amplitudes varied from 0 to 24 °C in steps of 6 °C; i.e. 22 ± 0, 22 ± 3, 22 ± 6, 22 ± 9 and 22 ± 12 °C. Temperature changed every 24 h between a low and an upper value, but without changing the average temperature (22 °C). The number of eggs laid by five females for 24 h was slightly lower at 22 ± 12 °C than at constant temperature (22 ± 0 °C), and egg hatchability differed among the five temperature regimes. Developmental time at 22 ± 0 °C was shorter than that at 22 ± 3 and 22 ± 6 °C, but longer than that at 22 ± 9 and 22 ± 12 °C. The oviposition period, total fecundity per female and adult longevity gradually decreased with increasing amplitudes. Sex ratio was similar at all five temperature regimes. The intrinsic rate of natural increase (r _m) was affected by temperature amplitude and the r _m-values at all amplitudes except 22 ± 12 °C were higher than that at constant temperature. Thus, this study showed that variable temperature regimes influence population growth rates of T. urticae and that large amplitude regimes are stressful for this species.     

Effects of temperature on growth and efficiency of food utilization in fifth-instar caterpillars of the tobacco hornworm, Manduca sexta

Fifth-instar larvae of Manduca sexta were reared from hatching on artificial diet at 15, 20, 25, 30 and 35°C. Total development time decreased with increasing temperature. Very few larvae (12%) survived at 15°C, so this temperature was not considered further. There was some mortality at 30°C (11%), and at 35°C (50%).The absolute rate of growth in the fifth instar was faster at 25 than at 20°C, but was similar at 25, 30 and 35°C. This was true both for caterpillars that were chronically exposed to experimental temperatures (i.e. since hatching) and for those acutely exposed (i.e. reared up to fifth instar at 25°C).There was a progressive decrease with higher rearing temperatures in both the initial and final sizes of chronically exposed fifth-instar larvae. Acutely exposed caterpillars matched for initial size showed smaller temperature related differences in final size. Because of these size differences there were differences in relative growth rate which did not reflect true differences in absolute growth rate.Total food consumed by chronically exposed caterpillars was greatest at the lowest temperature (20°C), and decreased progressively with increasing temperature. The absolute rate of food consumption increased from 20 to 25°C, but did not vary significantly between 25 and 35°C. Differences in the sizes of the insects at the different temperatures meant that there were differences among relative measures of consumption that did not reflect absolute food consumption.For chronically exposed caterpillars, none of the three usual indices of food conversion efficiency (AD, ECI and ECD) varied significantly with temperature between 20 and 35°C. This implies that the effects of temperature on metabolic costs are closely matched to food consumption.Oxygen consumption increased with temperature between 20 and 25°C but was temperature compensated between 25 and 35°C.These findings are discussed in terms of their implications for the optimal temperature for growth in Manduca.     

Effects of temperature on growth and water relations of cacao (Theobroma cacao var.Comum) seedlings

Growth of 55-day-oldTheobroma cacao var.Comum seedlings varied with temperature regimes, various plant parts, growth parameters, and time of harvesting. Over a 60-day period the optimal day-temperature regimes were near 33.3°C for dry weight increase and relative growth rates of seedlings and leaves; 30.5°C for increase in leaf area, height growth, and leaf abscission; 22.2°C for dry weight increase of stems or roots, stem diameter growth, and root-shoot ratio. The rates of increase in dry weights of stems or roots as well as root-shoot ratios declined progressively at temperatures above 22.2°C Partitioning of dry matter was affected by temperature regime, with proportionally more photosynthate retained by shoots and less translocated to roots at high temperatures. The progressive decrease in the root-shoot ratio at temperatures above 22.2°C may decrease drought tolerance of seedlings because roots will be less capable of absorbing endugh water to replace transpirational losses. This was shown by more negative shoot water potentials at high temperatures. Research supported by the College of Agricultural and Life Science. University of Wisconsin, Madison, Wi, USA and the Centro de Pesquisas do Cacau (CEPLAC/CEPEC), 45600 Itabuna, Ba, Brazil.     

A review of the history of research and control of <Emphasis Type="Italic">Rhipicephalus</Emphasis> (<Emphasis Type="Italic">Boophilus</Emphasis>) <Emphasis Type="Italic">microplus</Emphasis>, babesiosis and anaplasmosis in Uruguay

The effect of five constant temperatures (16, 20, 24, 28 and 32 °C) on the development, survival and reproduction of Tetranychus cinnabarinus (Boisduval) [=?Tetranychus urticae Koch (red form)] fed on cassava leaves was examined in the laboratory at 85% relative humidity. Development time of various immature stages decreased with increasing temperature, with total egg-to-adult development time varying from 27.7 to 6.7 days. The lower thermal threshold for development was 10.8 °C and the thermal constant from egg to adult was 142.4 degree-days. Pre- and post-oviposition period and female longevity all decreased as temperature increased. The longest oviposition period was observed at 20 °C with 20.4 days. Under different temperatures, mated females laid, on average, 1.0, 2.9, 4.7, 4.7 and 4.9 eggs per day, respectively. The maximum fecundity (81.5 eggs per female) was at 28 °C and the intrinsic rate of increase (r _m ) was highest (0.25) at 32 °C. The results of this study indicate that T. cinnabarinus population could increase rapidly when cassava leaves serve as a food source. At the appropriate temperature T. cinnabarinus could seriously threaten growth of cassava.     

Host Range,Temperature Response,Survival, and Overwintering of Alternaria cirsinoxia

Alternaria cirsinoxia was evaluated for its host range, the influence of temperature on mycelial growth, and survival and overwintering on Canada thistle (Cirsium arvense) in Saskatchewan. With the exception of leafy spurge, the host range of A. cirsinoxia was limited to species within the Asteraceae. Canada thistle, safflower, and sunflower were most susceptible to A. cirsinoxia, the latter two being crop species of lesser importance in Saskatchewan. Mycelium of A. cirsinoxia grew best at a constant temperature of 25°C and in temperature cycles which alternated around a mean of 20–25°C. Mycelium did not grow when exposed to constant temperatures of 0, 40, or 45°C for 7 days. However, at 0°C, mycelium survived and was able to resume growth, whereas at 40 or 45°C, mycelium was killed. In the field, A. cirsinoxia produced viable conidia on senescent, basal Canada thistle leaves for at least 3–4 months after inoculation in 1998 and 1999. Sporulation tended to be higher in 1998 than in 1999, possibly favored by the warmer, drier, and sunnier conditions prevailing during July to mid-September in 1998. A. cirsinoxia also overwintered and produced viable conidia on infected Canada thistle leaves in the field, and at constant 4°C, when sampled from November 1998 until April 1999. Sporulation of leaves overwintering in the field was lowest in April 1999, probably due to inoculum degradation as a result of surface flooding in the plots. Clusters and chains of chlamydospores were abundant on overwintering leaf and stem debris of Canada thistle in field plots inoculated 10 months previously. A. cirsinoxia subsequently sporulated on this infected debris. Based on these host-range tests, the risks to major nontarget crop species in Saskatchewan should be minimal after the inundative application of A. cirsinoxia as a bioherbicide for Canada thistle. However, this pathogen appears able to persist and remain potentially infectious in the field for a prolonged period of time after inoculation. Hence, longevity and spread of A. cirsinoxia should be evaluated further to minimize the potential risks to susceptible minor crop species.     

Effects of temperature, feeding position and crop growth stage on the population dynamics of the rose grain aphid, Metopolophium dirhodum (Hemiptera: Aphididae)

The population dynamics of Metopolophium dirhodum were studied on winter wheat seedlings at constant (10°C, 15°C, 20°C, 25°C and 30°C) and fluctuating (12(night)-22(day)°C) temperatures, and during booting to early inflorescence, and anthesis to early milky ripe stage, at 19°C. The pre-reproductive development time was decreased by increasing the temperature from 10°C to 25°C. It was significantly shorter when the aphids were feeding during booting to early inflorescence than during anthesis to early milky ripe stage but was similar when the aphids were feeding on the flag, second or third leaves. The total number of nymphs produced/apterous adult was not significantly affected by temperature from 10°C to 25°C but adult reproductive lifespan was reduced by increasing temperature from 10°C and 12–22°C to 15°C, 20°C and 25°C. The daily intrinsic rate of increase changed from 0.11 to 0.25, and the cohort generation time decreased from 31 to 12 days, with increase of temperature from 10°C to 25°C. Reproductive rate was similar when the aphids were feeding on the flag, second or third leaves during booting to early inflorescence at 19°C. The reproductive rate was higher when the aphids fed from mid-inflorescence to mid-milky ripe stage than from mid-milky to early ripe stage. These results were compared with those from other studies. Predictions from a simulation model using development and reproductive rates from this study and literature were compared and the former rates resulted in a more accurate prediction of field observations in 1979, an outbreak year.     

Effects of temperature on infection of French bean leaves (Phaseolus vulgaris L.) by lucerne mosaic virus

The effect of temperature on the number of lesions and the time of their appearance was studied by inoculating French bean leaves (Phaseolus vulgaris L. cv. Perli?ka) with lucerne mosaic virus either 24 or 48 h before or, 24 or 48 h after they were exposed to various temperatures. The temperatures tested were 23, 25, 27, 30, 33 and 36° C. Before and after such exposures the plants were kept in a constant temperature of 25° C. By increasing the temperature before inoculation the number of lesions increased in comparison with the control. The optimal temperature for the maximum number of lesions is between 27° and 30° C. There is no significant difference between those experiments when the exposure time was 24 h or 48 h before inoculation. The same temperatures applied for 24 or 48 h after inoculation have a decreasing effect upon the number of lesions formed by LMV on French bean leaves. The decrease is 30 to 75%. In this case the first necrotic local lesions appeared 42 h after inoculation when exposed to higher temperatures above 27° C for 24 h, and 60 h after inoculation when exposed to these temperatures for 48 h. The shape of lesions varied a little in both cases as the pictures show.     

Seed germination at different temperatures and seedling emergence at different depths of Rhamnus spp

Rhamnus alaternus and R. ludovici-salvatoris, two Mediterranean shrubs with different geographic distributions, have shown important differences in seedling recruitment capacity. The objectives of this work were to determine the ability of these species to germinate seeds under different temperature ranges, as well as the capacity of seedlings to emerge from different burial depths, in order to better understand their regeneration processes. Two different experiments were performed. In the first one, seed germination was studied in Petri dishes and in the dark at different temperature regimes: a) 5–15°C, b) 10–20°C and c) 15–25°C (12h/12h). In the second experiment, seedling emergence capacity from different burial depths (0.5, 2 and 5 cm) was tested. R. ludovici-salvatoris showed a significantly higher final germination rates, a lower dormancy period, and average time response at 10–20°C than at other temperature ranges, although differences were much greater when seeds were subjected to the 5–15°C temperature regime. By contrast, R. alaternus did not show significant differences between treatments (5–15°C and 10–20°C) in germination behavior. Seedling emergence of both species was lower and slower when seeds were buried at 5 cm. However, R. ludovici-salvatoris always showed a lower seedling emergence capacity than R. alaternus at any burial depth. The low ability of R. ludovici-salvatoris to germinate seeds and emerge between 5–15°C, even from shallow depths, is discussed in relation to its low regeneration capacity and declining geographic distribution.     

Prolonging the hydration and active metabolism from light periods into nights substantially enhances lichen growth

This study investigates how hydration during light and dark periods influences growth in two epiphytic old forest lichens, the green algal Lobaria pulmonaria and the cyanobacterial L. scrobiculata. The lichens were cultivated in growth chambers for 14 days (200 μmol m^?1 s^?2; 12 h photoperiod) at four temperature regimes (25/20 °C, 21/16 °C, 13/8 °C, and 6/1 °C; day/night temperatures) and two hydration regimes (12 h day-time hydration; 12 h day-time + 12 h night-time hydration). Growth was highly dynamic, showing that short-term growth experiments in growth cabinets have a high, but largely unexplored potential in functional lichen studies. The highest measured growth rates were not far from the maximal dry matter gain estimated from published net photosynthetic CO₂ uptake data. For the entire data set, photobiont type, temperature, hydration regime and specific thallus mass accounted for 46.6 % of the variation in relative growth rate (RGR). Both species showed substantially higher relative growth rates based on both biomass (RGR) and thallus area (RT_AGR) when they were hydrated day and night compared to hydration in light only. Chronic photoinhibition was substantial in thalli hydrated only during the day time and kept at the highest and lowest temperature regimes, resulting in exponential increases in RGR with increasing maximal PSII efficiency (F _v/F _m) in both species. However, the depression in F _v/F _m was stronger for the cyanolichen than for the cephalolichen at extreme temperatures. The growth-stimulating effect of night-time hydration suggests that nocturnal metabolic activity improves recovery of photoinhibition and/or enhances the conversion rate of photosynthates into thallus extension.     

Temperature responses of tropical to warm temperateCladophora species in relation to their distribution in the North Atlantic Ocean

The relationship between distribution boundaries and temperature responses of some North AtlanticCladophora species (Chlorophyta) was experimentally examined under various regimes of temperature, light and daylength. Experimentally determined critical temperature intervals, in which survival, growth or reproduction was limited, were compared with annual temperature regimes (monthly means and extremes) at sites inside and outside distribution boundaries. The species tested belonged to two phytogeographic groups: (1) the tropical West Atlantic group (C. submarina: isolate from Curaçao) and (2) the amphiatlantic tropical to warm temperate group (C. prolifera: isolate from Corsica;C. coelothrix: isolates from Brittany and Curaçao; andC. laetevirens: isolates from deep and shallow water in Corsica and from Brittany). In accordance with distribution from tropical to warm temperate regions, each of the species grew well between 20–30°C and reproduction and growth were limited at and below 15°C. The upper survival limit in long days was <35°C in all species but high or maximum growth rates occurred at 30°C.C. prolifera, restricted to the tropical margins, had the most limited survival at 35°C. Experimental evidence suggests thatC. submarina is restricted to the Caribbean and excluded from the more northerly American mainland and Gulf of Mexico coasts by sporadic low winter temperatures in the nearshore waters, when cold northerly weather penetrates far south every few years. Experimental evidence suggests thatC. prolifera, C. coelothrix andC. laetevirens are restricted to their northern European boundaries by summer temperatures too low for sufficient growth and/or reproduction. Their progressively more northerly located boundaries were accounted for by differences in growth rates over the critical 10–15°C interval.C. prolifera andC. coelothrix are excluded or restricted in distribution on North Sea coasts by lethal winter temperatures, again differences in cold tolerance accounting for differences in their distribution patterns. On the American coast, species were probably restricted by lethal winter temperatures in the nearshore and, in some cases, by the absence of suitable hard substrates in the more equable offshore waters. Isolates from two points along the European coast (Brittany, Corsica) ofC. laetevirens showed no marked differences in their temperature tolerance but the Caribbean and European isolates ofC. coelothrix differed markedly in their tolerance to low temperatures, the lethal limit of the Caribbean isolate lying more than 5°C higher (at ca 5°C).     

Development rate,number of mature oocytes at emergence and adult size ofEncarsia tricolor at constant and variable temperatures

The duration of the development of the aphelinidEncarsia tricolor Föerster (a parasitoid of the aleyrodidTrialeurodes vaporariorum (Westwood), adult size and number of mature oocytes at emergence were determined under constant and variable temperature regimes. Females developed successfully from 14 to 32°C, but a 100% of pupal mortality was observed at 34°C. Males developed successfully from 16 to 28°C and they developed faster than females. Female and male, egg to adult development at constant temperatures ranged from 51.1 (14°C) to 14.3 (28°C) days and from 32.6 (16°C) to 11.8 (28°C) days, respectively. Predictions of the rate of development at variable temperatures were more accurate when made from 2nd and 3rd degree polynomials than from linear regressions. The number of mature oocytes at emergence ranged from 0.1 (30°C) to 2.2 (20°C). FemaleE. tricolor attained the greatest size at 20–24°C. The comparison with literature data shows thatE. tricolor develops faster thanT. vaporariorum at temperatures above 15°C.