Growth Temperature Responses Research Articles

The intra-annual rhythm of Pinus sylvestris growth-climate responses under a warming climate at its southern distribution limits

Warming climate has posed a pressing threat on boreal forests and an improved understanding of the intra-annual pattern of climatic influences on the tree growth can help interpret the response of boreal forest to climate change. Here, we systematically examined the growth-climate relationship, cambium phenology, and xylem cell dynamics of Pinus sylvestris (PS) to disentangle its intra-annual growth rhythm to external drivers and internal physiological process at its southern distribution limits across Eurasia. We showed the intra-annual rhythm of PS to temperature and precipitation is anti-phase and synchronous at its southern limits. Temperature had both promoting and inhibiting effects on PS growth over growing season where the growth-temperature response gradually changed from positive in winter-early spring to negative in late spring-summer, and then returned to positive in autumn. Precipitation enhanced PS growth in late spring-summer. Temperature dominated the intra-annual growth-climate response rhythm, and the response shifted to negative when temperature reached 13.72 °C in spring-summer and shifted to positive when temperature reached 17.41 °C in summer-autumn in Shenyang, respectively. A high water demand for the rapid earlywood cell formation in spring-summer and heat requirement for cambial cell division in summer-autumn caused the shifts in growth-temperature response, respectively. Climatic warming advances and prolongs the time of summer water availability that limits PS growth at its southern distribution limits and thus warming climate may pose a greater threat to the southern population of PS.

Reassessment of growth-climate relations indicates the potential for decline across Eurasian boreal larch forests

Larch, a widely distributed tree in boreal Eurasia, is experiencing rapid warming across much of its distribution. A comprehensive assessment of growth on warming is needed to comprehend the potential impact of climate change. Most studies, relying on rigid calendar-based temperature series, have detected monotonic responses at the margins of boreal Eurasia, but not across the region. Here, we developed a method for constructing temporally flexible and physiologically relevant temperature series to reassess growth-temperature relations of larch across boreal Eurasia. Our method appears more effective in assessing the impact of warming on growth than previous methods. Our approach indicates widespread and spatially heterogeneous growth-temperature responses that are driven by local climate. Models quantifying these results project that the negative responses of growth to temperature will spread northward and upward throughout this century. If true, the risks of warming to boreal Eurasia could be more widespread than conveyed from previous works.

Insights into the potential host range ofPhytophthora foliorum

AbstractDuring a survey forPhytophthora ramorumundertaken in north‐west Scotland in early 2016,Phytophthora foliorumwas found infecting foliage of the invasive shrubRhododendron ponticum. Prior to this,P. foliorumhad only been reported from foliage of hybrid azaleas in nurseries in California and Tennessee and from azalea plants in an ornamental nursery in Spain. No other hosts were known, and much of the behaviour ofP. foliorumremained enigmatic. The species is classified inPhytophthoraClade 8c, with closest relatives,P. ramorumandPhytophthora lateralis, both of which are highly damaging tree pathogens. To explore the threat thatP. foliorummight pose to trees, its growth–temperature responses on agar media and ability to cause lesions in the living bark of various hosts were contrasted with the behaviours ofP. ramorumandP. lateralis.Phytophthora foliorumproved faster growing and more tolerant of temperature extremes than the otherPhytophthoraspecies. Comparisons of bark colonization initially focussed onR. ponticumand larch speciesLarix deciduaandLarix kaempferias all three are significant hosts ofP. ramorumin the UK. Further experiments included anotherP. ramorumhost,Fagus sylvatica(European beech), and the main host ofP. lateralis,Chamaecyparis lawsoniana(Lawson cypress). Findings suggested that as well as being a significant pathogen ofR. ponticum, damage caused byP. foliorumto both species of larch and beech was very similar to that of the EU1 lineage ofP. ramorum, although growth in host tissue was also influenced by season.

Adaptation of soil microbial growth to temperature: Using a tropical elevation gradient to predict future changes.

Terrestrial biogeochemical feedbacks to the climate are strongly modulated by the temperature response of soil microorganisms. Tropical forests, in particular, exert a major influence on global climate because they are the most productive terrestrial ecosystem. We used an elevation gradient across tropical forest in the Andes (a gradient of 20°C mean annual temperature, MAT), to test whether soil bacterial and fungal community growth responses are adapted to long‐term temperature differences. We evaluated the temperature dependency of soil bacterial and fungal growth using the leucine‐ and acetate‐incorporation methods, respectively, and determined indices for the temperature response of growth: Q 10 (temperature sensitivity over a given 10oC range) and T min (the minimum temperature for growth). For both bacterial and fungal communities, increased MAT (decreased elevation) resulted in increases in Q 10 and T min of growth. Across a MAT range from 6°C to 26°C, the Q 10 and T min varied for bacterial growth (Q 10–20 = 2.4 to 3.5; T min = −8°C to −1.5°C) and fungal growth (Q 10–20 = 2.6 to 3.6; T min = −6°C to −1°C). Thus, bacteria and fungi did not differ significantly in their growth temperature responses with changes in MAT. Our findings indicate that across natural temperature gradients, each increase in MAT by 1°C results in increases in T min of microbial growth by approximately 0.3°C and Q 10–20 by 0.05, consistent with long‐term temperature adaptation of soil microbial communities. A 2°C warming would increase microbial activity across a MAT gradient of 6°C to 26°C by 28% to 15%, respectively, and temperature adaptation of microbial communities would further increase activity by 1.2% to 0.3%. The impact of warming on microbial activity, and the related impact on soil carbon cycling, is thus greater in regions with lower MAT. These results can be used to predict future changes in the temperature response of microbial activity over different levels of warming and over large temperature ranges, extending to tropical regions.

Simulating Effects of Variable Stoichiometry and Temperature on Mixotrophy in the Harmful Dinoflagellate Karlodinium veneficum

Results from a dynamic mathematical model are presented simulating the growth of the harmful algal bloom (HAB) mixotrophic dinoflagellate Karlodinium veneficum and its algal prey, Rhodomonas salina. The model describes carbon-nitrogen-phosphorus-based interactions within the mixotroph, interlinking autotrophic and phagotrophic nutrition. The model was tuned to experimental data from these species grown under autotrophic conditions and in mixed batch cultures in which nitrogen:phosphorus stoichiometry (input molar N:P of 4, 16, and 32) of both predator and prey varied. A good fit was attained to all experimentally derived carbon biomass data. The potential effects of temperature and nutrient changes on promoting growth of prey and thus K. veneficum bloom formation were explored using this simulation platform. The simulated biomass of K. veneficum was highest when they were functioning as mixotrophs and when they consumed prey under elevated N:P conditions. The scenarios under low N:P responded differently, with simulations showing larger deviation between mixotrophic and autotrophic growth, depending on temperature. When inorganic nutrients were in balanced proportions, lower biomass of the mixotroph was attained at all temperatures in the simulations, suggesting that natural systems might be more resilient against Karlodinium HAB development in warming conditions if nutrients were available in balanced proportions. These simulations underscore the need for models of HAB dynamics to include consideration of prey; modeling HAB as autotrophs is insufficient. The simulations also imply that warmer, wetter springs that may bring more N with lower N:P, such as predicted under climate change scenarios for Chesapeake Bay, may be more conducive to development of these HABs. Prey availability may also increase with temperature due to differential growth temperature responses of K. veneficum and its prey.

Temperature response of growth of larval dragonflies – an overview

We review the knowledge about the thermal reaction norms of larval growth in Odonata with a focus on the temperature response function. We re-analyze literature data and present our own results on growth rates of larvae of 14 species of Libellulidae reared at different temperatures. Temperature response curves (TRC) were fitted in order to estimate two relevant components of the thermal reaction, namely the optimum temperature for growth (Topt) and the increase of growth rate with temperature (Q10). We also examined what is known about the thermal minimum (Tmin) and the thermal maximum (Tmax) for growth to delimit the thermal ranges of odonates. All information indicates that larval growth is generally warm adapted, with species-specific variation of Topt of 21–31°C, Tmin of 8–12°C, and Tmax of up to 44°C (the latter being the upper lethal limit, the true Tmax for growth remains unknown). The values of Q10 distinguish some more specialized species, mostly with high Topt and of tropical origin, and others ...

Calorespirometry as a tool for studying temperature response in carrot (Daucus carota L.)

Calorespirometric measurements of metabolic heat rates and CO2 emission rates of respiring tissues as functions of temperature enable rapid determination of the temperatures that plants are adapted to without growing them in different environmental temperatures. However, the correct choice of target material for measurements that enable prediction of growth temperature responses is crucial, and needs to be identified in a species‐ and trait‐specific manner. In this study, different carrot materials were tested: a primary culture system proposed as an in vitro test system for carrot yield potential, taproots of young plants, and the root meristem of actively growing plants during secondary root growth. The central root meristem is the most suitable for studying temperature response by calorespirometry for genotype comparison. Calorespirometric methods for predicting genotype‐specific temperature responses of crop plant cultivars can be used to predict productivity in environments with differing temperature conditions.

Pseudomonas syringae pv. aesculi: foliar infection of Aesculus species and temperature–growth relationships

SummarySince 2001, the incidence of bleeding canker of horse chestnut (Aesculus hippocastanum) has increased markedly in western Europe. The causal agent, the bacterium Pseudomonas syringae pv. aesculi, originally isolated from foliar lesions on Indian horse chestnut (Aesculus indica) in India, is a bark killing pathogen on A. hippocastanum. In this study, P. syringae pv. aesculi was found as a foliar epiphyte on both A. hippocastanum and A. indica trees growing in the UK. When Aesculus leaves were challenged with cell suspensions (109 CFU ml−1) of Pseudomonas syringae pv. aesculi, a high level of asymptomatic infection occurred in all the species tested. The degree of re‐isolation of the bacterium after surface sterilization of leaves ranged from 33% (A. pavia) to 84 and 97% for A. hippocastanum and A. chinensis, respectively. The studies suggest both epiphytic and intrafoliar populations of P. syringae pv. aesculi could play a role in the incidence and spread of bleeding canker of horse chestnut. Growth–temperature responses of P. syringae pv. aesculi indicated a minimum of approximately −4°C and a maximum of approximately 35°C, with an optimum of approximately 25°C. These findings show that P. syringae pv. aesculi is not restricted to bark lesions but is likely to be widespread in the environment. It is also capable of causing foliar infection of several Aesculus species and could persist under extremes of weather in the UK.

Temperature responses of growth, photosynthesis, fatty acid and nitrate reductase in Antarctic and temperate Stichococcus

Stichococcus, a genus of green algae, distributes in ice-free areas throughout Antarctica. To understand adaptive strategies of Stichococcus to permanently cold environments, the physiological responses to temperature of two psychrotolerants, S. bacillaris NJ-10 and S. minutus NJ-17, isolated from rock surfaces in Antarctica were compared with that of one temperate S. bacillaris FACHB753. Two Antarctic Stichococcus strains grew at temperature from 4 to 25°C, while the temperate strain could grow above 30°C but could not survive at 4°C. The photosynthetic activity of FACHB753 at lower than 10°C was less than that of Antarctic algae. Nitrate reductase in NJ-10 and NJ-17 had its optimal temperature at 20°C, in comparison, the maximal activity of nitrate reductase in FACHB753 was found at 25°C. When cultured at 4-15°C a large portion of unsaturated fatty acids in the two Antarctic species was detected and the regulation of the degree of unsaturation of fatty acids by temperature was observed only above 15°C, though the content of the major unsaturated fatty acid αC18:3 in FACHB753 decreased with the temperatures elevated from 10 to 25°C. Elevated nitrate reductase activity and photosynthetic rates at low temperatures together with the high proportion of unsaturated fatty acids contribute to the ability of the Antarctic Stichococcus to thrive.

Isolation and characterization of Bacillus thuringiensis from soils in contrasting agroecological zones of Ethiopia

Phenotypic and molecular methods were used to isolate and characterize B. thuringiensis from diverse agro-ecological zones of Ethiopia. Bioassays were used to test the insecticidal activity of B. thuringiensis strains against the major malaria vector, Anopheles arabiensis (Diptera). B. thuringiensis were isolated from 32% of the total 503 soil samples collected from the 16 agro-ecological zones. All sequenced isolates were 99%–100% identical to each other and to B. thuringiensis entries in Genbank. B. thuringiensis with similar 16S rRNA gene sequences from these different zones were characterized with regard to maximum growth rate and temperature optima for growth to test if there was local adaptation in these functional traits. The result showed a narrow temperature range around 30°C for maximal growth rate, and there were no significant differences between agro-ecological zones. Of 110 Bacillus thuringiensis isolates analyzed for the presence of crystal protein genes, 7 tested positive for cry 4, cry 11, and cyt toxin genes. Sequencing of these genes in positive strains demonstrated 99–100 % homology to known mosquitocidal cry and cyt genes in Bacillus thuringiensis subsp. israelensis. The present study shows that this biotechnologically important species is wide spread in Ethiopian soils and that it does not demonstrate local adaptation to temperature regimes, at least not for basic functions such as growth-temperature response. Our finding also pointed the potential for exploiting this species in vector control programs.

Growth Temperature Exerts Differential Physiological and Transcriptional Responses in Laboratory and Wine Strains of Saccharomyces cerevisiae

Laboratory strains of Saccharomyces cerevisiae have been widely used as a model for studying eukaryotic cells and mapping the molecular mechanisms of many different human diseases. Industrial wine yeasts, on the other hand, have been selected on the basis of their adaptation to stringent environmental conditions and the organoleptic properties that they confer to wine. Here, we used a two-factor design to study the responses of a standard laboratory strain, CEN.PK113-7D, and an industrial wine yeast strain, EC1118, to growth temperatures of 15 degrees C and 30 degrees C in nitrogen-limited, anaerobic, steady-state chemostat cultures. Physiological characterization revealed that the growth temperature strongly impacted the biomass yield of both strains. Moreover, we found that the wine yeast was better adapted to mobilizing resources for biomass production and that the laboratory yeast exhibited higher fermentation rates. To elucidate mechanistic differences controlling the growth temperature response and underlying adaptive mechanisms between the strains, DNA microarrays and targeted metabolome analysis were used. We identified 1,007 temperature-dependent genes and 473 strain-dependent genes. The transcriptional response was used to identify highly correlated gene expression subnetworks within yeast metabolism. We showed that temperature differences most strongly affect nitrogen metabolism and the heat shock response. A lack of stress response element-mediated gene induction, coupled with reduced trehalose levels, indicated that there was a decreased general stress response at 15 degrees C compared to that at 30 degrees C. Differential responses among strains were centered on sugar uptake, nitrogen metabolism, and expression of genes related to organoleptic properties. Our study provides global insight into how growth temperature affects differential physiological and transcriptional responses in laboratory and wine strains of S. cerevisiae.

Temperature responses of growth and wood anatomy in European beech saplings grown in different carbon dioxide concentrations

Effects of temperature on growth and wood anatomy were studied in young European beech (Fagus sylvatica L.) grown in 7-l pots for 2.5 years in field-phytotron chambers supplied with an ambient (approximately 400 micromol mol-1) or elevated (approximately 700 micromol mol-1) carbon dioxide concentration ([CO2]). Temperatures in the chambers ranged in increments of 2 degrees C from -4 degrees C to +4 degrees C relative to the long-term mean monthly (day and night) air temperature in Berlin-Dahlem. Soil was not fertilized and soil water and air humidity were kept constant. Data were evaluated by regression analysis. At final harvest, stem diameter was significantly greater at increased temperature (Delta1 degrees C: 2.4%), stems were taller (Delta1 degrees C: 8.5%) and stem mass tree-1 (Delta1 degrees C: 10.9%) and leaf area tree-1(Delta1 degrees C: 6.5%) were greater. Allocation pattern was slightly influenced by temperature: leaf mass ratio and leaf area ratio decreased with increasing temperature (Delta1 degrees C: 2.3% and 2.2% respectively), whereas stem mass/total mass increased (Delta1 degrees C: 2.1%). Elevated [CO2] enhanced height growth by 8.8% and decreased coarse root mass/total mass by 10.3% and root/shoot ratio by 11.7%. Additional carbon was mainly invested in aboveground growth. At final harvest a synergistic interaction between elevated [CO2] and temperature yielded trees that were 3.2% taller at -4 degrees C and 12.7% taller at +4 degrees C than trees in ambient [CO2]. After 2.5 seasons, cross-sectional area of the oldest stem part was approximately 32% greater in the +4 degrees C treatment than in the -4 degrees C treatment, and in the last year approximately 67% more leaf area/unit tree ring area was produced in the highest temperature regime compared with the lowest. Elevated [CO2] decreased mean vessel area of the 120 largest vessels per mm2 by 5.8%, causing a decrease in water conducting capacity. There was a positive interaction between temperature and elevated [CO2] for relative vessel area, which was approximately 38% higher at +4 degrees C than at -4 degrees C in elevated [CO2] compared with ambient [CO2]. Overall, temperature had a greater effect on growth than [CO2], but elevated [CO2] caused quantitative changes in wood anatomy.

Temperature responses of growth, photosynthesis, respiration and NADH: nitrate reductase in cryophilic and mesophilic algae.

• Temperature effects on growth, photosynthesis, respiration and nitrate reductase (NR) were studied in the cryophilic algae Koliella antarctica and 'Chlorella'saccharophila, and in the mesophilic Chlorella sorokiniana. • Growth rate was measured as increase in optical density. Photosynthesis at saturating light and respiration in darkness were measured as O2 exchange. NADH: NR was assayed in crude extracts. • The two cryophilic algae grew below 15°C, and C.sorokiniana above 20°C. Photosynthetic and respiration rates of K.antarctica and 'C.'saccharophila were elevated at 5°C, and peaked at 30°C. Arrhenius plots from 5 to 25°C were linear in K.antarctica, whereas in 'C.'saccharophila and C.sorokiniana they exhibited breaks at 15 and 20°C, respectively. Values for activation energy (Ea ) and the factor by which the rate increases with raising the temperature 10°C (Q10 ) differed. Nitrate reductase had its optimum at 25°C in cryophilic algae and at 35°C in C.sorokiniana. • We conclude that growth of cryophilic algae at low temperature is favoured by elevated photosynthesis and respiration rates, but that it could be limited by a high respiration:photosynthesis ratio.

No whirlwind romance: typhoons, temperature and the failure of reproduction in Caulacanthus okamurae (Gigartinales, Rhodophyta)

The red alga Caulacanthus okamurae Yamada occurs commonly on the coasts of South Korea, but reproductive plants have rarely been found in the field. Seasonality of field populations was examined and the temperature responses of growth and reproduction were determined in laboratory cultures. In the field, monthly average temperatures of surface seawater ranged from 12·7°C±0·73 (SD) to 21°C±1·19. Monthly mean biomass in 25×25 cm quadrats (n=3) ranged from 11·2±9·6 g m−2 (SD) to 148·8±19·2 g m−2 in wet weight with minimal biomass in February 1995 and maximal values in August. In culture, the growth of vegetative plants and germination of tetraspores of C. okamurae occurred at temperatures from 13 to 27°C. Tetrasporangia, gametangia and cystocarps were formed at 19°C and above, but not at 13 or 16°C, indicating that reproduction is directly affected by seawater temperature. On the basis of these data, seawater temperature was above the critical temperature for reproduction from August to October (20–21°C) yet...

No whirlwind romance: typhoons, temperature and the failure of reproduction in Caulacanthus okamurae (Gigartinales, Rhodophyta)

The red alga Caulacanthus okamurae Yamada occurs commonly on the coasts of South Korea, but reproductive plants have rarely been found in the field. Seasonality of field populations was examined and the temperature responses of growth and reproduction were determined in laboratory cultures. In the field, monthly average temperatures of surface seawater ranged from 12·7°C±0·73 (SD) to 21°C±1·19. Monthly mean biomass in 25×25 cm quadrats (n=3) ranged from 11·2±9·6 g m−2 (SD) to 148·8±19·2 g m−2 in wet weight with minimal biomass in February 1995 and maximal values in August. In culture, the growth of vegetative plants and germination of tetraspores of C. okamurae occurred at temperatures from 13 to 27°C. Tetrasporangia, gametangia and cystocarps were formed at 19°C and above, but not at 13 or 16°C, indicating that reproduction is directly affected by seawater temperature. On the basis of these data, seawater temperature was above the critical temperature for reproduction from August to October (20–21°C) yet only three plants with tetrasporangial branches were found in the field. In September the biomass of C. okamurae declined sharply following severe storm damage. Thus, the absence of reproductive organs in field populations of C. okamurae may occur because they inhabit a seasonally stressful habitat, in which typhoon damage removes branches before the water temperature becomes favourable for reproduction.

A new Chaetomium from Thailand

Chaetomium floriforme sp. nov., isolated from unidentified fallen leaves collected in the north of Thailand, is described and illustrated. The fungus is distinguished by its typical obovate ascomata with articular ascomatal hairs, broadly limoniform ascospores with an apical or subapical germ pore, a Humicola anamorph and its growth temperature response.

Isolation and characterization of non cerato-ulmin producing laboratory induced mutants of Ophiostoma novo-ulmi

Five laboratory mutants of Ophiostoma novo-ulmi EAN isolate H328 were obtained from uv-irradiated and unirradiated blastoconidia. Although the mutants were initially selected on the basis of various characteristics, including failure to produce cerato-ulmin (CU) in the culture filtrate, growth-temperature responses and colony morphology, they all were eventually also found unable to produce CU when grown in liquid shake culture at 23 °C and 33°, or they produced CU only in negligible amounts. This association suggests possible linkages between CU production and other fungal metabolic pathways. Genetic analysis of crosses between the mutants and a wild type isolate of EAN O. novo-ulmi suggested that each mutant involved a change at a single-locus, at least as far as segregations for colony morphology were concerned. Pathogenicity trials using the five mutants were carried out on four-year old Ulmus carpinifola and U. procera . Two out of the five mutants showed a significant reduction in pathogenicity in comparison to the O. novo-ulmi wild type isolate H328.

Local Adaptation to Regional Climates in Papilio Canadensis (Lepidoptera: Papilionidae)

Papilio canadensis encounters shorter, cooler summers in interior Alaska than in northern Michigan: average thermal sums are 583 vs. 985 Celsius degree—days (10°C base); mean daily temperature is 14.4 vs. 18.8°. The temperature physiology of P. canadensis could be evolutionarily conserved, or the species may be a composite of regionally adapted populations. We evaluated these hypotheses by comparing the developmental physiology of P. canadensis from Alaska and Michigan across a range of temperatures in the laboratory and field. Higher temperatures generally resulted in more rapid larval development, but the effects varied with insect population and host. At low temperatures (12°), Alaskan larvae grew faster than Michigan larvae (fifth instars doubled their fresh mass in 5.8 vs. 9.1 d), primarily due to 40% higher consumption rates. At high temperatures (30°), Alaskan larvae grew slower, faster, or the same as Michigan larvae, depending upon host. Effects of host quality were greatest at high temperatures. Elevated respiratory expenses in Alaskan larvae (35% higher than Michigan larvae) made them especially sensitive to host quality at high temperatures. Dry matter digestibility and nitrogen use efficiency differed across hosts, but not between populations or across temperatures. Molting accounted for 35—51% of development time. Alaskan larvae completed their fifth molt faster than Michigan larvae at 12° (11.8 vs. 17.8 d), but not at 30° (3.1 vs. 2.9 d). In both populations, molt was more temperature sensitive than growth at low temperatures (Q10 of 5.65 vs. 3.04 from 12 to 18°), but less temperature sensitive at high temperatures (Q10 of 1.60 vs. 2.06 from 18 to 30°). Survival differed across temperatures, but not between populations. Under ideal basking conditions, larvae in the field were able to elevate body temperatures °10° above ambient, but such conditions were rare in Alaska and larvae were usually near ambient temperature. Alaskan larvae were no better than Michigan larvae at selecting high radiation microsites or converting solar radiation into heat. Growth rates of Alaskan larvae were the same in the field and laboratory when fed the same foliage and exposed to the same mean daily air temperature. We incorporated P. canadensis temperature responses into a life history development model, then used a 48—yr climatic record to evaluate the fitness contributions of apparent adaptations to Alaskan summers. On a good host, at Alaskan temperatures, Alaskan P. canadensis had an estimated fitness 3.0 times greater than Michigan P. canadensis. Furthermore, the Michigan population was predicted to go extinct in 31 of 48 yr at Alaskan temperatures. Changes in growth temperature responses made the greatest contribution to enhanced fitness in Alaska, followed by increased mass of neonates, enhanced molting abilities at low temperatures, and a reduced size threshold for pupation. Analysis of fitness trade—offs suggested that extreme summers have been more important than average summers in shaping adaptive responses. Regional adaptation to climate allows P. canadensis to maintain a broader geographic distribution than would otherwise be possible, but northern distribution limits are probably still constrained by summer temperatures.

Thermophilic sulfate-reducing bacteria in cold marine sediment

Sulfate reduction was measured with the 35SO42− -tracer technique in slurries of sediment from Aarhus Bay, Denmark, where seasonal temperatures range from 0° to 15°C. The incubations were made at temperatures from 0°C to 80°C in temperature increments of 2°C to search for presence of psychrophilic, mesophilic and thermophilic sulfate-reducing bacteria. Detectable activity was initially only in the mesophilic range, but after a lag phase sulfate reduction by thermophilic sulfate-reducing bacteria were observed. No distinct activity of psychrophilic sulfate-reducing bacteria was detected. Time course experiments showed constant sulfate reduction rates at 4°C and 30°C, whereas the activity at 60°C increased exponentially after a lag period of one day. Thermophilic, endospore-forming sulfate-reducing bacteria, designated strain P60, were isolated and characterized as D esulfotomaculum kuznetsovii. The temperature response of growth and respiration of strain P60 agreed well with the measured sulfate reduction at 50°–70°C. Bacteria similar to strain P60 could thus be responsible for the measured thermophilic activity. The viable population of thermophilic sulfate-reducing bacteria and the density of their spores was determined in most probable number (MPN) dilutions. The density was 2.8·104 cells·.g−1 fresh sediment, and the enumerations suggested that they were all present as spores. This result agrees well with the observed lag period in sulfate reduction above 50°C. No environment with temperatures supporting the growth of these thermophiles is known in the region around Aarhus Bay.

Inheritance and inter-relationship of fitness characters in progeny of an aggressive × non-aggressive cross of Ophiostoma ulmi

The inheritance patterns and inter-relationships of nine potential fitness characters were studied in 30 F 1 progeny of a cross between the evolutionarily divergent aggressive (NAN) and non-aggressive subgroups of Ophiostoina ulmi . Continuous inheritance was demonstrated for elm bark colonizing ability and for in vitro ceratoulmin wilt toxin production, and confirmed for linear growth rate at 20 °C and for vascular wilt ability on elm. Inheritance of mycelial density on elm sapwood discs was skewed towards the NAN parental type whereas that for synnemetal and protoperithecial production was skewed towards the non-aggressive type. Growth-temperature response and fertility of the progeny as sexual donors (♂) on a NAN recipient (♀) both followed a bimodal inheritance pattern coinciding with the parental types, the NAN-like type being predominant in each case. As recipients (♀) the majority of the progeny were sexually sterile, a proportion showed a NAN-like response in strongly rejecting the non-aggressive as donor, and one showed a unique response in being more fertile with the non-aggressive donor than with the NAN. Only growth-temperature response and vascular wilt ability were correlated in the F 1 s, where progeny with a non-aggressive type temperature response were shown to be less pathogenic than those with a NAN-type response. The results further explain the lack of aggressive x non-aggressive hybrids in nature. Many of the progeny exhibited poor performance in potential fitness characters such as vascular wilt ability and bark colonizing ability, or were sexually sterile. Progeny showing a good performance in some characters were detected, but since the characters were inherited mainly at random, the chance of a hybrid genotype being sufficiently fitted overall to compete with the aggressive subgroup must be low. Nevertheless, there may be some potential in experimentally pursuing the breeding of a hybrid form of O. ulmi which could compete with the aggressive subgroup in nature.