Temperature Gradient Plate Research Articles

Germination at Extreme Temperatures: Implications for Alpine Shrub Encroachment.

Worldwide, shrub cover is increasing across alpine and tundra landscapes in response to warming ambient temperatures and declines in snowpack. With a changing climate, shrub encroachment may rely on recruitment from seed occurring outside of the optimum temperature range. We used a temperature gradient plate in order to determine the germination niche of 14 alpine shrub species. We then related the range in laboratory germination temperatures of each species to long-term average temperature conditions at: (1) the location of the seed accession site and (2) across each species geographic distribution. Seven of the species failed to germinate sufficiently to be included in the analyses. For the other species, the germination niche was broad, spanning a range in temperatures of up to 17 °C, despite very low germination rates in some species. Temperatures associated with the highest germination percentages were all above the range of temperatures present at each specific seed accession site. Optimum germination temperatures were consistently within or higher than the range of maximum temperatures modelled across the species’ geographic distribution. Our results indicate that while some shrub species germinate well at high temperatures, others are apparently constrained by an inherent seed dormancy. Shrub encroachment in alpine areas will likely depend on conditions that affect seed germination at the microsite-scale, despite overall conditions becoming more suitable for shrubs at high elevations.

Thermal Requirements Underpinning Germination Allude to Risk of Species Decline from Climate Warming.

The storage of seeds is a commonly used means of preserving plant genetic diversity in the face of rising threats such as climate change. Here, the findings of research from the past decade into thermal requirements for germination are synthesised for more than 100 plant species from southern Western Australia. This global biodiversity hotspot is predicted to suffer major plant collapse under forecast climate change. A temperature gradient plate was used to assess the thermal requirements underpinning seed germination in both commonly occurring and geographically restricted species. The results suggest that the local climate of the seed source sites does not drive seed responses, neither is it indicative of temperatures for optimal germination. The low diurnal phase of the temperature regime provided the most significant impact on germination timing. Several species germinated optimally at mean temperatures below or close to current wet quarter temperatures, and more than 40% of species were likely to be impacted in the future, with germination occurring under supra-optimal temperature conditions. This research highlights both species vulnerability and resilience to a warming climate during the regeneration phase of the life cycle and provides vital information for those aiming to manage, conserve and restore this regional flora.

Effects of temperature on germination in eight Western Australian herbaceous species

Germination is a high-risk phase in a plant’s life cycle and is directly regulated by temperature. Seeds germinate over a range of temperatures within which there is an optimum temperature, with thresholds above and below which no germination occurs. Rapid changes in temperature associated with global warming may cause a disconnect between temperatures a seed experiences and temperatures over which germination can occur. This paper explores the temperature dimension of the germination niche of eight herbaceous species from South West Western Australia as part of a broader assessment of endemic native species at risk of decline under global warming. The data obtained from germination studies on a temperature gradient plate were used to populate models to predict optimum germination responses (mean time to germination, germination timing and success) under current (1950–2000 averages) and future (2070 high greenhouse gas emission) temperature scenarios. The species exhibited a mix of germination responses, often with high tolerance to high diurnal temperatures. A number of species did not reach their full potential within the experimental period, indicating the presence of dormancy not overcome due to temperature alone. Modelling revealed that for some species the opportunity for germination may decline due to rising temperatures, but for others there would be little change, though a shift in germination timing may be expected. This approach to identifying extinction risk contributes tangibly to efforts to predict plant responses to environmental change and can help prioritize species for management actions, direct limited resources towards further investigations and supplement bioclimatic modelling.

Temperature thresholds for germination in 20 short-range endemic plant species from a Greenstone Belt in southern Western Australia.

The study of climate-driven effects on seed traits such as germination has gained momentum over the past decade as the impact of global warming becomes more apparent on the health and survival of plant diversity. Seed response to warming was evaluated in a suite of short-range endemic species from the biodiverse Greenstone Belt of southern Western Australia. The temperature dimensions for germination in 20 woody perennials were identified using small unreplicated samples over 6weeks on a temperature gradient plate (constant and fluctuating temperatures between 5 and 40°C). These data were subsequently modelled against current and forecast (2070) mean monthly minimum and maximum temperatures to illustrate seasonal changes to germination timing and final percentage germination. All but one species attained full germination in at least one cell on the gradient plate. Modelling of the data suggested only minimal changes to percentage germination despite a forecast rise in diurnal temperatures over the next 50years. Nine species were predicted to experience declines of between <1% and 7%, whilst 11 species were predicted to increase their germination by <1% to 3%. Overall, the speed of germination is predicted to increase but the timing of germination for most species shifts seasonally (both advances and delays) as a result of changing diurnal temperatures. The capacity of this suite of species to cope with warmer temperatures during a critical early life stage shows a degree of adaptation to heterogeneous environments. Predicting the effects of global change on terrestrial plant communities is crucial to managing and conserving plant diversity.

Provenance modulates sensitivity of stored seeds of the Australian native grass Neurachne alopecuroidea to temperature and moisture availability

In the present study we assessed the sensitivity of stored seeds of the common grass Neurachne alopecuroidea R.Br. from south-western Australian sources to varying temperature and moisture conditions as a tool to anticipate potential adaptability of seeds to climate change. We examined among-population germination responses, focusing on germination of excised seeds to overcome possible dormancy imparted by the lemma and palea. We hypothesised that temperature above and below the optimum and low moisture potentials would adversely affect germination, and that conditions for successful germination would be associated with the local climate at each seed source site. Experiment 1 used a bi-directional temperature gradient plate to measure responses to constant and alternating temperatures (5–40°C). Experiment 2 examined responses to moisture availability using polyethylene glycol (PEG 8000) solutions at different temperatures. Temperature optima varied among populations with significant reductions in germination occurring only below 15°C. Germination speed and success declined with decreasing moisture availability, with greater impact at higher temperatures. Significant population variation was observed. Tolerance to temperature and moisture availability was higher than expected and some of this variation suggests adaptation to local climates across the species Western Australian distribution. We discuss these results in the context of seed use in restoration and global warming.

Modelling seed germination response to temperature inEucalyptusL'Her. (Myrtaceae) species in the context of global warming

AbstractSeed germination is vital for persistence of many plant species, and is linked to local environmental conditions. Small increases in temperature during this critical life history transition may threaten species by altering germination timing and success. Such changes in turn may influence population dynamics, community composition and the geographic distributions of species. In this investigation, a bi-directional temperature gradient plate was used to profile thermal constraints for germination in 26 common, threatened and geographically restrictedEucalyptusspecies (Myrtaceae) from southern Western Australia. These observed data were used to populate models to predict optimum germination responses (mean time to germination, germination timing and success) under current (1950–2000 averages) and future (2070 high greenhouse gas emission climate scenario) mean monthly minimum and maximum temperatures. Many species demonstrated wide physiological tolerance for high germination temperatures and an ability to germinate outside current and forecast future autumn–winter wet season temperatures, suggesting that climatic distribution is a poor proxy for thermal tolerance forEucalyptusseed germination. Germination for some species is predicted to decline under forecast conditions, but the majority will maintain or improve germination particularly during the cooler winter months of the year. Although thermal tolerance may benefit persistence of manyEucalyptusspecies in southern Western Australia as warming becomes more severe, large rainfall declines are also forecast which may prove more detrimental to plant survival. Nonetheless, this framework has the potential to identify seed resilience to heat stress in an early life history phase and hence species vulnerability to one characteristic of forecast environmental change.

Can sensitivity to temperature during germination help predict global warming vulnerability?

AbstractSeed germination is vital for persistence in species that rely on seeds for post-disturbance regeneration. It is a high-risk phase and vulnerable to environmental parameters. Here, I assessed temperature sensitivity for germination in Banksia L.f. (Proteaceae) from south-western Australia, screening all 38 endemic obligate seeder species. A bi-directional temperature gradient plate with 49 temperature combinations (constant and fluctuating) between 5 and 40°C was used to profile germination temperature requirements and identify upper and lower temperature thresholds for germination. Using these data the impact of increasing temperatures on germination in these species was modelled under high and low greenhouse gas scenarios for 2050 and 2070. The results suggest that many Banksia species from the region have wide physiological tolerance for high germination temperatures, although a number of common, but geographically restricted species, such as B. praemorsa, B. oreophila and B. quercifolia, have more narrow temperature windows for germination than at least one of the rarer species (B. verticillata). Only B. dryandroides is expected to decline in germination in the future; however, the optimal germination timing for many species is predicted to occur later under climate warming. In conjunction with declining rainfall, this germination delay will place seedlings closer to the summer dry in this seasonal Mediterranean-climate ecosystem and thus they will be more vulnerable to desiccation. The framework developed here can be used to identify vulnerable species for monitoring of early population decline.

Comparison between temperature gradient and heat flux plate methods and effect of heat storage for determination of soil heat flux at near soil surface

Comparison between temperature gradient and heat flux plate methods and effect of heat storage for determination of soil heat flux at near soil surface

Effects of Scarification with Sulfuric Acid and Matric Priming on Seed Germination of Seed Propagation Type of F1 Hybrid Strawberry (Fragaria × ananassa Duch.)

For practical use of the seed propagation type of F1 hybrid strawberry, high germination percentage and germination uniformity are necessary. The effects of scarification with concentrated sulfuric acid and matric priming on seed germination of this strawberry were investigated in order to improve the germination performance. Open-pollinated seeds of ‘Tochiotome’ and seeds from the seed propagation type of the F1 hybrid strawberry cultivar ‘Chiba F-1 go’, bred by ourselves, were used. Germination tests were carried out on a temperature-gradient plate to investigate the response to temperature. The number of germinated seeds was counted for 7 days after sowing. The final germination percentage (FGP) of seeds scarified with 36 N sulfuric acid for 10 min exceeded 83% in the optimal temperature range of around 24–27°C, whereas untreated seeds did not germinate. FGP increased to more than 82% in the wide temperature range of 18–32°C with matric priming in vermiculite (−1.5 MPa) for 12 days after scarification. The effect of scarification time on germination was investigated for the seeds of ‘Chiba F-1 go’. The highest percentage (84%) was obtained in the seeds scarified for 35 min. Furthermore, the germination speed and uniformity increased with extension of the duration of matric priming from 0 to 14 days. Germination performance of the seeds of ‘Chiba F-1 go’ was improved for practical use by scarification with concentrated sulfuric acid and scarification plus matric priming.

Seed dormancy and germination of Ficus lundellii and tropical forest restoration

We investigated seed dormancy and germination in Ficus lundellii Standl. (Moraceae), a native species of Mexico's Los Tuxtlas tropical rain forest. In an 8-h photoperiod at an alternating diurnal (16/8 h) temperature of 20/30 degrees C, germination was essentially complete (96%) within 28 days, whereas in darkness, all seeds remained dormant. Neither potassium nitrate (0.05-0.2%) applied continuously nor gibberellic acid applied either continuously (10-200 ppm) or as a 24 hour pretreatment (2000 ppm) induced germination in the dark. Germination in the light was not reduced by a 24-h hydrochloric acid (0.1-1%) pretreatment, but it was reduced both by a 24-h pretreatment with either H(2)O(2) (0.1-5 M) or 5% HCl, or by more than 5 days of storage at 40 degrees C (4.5% seed water content). In a study with a 2-dimensional temperature gradient plate, seeds germinated fully and rapidly in the light at a constant temperature of 30 degrees C, and fully but less rapidly in the light at alternating temperatures with low amplitudes (< 12 degrees C) about the optimal constant temperature. The base, optimal and ceiling temperatures for rate of germination were estimated as 13.8, 30.1 and 41.1 degrees C, respectively. In all temperature regimes, light was essential for the germination of F. lundellii seeds.

Factors influencing the germination of myrtle (Lagerstroemia speciosa (L.) Pers. and L. floribunda Jack) seeds

Gibberellic acid and potassium nitrate did not promote the germination of myrtle seeds when tested at 20/30degreesC (16/8h). Germination was promoted considerably by alternating temperatures. The results of an investigation on a two-dimensional temperature gradient plate showed that myrtle seeds germinated most rapidly (within 14 days) and fully (all viable seeds) at 35/22.5degreesC (16/8 h) and similar regimes. Tests on five seed lots of Lagerstroemia speciosa and L. floribunda showed the efficacy of the alternating temperature regime of 35/20degreesC (16/8 h) in promoting germination. Thus we recommend myrtle seeds be tested for germination in this regime for 28 days.

The effect of low temperatures on Colletotrichum acutatum and Colletotrichum gloeosporioides causing body rots of avocados in New Zealand

The effect of extended periods at low temperatures on spore germination, survival and appressorial formation in Colletotrichum acutatum and C. gloeosporioides, and on pre-formed appressoria of C. gloeosporioides, was studied on water agar on glass slides on a temperature gradient plate. C. acutatum was more tolerant of low temperatures than was C. gloeosporioides. The addition of peptone to simulate endogenous nutrients on the avocado fruit surface affected spore germination and survival only slightly, and the effect was not statistically significant. These trends in vitro were also apparent in isolations from fruit rots. Infections by C. acutatum were not reduced by storage at 5.5°C before ripening. Incidence of infections caused by C. gloeosporioides was significantly fewer in fruit coolstored at 5.5°C for 30 days prior to ripening at 20°C than in fruit stored at 20°C. In the two lines of fruit studied, coolstorage reduced body rots in one line but not the other. The rots on the line of fruit not affected by coolstorage were mainly caused by C. acutatum. These results suggest that in coolstored fruit, the reduction in incidence of rots caused by C. gloeosporioides, but not of rots caused by the closely related fungus C. acutatum, was due to the greater sensitivity of spores of C. gloeosporioides to cold temperatures. Survival of pre-formed appressoria of C. gloeosporioides was not affected by temperatures used for coolstorage of avocados.

Base growth temperatures, germination rates and growth response of contemporary spring wheat ( Triticum aestivum L .) cultivars from the US Pacific Northwest

In eastern Washington, spring wheat cultivars that germinate and grow fast at low temperatures will provide the crop with a competitive advantage over spring emerging weeds in commercial production fields compared to cultivars that germinate and grow more slowly. The objective of this research was to develop a protocol to identify spring wheat cultivars that would germinate and grow more quickly at low temperatures. A novel data analysis method was used to separate the germination process into three components: (1) base temperature, (2) time to initiation of germination, and (3) germination rate. Spring wheat cultivars Edwall, Vanna, Wawawai, Wampum, Express, and Spillman were assessed through a series of controlled temperature gradient plate experiments. Base temperatures were not different ( P=0.1) across cultivars, and once germination was initiated, germination rates among varieties were uniform ( P=0.5). However, significant ( P<0.001) differences were detected among varieties for time to germination. A subsequent growth chamber experiment confirmed differences in emergence and growth rate among spring wheat cultivars.

Comparison of North Carolina, Georgia, and Florida Isolates of Cylindrocladium parasiticum

Abstract Thirteen isolates of Cylindrocladium parasiticum Crous, Wingfield &amp; Alfenas from North Carolina and 11 from Georgia were grown on plates of PDA at 20,25, and 30 C on a temperature-gradient plate. Culture diameters were measured daily for 6 d. Significant differences were not observed among isolates grown at 20 C and cultures was smaller as compared with those grown at 25 and 30 C. At 25 and 30 C, isolates varied consistently in growth. On average, Georgia isolates grew slightly less than North Carolina isolates, and all isolates grew better at the warmer temperature. Growth of three North Carolina isolates was compared to four Florida isolates in a second experiment. Florida isolates grew significantly faster than North Carolina isolates at all temperatures. Isolates from the three states were compared for their ability to cause root rotting on peanut at 25 and 30 C. Plants were grown in soil infested at a standardized inoculum density in temperature-controlled water bath tanks for 7 wk at which time roots were rated for Cylindrocladium black rot development. Georgia isolates caused more root rot than either North Carolina or Florida isolates at both temperatures and also caused more seedling disease. State effects were significant; Florida isolates caused less root rot than Georgia isolates. Temperature by state interactions were not significant which means that high temperature-tolerant isolates of C. parasiticum have not evolved from regional differences in soil temperature. Further, North Carolina field isolates do not appear to have changed in temperature optima since the 1970s.

Effect of temperature on seed germination rate of Striga hermonthica (Del.) Benth.

The effect of a range of constant temperatures (15–45 °C) on the germination of S. hermonthica (Del.) Benth. seed was investigated on a temperature gradient plate to quantify the relationship between temperature and the rate of seed germination and to study the effect of conditioning temperature on the relationship. Seeds were conditioned on moist filter paper either at 30 °C for 14 days or 20 °C for 15 days in an incubator. A synthetic stimulant, GR-7, was applied to conditioned seeds prior to exposure to the various temperatures. No seeds of S. hermonthica conditioned at 30 °C, germinated at < 20 °C or > 42.5 °C within 312 h. For seeds conditioned at 20 °C, germination occurred at temperatures between 25 and 42.5 °C within 312 h. The base ( T b, estimated from extrapolation, optimum ( T o) and ceiling ( T c) temperatures determined were: T b = 22.7 °C, T o = 40 °C and T c > 42.5 °C for seeds conditioned at 20 °C compared with T b = 18.9 °C, T o = 32–35 °C and T c > 42.5 °C for seeds conditioned at 30 °C. Positive linear relationships were established between the rate (reciprocal of time taken) of germination of 90% of the final germination percentage and temperature up to the respective optimal temperatures. The rate of germination for seed conditioned at 20 °C was lower ( P < 0.0001) than for seed conditioned at 30 °C. Similarly base and optimum temperatures were lower ( P < 0.0001) for seed conditioned at 30 °C. The base temperatures reported here are about twice those reported for the host crops of maize, sorghum and millet.

Constant temperatures and the rate of seed germination in maize (Zea mays L.) of contrasting endosperm

The germination of quality protein maize (QPM) cultivar, Obatanpa, was compared to normal endosperm (NEM) cultivar, Okomasa, on a temperature gradient plate at constant temperatures ranging from 15-45 oC. Germination occurred at all temperatures except at 42.5 oC for the QPM cultivar and 45 oC for the NEM cultivar. The rate of germination of the NEM cultivar was faster than that of the QPM cultivar at all temperatures. The thermal times for median germination were 46 for QPM and 40.7 oCd for the NEM cultivar. The cardinal temperatures (base, Tb, optimum, To and ceiling, Tc) for the NEM cultivar were Tb: 7, To: 30 and Tc: 48.2 oC. The corresponding values for the QPM cultivar were Tb: 7.6, To: 27.5 and Tc: 43.4 oC. The base and optimal temperatures were not significantly different but the ceiling temperature for the QPM was significantly lower(P (Ghana Journal of Agricultural Science, 1996, 29(2): 33-38)

Survival ofPhytophthora lateralisin Infected Roots of Port Orford Cedar

Short-term and long-term survival of Phytophthora lateralis in infected Port Orford cedar rootlets in soil was tested under a variety of conditions. Survival was measured by baiting infected rootlets with cedar foliage baits or by planting cedar seedlings into the infested soil. On the temperature gradient plate, recovery after 7 and 18 days at 10°C was near 100%, but reisolation was sharply reduced from moist soil at 20 and 30°C, and there was no recovery at 40°C. In soil allowed to air-dry at the various temperatures, there was no recovery at 20°C or above. Outdoors, the fungus survived at least 7 days in rootlets buried 10 cm deep in dry soil, and in rootlets on the soil surface, if shaded. There was no recovery from rootlets exposed to the sun. Temperatures did not exceed 25°C in any treatment where the fungus was recovered. Long-term survival of P. lateralis in infected cedar roots was tested in litter bags buried in forest and cold frame conditions, and in intact root systems of cedar trees killed by P. lateralis. Direct isolation onto selective medium was attempted from forest trees killed at different times in the past. P. lateralis was not isolated from any tree dead for more than 2 years. The fungus was recovered by baiting from litter bags after 5 years but not after 6 years, and from root systems in buried pots through the 7 years of the test. Rate of recovery was sharply reduced in the last year in both cases.

Alternating Temperatures and Rate of Seed Germination in Lentil

The effect of alternating temperatures on the times taken by seeds of lentil (Lens culinaris Medikus) to germinate was investigated using a two-way temperature-gradient plate. Between 5 and 25°C, warmer temperatures increased the rate of germination. Variation among the individual seeds in the times required for germination at different constant temperatures within this range were described well by a log-normal distribution of thermal times, accumulated above a base temperature of 1·5°C. Even with amplitudes as great as 20°C, no effect of alternation per se on the thermal time required for germination was detected—whether the cool temperature was applied for 8 or 16 h d-1. Similarly, in alternating temperature regimes where the minimum temperature of the diurnal cycle was between 0°C and the base temperature, the thermal times required for germination (where no thermal time accrued during the periods when temperature was below Tb) were in close agreement with those values provided by the model determined at warmer constant temperatures. However, where the minimum temperature applied was < 0°C the germination of all but the earliest germinators was delayed beyond model predictions, and more so where the sub-zero minimum temperature was applied for 16 rather than 8 h d-1. The results, therefore, contradict the view that alternation in temperature per se reduces the thermal time required for seed germination. Rather, rate of germination responds instantaneously to current temperature, but prolonged exposure to sub-zero temperatures can result in damage sufficient to delay germination when seeds are returned to regimes warmer than the base temperature.

Growth and reproduction of Scytosiphon lomentaria (Fucophyceae) in relation to temperature in two populations from Denmark

Two strains of Scytosiphon lomentaria from Denmark have been grown under long-day conditions on a temperature-gradient plate. The material from north-west Jutland (strain No. 46) has a reduced prostrate system (a few-celled lump) whereas the other material from the Sound (strain No. S41) has a well-developed crust. This difference plays a significant role in growth and reproductive patterns. Strain No. 46 rapidly produces a great number of cylindrical macrothalli. Within a four-week experimental period, formation of swarmers from plurilocular sporangia on the macrothalli takes place and results in a maximum dry weight of 32.9 mg at 18.2°C. Swarmers from the macrothalli of strain S41 always develop into knot-filamentous or crust-shaped thalli. The development of the macrothalli, therefore, takes a longer time than in strain 46 and the maximum dry weight is only 16.5 mg at 16°C even within an experimental period of six weeks. The reproductive pattern is more complex than in strain 46. The crusts produce unilocular sporangia at temperatures between 16°C and 23.8°C, and function, therefore, as the reproductive system during the summer as macrothalli disappear at temperatures above 18°C both in nature and in culture. Formation of plurilocular sporangia on macrothalli starts when they are from 6–9 weeks old at temperatures between 11°C and 18°C. The temperature range for growth in the two strains also differs: Strain 46 grows from 7.3–24.4°C while strain S41 grows at least from 4–5.1°C to an upper limit of 27.1°C, but lower limit has not been determined precisely in the present experiment. These results indicate that temperature ecotypes exist, even within a limited geographic area.

The temperature acclimatized swimming speed of selected marine dinoflagellates

Video measurements were used to monitor the temperature acclimatized swimming speeds (24 hours exposure) of 11 species of marine dinoflagellates, some represented by different clones, on a temperature gradient plate. Although the inherent variability among individuals within a population under the same treatment was high, each species or clone could be represented by a response scatter plot that characterized its temperature-dependent swimming ability. A curve-fitting treatment of the data demonstrated the similarity of the swimming speed versus temperature responses for repetitive trials on a single clone or for different clones and the diversity of the swimming speed versus temperature responses among different species. Comparisons among populations included viable temperature range, maximum swimming speed and response curve shape. All species swam over a broader temperature range than that over which growth was detected. Maximum swimming speed within the measured group occurred at a cell length of -35 μg This possible optimum in cell size may result from the hydrodynamic characteristics of dinoflagellate swimming. Swimming speed variation among dinoflagellate species can influence the competitive interactions within the group or with other kinds of phytoplankton and can affect predator-prey interactions with herbivores.