Cardinal Temperatures Research Articles

Germination response of three Setaria species (S. viridis, S. verticillata, and S. glauca) to water potential and temperature using non-linear regression and hydrothermal time models

Understanding factors influencing the time of weed seedling establishment can contribute to developing predictive models for control measures at early growth stages. Non-linear regression models (Dent-like and Quadratic polynomial) and hydrothermal time models were considered for estimating cardinal temperature and predicting the emergence time of the Setaria species (S. viridis, S. verticillata, and S. glauca) at different constant temperatures and water potentials. Field experiments were also conducted, in which seeds of the species were sown and seedling emergence was recorded daily. The optimum temperature for germination was 27.7, 30.2, and 30.5 °C as estimated by a Dent-like model at 0 MPa water potential for S. glauca, S. viridis and S. verticillata, respectively. According to the hydrotime model, the minimum amount of base water potential (Ψb) was observed at the optimum temperatures, while it reached its highest value at temperatures exceeding the optimum. Overall, at sub-optimal temperatures, with the decrease in water potential, the thermal time (TT) constant increased linearly until − 0.6 MPa, but this trend was downward at supra-optimal temperatures. The hydrothermal time constant (θHT) was 213.5, 228.8, and 318.8 MPa °C h for S. viridis, S. verticillata, and S. glauca, respectively. Non-linear regression and hydrothermal models showed that S. glauca can emerge earlier than other species because of lower base temperature and a higher hydrothermal time constant. Setaria species did not show a significant difference in their tolerance to water stress by similar base water potential (Ψb(50) ~ − 0.5).

Climatic determinants of lowland rice development

AbstractAccurate modelling of plant development is the basis for any assessment of climate change impact on crop yields. Most rice models simulate development (phenology) based on temperature and photoperiod, but often the reliability of these models is reduced beyond the environment they were calibrated for. In our study, we tested the effects of relative air humidity and solar radiation on leaf appearance rate in greenhouse experiments and analysed data sets from field studies conducted in two extremely different rice‐growing environments in Nepal and Senegal. We also analysed environmental effects on duration to flowering of one popular IRRI material (IR64) for eight different sites covering the entire temperature range where rice is widely cultivated. Both low relative air humidity and low solar radiation significantly decreased leaf appearance rate. Mean air temperature explained 81% of the variation in duration to flowering across sites, which was furthermore significantly influenced by relative air humidity. Across all sites, a simple linear regression approach including mean air temperature and mean relative humidity in the calculation of duration to flowering led to a root mean square error (RMSE) of 10 days, which was slightly lower than the RMSE of 11 days achieved with an automated calibration tool for parameter optimization of cardinal temperatures and photoperiod sensitivity. Parameter optimization for individual sites led to a much smaller prediction error, but also to large differences in cardinal temperatures between sites, mainly lower optimum temperatures for the cooler sites. To increase the predictive power of phenological models outside their calibration range and especially in climate change scenarios, a more mechanistic modelling approach is needed. A starting point could be including relative air humidity and radiation in the simulation procedure of crop development, and presumably, a closer link between growth and development procedures could help to increase the robustness of phenological models.

Bacillus firmus Strain I-1582, a Nematode Antagonist by Itself and Through the Plant.

Bacillus firmus I-1582 is approved in Europe for the management of Meloidogyne on vegetable crops. However, little information about its modes of action and temperature requirements is available, despite the effect of these parameters in its efficacy. The cardinal temperatures for bacterial growth and biofilm formation were determined. The bacteria was transformed with GFP to study its effect on nematode eggs and root colonization of tomato (Solanum lycopersicum) and cucumber (Cucumis sativus) by laser-scanning confocal microscopy. Induction of plant resistance was determined in split-root experiments and the dynamic regulation of genes related to jasmonic acid (JA) and salicylic acid (SA) by RT-qPCR at three different times after nematode inoculation. The bacteria was able to grow and form biofilms between 15 and 45°C; it degraded egg-shells and colonized eggs; it colonized tomato roots more extensively than cucumber roots; it induced systemic resistance in tomato, but not in cucumber; SA and JA related genes were primed at different times after nematode inoculation in tomato, but only the SA-related gene was up-regulated at 7 days after nematode inoculation in cucumber. In conclusion, B. firmus I-1582 is active at a wide range of temperatures; its optimal growth temperature is 35°C; it is able to degrade Meloidogyne eggs, and to colonize plant roots, inducing systemic resistance in a plant dependent species manner.

Microbial Heat and Organic Matter Loss in an Aerobic Corn Stover Storage Reactor: A Model Validation and Prediction Approach Using Lumped-Parameter Dynamical Formulation.

Corn stover dry matter loss effects variability for biofuel conversion facility and technology sustainability. This research seeks to understand the dynamic mechanisms of the thermal system, organic matter loss, and microbial heat generation in corn stover storage operations through system dynamics, a mathematical modeling approach, and response analysis to improve the system performance. This study considers epistemic uncertainties including cardinal temperatures of microbial respiratory activity, specific degradation rate, heat evolution per unit substrate degraded, and thermal conductivity in corn stover storage reactors. These uncertainties were managed through calibration, a process of improving the agreement between the computational and benchmark experimental results by adjusting the parameters of the model. Model calibration successfully predicted the temperature of the system as quantified by the mean absolute error, 0.6°C, relative to the experimental work. The model and experimental dry matter loss after 30 days of storage were 5.1% and 4.9 ± 0.28%. The model was further validated using additional experimental results to ensure that the model accurately represented the system. Model validation obtained a temperature mean absolute relative error of 0.9 ± 0.3°C and dry matter loss relative error of 3.1 ± 1.5%. This study presents a robust prediction of corn stover storage temperature and demonstrates that an understanding of carbon sources, microbial communities, and lag-phase evolution in bi-phasic growth are essential for the prediction of organic matter preservation in corn stover storage systems under environment’s variation.

Germination response to temperature and water potential for Sprawling bauhinia (Tylosema fassoglense), a potential crop for Kenya

The knowledge of cardinal temperatures is critical for understanding environmental tolerance limits for germinating plant species. However, this information is not readily available for Tylosema fassoglense [Family: Fabaceae]; despite its potential as a future crop to improve nutrition and enhance sustainable agriculture in Kenya.The objective of this study was to characterise seed germination responses to temperature and water potential of seed lots of T. fassoglenseseeds collected from three counties in Kenya; namely Busia, Migori and Siaya.Scarified seeds were germinated at a wide range of constant temperatures from 10 to 45 °C with intervals of 5 °C and water potentials from 0, -0.25, -0.5, -1.0, -1.5 Megepascal (MPa) at 25 °C.Seeds of T. fassoglense had a wide range of germination temperature of 20 °C (from 15 to 35 °C). Low (10 °C) and high (≥40 °C) temperatures significantly reduced germination in the three seed lots. Busia seed lot had the lowest final germination of 5% at 10 °C while germination was zero at 45 °C in all the seed lots tested. The calculated base, optimal and ceiling temperature (Tb, To and Tc) ranges were 4.05 - 8.0 °C; 33.61 - 35.75 °C; and 46.54 - 47.24 °C, respectively. Suboptimal and supraoptimal thermal time (θT(50)) ranged between 76.19 – 89.02 degree celcius days (°C d) and 30.3–41.89 °C d respectively. Water potential of -0.5 MPa significantly reduced final germination to less than 50% in all seed lots while germination was zero at both -1.0 and -1.5 MPa. The base water potential (Ψb) and hydro time (θH(20)) was between -0.92 to -0.97 MPa and 3.95–4.11 Megapascal days (MPad) respectively.The optimum temperature range for germination was 30–35 °C and seeds were tolerant to low water potential up to -0.5 MPa. However, further studies will need to be carried out on germination in the supraoptimal temperature range and water potential between 0 and -1.0 MPa. The findings in this study will be useful in future research contributing towards domestication of T. fassoglense.

Simulating the Influences of Soil Water Stress on Leaf Expansion and Senescence of Winter Wheat

Current crop models usually need a lot of input information to simulate crop leaf area index and have relatively large simulation errors under soil water stress, which need to be improved. In this study, based on experiments conducted in glass soil columns and field under rainout shelters in four years (2012-2016) in Yangling, Shaanxi Province in China, we attempted to establish a dynamic model for simulating leaf expansion and senescence of winter wheat under soil water stress. First, a temperature response function was established with four cardinal temperatures (base temperature, lower optimum temperature, higher optimum temperature, and maximum temperature). Then two soil water stress functions were established to quantify the effect of soil water stress on the processes of leaf expansion and leaf senescence of main stem per plant. The first order derivative of a logistic function was then modified with the temperature and soil water stress response function and was used to simulate the daily rate of leaf area expansion and senescence of main stem. The parameters of the new model were estimated using the Solver add-in in MS Excel and then validated based on the data of soil column experiments in 2014-2015 growing season. Then the new model was evaluated with another dataset of column experiments conducted in 2015-2016. Furthermore, the influence of soil water stress on wheat tillering was included in the new model based on open field experiments in 2012-2013 growing season. Then, the new leaf area index (LAI) simulation model was further verified with the data of open field experiments under rainout shelter (2013-2014) and rainfed condition (2004-2005, 2005-2006, and 2008-2009) in different sites. A comparison was conducted between new LAI model and the original LAI module of CERES-Wheat. The results showed that the leaf expansion rate was not affected when the relative soil water availability was greater than 0.7; water stress inhibited the leaf expansion when relative soil water availability was between 0.2 and 0.7; leaves withered and yellowed when relative soil water availability was less than 0.2. The overall average root mean square error (RMSE) and residual accumulation coefficient (CRM) were 9.78 cm2 plant−1, -0.03, and 6.51 cm2 plant−1; 0.05 for model calibration and validation, respectively. The RMSE of LAI decreased by an average of 47.89% compared with the original LAI module of CERES-Wheat. The results of this study can help to improve the current CERES-Wheat model for model applications in the arid and semi-arid regions of China.

Dormancy and cardinal temperatures for germination in seed from nine quinoa genotypes cultivated in Chile

AbstractIn Chile, two quinoa ecotypes are grown: salares, also present in the highlands of Bolivia, and coastal, in central and southern areas of the country, at sea level. Genotypes from the coastal ecotype have characteristics that differentiate them from the most popular quinoa genotypes grown in the Andean Region of South America. The objectives of this study were: (1) to determine the cardinal temperatures for seed germination in quinoa genotypes from coastal and salares ecotypes cultivated in Chile, and (2) to study the presence of physiological dormancy (PD) in these genotypes. Seed germination from nine quinoa genotypes, two from salares and seven from coastal ecotypes, was evaluated in a gradient of temperatures between 11 and 42°C. Germination was also evaluated at 20°C at 0, 7 and 15 months from harvest. Results showed that seed from the nine genotypes germinated at their maximum percentage between 11 and 35°C. However, their faster germination occurred between 25 and 35°C. There was a significant difference between optimum temperature for germination between genotypes from coastal (28°C) and salares (30°C). An increase in germination rates after 7 months of storage suggested the presence of a non-deep PD in seeds from coastal ecotype, which may be useful to improve pre-harvest sprouting resistance in quinoa breeding programmes.

Experimental and Model-Based Analysis to Optimize Microalgal Biomass Productivity in a Pilot-Scale Tubular Photobioreactor.

A dynamic coarse-grained model of microalgal growth considering light availability and temperature under discontinuous bioprocess operation was parameterized using experimental data from 15 batch cultivations of Nannochloropsis granulata in a pilot-scale tubular photobioreactor. The methodology applied consists of a consecutive two-step model parameter estimation using pooled, clustered and reorganized data to obtain initial estimates and multi-experiment fitting to obtain the final estimates, which are: maximum specific growth rate μmax = 1.56 d−1, specific photon half-saturation constant KS,ph = 1.89 , specific photon maintenance coefficient mph = 0.346 and the cardinal temperatures Tmin = 2.3°C, Topt = 27.93°C and Tmax = 32.59°C. Biomass productivity prediction proved highly accurate, expressed by the mean absolute percent error MAPE = 7.2%. Model-based numerical optimization of biomass productivity for repeated discontinuous operation with respect to the process parameters cultivation cycle time, inoculation biomass concentration and temperature yielded productivity gains of up to 35%. This optimization points to best performance under continuous operation. The approach successfully applied here to small pilot-scale confirms an earlier one to lab-scale, indicating its transferability to larger scale tubular photobioreactors.

Effect of temperature and water potential on Alyssum homolocarpum seed germination: Quantification of the cardinal temperatures and using hydro thermal time

This research was carried out to quantify the rate of Alyssum homolocarpum germination in response to temperature, and water potential. We compared three nonlinear regression models (Dent-like, segmented, and beta) to describe the germination rate-temperature relationships of Alyssum homolocarpum. The seeds were germinated at seven temperatures (5,10,15,20,25,30 and 35 °C) and six water potentials (0,-0.2,-0.4,-0.6,-0.8 and -1 MPa). The results revealed that the segmented function (RMSE = 0.28, R2 = 0.82, and r = 0.90) is suitable for describing the response to temperature, and water potential. Seeds did not germinate at 5 and 35 °C. Under different water potentials, base, optimum and ceiling temperatures ranged in 4.96 to 6.37 °C, 13.98 to 15.00 °C, and 28.7 to30 °C, respectively. The hydro time constant for SSG (θH), the middle value for the base water potential (Ψb(50), the standard deviation in base water in the water potential (σyb) and the thermal time constant for SSG (θT) spanned the values of 2.38–133.48 MPa h, −1.64–0.09 bar and 345.3–1477.3 °C h, respectively. The hydrothermal time parameters were 845.12 bar °C h, −1.114 MPa and, 57.3 °C for θHT (hydrothermal time constant), and Ψb(50) (median base water potential), Tb (base temperature) in temperatures and water potentials, respectively This low-temperature range for germination and the ability to germinate rapidly suggest the high potential of Alyssum homolocarpum to establish in most areas.

Comparing temperature sensitivity of bacterial growth in Antarctic marine water and soil.

The western Antarctic Peninsula is an extreme low temperature environment that is warming rapidly due to global change. Little is known, however, on the temperature sensitivity of growth of microbial communities in Antarctic soils and in the surrounding oceanic waters. This is the first study that directly compares temperature adaptation of adjacent marine and terrestrial bacteria in a polar environment. The bacterial communities in the ocean were adapted to lower temperatures than those from nearby soil, with cardinal temperatures for growth in the ocean being the lowest so far reported for microbial communities. This was reflected in lower minimum (Tmin ) and optimum temperatures (Topt ) for growth in water (-17 and +20°C, respectively) than in soil (-11 and +27°C), with lower sensitivity to changes in temperature (Q10 ; 0-10°C interval) in Antarctic water (2.7) than in soil (3.9). This is likely due to the more stable low temperature conditions of Antarctic waters than soils, and the fact that maximum in situ temperatures in water are lower than in soils, at least in summer. Importantly, the thermally stable environment of Antarctic marine water makes it feasible to create a single temperature response curve for bacterial communities. This would thus allow for calculations of temperature-corrected growth rates, and thereby quantifying the influence of factors other than temperature on observed growth rates, as well as predicting the effects of future temperature increases on Antarctic marine bacteria.

Increasing the species diversity in the Aspergillus section Nidulantes: Six novel species mainly from the indoor environment

ABSTRACTAspergillus section Nidulantes encompasses almost 80 homothallic and anamorphic species, mostly isolated from soil, plant material, or the indoor environment. Some species are clinically relevant or produce mycotoxins. This study reevaluated the species boundaries within several clades of section Nidulantes. Five data sets were assembled, each containing presumptive new species and their closest relatives, and phylogenetic and phenotypic analyses were performed. We tested the hypotheses that the newly isolated or reexamined strains constitute separate species (splitting approach) or should be treated as part of broadly defined species (lumping approach). Four DNA sequence loci were amplified, internal transcribed spacer (ITS) and large subunit (LSU) regions of the rDNA and partial sequences of the β-tubulin (benA), calmodulin (CaM), and RNA polymerase II second largest subunit (RPB2) genes. The latter three loci were used for the phylogenetic analysis and served as input for single-locus (GMYC, bGMYC, PTP, and bPTP) and multilocus (STACEY and BP&P) species delimitation analyses. The phenotypic analysis comprised macro- and micromorphology (including scanning electron microscopy) and comparison of cardinal growth temperatures. The phylogenetic analysis supported the splitting hypothesis in all cases, and based on the combined approach, we propose six new species, four that are homothallic and two anamorphic. Four new species were isolated from the indoor environment (Jamaica, Trinidad and Tobago, USA), one originated from soil (Australia), and one from a kangaroo rat cheek pouch (USA).

Simulation of plant height of winter wheat under soil Water stress using modified growth functions

Plant height is an important trait that influences the yield and sustainability of wheat productions. It is also an important objective for agronomic breeding and a critical indicator to represent the status of crop growth and nitrogen absorption in the vegetative stage. Wheat is the main crop in arid regions. However, there is insufficient understanding of wheat plant height response to soil water stress. In this study, we tried to explore a new algorithm for simulating dynamics of winter wheat height under different scenarios of soil water stress based on soil column and field experiments conducted under rainout shelters between 2012 and 2016 at Yangling, Shaanxi province, China. First, we established a temperature response function of wheat plant height based on four cardinal temperatures (i.e. base temperature, lower optimal temperature, higher optimal temperature, and ceiling temperature). And we also constructed a water stress response function of wheat plant height using relative soil water availability (Aw) as water stress index. Then, these two functions were used as multipliers to modify the first-order derivative of six distinct growth functions (i.e. Gompertz, Logistic, Mischerlich, Richards, Von Bertalanffy, and Weibull) to represent the elongation rate of wheat plant height under soil water stresses. Consequently, six modified simulation models for wheat plant height were established and identified as Mod-Geo, Mod-Log, Mod-Mis, Mod-Ric, Mod-Von, and Mod-Wei, respectively, among which an optimal simulation model was selected for winter wheat growth under soil water stresses. Based on experimental data of 2014–2015 used for model calibration, it was found that when Aw was greater than 0.65, elongation rate of wheat height was not influenced by soil water content; when Aw was between 0.3 and 0.65, elongation rate of wheat height gradually reduced following an exponential function driven by water stress; when Aw was less than 0.30, elongation rate of wheat height rapidly and linearly reduced driven by water stress until Aw was close to 0 at which the elongation stopped. After that, the data of soil column experiment of 2014–2015 growing season were used to assess the parameters of the six newly established models. The results of model calibration showed that the mean value of the Willmott Index of Agreement (WIA) between measured and simulated wheat heights of the six cultivars were all less than 0.90 for all treatments in the experiment, except for the Mod-Log model (0.95). The data of soil column experiment in 2015–2016 seasons were used to validate the six calibrated new models. The results of model validation with mean value of WIA 0.93 which were even better than model calibration. Finally, the data of two growing seasons (2012–2013 and 2013–2014) of field experiments conducted under a giant rainout shelter were used for further verification of the six new models under field conditions. Among the six different plant height simulation model, Mod-Log model obtained the best values of RMSE and WIA.

Media preferences, micro-morphometric analysis, and cardinal growth temperature determination for Phytophthora infestans sensu lato isolated from different hosts in Colombia.

During the last years Phytophthora infestans sensu lato (Mont. De Bary) has caused epidemics in Colombia in Andean fruit crops such as Solanum quitoense and Solanum betaceum. Establishment of new or modified experimental procedures to study this pathogen is a mandatory subject for scientists. Twelve isolates of Phytophthora spp. obtained from six different Solanum hosts in Colombia were used to evaluate the effect of five different solid media for growth and ability to produce sporangia and liberate zoospores. Determination of the best media culture and optimal growth temperature were necessary to perform measurements and correlate the provenance of isolates with phenotypic traits. Modifications were made to use ingredients available in local markets on the following media: lime bean agar (LBA), Tree tomato or tree tomato agar (TA), carrot agar (AZ), Rye A modified agar and 32% non-clarified V8 agar. Cardinal temperature determination was performed at 10, 15, 20, and 25 °C. Morphometric traits were measured once the optimal media culture and temperature were defined. Correlation analysis showed that there is a relationship between the host and isolate's preferences for media culture and optimal growth temperature. In addition, the production of characteristic sporangia, sporangiophore and mycelia was related with the media type used and host from which the isolate was collected. In this work useful information was provided to make studies about the biology and development of isolates gathered from cultivated and wild non-traditional hosts.

Combining Simple Phenotyping and Photothermal Algorithm for the Prediction of Soybean Phenology: Application to a Range of Common Cultivars Grown in Europe.

Developing new cropping strategies (very early sowing, crop expansion at higher latitudes, double cropping) to improve soybean production in Europe under climate change needs a good prediction of phenology under different temperature and photoperiod conditions. For that purpose, a simple phenology algorithm (SPA) was developed and parameterized for 10 contrasting soybean cultivars (maturity group 000 to II). Two experiments were carried out at INRA Toulouse (France) for parameterization: 1) Phenological monitoring of plants in pots on an outdoor platform with 6 planting dates. 2) Response of seed germination to temperature in controlled conditions. Multi-location field trials including 5 sites, 4 years, 2 sowing dates, and 10 cultivars were used to evaluate the SPA phenology predictions. Mean cardinal temperatures (minimum, optimum, and maximum) for germination were ca. 2, 30, and 40°C, respectively with significant differences among cultivars. The photoperiod sensitivity coefficient varied among cultivars when fixing Popt and Pcrt, optimal and critical photoperiods respectively, by maturity group. The parameterized algorithm showed an RMSE of less than 6 days for the prediction of crop cycle duration (i.e. cotyledons stage to physiological maturity) in the field trials including 75 data points. Flowering (R1 stage), and beginning of grain filling (R5 stage) dates were satisfactorily predicted with RMSEs of 8.2 and 9.4 days respectively. Because SPA can be also parameterized using data from field experiments, it can be useful as a plant selection tool across environments. The algorithm can be readily applied to species other than soybean, and its incorporation into cropping systems models would enhance the assessment of the performance of crop cultivars under climate change scenarios.

Characterization and pathogenicity of threePhytophthoraspp. recovered from rivers in Bulgaria

AbstractManyPhytophthoraspecies are pathogens on fruit trees and may cause destructive diseases. In the current study, we examined sixPhytophthoraisolates recovered from rivers in Bulgaria, representatives of the following three species:Phytophthora chlamydospora,P. pseudocryptogeaandP. syringae. Morphological traits, cardinal temperatures and growth rates of the isolates were described. We found considerable variation in the size of sporangia and significant difference in the mycelial growth rates of the twoP. pseudocryptogeaisolates, along with multiple polymorphic sites in the ITS region of one of them. In the cases of the other twoPhytophthoraspecies, no such differences were found between the isolates. BothP. chlamydosporaisolates had a lower optimum growth temperature compared with the reported in the literature for this species. In pathogenicity tests against leaves and fruits of apple, pear, cherry, apricot and plum, the isolates proved to be capable of causing infections with varying severity.P. chlamydosporashowed to be the most aggressive towards the leaves, whileP. pseudocryptogeaisolates induced the highest percentage of decay on the fruits of all tested tree species, which may suggest partial organ or tissue specificity. The demonstrated infection capacity of the described isolates points out the investigatedPhytophthoraspecies as a potential threat for the orchards in Bulgaria, if favourable conditions are available.

Germination and seed ecology of Buchenavia tomentosa Eichler (Combretaceae)

Abstract: Buchenavia tomentosa produces fruits with ecological function for Cerrado’s fauna. The aims of this paper were to quantify seed germination and behavior on thermal conditions and explain about water absorption of dispersal structure in B. tomentosa seeds. Ripe fruits were pulped, the endocarp removed, and seeds used in the germination tests at temperatures of 10 to 45 °C. Seeds were placed in rolls of filter paper and then placed in germination chambers, at twelve hours of photoperiod. Germination models at sub and supra optimal temperatures were made from the germination rate (Tg), from the time to germination of 50% of the seeds (t50). Germination speed index (GSI), measurements of shoot and root lengths and dry mass at each temperature were obtained. The water imbibition curve of seed with or without endocarp adhered and scarified or not was made and other samples were tested for emergence in sand. Cardinal temperatures were: base temperature (Tb) of 9.23 °C; maximum temperature (Tmax) of 44.6 °C; optimum temperature (To) of 29.24 °C and thermal time of 89.71 °C.days. Seedlings showed higher GSI, root and aerial part length and higher root dry mass at the optimal temperature. The endocarp retards, but does not prevent water absorption and emergence.

Germination behaviour of Conyza bonariensis to constant and alternating temperatures across different populations

AbstractConyza bonariensis is one of the most problematic weed species throughout the world. It is considered highly noxious due to its interference with human activities, and especially the competition it poses with economically important crops. This research investigated the temperature requirements for seed germination of four populations of C. bonariensis with distinct origin and the influence of daily alternating temperatures. For this, a set of germination tests were performed in growth chambers to explore the effect of constant and alternating temperatures. Seeds of the four populations (from Lleida, Badajoz and Seville, Spain and Bahía Blanca, Argentina) were maintained at constant temperatures ranging from 5 to 35°C. The final germination and cardinal temperatures (base, optimum and maximum) of each population were obtained. We also tested the influence of daily alternating temperatures on final germination. To do so, seeds were exposed to two temperature regimes: 5/15, 10/20, 15/25, 20/30 and 25/35°C night/day temperature (intervals increasing 5°C, with constant oscillation of 10°C) and to 18/22, 16/24, 14/26, 12/28 and 10/30°C night/day temperature (intervals with average of 20°C, but increasing the oscillation in 4°C between intervals). In general, all populations behaved similarly, with the highest germination percentages occurring in the optimum temperature range (between 21.7°C and 22.3°C) for both constant and alternating temperatures. In general, climatic origin affected germination response, where seeds obtained from the coldest origin exhibited the highest germination percentage at the lowest temperature assayed. In addition, we observed that the alternating temperatures can positively affect total germination, especially in oscillations that were further from the average optimum temperature (20°C), with high germination percentage for the oscillations of 15/25, 20/30, 18/22, 16/24, 14/26, 12/28 and 10/30°C in all populations. The cardinal temperatures obtained were significantly different across the populations. These results provide information that will facilitate a better understanding of the behaviour of Conyza and improve current field emergence models.

Guar responses to temperature: Estimation of cardinal temperatures and photosynthetic parameters

Temperature is the primary environmental determinant of geographic distribution and productivity of plant species. There has been increased interest in the cultivation of guar [Cyamopsis tetragonoloba (L.) Taub.] in many countries including the United States due to the high demand of guar gum in the oil fracking industry. However, information on gaur response to temperature is still lacking in the current literature. An experiment was conducted using six different day/night temperature regimes (20/12, 24/16, 28/20, 32/24, 36/28 and 40/32 °C) maintained inside walk-in growth chambers of the Controlled Environment Research Facility at Oklahoma State University. The objectives of this study were to evaluate the temperature responses of vegetative growth, development, and reproduction of guar to estimate cardinal temperatures, and to evaluate photosynthetic responses to temperature gradient. The vegetative growth of guar was sensitive to low temperature (<20 °C), and has high mean cardinal temperatures (Tmin, Topt, and Tmax) for biomass accumulation (14.2, 34.1 and 48.2 °C). Plants exhibited reproductive development within a narrow range (19–31 °C) with maximum pod yields observed at a Topt of 25 °C. Higher temperature regimes (36/28 and 40/32 °C) completely suppressed flower initiation in guar. Responses of photosynthesis to both light and internal CO2 concentration (A-Ci) suggested guar photosynthetic rates increased under high temperature through an increased rate of electron transport. The identified cardinal temperatures and photosynthesis parameters can be used to develop mechanistic crop models to simulate adaptation strategies for guar. Further research is required to investigate the basis for suppression of flower bud initiation under heat stress.

Cardinal temperatures and modeling of vegetative development in guava

ABSTRACT The aim of this study was to estimate cardinal temperatures (base, optimum, and maximum), and simulate the vegetative development of guava crop through phyllochron (linear) and Wang and Engel (nonlinear) models at the seedling phase. The experiment was conducted in Itajubá, MG, Brazil (22° 24’ 46.43” S 45° 26’ 48.94” W), for two years in a completely randomized design with twelve sowing dates and five experimental units per treatment, totaling sixty experimental units. The cardinal temperatures were estimated using twelve methods described in the literature and the values were: base, 10.9 °C, optimum, 17.3 °C and maximum, 51.2 °C. The phyllochron model was superior to Wang and Engel’s model for simulation of vegetative growth of guava, with root mean square error of 1.5 leaves.

The risk-takers and -avoiders: germination sensitivity to water stress in an arid zone with unpredictable rainfall.

Water availability is a critical driver of population dynamics in arid zones, and plant recruitment is typically episodic in response to rainfall. Understanding species’ germination thresholds is key for conservation and restoration initiatives. Thus, we investigated the role of water availability in the germination traits of keystone species in an arid ecosystem with stochastic rainfall. We measured seed germination responses of five arid species, along gradients of temperature and water potential under controlled laboratory conditions. We then identified the cardinal temperatures and base water potentials for seed germination, and applied the hydrotime model to assess germination responses to water stress. Optimum temperatures for germination ranged from 15 to 31 °C under saturated conditions (0 MPa), and three species had low minimum temperatures for germination (<3 °C). A small proportion of seeds of all species germinated under dry conditions (Ψ ≤ −1 MPa), although base water potential for germination (Ψ b50) ranged from −0.61 to −0.79 MPa. Species adhered to one of two germination traits: (i) the risk-takers which require less moisture availability for germination, and which can germinate over a wider range of temperatures irrespective of water availability (Casuarina pauper and Maireana pyramidata), and (ii) the risk-avoiders which have greater moisture requirements, a preference for cold climate germination, and narrower temperature ranges for germination when water availability is low (Atriplex rhagodioides, Maireana sedifolia and Hakea leucoptera). High seed longevity under physiological stress in H. leucoptera, combined with a risk-avoiding strategy, allows bet-hedging. The hydrotime model predicted lower base water potentials for germination than observed by the data, further supporting our assertion that these species have particular adaptations to avoid germination during drought. This study provides insights into the complex physiological responses of seeds to environmental stress, and relates seed germination traits to community dynamics and restoration in arid zones.