Leaf and environmental parameters influencing transpiration: Theory and field measurements

Summary The influence of variations in the boundary air layer thickness on transpirtion due to changes in leaf dimension or wind speed was evaluated at a given stomatal resistance (r _s) for various combinations of air temperature (T _a) and total absorbed solar energy expressed as a fraction of full sunlight (S _ffs). Predicted transpiration was found to either increase or decrease for increases in leaf size depending on specific combinations of T _a, S _ffs, and r _s. Major reductions in simulated transpiration with increasing leaf size occurred for shaded, highly reflective, or specially oriented leaves (S _ffs=0.1) at relatively high T _a when r _s was below a critical value of near 500 s m^-1. Increases in S _ffs and decreases in T _a lowered this critical resistance to below 50 s m^-1 for S _ffs=0.7 and T _a=20°C. In contrast, when r _s was above this critical value, an increase in leaf dimension (or less wind) resulted in increases in transpiration, especially at high T _a and S _ffs. For several combinations of T _a, S _ffs, and r _s, transpiration was minimal for a specific leaf size. These theoretical results were compared to field measurements on common desert, alpine, and subalpine plants to evaluate the possible interactions of leaf and environmental parameters that may serve to reduce transpiration in xeric habitats.     

The effect of water activity on growth and end-product formation of two Lactobacillus spp. and Brochothrix thermosphacta ATCC 11509T

Summary The effect of water activity (a_w) on the growth and end-product formation of Lactobacillus viridescens SMRICC 174, Lactobacillus SMRICC 173 (homofermentative) and Brochothrix thermosphacta ATCC 11509^T was studied. All strains orginated from meat or meat products. The a_w was adjusted in the range 0.94–0.99 with NaCl or glycerol. A greater reduction in growth rates was found for L. viridescens and B. thermosphacta when a_w was regulated with NaCl rather than with glycerol, the opposite was true for Lactobacillus 173. L. viridescens grew at a_w >-0.94. At 0.94 a_w B. thermosphacta was totally inhibited when NaCl was the solute and Lactobacillus 173 when glycerol was the solute. Only minor variations in the end-product formation of the Lactobacillus spp. were found at different a_w values. In aerobic culture B. thermosphacta produced less l-lactic acid and more acetic acid as the a_w was decreased with NaCl, while the yields were unaffected when glycerol was used.     

Effect of water activity on the mechanical glass transition and dynamical transition of bacteria

The purpose of this study was to clarify the glass-transition behavior of bacteria (Cronobacter sakazakii) as a function of water activity (a_w). From the water sorption isotherm (298 K) for C. sakazakii, monolayer water content and monolayer a_w were determined to be 0.0724 g/g-dry matter and 0.252, respectively. Mechanical relaxation was investigated at 298 K. In a higher a_w range of over 0.529, the degree of mechanical relaxation increased with an increase in a_w. From the effect of a_w on the degree of mechanical relaxation, the mechanical a_wc (a_w at which mechanical glass transition occurs at 298 K) was determined to be 0.667. Mean-square displacement of atoms in the bacteria was investigated by incoherent elastic neutron scattering. The mean-square displacement increased gradually with an increase in temperature depending on the a_w of samples. From the linear fitting, two or three dynamical transition temperatures (low, middle, and high T_ds) were determined at each a_w. The low-T_d values (142–158 K) were almost independent from a_w. There was a minor effect of a_w on the middle T_d (214–234 K) except for the anhydrous sample (261 K). The high T_d (252–322 K) largely increased with the decrease in a_w. From the a_w dependence of the high T_d, the dynamical a_wc was determined to be 0.675, which was almost equivalent to the mechanical a_wc. The high T_d was assumed to be the glass-transition temperature (T_g), and anhydrous T_g was estimated to be 409 K. In addition, molecular relaxation time (τ) of the bacteria was calculated as a function of a_w. From the result, it is suggested that the progress of metabolism in the bacterial system requires a lower τ than approximately 6 × 10^?5 s.     

Water and water activity in the solid state fermentation of cassava starch by Aspergillus niger

Summary During the solid state fermentation (SSF) of cassava starch by Aspergillus niger estimations were made of total water, consumed water and the residual water remaining in small quantities after 23 h. A theoretical calculation based on the Ross equation showed that the water activity (a _w) of the substrate decreased to 0.85 towards the end of the culture. Such low values were assumed to be inhibitory to growth. The a _w of the substrate was increased when sugarcane bagasse was used as a high water retention capacity support. Higher growth rates and substrate conversion to biomass were obtained with this system, confirming that water availability is a critical factor in the SSF of starch substrates.Abbreviations A, B Experimental constants - a _w Water activity - H₂O_c Consumed water - H₂O_R Residual water - H₂O_T Total water - IDW Initial dry weight - IMC Initial moisture content - OUR Oxygen uptake rate - S Substrate dry weight - Sc Substrate conversion: consumed substrate/initial substrate - S _H Amount of sugars hydrolysed - SSF Solid state fermentation - X Biomass dry weight - W ^* Amount of solids/g of water     

Stomatal responses to humidity and temperature in darkness

Stomatal responses to leaf temperature (T_l) and to the mole fractions of water vapour in the ambient air (w_a) and the leaf intercellular air spaces (w_i) were determined in darkness to remove the potential effects of changes in photosynthesis and intercellular CO₂ concentration. Both the steady‐state and kinetic responses of stomatal conductance (g_s) to w_a in darkness were found to be indistinguishable from those in the light. g_s showed a steep response to the difference (Δw) between w_a and w_i when w_a was varied. The response was much less steep when w_i was varied. Although stomatal apertures responded steeply to T_l when Δw was held constant at 17 mmol mol^?1, the response was much less steep when Δw was held constant at about zero. Similar results were obtained in the light for Δw = 15 mmol mol^?1 and Δw ≈ 0 mmol mol^?1. These results are discussed in the context of mechanisms for the stomatal response to humidity.     

Thermodynamic analysis of the physical state of water during freezing in plant tissue, based on the temperature dependence of proton spin-spin relaxation

Multi-proton spin-echo images were collected from cold-acclimated winter wheat crowns (Triticum aestivum L.) cv. Cappelle Desprez at 400 MHz between 4 and ?4 °C. Water proton relaxation by the spin-spin (T2) mechanism from individual voxels in image slices was found to be mono-exponential. The temperature dependence of these relaxation rates was found to obey Arrhenius or absolute rate theory expressions relating temperature, activation energies and relaxation rates, Images whose contrast is proportional to the Arrhenius activation energy (E_a), Gibb's free energy of activation (ΔG^?), and the entropy of activation (ΔS^?) for water relaxation on a voxel basis were constructed by post-image processing. These new images exhibit contrast based on activation energies rather than rules of proton relaxation. The temperature dependence of water proton T₂ relaxation rates permits prediction of changes in the physical state of water in this tissue over modest temperature ranges. A simple model is proposed to predict the freezing temperature kof various tissue in wheat crowns. The average E_a and ΔH^? for water proton T₂ relaxation over the above temperature range in winter wheat tissue were ?6.4 ± 14.8 and ?8.6 ± 14.8kj mol^?1, respectively. This barrier is considerably lower than the E_a for proton translation in ice at 0°C, which is reported to be between 46.0 and 56.5 kj mol^?1     

近50年中国典型木本植物展叶始期温度敏感度变化及原因

展叶始期的温度敏感度是指气温每变化1℃,物候期变化的天数。展叶始期对温度响应更敏感的植物能够在生长季初期占据更多的资源从而在种间竞争中占据优势,因此研究展叶始期的温度敏感度变化有助于评估植物对气候变化的适应能力。选择1963-2014年10个站点163种植物的展叶始期资料,利用滑动分析法计算了每15a各植物的展叶始期温度敏感度。在此基础上,分析了温度敏感度的变化趋势及空间格局,并讨论了导致展叶始期温度敏感度变化的可能原因。主要结论为：在全部313条展叶始期时间序列中,60.1%的序列温度敏感度呈升高趋势,其中显著升高的占40.0%（P < 0.05）;39.9%的序列温度敏感度降低,其中显著降低的占28.4%。在空间分布上,温带地区的6个站点展叶始期温度敏感度平均呈升高趋势。其中,北京地区植物展叶始期温度敏感度升高最为普遍,显著升高的物种比例达到75.0%（P < 0.05）。而亚热带站点（除合肥外）的展叶始期温度敏感度主要呈降低趋势。其中,长沙植物展叶始期温度敏感度显著降低的物种比例最高,达68.4%。冬季冷激量和春季气温变率是影响植物展叶始期温度敏感度随时间变化的主要因素。冬季冷激量降低将导致植物展叶始期温度敏感度降低,而春季气温变率降低将导致植物展叶始期温度敏感度升高。     

Impact of some environmental factors on growth and production of ochratoxin A of/by <Emphasis Type="Italic">Aspergillus tubingensis,A. niger</Emphasis>, and <Emphasis Type="Italic">A. carbonarius</Emphasis> isolated from moroccan grapes

The effects of temperature, water activity (a_w), incubation time, and their combinations on radial growth and ochratoxin A (OTA) production of/by eight Aspergillus niger aggregate strains (six A. tubingensis and two A. niger) and four A. carbonarius isolated from Moroccan grapes were studied. Optimal conditions for the growth of most studied strains were shown to be at 25°C and 0.95 a_w. No growth was observed at 10°C regardless of the water activity and isolates. The optimal temperature for OTA production was in the range of 25°C∼30°C for A. carbonarius and 30°C∼37°C for A. niger aggregate. The optimal a_w for toxin production was 0.95∼0.99 for A. carbonarius and 0.90∼0.95 for A. niger aggregate. Mean OTA concentration produced by all the isolates of A. niger aggregate tested at all sampling times shows that maximum amount of OTA (0.24 μg/g) was produced at 37°C and 0.90 a_w. However, for A. carbonarius, mean maximum amounts of OTA (0.22 μg/g) were observed at 25°C and 0.99 a_w. Analysis of variance showed that the effects of all single factors (a_w, isolate, temperature and incubation time) and their interactions on growth and OTA production were highly significant.     

Potential of ochratoxin A production by Aspergillus carbonarius strains isolated from grapes at different ecological factors

Aspergillus carbonarius is known to colonize and produce ochratoxin A (OTA) on grapes and its derived products which is harmful to humans. We screened and tested A. carbonarius strains which isolated from grapes for production of OTA and selected three high OTA producing strains (ACSP1, ACSP2, ACSP3) for this study. These strains were further tested for their ability to produce OTA at different ecological factors [temperature 15, 25, 30, 35°C; water activity (a_w) 0.98, 0.95, 0.90, 0.88; and pH 4.0, 7.0, 9.0, 10.0]. Out of the three strains tested, A. carbonarius ACSP3 produced high levels of OTA than ACSP2 and ACSP1 in all the ecological factors. At 30°C A. carbonarius strains produced the highest OTA compared with other temperature regimes. With reference to water activity, a_w 0.98 favoured mycelial growth and accumulation of more OTA with all the three A. carbonarius strains. Further, pH 4.0 was encouraged the greatest production of OTA in all the strains. No growth was observed at a_w 0.88 and pH 10.0 in all the three strains except the strain ACSP3 at high pH. Our work demonstrated that temperature 30°C, a_w 0.98 and pH 4.0 is optimum for growth and production of OTA by A. carbonarius strains. Maximum amounts of OTA were found at earlier growth stages (7–9 days of incubation) in all the strains of A. carbonarius. The present study revealed that different ecological factors had great impact on OTA production by A. carbonarius which is useful for understanding OTA contamination and to develop proper management practices in future research programmes.     

The effects of gap size on some microclimate variables during late summer and autumn in a temperate broadleaved deciduous forest

The creation of gaps can strongly influence forest regeneration and habitat diversity within forest ecosystems. However, the precise characteristics of such effects depend, to a large extent, upon the way in which gaps modify microclimate and soil water content. Hence, the aim of this study was to understand the effects of gap creation and variations in gap size on forest microclimate and soil water content. The study site, in North West England, was a mixed temperate broadleaved deciduous forest dominated by mature sessile oak (Quercus petraea), beech (Fagus sylvatica) and ash (Fraxinus excelsior) with some representatives of sycamore (Acer pseudoplatanus). Solar radiation (I), air temperature (T _A), soil temperature (T _S), relative humidity (h), wind speed (v) and soil water content (Ψ) were measured at four natural treefall gaps created after a severe storm in 2006 and adjacent sub-canopy sites. I, T _A, T _S, and Ψ increased significantly with gap size; h was consistently lower in gaps than the sub-canopy but did not vary with gap size, while the variability of v could not be explained by the presence or size of gaps. There were systematic diurnal patterns in all microclimate variables in response to gaps, but no such patterns existed for Ψ. These results further our understanding of the abiotic and consequent biotic responses to gaps in broadleaved deciduous forests created by natural treefalls, and provide a useful basis for evaluating the implications of forest management practices.     

Strategies of thermoregulation and foraging in two vespid wasps,Dolichovespula maculata andVespula vulgaris

Summary D. maculata, the white-faced hornet, stabilized (regulated) thoracic temperature (T _Th) over wide ranges of ambient temperature (T _a), whileV. vulgaris, the common yellowjacket, regulatedT _Th poorly. The hornets also maintained a higherT _Th than the wasps, sometimes heating 38°C aboveT _a. Attacking individuals of both species had higherT _Th than those either leaving or returning to the nest from foraging. The hornets, who are primarily hunters of live prey, showed peak activity near dawn, and they were as active atT _a=2°C as at 20°C. Being able to regulate theirT _Th and fly at the lowT _a should enhance their ability to capture small insects that are usually torpid at theseT _a. The yellowjacket wasps, on the other hand, who are scavengers as well as hunters, did not leave the nest at 2°C; their activity decreased greatly with decreasingT _a. Differences in the foraging technique of the two vespids may be related to their different abilities to thermoregulate.     

Optimization of erythritol and glycerol accumulation in conidia of Beauveria bassiana by solid-state fermentation, using response surface methodology

Entomopathogenic fungi are widely produced for use as mycoinsecticides. Therefore, improvement of the shelf life of fungal propagules under good and adverse conditions should be a pre-requisite of their production. In order to improve conidial physiology as well as mycoinsecticide efficiency, culture conditions may be varied. The Doehlert design was used to generate response surfaces with an estimation of the parameters of the quadratic model allowing the study of three different factors at a different number of levels. This experimental design was applied to optimize water activity (a _w), pH, and fermentation time for Beauveria bassiana conidial production and accumulation of polyols in solid-state fermentation. Thus, it was possible to identify the region in the experimental range in which the optimum values of these parameters were simultaneously achieved. Maximal conidia production was achieved at pH 5–6 and a _w=0.999. Under these conditions, polyol accumulation was 3 mg erythritol/g conidia and 29.6 mg glycerol/g conidia. However, maximal polyol accumulation was achieved at pH 4.5 and a _w 0.950; erythritol production increased 33-fold and glycerol production 4.5-fold. Under these conditions conidia production was 1,000 times lower. The possibilities of increasing the quality of the biocontrol agent without neglecting yield are discussed.     

Standard operative temperatures and cost of thermoregulation in the arctic ground squirrel,Spermophilus undulatus

Summary Body temperatures (T _b) and daily activity patterns of free-living arctic ground squirrells (Spermophilus undulatus) were determined via telemetry at a field site in northern Alaska. Simultaneous measurements were made of ambient temperature (T _a), wind speed (V), and incident solar radiation. The operative environmental temperature (T _e) for ground squirrels was obtained from fur-covered, thin metal taxidermic models of the animals. Standard operative temperature (T _es), a comparative index of heat flow, was calculated from T _e, V, and laboratory measurements of thermal conductivity.During the period of the study (August), S. undulatus were active for about 14 h per day (06.00 to 20.00 h). T _b was high throughout the daily cycle, averaging 38–39°C. Circadian variations in T _b were slight; average T _b values dropped <1°C at night. Daytime T _b fluctuations were not closely correlated to activity or to changes in environmental conditions. Air temperatures during the study were low, usually between 10 and 15°C during the day. However, T _es in exposed areas was normally higher, even though skies were generally overcast. During periods of sunshine, T _es may be as high as 34°C. The absence of nocturnal activity may result from increased costs of thermoregulation at night, which sharply reduces foraging efficiency. The high and stable body temperatures of S. undulatus probably result from thermoneutral daytime T _es, low activity levels, and the use of well-insulated nests.     

The Relative Rates of Thiol–Thioester Exchange and Hydrolysis for Alkyl and Aryl Thioalkanoates in Water

This article reports rate constants for thiol–thioester exchange (k _ex), and for acid-mediated (k _a), base-mediated (k _b), and pH-independent (k _w) hydrolysis of S-methyl thioacetate and S-phenyl 5-dimethylamino-5-oxo-thiopentanoate—model alkyl and aryl thioalkanoates, respectively—in water. Reactions such as thiol–thioester exchange or aminolysis could have generated molecular complexity on early Earth, but for thioesters to have played important roles in the origin of life, constructive reactions would have needed to compete effectively with hydrolysis under prebiotic conditions. Knowledge of the kinetics of competition between exchange and hydrolysis is also useful in the optimization of systems where exchange is used in applications such as self-assembly or reversible binding. For the alkyl thioester S-methyl thioacetate, which has been synthesized in simulated prebiotic hydrothermal vents, k _a = 1.5 × 10⁻⁵ M⁻¹ s⁻¹, k _b = 1.6 × 10⁻¹ M⁻¹ s⁻¹, and k _w = 3.6 × 10⁻⁸ s⁻¹. At pH 7 and 23°C, the half-life for hydrolysis is 155 days. The second-order rate constant for thiol–thioester exchange between S-methyl thioacetate and 2-sulfonatoethanethiolate is k _ex = 1.7 M⁻¹ s⁻¹. At pH 7 and 23°C, with [R″S(H)] = 1 mM, the half-life of the exchange reaction is 38 h. These results confirm that conditions (pH, temperature, pK _a of the thiol) exist where prebiotically relevant thioesters can survive hydrolysis in water for long periods of time and rates of thiol–thioester exchange exceed those of hydrolysis by several orders of magnitude.     

Factors affecting the daily rhythm of body temperature of captive mouse lemurs (<Emphasis Type="Italic">Microcebus murinus</Emphasis>)

Microcebus murinus, a small nocturnal Malagasy primate, exhibits adaptive energy-saving strategies such as daily hypothermia and gregarious patterns during diurnal rest. To determine whether ambient temperature (T_a), food restriction and nest sharing can modify the daily body temperature (T_b) rhythm, T_b was recorded by telemetry during winter in six males exposed to different ambient temperatures (T_a=25, 20, 15°C) and/or to a total food restriction for 3 days depending on social condition (isolated versus pair-grouped). At 25°C, the daily rhythm of T_b was characterized by high T_b values during the night and lower values during the day. Exposure to cold significantly decreased minimal T_b values and lengthened the daily hypothermia. Under food restriction, minimal T_b values were also markedly lowered. The combination of food restriction and cold induced further increases in duration and depth of torpor bouts, minimal T_b reaching a level just above T_a. Although it influenced daily hypothermia less than environmental factors, nest sharing modified effects of cold and food restriction previously observed by lengthening duration of torpor but without increasing its depth. In response to external conditions, mouse lemurs may thus adjust their energy expenditures through daily modifications of both the duration and the depth of torpor.     

Physiological responses of naloxone-treated pigeons to changes in ambient temperature

1. In pigeons given single intramuscular injection of naloxone, the heart rate (HR), breathing frequency (BF), oxygen consumption (VO₂), cloacal temperature (T_c) and foot temperature (T_f) were monitored during gradual lowering of the ambient temperature (T,) from 34°C to 6° in 6 hr.2. The two doses of naloxone tested (2 mg and 5 mg/kg b.w.) had an inhibitory effect on HR, the effect being greater with the higher dose as well as with the fall in T_a.3. The higher dose showed a tendency to have a stimulatory effect on BF in T_a above 22°C and an inhibitory effect in T_a below 22°C. With the lower dose, BF remained unaltered except in T_a below 12°C during which it showed a trend toward a decrease.4. VO₂ decreased with the higher dose, the extent of decrease being greater with drop in T_a. With the lower dose, VO₂ was not affected at or below T_a 26°C, but showed a trend toward an increase at T_a above 26°.5. The higher dose produced hyperthermia when T_a was below 14°C, whereas with the lower dose, T_c showed no significant change except for a slight drop at T_a 6°C.6. T_fwas not significantly affected by naloxone treatment.7. It is suggested that these effects were caused by the inhibition of endorphine-mediated catecholamine release by naloxone.     

Effect of temperature and water activity on spore germination and mycelial growth of three fungal biocontrol agents against water hyacinth (Eichhornia crassipes)

Aims: To determine the effect of water activity (a_w = 0·880–0·960) and temperature (15–35°C) on the percentage of viable conidia and mycelial growth of three biocontrol agents effective against water hyacinth in Mali: Alternaria sp. isolate Mlb684, Fusarium sacchari isolate Mln799 and Cadophora malorum isolate Mln715. Methods and Results: The fungi were grown in vitro on plates containing potato dextrose agar medium at different a_w values (glycerol being added to adjust the a_w). The percentage of viable conidia and radial growth rate decreased with decreasing water activity. Statistical analysis showed a significant effect of a_w, temperature and the a_w × temperature interaction on mycelial growth (P < 0·0001). Water activity emerged as the factor exerting the greatest influence. Differences were observed between the fungi tested, the C. malorum appearing more tolerant to low a_w and the F. sacchari more tolerant to high temperature (35°C). Growth models predicting the combined effect of a_w and temperature were developed and response surfaces generated, showing fairly good agreement with the experimental values. Conclusions: Our results confirm the previous finding that a_w has a greater influence than temperature on fungal growth. Under most conditions, variation of environmental factors has a detrimental influence on the percentage of viable conidia and mycelial growth rate of fungal isolates. Significance and Impact of the Study: The developed models may contribute to predicting the best environmental conditions for use of these fungi as effective biocontrol agents against water hyacinth.     

Thermoregulatory responses of Japanese Quail to various air temperatures and humidities

Measurements of rectal temperature (T_re), feather surface temperature (T_s), heart rate (HR) and breathing rate (BR) of adult Japanese Quail were taken at combinations of four mean relative humidities (rh) and stable or rising air temperature (T_a). T_re increased about 1.7° and 2.5°C at a stable T_a of 40°C from a T_a of 25°C at low (<50%) and high (> 80%) rh, respectively. T_s passively increased with T_a while remaining above T_a as high as 41°C. Panting and gular flutter rates were synchronous and approached rates of 800/min at high rh and stable T_a of 40°C. The steady-state panting rate was a direct curvilinear function of ambient water-vapor pressure (P_w). HR was depressed at successively higher, stable T_a's or with slowly increasing T_a. This thermal bradycardia may be related to the degree of discomfort or stress experienced by the animal.

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Zusammenfassung Bei Kombinationen von 4 relativen Feuchtigkeiten (rh) und konstanter oder ansteigender Temperatur (T_a) wurden Messungen der Rektaltemperatur (T_re), Federoberflächentemperatur (T_s), Herzfrequenz (HR) und Atemfrequenz (BR) an ausgewachsenen japanischen Wachteln vorgenommen. Bei T_a 40°C stieg T_re zwischen 1,7°–2,5°C an ausgehend von T_a 25°C bei <50% und > 80% rh. Die T_s folgte diesem Anstieg von T_a und überschritt ihn bis auf 41°C. Hecheln und Gurren stiegen synchron an bis auf 800/min bei hoher rh und 40°C T_a. Die erhöhte Hechelfrequenz war eine direkte lineare Funktion des Wasserdampfdruckes. HR war verlangsamt bei erhöhter, konstanter T_a. Die Hitzebradykardie steht vermutlich in enger Beziehung zu dem Ausmass der von dem Tier empfundenen Belastung.

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Resume On a soumis des cailles du Japon adultes à 4 taux différents d'humidité relative (rh) par température constante ou en hausse et mesuré la température rectale (T_re), la température superficielle des plumes (T_s), les battements du coeur (HR) et la vitesse de respiration (BR). T_re a augmenté de 1,7°C, respectivement de 2,5°C par suite d'une hausse de T_a de 25°C à 40°C par humidité basse (<50%), respectivement élevée (>80%). T_s a suivi la hausse de T_a et l'a même dépassée jusqu'à atteindre 41°C. Halètement et palpitations ont suivi la courbe de T_a pour atteindre 800/min par rh élevée et 40°C de T_a. La vitesse de respiration s'est élevée en fonction linéaire de la pression de vapeur. HR se sont ralentis par T_a élevée, mais constante. La bradycardie de chaud est probablement étroitement liée à la contrainte ressentie par l'animal.

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This investigation was supported in part by funds provided for medical and biological research by State of Washington Initiative Measure No. 171.