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1.
Specific growth rate of Cryptomonas ovata var. palustris Pringsheim was measured in batch culture at 14 light-temperature combinations. Both the maximum growth rate (μ m) and optimum light intensity (Iopt) fit an empirical function that increases exponentially with temperature up to an optimum (Topt), then declines rapidly as temperature exceeds Topt. Incorporation of these functions into Steele's growth equation gives a good estimate of specific growth rate over a wide range of temperature and light intensity. Rates of phosphate, ammonium and nitrate uptake were measured separately at 16 combinations of irradiance and temperature and following a spike addition of all starved cells initially took up nutrient at a rapid rate. This transitory surge was followed by a period of steady, substrate-saturated uptake that persisted until external nutrient concentration fell. Substrate-saturated NO 3?-uptake proceeded at very slow rates in the dark and was stimulated by both increased temperature and irradiance; NH 4+-uptake apparently proceeded at a basal rate at 8 and l4 C and was also stimulated by increased temperature and irradiance. Rates of NH 4?-uptake were much higher than NO 3?-uptake at all light-temperature combinations. Below 20 C, PO 4?3-uptake was more rapid in dark than in light, but was light enhanced at 26 C. 相似文献
2.
The influence of sub-optimal temperatures (T) on the microbial growth rate (μ) has been assessed by means of dimensionless
variables: T dim = [T−T min]/[T opt−T min] and μ dim = μ/μ opt. T min represents the temperature at which there is no growth, T opt the optimum temperature at which the growth rate, μ opt, is maximum. Data sets, growth rate vs temperature, have been taken from the literature for 12 organisms (psychrotrophs, mesophiles and thermophiles). In order
to compare these organisms, the power law function has been used: [μ dim] = [T dim] α. The parameters μ opt and T opt are determined from direct readings whereas T min and αare estimated by means of a non-linear regression. An accurate estimation of T min is obtained providing low growth rate data are available. A wide range of optimal temperatures where the growth rate almost
equals μ opt prevents one from obtaining a narrow confidence interval forα. On the basis of the analysis hereafter developed, thermophiles
are characterized by values of the power α less than mesophiles and psychrotrophs. Almost all of these values are significantly
different from two, previously determined for Staphylococcus xylosus and widely used for predicting the microbial growth in foods.
Received 15 May 1998/ Accepted in revised form 25 September 1998 相似文献
3.
Rising temperatures caused by climate change could negatively alter plant ecosystems if temperatures exceed optimal temperatures for carbon gain. Such changes may threaten temperature‐sensitive species, causing local extinctions and range migrations. This study examined the optimal temperature of net photosynthesis ( Topt) of two boreal and four temperate deciduous tree species grown in the field in northern Minnesota, United States under two contrasting temperature regimes. We hypothesized that Topt would be higher in temperate than co‐occurring boreal species, with temperate species exhibiting greater plasticity in Topt, resulting in better acclimation to elevated temperatures. The chamberless experiment, located at two sites in both open and understory conditions, continuously warmed plants and soils during three growing seasons. Results show a modest, but significant shift in Topt of 1.1 ± 0.21 °C on average for plants subjected to a mean 2.9 ± 0.01 °C warming during midday hours in summer, and shifts with warming were unrelated to species native ranges. The 1.1 °C shift in Topt with 2.9 °C warming might be interpreted as suggesting limited capacity to shift temperature response functions to better match changes in temperature. However, Topt of warmed plants was as well‐matched with prior midday temperatures as Topt of plants in the ambient treatment, and Topt in both treatments was at a level where realized photosynthesis was within 90–95% of maximum. These results suggest that seedlings of all species were close to optimizing photosynthetic temperature responses, and equally so in both temperature treatments. Our study suggests that temperate and boreal species have considerable capacity to match their photosynthetic temperature response functions to prevailing growing season temperatures that occur today and to those that will likely occur in the coming decades under climate change. 相似文献
4.
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. 相似文献
5.
Given prior evidence for local ecotypic and species-specific adaptation in trees, we hypothesized that: (1) Acer rubrum and Quercus rubra provenances with different climate origins should differ in photosynthetic temperature optimum ( T
opt) even after long-term growth in a common environment; (2) congeneric species Populus tremuloides and Populus deltoides with differing but overlapping ranges should not differ in T
opt when co-occurring, due to the likelihood of both ecotypic thermal adaptation and phenotypic thermal acclimation. To address
these questions, we investigated the temperature responses of pairs of A. rubrum and Q. rubra provenances planted in a common garden and the temperature responses of P. tremuloides and P. deltoides at four sites where the species ranges overlap in Minnesota, USA. Both studies showed significant signals of temperature
adaptation. The provenances of both A. rubrum and Q.
rubra that originated from northern sites with lower ambient temperature had lower T
opt. This supported the hypothesis about the dominance of local ecotypic adaptation of photosynthesis to temperature despite
opportunity for both long-term (12-year) acclimation to the common-garden temperature regime and short-term temperature acclimation.
However, acclimation capacity to the temperatures experienced in the days and weeks before the gas exchange measurements differed
among the contrasting provenances suggesting that the observed differences in T
opt could be due to either fixed genotypic differences (e.g., adaptive T
opt), acclimation of T
opt, or both. In contrast, the Populus species with the colder home range, P. tremuloides, showed significantly ( P < 0.05) lower T
opt on average than co-occurring P. deltoides. Thus, despite the opportunity for both ecotypic adaptation and local acclimation, phylogenetic inertia still constrained
the species with the colder overall range to a different temperature optimum than the one with a warmer overall range. Our
results also imply that rapid but modest climate change may create mismatches between photosynthetic physiology and local
climate because of lags in population or species-level adaptation. 相似文献
6.
Extreme climatic events, such as heat waves, cold snaps and drought spells, related to global climate change, have become more frequent and intense in recent years. Acclimation of plant physiological processes to changes in environmental conditions is a key component of plant adaptation to climate change. We assessed the temperature response of leaf photosynthetic parameters in wheat grown under contrasting water regimes and growth temperatures ( Tgrowth). Two independent experiments were conducted under controlled conditions. In Experiment 1, two wheat genotypes were subjected to well-watered or drought-stressed treatments; in Experiment 2, the two water regimes combined with high, medium and low Tgrowth were imposed on one genotype. Parameters of a biochemical C 3-photosynthesis model were estimated at six leaf temperatures for each factor combination. Photosynthesis acclimated more to drought than to Tgrowth. Drought affected photosynthesis by lowering its optimum temperature ( Topt) and the values at Topt of light-saturated net photosynthesis, stomatal conductance, mesophyll conductance, the maximum rate of electron transport ( Jmax) and the maximum rate of carboxylation by Rubisco ( Vcmax). Topt for Vcmax was up to 40°C under well-watered conditions but 24–34°C under drought. The decrease in photosynthesis under drought varied among Tgrowth but was similar between genotypes. The temperature response of photosynthetic quantum yield under drought was partly attributed to photorespiration but more to alternative electron transport. All these changes in biochemical parameters could not be fully explained by the changed leaf nitrogen content. Further model analysis showed that both diffusional and biochemical parameters of photosynthesis and their thermal sensitivity acclimate little to Tgrowth, but acclimate considerably to drought and the combination of drought and Tgrowth. The commonly used modelling approaches, which typically consider the response of diffusional parameters, but ignore acclimation responses of biochemical parameters to drought and Tgrowth, strongly overestimate leaf photosynthesis under variable temperature and drought. 相似文献
7.
Climate is an important factor limiting tree distributions and adaptation to different thermal environments may influence how tree populations respond to climate warming. Given the current rate of warming, it has been hypothesized that tree populations in warmer, more thermally stable climates may have limited capacity to respond physiologically to warming compared to populations from cooler, more seasonal climates. We determined in a controlled environment how several provenances of widely distributed Eucalyptus tereticornis and E. grandis adjusted their photosynthetic capacity to +3.5°C warming along their native distribution range (~16–38°S) and whether climate of seed origin of the provenances influenced their response to different growth temperatures. We also tested how temperature optima ( Topt) of photosynthesis and Jmax responded to higher growth temperatures. Our results showed increased photosynthesis rates at a standardized temperature with warming in temperate provenances, while rates in tropical provenances were reduced by about 40% compared to their temperate counterparts. Temperature optima of photosynthesis increased as provenances were exposed to warmer growth temperatures. Both species had ~30% reduced photosynthetic capacity in tropical and subtropical provenances related to reduced leaf nitrogen and leaf Rubisco content compared to temperate provenances. Tropical provenances operated closer to their thermal optimum and came within 3% of the Topt of Jmax during the daily temperature maxima. Hence, further warming may negatively affect C uptake and tree growth in warmer climates, whereas eucalypts in cooler climates may benefit from moderate warming. 相似文献
8.
Traits‐based approaches in microbial ecology provide a valuable way to abstract organismal interaction with the environment and to generate hypotheses about community function. Using macromolecular rate theory (MMRT), we recently identified that temperature sensitivity can be characterized as a distinct microbial trait. As temperature is fundamental in controlling biological reactions, variation in temperature sensitivity across communities, organisms, and processes has the potential to vastly improve understanding of microbial response to climate change. These microbial temperature sensitivity traits include the heat capacity (), temperature optimum ( Topt), and point of maximum temperature sensitivity (TS max), each of which provide unique insights about organismal response to changes in temperature. In this meta‐analysis, we analyzed the distribution of these temperature sensitivity traits from bacteria, fungi, and mixed communities across a variety of biological systems (e.g., soils, oceans, foods, wastewater treatment plants) in order to identify commonalities in temperature responses across these diverse organisms and reaction rates. Our analysis of temperature sensitivity traits from over 350 temperature response curves reveals a wide distribution of temperature sensitivity traits, with Topt and TS max well within biological relevant temperatures. We find that traits vary significantly depending on organism type, microbial diversity, source environment, and biological process, with higher temperature sensitivity found in fungi than bacteria and in less diverse systems. Carbon dioxide production was found to be less temperature sensitive than denitrification, suggesting that changes in temperature will have a potentially larger impact on nitrogen‐related processes. As climate changes, these results have important implications for basic understanding of the temperature sensitivity of biological reactions and for ecological understanding of species’ trait distributions, as well as for improved treatment of temperature sensitivity in models. 相似文献
9.
Soil microorganisms, the central drivers of terrestrial Antarctic ecosystems, are being confronted with increasing temperatures as parts of the continent experience considerable warming. Here we determined short‐term temperature dependencies of Antarctic soil bacterial community growth rates, using the leucine incorporation technique, in order to predict future changes in temperature sensitivity of resident soil bacterial communities. Soil samples were collected along a climate gradient consisting of locations on the Antarctic Peninsula (Anchorage Island, 67 °34′S, 68 °08′W), Signy Island (60 °43′S, 45 °38′W) and the Falkland Islands (51 °76′S 59 °03′W). At each location, experimental plots were subjected to warming by open top chambers (OTCs) and paired with control plots on vegetated and fell‐field habitats. The bacterial communities were adapted to the mean annual temperature of their environment, as shown by a significant correlation between the mean annual soil temperature and the minimum temperature for bacterial growth ( Tmin). Every 1 °C rise in soil temperature was estimated to increase Tmin by 0.24–0.38 °C. The optimum temperature for bacterial growth varied less and did not have as clear a relationship with soil temperature. Temperature sensitivity, indicated by Q10 values, increased with mean annual soil temperature, suggesting that bacterial communities from colder regions were less temperature sensitive than those from the warmer regions. The OTC warming (generally <1 °C temperature increases) over 3 years had no effects on temperature relationship of the soil bacterial community. We estimate that the predicted temperature increase of 2.6 °C for the Antarctic Peninsula would increase Tmin by 0.6–1 °C and Q10 (0–10 °C) by 0.5 units. 相似文献
10.
A thermotolerant yeast species of Lodderomyces elongisporus EH 60 was isolated and physiologically characterized. This yeast possesses a high specific growth rate with μ max = 0.61 h ?1. The dependence of the specific growth rate and cell yield on temperature, dilution rate, sucrose concentration and pH-value is investigated. Sucrose concentrations greater than 10 g/l inhibit the growth velocity. The specific growth rate μ can be calculated by a simple combination equation in the form: . The total optimum values for a sucrose-based continuous growth process with regard to the optimum cell yeild are: YS = 0.50 g DM/g S. Topt. = 38,6 °C and Dopt. = 0,35 h ?1. The function YS = f( D, T) is represented by a total model. 相似文献
11.
Responses of foliar light-saturated net assimilation rate ( Amax), capacity for photosynthetic electron transport ( Jmax) and mitochondrial respiration rate ( Rd) to long-term canopy light and temperature environment were investigated in a temperate deciduous canopy composed of Populus tremula L. in the upper (17–28 m) and of Tilia cordata Mill. in the lower canopy layer (4–17 m). Climatic measurements indicated that seasonal average daily maximum air temperature ( Tmax) was 5·5 °C (range 0·7–10·5 °C) higher in the top than in the bottom of the canopy, and strong positive correlations were observed between Tmax and seasonal average integrated quantum flux density ( Qint), as well as between seasonal average daily mean temperature and Qint. Because of changes in leaf dry mass and nitrogen per unit area, Amax, Jmax, and Rd scaled positively with Qint in both species at a common leaf temperature ( T). According to Jmax versus T response curves and dark chlorophyll fluorescence transients, photosynthetic electron transport was less heat resistant in P. tremula with optimum temperature of Jmax, Topt, of 33·5 ± 0·6 °C than in T. cordata with Topt of 40·7 ± 0·6 °C. This difference was suggested to manifest evolutionary adaptation of photosynthetic electron transport to cooler environments in P. tremula, the range of which extends farther north than that in T. cordata. Possibly because of acclimation to long-term canopy temperature environment, Topt was positively related to Qint in P. tremula, foliage of which was also exposed to higher irradiances and temperatures, but not in T. cordata, in the canopy of which quantum flux densities and temperatures were lower, and gradients in the environmental factors less pronounced. Parallel to changes in Topt, the activation energy for photosynthetic electron transport decreased with increasing Qint in P. tremula, indicating that Jmax of leaves acclimated to colder environment was more responsive to T in lower temperatures than that of high T acclimated leaves. Similar alterations in the activation energy for mitochondrial respiration rate were also observed, indicating that acclimation to temperature of mitochondrial and chloroplastic electron transport proceeds in a co-ordinated manner, and possibly involves long-term changes in membrane fluidity properties. We conclude that, because of correlations between temperature and light, the shapes of Jmax versus T, and Rd versus T response curves vary within tree canopies, and this needs to be taken account in modelling whole canopy photosynthesis. 相似文献
12.
Ectotherm thermal physiology is frequently used to predict species responses to changing climates, but for amphibians, water loss may be of equal or greater importance. Using physical models, we estimated the frequency of exceeding the thermal optimum ( Topt) or critical evaporative water loss (EWL crit) limits, with and without shade‐ or water‐seeking behaviours. Under current climatic conditions (2002–2012), we predict that harmful thermal (> Topt) and hydric (>EWL crit) conditions limit the activity of amphibians during ~70% of snow‐free days in sunny habitats. By the 2080s, we estimate that sunny and dry habitats will exceed one or both of these physiological limits during 95% of snow‐free days. Counterintuitively, we find that while wet environments eliminate the risk of critical EWL, they do not reduce the risk of exceeding Topt (+2% higher). Similarly, while shaded dry environments lower the risk of exceeding Topt, critical EWL limits are still exceeded during 63% of snow‐free days. Thus, no single environment that we evaluated can simultaneously reduce both physiological risks. When we forecast both temperature and EWL into the 2080s, both physiological thresholds are exceeded in all habitats during 48% of snow‐free days, suggesting that there may be limited opportunity for behaviour to ameliorate climate change. We conclude that temperature and water loss act synergistically, compounding the ecophysiological risk posed by climate change, as the combined effects are more severe than those predicted individually. Our results suggest that predictions of physiological risk posed by climate change that do not account for water loss in amphibians may be severely underestimated and that there may be limited scope for facultative behaviours to mediate rapidly changing environments. 相似文献
13.
The effects of temperature on the development and survival of Lycaeides argyrognomon were examined in the laboratory. The eggs, larvae and pupae were reared at temperatures of 15, 17.5, 20, 25, 30 and 33°C under a long‐day photoperiod of 16‐h light and 8‐h darkness. The survival rates of the first–third instars ranged from 40.0 to 82.4%. The mortalities of the fourth instar were lower than those of the first–third instars. The development time of the overall immature stage decreased from 78.33 days at 15°C to 21.07 days at 30°C, and then increased to 24.33 days at 33°C. The common linear model and the Ikemoto–Takai model were used to estimate the thermal constant ( K) and the developmental zero ( T0). The values of T0 and K for the overall immature stages were 10.50°C and 418.83 degree‐days, and 9.71°C and 451.68 degree‐days by the common model and the Ikemoto–Takai model, respectively. The upper temperature thresholds ( Tmax) and the optimal temperatures ( Topt) of the egg, the first–third instars and the overall immature stages were estimated by the three nonlinear models. The ranges of Topt estimated were from 30.33°C to 32.46°C in the overall immature stages and the estimates of Tmax of the overall immature stages by the Briere‐1 and the Briere‐2 models were 37.18°C and 33.00°C, respectively. The method to predict the developmental period of L. argyrognomon using the nonlinear models was discussed based on the data of the average temperature per hour. 相似文献
14.
Ambient temperatures are major factors regulating the growth rates, yields, and geographical distribution of crop species. The cultivation of sesame (Sesamum indicum L.) is expanding with the rising demand in regions where it is not traditionally grown, and sub-optimal yields due to extremely low or high temperatures could occur. Currently literature lacks information on the temperature responses of sesame growth. An experiment was conducted to quantify the effects of different temperatures on vegetative growth and reproductive development of sesame, and to estimate its cardinal temperature limits (Topt; Tmin; Tmax). Plants were subjected to six different day/night temperature treatments of 40/32, 36/28, 32/24, 28/20, and 20/12 °C using walk-in growth chambers. Vegetative growth of sesame was sensitive to low temperatures (<?15 °C), but tolerant of high temperatures. The cardinal temperature limits of 15.7 °C (Tmin), 27.3 °C (Topt), and 44.6 °C (Tmax) were observed for rate of biomass accumulation. Sesame reached the flowering stage under moderate to high temperature conditions; however, reproductive yields progressively declined above 25 °C, and no seed yields were obtained beyond 33 °C. The estimated temperature limits could be employed to develop crop models for simulating management and adaptation strategies of sesame under current and future climate scenarios, and adaptation to regions where the crop is not currently grown. Future research should focus on understanding factors controlling the temperature tolerance of reproductive development in sesame, to provide a broader geographical adaptation. 相似文献
15.
G:C pairs are more stable than A:T pairs because they have an additional hydrogen bond. This has led to many studies on the
correlation between the guanine+cytosine (G+C) content of nucleic acids and temperature over the last 20 years. We collected
the optimal growth temperatures (T opt) and the G+C contents of genomic DNA; 23S, 16S, and 5S ribosomal RNAs; and transfer RNAs for 764 prokaryotic species. No
correlation was found between genomic G+C content and T opt, but there were striking correlations between the G+C content of ribosomal and transfer RNA stems and T opt. Two explanations have been proposed—neutral evolution and selection pressure—for the approximate equalities of G and C (respectively,
A and T) contents within each strand of DNA molecules. Our results do not support the notion that selection pressure induces
complementary oligonucleotides in close proximity and therefore numerous secondary structures in prokaryotic DNA, as the genomic
G+C content does not behave in the same way as that of folded RNA with respect to optimal growth temperature.
Received: 25 September 1996 / Accepted: 21 January 1997 相似文献
16.
Short episodic high temperature events can be lethal for migrating adult Pacific salmon ( Oncorhynchus spp.). We downscaled temperatures for the Fraser River, British Columbia to evaluate the impact of climate warming on the frequency of exceeding thermal thresholds associated with salmon migratory success. Alarmingly, a modest 1.0 °C increase in average summer water temperature over 100 years (1981–2000 to 2081–2100) tripled the number of days per year exceeding critical salmonid thermal thresholds (i.e. 19.0 °C). Refined thresholds for two populations (Gates Creek and Weaver Creek) of sockeye salmon ( Oncorhynchus nerka) were defined using physiological constraint models based on aerobic scope. While extreme temperatures leading to complete aerobic collapse remained unlikely under our warming scenario, both populations were increasingly forced to migrate upriver at reduced levels of aerobic performance (e.g. in 80% of future simulations, ≥90% of salmon encountered temperatures exceeding population‐specific thermal optima for maximum aerobic scope; Topt=16.3 °C for Gates Creek and Topt=14.5 °C for Weaver Creek). Assuming recent changes to river entry timing persist, we also predicted dramatic increases in the probability of freshwater mortality for Weaver Creek salmon due to reductions in aerobic, and general physiological, performance (e.g. in 42% of future simulations≥50% of Weaver Creek fish exceeded temperature thresholds associated with 0–60% of maximum aerobic scope). Potential for adaptation via directional selection on run‐timing was more evident for the Weaver Creek population. Early entry Weaver Creek fish experienced 25% (range: 15–31%) more suboptimal temperatures than late entrants, compared with an 8% difference (range: 0–17%) between early and late Gates Creek fish. Our results emphasize the need to consider daily temperature variability in association with population‐specific differences in behaviour and physiological constraints when forecasting impacts of climate change on migratory survival of aquatic species. 相似文献
17.
Most plants show considerable capacity to adjust their photosynthetic characteristics to their growth temperatures (temperature acclimation). The most typical case is a shift in the optimum temperature for photosynthesis, which can maximize the photosynthetic rate at the growth temperature. These plastic adjustments can allow plants to photosynthesize more efficiently at their new growth temperatures. In this review article, we summarize the basic differences in photosynthetic reactions in C 3, C 4, and CAM plants. We review the current understanding of the temperature responses of C 3, C 4, and CAM photosynthesis, and then discuss the underlying physiological and biochemical mechanisms for temperature acclimation of photosynthesis in each photosynthetic type. Finally, we use the published data to evaluate the extent of photosynthetic temperature acclimation in higher plants, and analyze which plant groups (i.e., photosynthetic types and functional types) have a greater inherent ability for photosynthetic acclimation to temperature than others, since there have been reported interspecific variations in this ability. We found that the inherent ability for temperature acclimation of photosynthesis was different: (1) among C 3, C 4, and CAM species; and (2) among functional types within C 3 plants. C 3 plants generally had a greater ability for temperature acclimation of photosynthesis across a broad temperature range, CAM plants acclimated day and night photosynthetic process differentially to temperature, and C 4 plants was adapted to warm environments. Moreover, within C 3 species, evergreen woody plants and perennial herbaceous plants showed greater temperature homeostasis of photosynthesis (i.e., the photosynthetic rate at high-growth temperature divided by that at low-growth temperature was close to 1.0) than deciduous woody plants and annual herbaceous plants, indicating that photosynthetic acclimation would be particularly important in perennial, long-lived species that would experience a rise in growing season temperatures over their lifespan. Interestingly, across growth temperatures, the extent of temperature homeostasis of photosynthesis was maintained irrespective of the extent of the change in the optimum temperature for photosynthesis ( T opt), indicating that some plants achieve greater photosynthesis at the growth temperature by shifting T opt, whereas others can also achieve greater photosynthesis at the growth temperature by changing the shape of the photosynthesis–temperature curve without shifting T opt. It is considered that these differences in the inherent stability of temperature acclimation of photosynthesis would be reflected by differences in the limiting steps of photosynthetic rate. 相似文献
18.
Air temperatures of greater than 35 °C are frequently encountered in groundnut‐growing regions, especially in the semi‐arid tropics. Such extreme temperatures are likely to increase in frequency under future predicted climates. High air temperatures result in failure of peg and pod set due to lower pollen viability. The response of pollen germination and pollen tube growth to temperature was quantified in order to identify differences in pollen tolerance to temperature among 21 groundnut genotypes. Plants were grown from sowing to harvest in a poly‐tunnel under an optimum temperature of 28/22 °C (day/night). Pollen was collected at anther dehiscence and was exposed to temperatures from 10° to 47·5 °C at 2·5 °C intervals. The results showed that a modified bilinear model most accurately described the response to temperature of percentage pollen germination and maximum pollen tube length. Genotypes were found to range from most tolerant to most susceptible based on both pollen characters and membrane thermostability. Mean cardinal temperatures ( Tmin, Topt and Tmax) averaged over 21 genotypes were 14·1, 30·1 and 43·0 °C for percentage pollen germination and 14·6, 34·4 and 43·4 °C for maximum pollen tube length. The genotypes 55‐437, ICG 1236, TMV 2 and ICGS 11 can be grouped as tolerant to high temperature and genotypes Kadiri 3, ICGV 92116 and ICGV 92118 as susceptible genotypes, based on the cardinal temperatures. The principal component analysis identified maximum percentage pollen germination and pollen tube length of the genotypes, and Tmax for the two processes as the most important pollen parameters in describing a genotypic tolerance to high temperature. The Tmin and Topt for pollen germination and tube growth, rate of pollen tube growth were less predictive in discriminating genotypes for high temperature tolerance. Genotypic differences in heat tolerance‐based on pollen response were poorly related ( R2 = 0·334, P = 0·006) to relative injury as determined by membrane thermostability. 相似文献
19.
Total lengths ( LT) at age and growth rates for south‐west Pacific Galeocerdo cuvier were estimated from vertebral growth‐band counts of 202 sagitally sectioned centra from 112 females (71–430 cm LT), 79 males (72–351 cm LT) and 11 of unknown sex. Captive growth data were also examined to complement vertebral age estimations. The sexes combined modelled growth coefficient ( k = 0·08) was smaller than previously reported for G. cuvier populations elsewhere. Split‐band and narrow banding patterns were identified as potential sources of age underestimation in this species. 相似文献
20.
As global temperatures rise, variation in annual climate is also changing, with unknown consequences for forest biomes. Growing forests have the ability to capture atmospheric CO 2 and thereby slow rising CO 2 concentrations. Forests’ ongoing ability to sequester C depends on how tree communities respond to changes in climate variation. Much of what we know about tree and forest response to climate variation comes from tree‐ring records. Yet typical tree‐ring datasets and models do not capture the diversity of climate responses that exist within and among trees and species. We address this issue using a model that estimates individual tree response to climate variables while accounting for variation in individuals’ size, age, competitive status, and spatially structured latent covariates. Our model allows for inference about variance within and among species. We quantify how variables influence aboveground biomass growth of individual trees from a representative sample of 15 northern or southern tree species growing in a transition zone between boreal and temperate biomes. Individual trees varied in their growth response to fluctuating mean annual temperature and summer moisture stress. The variation among individuals within a species was wider than mean differences among species. The effects of mean temperature and summer moisture stress interacted, such that warm years produced positive responses to summer moisture availability and cool years produced negative responses. As climate models project significant increases in annual temperatures, growth of species like Acer saccharum, Quercus rubra, and Picea glauca will vary more in response to summer moisture stress than in the past. The magnitude of biomass growth variation in response to annual climate was 92–95% smaller than responses to tree size and age. This means that measuring or predicting the physical structure of current and future forests could tell us more about future C dynamics than growth responses related to climate change alone. 相似文献
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