Thermal Time Model Research Articles

Spatio-temporal trends in the frost regime reveal late frost exposure to white spruce (Picea glauca [Moench] Voss) persists in northeastern America

Abstract The characteristics of the frost regime (intensity, frequency, and timings) contributed to shaping tree species adaptations and distribution as well as ecosystem productivity and functions. However, climate change increased the variability in extreme events; therefore, the different characteristics of the frost regime may diverge under climate change. Using the BioSim 11 software, we simulated daily air temperature at 512 locations over Eastern Canada between 1901-2021 to determine how the spatio-temporal trends in the frost regime varied over this complex landscape and if spatio-temporal trends in extreme climatic events such as frosts are stronger compared to changes in aggregated climate variables such as mean annual temperature and growing degree-days. We also used an eco-physiological model to conduct a study case focussing on white spruce to determine if trees are currently more exposed to growing season frosts than they were in the past by modelling the timings of budburst using the thermal time model. Our results showed that, at 353 sites, the day of the year of the last frost in spring (minimum daily air temperature < 0 °C) occurred, on average, earlier by seven days during 2001-2021 compared to 1901-1920, whereas it occurred, on average, later by five days at 159 sites. The average temporal trends in frost occurrence were similar in magnitude to the average trends in aggregated climate variables; however, their variances were larger compared to the aggregated climate metrics, showing that the frost regime does not change uniformly throughout our study area. Our study case also revealed that white spruce remains exposed to late frosts of low and intermediate intensities (minimum daily air temperature < 0; < -2 °C) compared to the past but is almost not exposed to late frosts of high intensity (minimum daily air temperature < -4 °C). Since extreme events such as late frosts diverge in their response to climate change compared to aggregated climate variables, the mean annual temperature is not sufficient to predict how climate change will impact ecosystems through frost regimes.

Unveiling the germination patterns of Alternaria porri (Ellis) by using regression analysis and hydrothermal time modeling

Purple blotch disease is a major fungal disease of Allium cepa L. plants which is caused by the fungus Alternaria porri. The best conditions for the growth of Alternaria porri are temperatures between 22 °C and 25 °C and relatively high humidity. The Hydrotime, Thermal Time, and Hydrothermal Time models were used to measure different parameters of seed germination; therefore, we used them to measure the interactive effects of temperature and water potential on the germination conidia of Alternaria porri. The laboratory experiments were carried out at five constant temperatures, between 5 and 30 °C, and five different water potentials between 0 MPa and − 6 MPa. The germination of Alternaria porri conidia was highest at 25 °C and 0 MPa and lowest at 5 °C and − 6 MPa. The percentage of conidia germination decreased rapidly after 25 oC. Conidia germination was also affected by different water potentials, decreasing at lower water potential. Models based on HTT showed a reasonable fit to the germination and growth rate datasets. The best fitting model for conidia germination (R2 = 0.98491) was based on variable base and maximum temperature as a function of water potential. Based on the TT, HT, and models, the highest and lowest values for θT1 were observed at -6.0 MPa at 30 °C, and 0 MPa at 5 °C and the highest and lowest θT2 values were recorded at -6.0 MPa at 5 °C and 0 MPa at 30 °C while the lowest and highest θH values were recorded at -6.0 MPa at 5 °C and 0 MPa at 25 °C, respectively, for the HTT model, the predicted θHTT average value is 16.32 (MPa°Ch-1). Based on the statistical analysis, the cardinal hydrothermal time constant (θHTT) accurately explains the interactive effect of T and Ψ on the germination of Alternaria porri conidia under different environmental conditions.

Longevity and persistence of arrowleaf sida seeds in soil and emergence modeling using thermal and hydrothermal time models

Arrowleaf sida (Sida rhombifolia L.) is a weed that has a fibrous stem, aggressive root system and waxy leaves that can hinder herbicide absorption. Based on knowledge of the environmental requirements for germination of this species, it is possible to predict emergence to assist in integrated management. The aim of this investigation was to characterize the air temperature and soil water potential requirements for arrowleaf sida germination, to model the emergence in the field using thermal and hydrothermal time models and to evaluate the longevity of the arrowleaf sida seed bank. Laboratory experiments were conducted to determine the temperature and water potential for seed germination by testing eight temperatures (10, 15, 20, 25, 30, 35, 40, and 45 °C) and 10 water potentials (0, −0.05, −0.1, −0.2, −0.4, −0.6, −0.9, −1.2, −1.5, and −2.0 MPa). Field experiments were conducted between 2014 and 2018 to model the emergence using three sampling times (starting on 10/20, 11/10, and 12/01), during which soybean seeds were sown. To evaluate the longevity and persistence of the seed bank, a factorial experiment was conducted, in which the first factor included three burial depths (0, 3, and 6 cm) and the second factor included five collection times (0, 1, 4, 10, and 16 months) after seed burial. The base, optimal and maximum temperatures for arrowleaf sida germination were 10.0, 24.8, and 42.5 °C, respectively, and the base water potential was −1.20 MPa. It is possible to predict the emergence of arrowleaf sida in the field by hydrothermal and thermal time models under different environmental conditions. In addition, this species has a persistent seed bank, with 30% of seeds being viable after 16 months of burial.

Developing a combined rotating and air-circulating system for improving radio frequency heating uniformity and controlling Aspergillus in almond kernels

It is important to improve radio frequency (RF) heating uniformity for developing effective pathogen control protocols before storage of almonds. The purpose of this study was to design a combined rotating and air-circulating system (CRACS) in the RF cavity for improving sample temperature uniformity during pasteurization, drying, and cooling of almond kernels. The results showed that the optimal rotating speed of 15 r/min and loading volume ratio of 60% of CRACS were determined to achieve the required RF pasteurization level. The pasteurization protocol was developed based on the above selected parameters of CRACS, RF heating/drying, and forced air cooling. Compared to the five-layer container (five single layers stacked vertically) used for RF pasteurization of almond kernels, the RF heating uniformity in almond kernels using CRACS was clearly improved, resulting in moisture content reduction of only 0.70% wet basis (w.b.). The pasteurization validation curve of almond kernels in CRACS was closer to the predicted survival one based on the cumulative thermal lethal time model, suggesting that CRACS was suitable for the effective RF pasteurization of almond kernels. The moisture content and color values of almond kernels after RF pasteurization were beneficial for maintaining their long-term storage and stable quality. This CRACS in the RF system may provide a practical and effective technology for pasteurizing almond kernels.

Application of the thermal death time model in predicting thermal damage accumulation in plants.

The thermal death time (TDT) model suggests that the duration an organism can tolerate thermal stress decreases exponentially as the intensity of the temperature becomes more extreme. This model has been used to predict damage accumulation in ectothermic animals and plants under fluctuating thermal conditions. However, the critical assumption of the TDT model, which is additive damage accumulation, remains unverified for plants. We assessed thermal damage in Thymus vulgaris under different heat and cold treatments and used TDT models to predict time to thermal failure of PSII. Additionally, thermal tolerance estimates from previous studies were used to create TDT models to assess the applicability of this framework in plants. We show that thermal damage is additive between 44 to 47 °C and -6.5 to -8 °C and that the TDT model can predict damage accumulation at both temperature extremes. Data from previous studies indicate a broad applicability of this approach across plant species and traits. The TDT framework reveals a thermal tolerance landscape describing the relationship between exposure duration, stress intensity and percentwise damage accumulation. The extreme thermal sensitivity of plants emphasizes that even 1°C increase in future extreme temperatures could impact their mortality and distribution.

Application of the thermal time model to assess the effects of priming treatments on seed germination of rice (Oryza sativa) cultivars in response to temperature

Application of the thermal time model to assess the effects of priming treatments on seed germination of rice (Oryza sativa) cultivars in response to temperature

The Impact of Water Potential and Temperature on Native Species' Capability for Seed Germination in the Loess Plateau Region, China.

Global warming is increasing the frequency and intensity of heat waves and droughts. One important phase in the life cycle of plants is seed germination. To date, the association of the temperature and water potential thresholds of germination with seed traits has not been explored in much detail. Therefore, we set up different temperature gradients (5-35 °C), water potential gradients (-1.2-0 MPa), and temperature × water potential combinations for nine native plants in the Loess Plateau region to clarify the temperature and water combinations suitable for their germination. Meanwhile, we elucidated the temperature and water potential thresholds of the plants and their correlations with the mean seed mass and flatness index by using the thermal time and hydrotime models. According to our findings, the germination rate was positively correlated with the germination percentage and water potential, with the former rising and the latter decreasing as the temperature increased. Using the thermal time and hydrotime models, the seed germination thresholds could be predicted accurately, and the germination thresholds of the studied species varied with an increase in germination percentage. Moreover, temperature altered the impact of water potential on the germination rate. Overall, the base water potential for germination, but not the temperature threshold, was negatively correlated with mean seed mass and was lower for rounder seeds than for longer seeds. This study contributes to improving our understanding of the seed germination characteristics of typical plants and has important implications for the management and vegetation restoration of degraded grasslands.

Emergence modeling of three‐lobe morning glory (Ipomoea triloba L.) and demographic parameters of seed longevity and persistence in the soil

AbstractThree‐lobe morning glory (Ipomoea triloba L.) is an annual weed, which presents vigorous growth, long cycle, and tolerance to glyphosate. Thus, knowledge of aspects related to germination and behavior in the seed bank of this species are essential for the adoption of appropriate management practices to reduce the population in agricultural fields. Therefore, the objective of this work was to characterize the requirements for three‐lobe morning glory germination, perform field emergence modeling using thermal and hydrothermal time models, and determine the longevity of the seed bank. Eight temperatures and 10 water potentials were tested in the laboratory to determine the base temperature and water potential for seed germination. For the modeling of the emergence, field experiments were conducted between the years 2014 and 2018 considering three sampling times (10/20, 11/10, and 12/01), which coincide with the sowing times of summer annual crops. To evaluate the longevity and persistence of the seed bank, a factorial experiment was conducted in which factor A consisted of three burial depths and factor B consisted of five harvesting times. Base values for three‐lobe morning glory emergence are base, optimum, and maximum temperatures of 12.32, 29.82, and 43.31°C, respectively, and base water potential of −0.80 MPa. Both models are adequate to predict the emergence of three‐lobe morning glory in the three sampling times. The species has a persistent seed bank, in which the greater the depth of seed burial, the greater the longevity of the seed bank, and can remain viable for up to 16 months.

The Invasive Weed Trianthema portulacastrum in Israel.

Trianthema portulacastrum L. (Aizoaceae), commonly known as desert horse purslane or black pigweed, is a C4 dicot succulent annual herb that is widespread in Southeast Asia, tropical America, Africa, and Australia. In Israel, it is an invasive weed of increasing importance in agricultural fields. The aim of this study was to investigate the biology of this invasive weed and its spread in the Hula Valley of Israel. Initial studies included the investigation of the T. portulacastrum specimens held at the Israel National Herbarium. On-site surveillance for the identification of weed infestation locations was conducted in the Hula Valley throughout 2019-2022, and an infestation map was assembled. In a study of the plant biology, greenhouse pot experiments revealed that T. portulacastrum seeds emerge best from the upper soil levels, and as seed depth increases, the emergence rate decreases, so that at 6 cm soil depth, there was no emergence. In controlled-environment growth chamber studies, there were no significant differences in germination with or without light. A maximum germination of 81% was observed for a 12 h night/day of 25/35 °C regime. Germination rates decreased with the decrease in temperature. A seed germination thermal time model that was developed for estimating the minimum temperature required for germination (Tbase) computed this temperature to be 10 °C. This study revealed the biology, in particular seed germination and emergence requirements, of the invasive weed T. portulacastrum that has spread in the Hula Valley in Israel and beyond. Future research will focus on an examination of control measures to combat this invasive weed.

The germination response of Zea mays L. to osmotic potentials across optimal temperatures via halo-thermal time model

The maize (Zea mays L.) is a monocot that is a member of the Poaceae family and a valuable feed for livestock, human food, and raw material for various industries. The halothermal time model determines how plants respond to salt (NaCl) stress under sub-optimal conditions. This model examines the relation between NaClb (g), GR, GP, salinity and temperature stress on germination of seeds dynamics in various crops. Five constant temperatures i.e. 20, 25, 30, 35, and 40 °C and five ψ levels (NaCl concentrations converted to ψ − 0, − 0.2, − 0.4, − 0.6, and − 0.8 MPa) were used in this experiment. In light of the results, the maximum halo-thermal time constant value was recorded at 35 °C temperature, while maximum germination percentage was detected at 30 °C in the controlled condition. Moreover, the lowermost value was recorded at 20 °C at − 0.8 MPa osmotic potential. The highest CAT, APX, and GPX activities were recorded at 15 °C at − 0.8 MPa, while the lowest values were observed for 0 MPa at 30 °C temperature. In conclusion, by employing the halo thermal time model, the germination of maize variety (var.30W52) was accurately predicted for the first time under varying levels of temperature and osmotic potentials.

Emergence timing of smallflower umbrella sedge (Cyperus difformis), barnyardgrass (Echinochloa crus-galli), and bearded sprangletop (Leptochloa fusca spp. fascicularis) in California water-seeded rice

Abstract Late-season weed emergence in California rice fields complicates decisions concerning the timing of control measures. The objective of this study was to predict the emergence of three problematic weed species in rice using thermal time models. Smallflower umbrella sedge, barnyardgrass, and bearded sprangletop seedlings were counted and removed daily at three locations across the Sacramento Valley rice-growing region in 2018. The accumulation of thermal time (growing degree days; GDD) commenced with the initial flooding of the fields at each location, utilizing the specific base temperatures corresponding to each species. The pattern of emergence as a function of GDD was modeled with a Weibull function. Root-mean-square values for comparing actual and model-predicted cumulative emergence values were 6% to 23%. Percent cumulative emergence initially increased rapidly for smallflower umbrella sedge and reached 90% emergence with accumulation of 13 GDD. Barnyardgrass emerged after smallflower umbrella sedge and reached 90% emergence with an accumulation of 124 GDD. Bearded sprangletop had a delay of 64 GDD compared to barnyardgrass to reach first emergence and reached 90% emergence at 215 GDD. The period of weed emergence at all field sites differed across the three species and led to a continuous spectrum of weed emergence over time. This study characterizes the emergence of three economically important rice weeds and provides useful information for the timing of weed management. Typical herbicide applications on the day of seeding may have less efficacy on the late-emerging weeds, causing reduced weed control. Delayed herbicide application, overlay of residual herbicides, or use of herbicides with longer residual activity are suggested to control late-emerging weeds.

A Thermal Time Basis for Comparing the Germination Requirements of Alfalfa Cultivars with Different Fall Dormancy Ratings

Fall dormancy plays important roles in the evaluation of alfalfa’s winter hardiness and in the selection of alfalfa breeding. A rapid and effective method to estimate the fall dormancy rating of alfalfa will shorten the breeding cycle. The purpose of this study is to test the correlations between the germination thermal time model parameters and the fall dormancy ratings and to evaluate the potential of the thermal-based fall dormancy methodology. Alfalfa cultivars with a series of fall dormancy ratings were used to study the responses of seed germination at six constant temperatures (5, 10, 15, 20, 25, 30 °C). The results showed that all cultivars had a relatively high germination percentage at all temperatures and the optimal temperature is 25 or 30 °C. Germination rate and base temperature significantly increased with the fall dormancy rating of alfalfa cultivars while thermal time (θT) decreased with the fall dormancy rating. The extremely significant linear regression relationships between the germination rate, base temperature (Tb), θT, and fall dormancy rating indicated that it is convenient and straightforward to predict the fall dormancy rating of unknown cultivars or lines using thermal time model parameters. This method can significantly shorten the selection and breeding cycles in alfalfa cultivation.

Onion (Allium cepa L.) seed germination affected by temperature and water potential: Hydrothermal time model

A useful implement for seed ecological studies is quantifying the germination behavior against variable environmental conditions. The influences of temperature and water potential on the germination response of onion seeds can be described by using the thermal time (TT), hydrotime (HT), and hydrothermal time (HTT) models. The germination behaviour of onion seeds (Allium cepa L.) was studied over a range of constant temperatures and water availability. The efficiency of hydrothermal time models was evaluated by the germination parameters for two onion cultivars (‘Sepidan’ and ‘Zargan’). The onion seeds were germinated in the laboratory over a water potential range from 0 to − 1 MPa at 5, 10, 15, 20, 25, 30, 35, and 40 °C. Final germination dropped with decreasing water potential, particularly at water potential less than − 0.2 MPa. The model analysis indicated that the dynamics of seed germination was generally well described by the TT model within water potential less than − 1 MPa (R2 = 0.69–0.97), HT (R2 = 0.94–0.99), and HTT models (R2 = 0.95–0.96). The Dent-like was found to be the best model to predict germination rate (RMSE = 0.00006, and 0.000133, R2 = 0.98, and 0.97 for ‘Sepidan’ and ‘Zargan’, respectively). The base, sub-optimum, supra-optimum and the ceiling temperatures for onion seed germination were estimated − 2.5, 19.3, 29.8, and 39.3 °C for ‘Sepidan’ and 0, 25.19, 27.37, and 42.39 °C for ‘Zargan’ at 0 MPa. Thermal time constants were 2650 and 3329.67 °C.h at − 0.8 MPa and 1602.83 and 1521.44 °C.h for ‘Sepidan’ and ‘Zargan’ seeds at 0 MPa. Hydrotime constants for ‘Sepidan’ and ‘Zargan’ seeds were 115.54 and 128.037 MPa.h at 5 °C and 20.8 and 26.93 MPa.h at 30 °C. Hydrothermal time constants for ‘Sepidan’ and ‘Zargan’ seeds were 1249.792 and 1122.78 MPa.°C.h.

Interspecific differences in thermal tolerance landscape explain aphid community abundance under climate change

A single critical thermal limit is often used to explain and infer the impact of climate change on geographic range and population abundance. However, it has limited application in describing the temporal dynamic and cumulative impacts of extreme temperatures. Here, we used a thermal tolerance landscape approach to address the impacts of extreme thermal events on the survival of co-existing aphid species (Metopolophium dirhodum, Sitobion avenae and Rhopalosiphum padi). Specifically, we built the thermal death time (TDT) models based on detailed survival datasets of three aphid species with three ages across a broad range of stressful high (34–40 °C) and low (−3∼−11 °C) temperatures to compare the interspecific and developmental stage variations in thermal tolerance. Using these TDT parameters, we performed a thermal risk assessment by calculating the potential daily thermal injury accumulation associated with the regional temperature variations in three wheat-growing sites along a latitude gradient. Results showed that M. dirhodum was the most vulnerable to heat but more tolerant to low temperatures than R. padi and S. avenae. R. padi survived better at high temperatures than Sitobion avenae and M. dirhodum but was sensitive to cold. R. padi was estimated to accumulate higher cold injury than the other two species during winter, while M. dirhodum accrued more heat injury during summer. The warmer site had higher risks of heat injury and the cooler site had higher risks of cold injury along a latitude gradient. These results support recent field observations that the proportion of R. padi increases with the increased frequency of heat waves. We also found that young nymphs generally had a lower thermal tolerance than old nymphs or adults. Our results provide a useful dataset and method for modelling and predicting the consequence of climate change on the population dynamics and community structure of small insects.

Application of the thermal time model of embryonic development duration to the culture of octopod cephalopods

Data about the effect of temperature on the duration of embryonic development, or the incubation process, are relatively abundant for octopod cephalopods. Experimental data can be used to fit the thermal time classic model of development in order to predict the duration of the process and the range of temperatures within which development proceeds according to the model and with high survival (permissive range), with potential applications for basic research and production activities. The present work is aimed at fitting this classical model to fourteen data sources dealing with eleven species of octopods, seven of them not being previously analyzed, and discussing the constraints and applications of the model. As a result, it is possible to hold that the thermal time model of development duration suitably fits experimental data in octopods, and can be used to schedule hatching events in a production facility. Nevertheless, the range of temperatures tested in the literature is usually too limited to allow an appropriate estimation of the permissive range, so an extension of the temperature range to the known limits of each species is suggested. In addition, when the model is applied to whole spawnings with culture purposes, it is recommended to set the very first hatchings as the criterion for the end of the incubation. Further research is needed to ascertain if temperature fluctuations within and/or out of the permissive range can have implications for the parameterization of the model in octopod species.

Modeling the influence of temperature, salt and osmotic stresses on seed germination and survival capacity of Stipa tenacissima L.

This work stands for a modelling approach to identify the cardinal temperature of germination of Stipa tenacissima L., its capacity to recover and its adaptation potential considering dormancy and viability after exposure to salinity and drought. Seed traits characterised before germination were tested. The seeds were incubated at temperatures of 10 to 30 °C and low osmotic potentials were induced using sodium chloride (NaCl) or polyethylene glycol (PEG 6000) solutions of 0 to −1.6 MPa. The capacity of seeds to recover and remain viable under stress conditions was quantified. Our results proved that the seed yields and sizes were uniform. The analysis of cardinal temperature by thermal time model exhibited an optimal germination temperature (T o) of about 19 °C, a base temperature (T b) of 0.6 °C and a ceiling temperature (T c) of 31 °C at 0 MPa. The base water potential Ψb (50) values ranged between −0.83 and −1.54 MPa and between −0.97 and −2.27 MPa for osmotic and salt stresses, at 30 °C and 20 °C, respectively. In conclusion, the species showed a lower seed recruitment related to a low drought tolerance (drought tolerance index = −0.5 MPa), To requirement and threshold sensitivity. Under salt stress, S. tenacissima used osmotic adjustment in order to germinate in a lower osmotic potential.

Comparison of the effect of temperature and water potential on the seed germination of five Pedicularis kansuensis populations from the Qinghai-Tibet plateau.

Temperature and water potentials are considered the most critical environmental factors in seed germinability and subsequent seedling establishment. The thermal and water requirements for germination are species-specific and vary with the environment in which seeds mature from the maternal plants. Pedicularis kansuensis is a root hemiparasitic weed that grows extensively in the Qinghai-Tibet Plateau's degraded grasslands and has seriously harmed the grasslands ecosystem and its utilization. Information about temperatures and water thresholds in P. kansuensis seed germination among different populations is useful to predicting and managing the weed's distribution in degraded grasslands. The present study evaluated the effects of temperature and water potentials on P. kansuensis seed germination in cool and warm habitats, based on thermal time and hydrotime models. The results indicate that seeds from cool habitats have a higher base temperature than those from warm habitats, while there is no detectable difference in optimum and ceiling temperatures between habitats. Seed germination in response to water potential differed among the five studied populations. There was a negative correlation between the seed populations' base water potential for 50% (Ψ b(50)) germination and their hydrotime constant (θ H). The thermal time and hydrotime models were good predictors of five populations' germination time in response to temperature and water potentials. Consequently, future studies should consider the effects of maternal environmental conditions on seed germination when seeking effective strategies for controlling hemiparasitic weeds in alpine regions.

Modeling Phenological Phases of Winter Wheat Based on Temperature and the Start of the Growing Season

The phenological phases of field crops have shifted to earlier times in the Czech Republic in recent decades; additionally, they have shown correlations with temperatures from previous spring months. Using a thermal time model called PhenoClim, the correlations between temperatures and phenophases allow us to evaluate the strongest predictors (i.e., maximum temperature) and indicators of base temperatures and growing degree days for the selected phenophases of winter wheat (Triticum aestivum L.). With the help of this model, it is possible to explain 0.6–0.82% of the phase variability and to estimate the onset of phenophases for the selected time period and stations (with the RMSE values of 9.4 days for jointing, 4.3 days for heading, and 5.3 days for full ripeness). To further refine the modeled onsets of phenophases, we used satellite data, specifically the normalized difference vegetation index and the enhanced vegetation index 2 from MODIS; based on these vegetation indices, the start of the growing season (SOS) was determined. After including SOS to model PhenoClim, we modeled the onsets of phenophases, with average accuracies ranging from 6.2 to 15.2. By combining the thermal time model and remote sensing data, specifically the data concerning the determination of SOS, we can refine the modeling of the onset of full ripeness in some locations.

Effect of temperature and water potential on the germination of seeds from three different populations of Bidens pilosa as a potential Cd hyperaccumulator

BackgroundBidens pilosa L., an annual herb, has recently been shown to be a potential Cd-hyperaccumulating plant. The germination characteristics of B. pilosa have been documented, while the difference among populations remains unclear. Understanding variability in seed germination among populations is crucial for determining which populations to use for soil remediation programs.ResultsPresent study was conducted to compare the requirements of temperature and water potential for germination of B. pilosa cypselae (the central type, hereafter seeds) from three populations using the thermal time, hydrotime, and hydrothermal time models. Seeds of three populations were incubated at seven constant temperatures (8, 12, 15, 20, 25, 30, and 35 °C) and at each of four water potentials (0, -0.3, -0.6, and -0.9 MPa). The results showed that germination percentage and rate of B. pilosa seeds were significantly by population, temperature, water potential and their interaction except for the interaction of population and water potential. Seeds from Danzhou population displayed a higher base temperature (Tb) for germination than those from Guilin and Baoshan population, however the ceiling temperature (Tc) had no consistent level among the populations but varied according to the water potential. In addition, the median base water potential [ψb(50)] for germination of seeds from Danzhou population was higher than that for seeds from Baoshan and Guilin population at low temperatures (< 25 °C), which was opposite at high temperatures (≥ 25 °C).ConclusionSeed germination requirements of B. pilosa on temperature and water differed significantly among populations. Differences in seed germination among populations may be complicated, which could not be simply explained by the temperature and rainfall conditions where the seeds were produced as previously reported. The results suggested that programme management should consider variation in seed germination traits when select which population could be applied to what kind of target remediation sites.

Finding the right thermal limit: a framework to reconcile ecological, physiological and methodological aspects of CTmax in ectotherms.

Upper thermal limits (CTmax) are frequently used to parameterize the fundamental niche of ectothermic animals and to infer biogeographical distribution limits under current and future climate scenarios. However, there is considerable debate associated with the methodological, ecological and physiological definitions of CTmax. The recent (re)introduction of the thermal death time (TDT) model has reconciled some of these issues and now offers a solid mathematical foundation to model CTmax by considering both intensity and duration of thermal stress. Nevertheless, the physiological origin and boundaries of this temperature-duration model remain unexplored. Supported by empirical data, we here outline a reconciling framework that integrates the TDT model, which operates at stressful temperatures, with the classic thermal performance curve (TPC) that typically describes biological functions at permissive temperatures. Further, we discuss how the TDT model is founded on a balance between disruptive and regenerative biological processes that ultimately defines a critical boundary temperature (Tc) separating the TDT and TPC models. Collectively, this framework allows inclusion of both repair and accumulation of heat stress, and therefore also offers a consistent conceptual approach to understand the impact of high temperature under fluctuating thermal conditions. Further, this reconciling framework allows improved experimental designs to understand the physiological underpinnings and ecological consequences of ectotherm heat tolerance.