Adaptation of malate dehydrogenase to environmental temperature variability in two populations of Potentilla glandulosa Lindl.

Summary The responses of the kinetic properties of malate dehydrogenase to environmental temperature variability were compared for two populations of Potentilla glandulosa (Rosaceae). The two populations are native to regions of contrasting climates, with the inland population experiencing a high level of temperature variability during growth and the coastal populaton a low level of temperature variability. The substrate binding ability, as measured by apparent K _m of both populations was relatively insensitive to assay temperature (Q ₁₀<2.0) over the range of temperatures likely to be encountered during growth. The breadth of this thermal optimum was different for the two populations with the K _m of the inland plants exhibiting relative temperature insensitivity over a much wider range of temperatures than the K _m of the coastal plants. There was no difference between the two populations in the thermal stability of MDH activity.     

Aggregation of apolar peptides in organic solvents. Concentration dependence of 1H-nmr parameters for peptide NH groups in 310 helical decapeptide fragment of suzukacillin

Peptide NH chemical shifts and their temperature dependences have been monitored as a function of concentration for the decapeptide, Boc-Aib-Pro-Val-Aib-Val-Ala-Aib-Ala-Aib-Aib-OMe in CDCl₃ (0.001–0.06M) and (CD₃)₂SO (0.001–0.03M). The chemical shifts and temperature coefficients for all nine NH groups show no significant concentration dependence in (CD₃)₂SO. Seven NH groups yield low values of temperature coefficients over the entire range, while one yields an intermediate value. In CDCl₃, the Aib(1) NH group shows a large concentration dependence of both chemical shift and temperature coefficient, in contrast to the other eight NH groups. The data suggest that in (CD₃)₂SO, the peptide adopts a 3₁₀ helical conformation and is monomeric over the entire concentration range. In CDCl₃, the 3₁₀ helical peptide associates at a concentration of 0.01M, with the Aib(1) NH involved in an intermolecular hydrogen bond. Association does not disrupt the intramolecular hydrogen-bonding pattern in the decapeptide.     

The role of temperature in enhancing the insecticidal activity of Bacillus thuringiensis against Spodoptera littoralis larvae

The present study scrutinised how far temperature would affect the velocity of the insecticidal activity of Bacillus thuringiensis, as the rapidity of pest control achievements is of a great concern. Third instar Spodoptera littoralis larvae were treated with Bt at three concentration levels under five different temperatures (15°C, 20°C, 25°C, 30°C and 35°C). LT₅₀s were evaluated in each case. The LT₅₀ values showed various levels of reductions as temperature and/or Bt concentration increased, indicating that the velocity of mortality (1/LT₅₀) and/or the rapidity of Bt activity was almost temperature dependant. However, relatively high and low reduction percentages in the LT₅₀ values on the elevation of 5°C were obtained at lower and higher temperature ranges, respectively. The temperature coefficient, Q ₁₀ values, determined within narrow ranges (5°C) showed great reductions when temperature increased from 15°C to 20°C at all Bt concentrations. Raising temperature by 5°C above 20°C or 25°C almost caused similar Q ₁₀ values indicating constant increase in the response of Bt activity within 20–30°C temperature range. Q ₁₀ values over 30°C were comparatively very low. This proved that decrease in Q ₁₀ values due to the rise of temperature was dependant on the starting temperature.     

Modeling soil CO<Subscript>2</Subscript> emissions from ecosystems

We present a new soil respiration model, describe a formal model testing procedure, and compare our model with five alternative models using an extensive data set of observed soil respiration. Gas flux data from rangeland soils that included a large number of measurements at low temperatures were used to model soil CO₂ emissions as a function of soil temperature and water content. Our arctangent temperature function predicts that Q₁₀ values vary inversely with temperature and that CO₂ fluxes are significant below 0 °C. Independent data representing a broad range of ecosystems and temperature values were used for model testing. The effects of plant phenology, differences in substrate availability among sites, and water limitation were accounted for so that the temperature equations could be fairly evaluated. Four of the six tested models did equally well at simulating the observed soil CO₂ respiration rates. However, the arctangent variable Q₁₀ model agreed closely with observed Q₁₀ values over a wide range of temperatures (r² = 0.94) and was superior to published variable Q₁₀ equations using the Akaike information criterion (AIC). The arctangent temperature equation explained 16–85% of the observed intra-site variability in CO₂ flux rates. Including a water stress factor yielded a stronger correlation than temperature alone only in the dryland soils. The observed change in Q₁₀ with increasing temperature was the same for data sets that included only heterotrophic respiration and data sets that included both heterotrophic and autotrophic respiration.     

Thermal clamping of temperature-regulating flowers reveals the precision and limits of the biochemical regulatory mechanism

The flowers of several families of seed plants warm themselves when they bloom. In some species, thermogenesis is regulated, increasing the rate of respiration at lower ambient temperature (T _a) to maintain a somewhat stable floral temperature (T _f). The precision of this regulation is usually measured by plotting T _f over T _a. However, such measurements are influenced by environmental conditions, including wind speed, humidity, radiation, etc. This study eliminates environmental effects by experimentally ‘clamping’ T _f at constant, selected levels and then measuring stabilized respiration rate. Regulating flowers show decreasing respiration with rising T _f (Q ₁₀ < 1). Q ₁₀ therefore becomes a measure of the biochemical ‘precision’ of temperature regulation: lower Q ₁₀ values indicate greater sensitivity of respiration to T _f and a narrower range of regulated temperatures. At the lower end of the regulated range, respiration is maximal, and further decreases in floral temperature cause heat production to diminish. Below a certain tissue temperature (‘switching temperature’), heat loss always exceeds heat production, so thermoregulation becomes impossible. This study compared three species of thermoregulatory flowers with distinct values of precision and switching temperature. Precision was highest in Nelumbo nucifera (Q ₁₀ = 0.16) moderate in Symplocarpus renifolius (Q ₁₀ = 0.48) and low in Dracunculus vulgaris (Q ₁₀ = 0.74). Switching temperatures were approximately 30, 15 and 20°C, respectively. There were no relationships between precision, switching temperature or maximum respiration rate. High precision reveals a powerful inhibitory mechanism that overwhelms the tendency of temperature to increase respiration. Variability in the shape and position of the respiration–temperature curves must be accounted for in any explanation of the control of respiration in thermoregulatory flowers.     

Evidence of temperature‐independent metabolic rates in diurnal Namib Desert tenebrionid beetles

To investigate whether the sensitivity to environmental temperature varies between nocturnal and diurnal species of tenebrionid beetle, the metabolic rates of three diurnal species (Onymacris plana Peringuey, Onymacris rugatipennis Haag and Physadesmia globosa Haag) and three nocturnal species (Epiphysa arenicola Penrith, Gonopus sp. and Stips sp.) of beetles from the Namib Desert are measured over a range of temperatures (15–40 °C) that are experienced by these beetles in their natural habitat. The diurnal species O. plana, O. rugatipennis and P. globosa exhibit temperature‐independent metabolic rates (mean Q₁₀ = 1.2) within temperature ranges that are ecologically relevant for diurnal desert beetles (30–40 °C). Onymacris plana, in particular, has a 20–40 °C rate–temperature slope (0.007 log₁₀ mL O₂ h^?1 g^?1 °C^?1; Q₁₀ = 1.1) that is less than half that of the other five beetle species (0.022–0.063 log₁₀ mL O₂ h^?1 g^?1 °C^?1; Q₁₀ ranges from 1.3–1.9), suggesting that O. plana is more metabolically independent of temperature than the other nocturnal and diurnal tenebrionids being investigated. Animals with metabolic rates that are decoupled from body temperature (or ambient temperature) may have an ecological advantage that allows them to exploit thermal and spatial niches during extreme temperature conditions.     

Adaptation of soil microbial growth to temperature: Using a tropical elevation gradient to predict future changes

Terrestrial biogeochemical feedbacks to the climate are strongly modulated by the temperature response of soil microorganisms. Tropical forests, in particular, exert a major influence on global climate because they are the most productive terrestrial ecosystem. We used an elevation gradient across tropical forest in the Andes (a gradient of 20°C mean annual temperature, MAT), to test whether soil bacterial and fungal community growth responses are adapted to long‐term temperature differences. We evaluated the temperature dependency of soil bacterial and fungal growth using the leucine‐ and acetate‐incorporation methods, respectively, and determined indices for the temperature response of growth: Q₁₀ (temperature sensitivity over a given 10oC range) and T_min (the minimum temperature for growth). For both bacterial and fungal communities, increased MAT (decreased elevation) resulted in increases in Q₁₀ and T_min of growth. Across a MAT range from 6°C to 26°C, the Q₁₀ and T_min varied for bacterial growth (Q_10–20 = 2.4 to 3.5; T_min = ?8°C to ?1.5°C) and fungal growth (Q_10–20 = 2.6 to 3.6; T_min = ?6°C to ?1°C). Thus, bacteria and fungi did not differ significantly in their growth temperature responses with changes in MAT. Our findings indicate that across natural temperature gradients, each increase in MAT by 1°C results in increases in T_min of microbial growth by approximately 0.3°C and Q_10–20 by 0.05, consistent with long‐term temperature adaptation of soil microbial communities. A 2°C warming would increase microbial activity across a MAT gradient of 6°C to 26°C by 28% to 15%, respectively, and temperature adaptation of microbial communities would further increase activity by 1.2% to 0.3%. The impact of warming on microbial activity, and the related impact on soil carbon cycling, is thus greater in regions with lower MAT. These results can be used to predict future changes in the temperature response of microbial activity over different levels of warming and over large temperature ranges, extending to tropical regions.     

Thermal adaptation of heterotrophic soil respiration in laboratory microcosms

Respiration of heterotrophic microorganisms decomposing soil organic carbon releases carbon dioxide from soils to the atmosphere. In the short term, soil microbial respiration is strongly dependent on temperature. In the long term, the response of heterotrophic soil respiration to temperature is uncertain. However, following established evolutionary trade‐offs, mass‐specific respiration (R_mass) rates of heterotrophic soil microbes should decrease in response to sustained increases in temperature (and vice‐versa). Using a laboratory microcosm approach, we tested the potential for the R_mass of the microbial biomass in six different soils to adapt to three, experimentally imposed, thermal regimes (constant 10, 20 or 30 °C). To determine R_mass rates of the heterotrophic soil microbial biomass across the temperature range of the imposed thermal regimes, we periodically assayed soil subsamples using similar approaches to those used in plant, animal and microbial thermal adaptation studies. As would be expected given trade‐offs between maximum catalytic rates and the stability of the binding structure of enzymes, after 77 days of incubation R_mass rates across the range of assay temperatures were greatest for the 10 °C experimentally incubated soils and lowest for the 30 °C soils, with the 20 °C incubated soils intermediate. The relative magnitude of the difference in R_mass rates between the different incubation temperature treatments was unaffected by assay temperature, suggesting that maximum activities and not Q₁₀ were the characteristics involved in thermal adaptation. The time taken for changes in R_mass to manifest (77 days) suggests they likely resulted from population or species shifts during the experimental incubations; we discuss alternate mechanistic explanations for those results we observed. A future research priority is to evaluate the role that thermal adaptation plays in regulating heterotrophic respiration rates from field soils in response to changing temperature, whether seasonally or through climate change.     

Reduction of metabolic rate and thermoregulation during daily torpor

Physiological mechanisms causing reduction of metabolic rate during torpor in heterothermic endotherms are controversial. The original view that metabolic rate is reduced below the basal metabolic rate because the lowered body temperature reduces tissue metabolism has been challenged by a recent hypothesis which claims that metabolic rate during torpor is actively downregulated and is a function of the differential between body temperature and ambient temperature, rather than body temperature per se. In the present study, both the steady-state metabolic rate and body temperature of torpid stripe-faced dunnarts, Sminthopsis macroura (Dasyuridae: Marsupialia), showed two clearly different phases in response to change of air temperature. At air temperatures between 14 and 30°C, metabolic rate and body temperature decreased with air temperature, and metabolic rate showed an exponential relationship with body temperature (r ²=0.74). The Q ₁₀ for metabolic rate was between 2 and 3 over the body temperature range of 16 to 32°C. The difference between body temperature and air temperature over this temperature range did not change significantly, and the metabolic rate was not related to the difference between body temperature and air temperature (P=0.35). However, the apparent conductance decreased with air temperature. At air temperatures below 14°C, metabolic rate increased linearly with the decrease of air temperature (r ²=0.58) and body temperature was maintained above 16°C, largely independent of air temperature. Over this air temperature range, metabolic rate was positively correlated with the difference between body temperature and air temperature (r ²=0.61). Nevertheless, the Q ₁₀ for metabolic rate between normothermic and torpid thermoregulating animals at the same air temperature was also in the range of 2–3. These results suggest that over the air temperature range in which body temperature of S. macroura was not metabolically defended, metabolic rate during daily torpor was largely a function of body temperature. At air temperatures below 14°C, at which the torpid animals showed an increase of metabolic rate to regulate body temperature, the negative relationship between metabolic rate and air temperature was a function of the differential between body temperature and air temperature as during normothermia. However, even in thermoregulating animals, the reduction of metabolic rate from normothermia to torpor at a given air temperature can also be explained by temperature effects.Abbreviations BM body mass - BMR basal metabolic rate - C apparent conductance - MR metabolic rate - RMR resting metabolic rate - RQ respiratory quotient - T _a air temperature - T _b body temperature - T _lc lower critical temperature - T _tc critical air temperature during torpor - TMR metabolic rate during torpor - TNZ thermoneutral zone - T difference between body temperature and air temperature - VO₂ rate of oxygen consumption     

Energy exploitation in Chirocephalus croaticus (Steuer, 1899) (Crustacea: Anostraca): survival strategy in an intermittent lake

Electron transport system (ETS) activity was measured in Chirocephalus croaticus from the intermittent lake, Petelinjsko Jezero. The ETS activities were measured at 5, 10, 15, 20, and 25 °C, and were studied separately in juveniles, females and males. Juveniles had significantly higher activity than adults at a standard temperature of 20 °C. The mass-specific ETS activity decreased with increasing size of the animals; the value b was 0.787. Respiration rates (R) were determined at 20 °C and the ratio ETS/R (±standard deviation) for C. croaticus was 1.43±0.46 (n=38). ETS activity increased with temperature. Females had higher Q₁₀ than males in higher temperature range (t-test; t=2.50; d.f.=8; p<0.05). Activation energy E_a was higher for females than males (t-test; t=2.35; d.f.=8; p<0.05). Females exhibited lower ETS activity than males over the lower temperature range, but their ETS could function more efficient at higher temperature.     

Improved temperature response functions for models of Rubisco-limited photosynthesis

Predicting the environmental responses of leaf photosynthesis is central to many models of changes in the future global carbon cycle and terrestrial biosphere. The steady-state biochemical model of C₃ photosynthesis of Farquhar et al. (Planta 149, 78–90, 1980) provides a basis for these larger scale predictions; but a weakness in the application of the model as currently parameterized is the inability to accurately predict carbon assimilation at the range of temperatures over which significant photosynthesis occurs in the natural environment. The temperature functions used in this model have been based on in vitro measurements made over a limited temperature range and require several assumptions of in vivo conditions. Since photosynthetic rates are often Rubisco-limited (ribulose, 1-5 bisphosphate carboxylase/oxygenase) under natural steady-state conditions, inaccuracies in the functions predicting Rubisco kinetic properties at different temperatures may cause significant error. In this study, transgenic tobacco containing only 10% normal levels of Rubisco were used to measure Rubisco-limited photosynthesis over a large range of CO₂ concentrations. From the responses of the rate of CO₂ assimilation at a wide range of temperatures, and CO₂ and O₂ concentrations, the temperature functions of Rubisco kinetic properties were estimated in vivo. These differed substantially from previously published functions. These new functions were then used to predict photosynthesis in lemon and found to faithfully mimic the observed pattern of temperature response. There was also a close correspondence with published C₃ photosynthesis temperature responses. The results represent an improved ability to model leaf photosynthesis over a wide range of temperatures (10–40 °C) necessary for predicting carbon uptake by terrestrial C₃ systems.     

SAR versus Sinc: What is the appropriate RF exposure metric in the range 1–10 GHz? Part II: Using complex human body models

This is the second of the two articles that present modeling data and reasoned arguments for specifying the appropriate crossover frequency at which incident power flux density (S_inc) replaces the peak 10 g averaged value of the specific energy absorption rate (SAR) as the designated basic restriction for protecting against radiofrequency electromagnetic heating effects in the 1–10 GHz range. In our first study, we compared the degree of correlation between these basic restrictions and the peak‐induced tissue temperature rise (ΔT) for a representative range of population/exposure scenarios using simple multi‐planar models exposed to plane wave conditions. In this complementary study, complex heterogeneous head models for an adult and 12‐year‐old child were analyzed at 1, 3, 6, 8, and 10 GHz for a variety of exposure conditions. The complex models indicate that peak ΔT is better correlated with peak 10 g SAR than S_inc at 1 and 3 GHz and with S_inc at 6–10 GHz, in contrast to the results from Part I. Considering the planar and complex body modeling results together, and given the equivocal indications of the two metrics in the 6–10 GHz range, we recommend that the breakpoint be set at 6 GHz. This choice is also based on other considerations such as ease of assessment. We also recommend that the limit level of S_inc should be adjusted to provide a better match with 10 g SAR in the induced tissue temperature rise. Bioelectromagnetics 31:467–478, 2010. © 2010 Wiley‐Liss, Inc.     

Temperature dependences of carbon assimilation processes in four dominant species from mountain grassland ecosystem

Temperature responses of carbon assimilation processes were studied in four dominant species from mountain grassland ecosystem, i.e. Holcus mollis (L.), Hypericum maculatum (Cr.), Festuca rubra (L.), and Nardus stricta (L.), using the gas exchange technique. Leaf temperature (T _L) of all species was adjusted within the range 13–30 °C using the Peltier thermoelectric cooler. The temperature responses of metabolic processes were subsequently modelled using the Arrhenius exponential function involving the temperature coefficient Q ₁₀. The expected increase of global temperature led to a significant increase of dark respiration rate (R _D; Q ₁₀ = 2.0±0.5), maximum carboxylation rate (V _Cmax; Q ₁₀ = 2.2±0.6), and maximum electron transport rate (J _max; Q ₁₀ = 1.6±0.4) in dominant species of mountain grassland ecosystems. Contrariwise, the ratio between J _max and V _Cmax linearly decreased with T _L [y = −0.884 T _L + 5.24; r ² = 0.78]. Hence temperature did not control the ratio between intercellular and ambient CO₂ concentration, apparent quantum efficiency, and photon-saturated CO₂ assimilation rate (P _max). P _max primarily correlated with maximum stomatal conductance irrespective of T _L. Water use efficiency tended to decrease with T _L [y = −0.21 T _L + 8.1; r ² = 0.87].     

Sensitivity of organic matter decomposition to warming varies with its quality

The relationship between organic matter (OM) lability and temperature sensitivity is disputed, with recent observations suggesting that responses of relatively more resistant OM to increased temperature could be greater than, equivalent to, or less than responses of relatively more labile OM. This lack of clear understanding limits the ability to forecast carbon (C) cycle responses to temperature changes. Here, we derive a novel approach (denoted Q_10?q) that accounts for changes in OM quality during decomposition and use it to analyze data from three independent sources. Results from new laboratory soil incubations (labile Q_10?q=2.1 ± 0.2; more resistant Q_10?q=3.8 ± 0.3) and reanalysis of data from other soil incubations reported in the literature (labile Q_10?q=2.3; more resistant Q_10?q=3.3) demonstrate that temperature sensitivity of soil OM decomposition increases with decreasing soil OM lability. Analysis of data from a cross‐site, field litter bag decomposition study (labile Q_10?q=3.3 ± 0.2; resistant Q_10?q=4.9 ± 0.2) shows that litter OM follows the same pattern, with greater temperature sensitivity for more resistant litter OM. Furthermore, the initial response of cultivated soils, presumably containing less labile soil OM (Q_10?q=2.4 ± 0.3) was greater than that for undisturbed grassland soils (Q_10?q=1.7 ± 0.1). Soil C losses estimated using this approach will differ from previous estimates as a function of the magnitude of the temperature increase and the proportion of whole soil OM comprised of compounds sensitive to temperature over that temperature range. It is likely that increased temperature has already prompted release of significant amounts of C to the atmosphere as CO₂. Our results indicate that future losses of litter and soil C may be even greater than previously supposed.     

Effects of temperature on the gas exchange of leaves in the light and dark

Summary Evolution of CO₂ into CO₂-free air was measured in the light and in the dark over a range of temperatures from 15 to 50°. Photosynthetic rates were measured in air and O₂-free air over the same range of temperatures. Respiration in the light had a different sensitivity to temperature compared with respiration in the dark. At the lower temperatures the rate of respiration in the light was higher than respiration in the dark, whereas at temperatures above 40° the reverse was observed. For any one species the maximum rates of photosynthesis and photorespiration occur at about the same temperature. The maximum rate for dark respiration generally is found at a temperature about 10° higher. Zea mays and Atriplex nummularia showed no enhancement of photosynthesis in O₂-free air nor any evolution of CO₂ in CO₂-free air at any of the temperatures.     

Low temperature slowing and cold-block of fast axoplasmic transport in mammalian nerves in vitro

1) Fast axoplasmic transport in mammalian nerve in vitro was studied using an isotope labeling technique. The rate of outflow in cat sciatic nerve fibers of 410 mm/day in vitro was reduced at temperatures below 38°C with a Q₁₀ of 2.0 in the range 38–18°C and a Q₁₀ of 2.3 at 38–13°C. 2) At a temperature of 11°C a partial failure of transport occurred. At temperatures below 11°C a complete block of fast axoplasmic transport occurred, a phenomenon termed “cold-block.” No transport at all was seen over the temperature range of 10–0°C for times lasting up to 48 hr. 3) Transport was resumed after a period of cold-block lasting up to 22 hr when the nerves were brought back to a temperature of 38°C. Some deleterious effects due to cold-block were seen in the recovery phase as indicated by a reduction in crest amplitude, change in its form, and slowed rate. 4) The ∼P level (combined ATP and creatine phosphate) remained near control level in nerves kept at low or cold-block temperatures for times as long as 64 hr. The reduction in fast axoplasmic transport rate seen at low temperatures for times up to 22 hr was therefore considered due to a decrease in the utilization of ATP, a concept in accord with the “transport filament” model proposed to account for fast axoplasmic transport. 5) The sloping of the front of the crest over the temperature range of 18–13°C suggests an additonal factor at the lower temperatures. A disassembly of microtubules is discussed as a possible explanation of the cold-block phenomenon.     

Respiration characteristics in temperate rainforest tree species differ along a long-term soil-development chronosequence

We measured the response of dark respiration (R_d) to temperature and foliage characteristics in the upper canopies of tree species in temperate rainforest communites in New Zealand along a soil chronosequence (six sites from 6 years to 120,000 years). The chronosequence provided a vegetation gradient characterised by significant changes in soil nutrition. This enabled us to examine the extent to which changes in dark respiration can be applied across forest biomes and the utility of scaling rules in whole-canopy carbon modelling. The response of respiration to temperature in the dominant tree species differed significantly between sites along the sequence. This involved changes in both R_d at a reference temperature (R₁₀) and the extent to which R_d increased with temperature (described by E_o, a parameter related to the energy of activation, or the change in R_d over a 10°C range, Q₁₀). Site averaged E_o ranged from 44.4 kJ mol^–1 K^–1 at the 60-year-old site to 26.0 kJ mol^–1 K^–1 at the oldest, most nutrient poor, site. Relationships between respiratory and foliage characteristics indicated that both the temperature response of respiration (E_o or Q₁₀) and the instantaneous rate of respiration increased with both foliar nitrogen and phosphorus content. The ratio of photosynthetic capacity (Whitehead et al. in Oecologia 2005) to respiration (A_max/R_d) attained values in excess of 15 for species in the 6- to 120-year-old sites, but thereafter decreased significantly to around five at the 120,000-year-old site. This indicates that shoot carbon acquisition is regulated by nutrient limitations in the retrogressing ecosystems on the oldest sites. Our findings indicate that respiration and its temperature response will vary according to soil age and, therefore, to soil nutrient availability and the stage of forest development. Thus, variability in respiratory characteristics for canopies should be considered when using models to integrate respiration at large spatial scales.     

The effect of temperature on the rate of oxygen consumption in the sea urchinStrongylocentrotus intermedius

InStrongylocentrotus intermedius acclimated to certain temperatures within the range of 5–20°C, the rate of oxygen consumption increases regularly as the temperature rises, the mean value of theQ ₁₀ coefficient being about 1.9.     

Ventilation and respiratory metabolism in the thermophilic desert ant,Cataglyphis bicolor (Hymenoptera,Formicidae)

The discontinuous ventilation cycle of the Saharan desert ant Cataglyphis bicolor was studied over the range 15–40°C, corresponding to a >2-fold increase in the rate of CO₂ output and hence metabolic rate (Q ₁₀=2.1). Over this range, metabolic rate modulated only ventilation frequency; the volume of CO₂ emitted per ventilation remained constant. The closed-spiracle phase accounted for a small, constant proportion (ca. 14%) of total CO₂ output. In the flutter phase, the rate of CO₂ output increased at a greater than exponential rate from 29% of total CO₂ output at 15°C to 52% at 40°C. CO₂ output rate in the ventilation phase increased, and its duration decreased, exponentially with temperature. Relative to total duration of discontinuous ventilation cycle, the length of each phase was constant over the entire range of metabolic rates measured. These data are the first thorough characterization of the effect of changing metabolic rate on all phases of the discontinuous ventilation cycle of an adult insect. Clearly, C. bicolor maximizes ventilation-phase emission volumes and enhances the contribution of the flutter phase to total CO₂ release relative to other ants for which comparable data are available, and does so in ways that may reduce respiratory water loss rates.Abbreviations BM body mass - C-phase closed-spiracle phase - cVCO₂ rate of carbon dioxyde leakage during the C phase - DVC discontinuous ventilation cycle - F-phase fluttering-spiracle phase - MR metabolic rate - Q ₁₀ factorial increase in MR with 10°C increase in temperature - RQ respiratory quotient - SMR standard metabolic rate - T body temperature (°C) - VCO₂ rate of carbon dioxide output - V-phase ventilation phase - vVCO₂ rate of CO₂ emission during the V-phase - fVCO₂ rate of CO₂ emission during the F-phase - VO₂ rate of oxygen consumption     

Thermodynamic theory explains the temperature optima of soil microbial processes and high Q10 values at low temperatures

Our current understanding of the temperature response of biological processes in soil is based on the Arrhenius equation. This predicts an exponential increase in rate as temperature rises, whereas in the laboratory and in the field, there is always a clearly identifiable temperature optimum for all microbial processes. In the laboratory, this has been explained by denaturation of enzymes at higher temperatures, and in the field, the availability of substrates and water is often cited as critical factors. Recently, we have shown that temperature optima for enzymes and microbial growth occur in the absence of denaturation and that this is a consequence of the unusual heat capacity changes associated with enzymes. We have called this macromolecular rate theory – MMRT (Hobbs et al., 2013 , ACS Chem. Biol. 8:2388). Here, we apply MMRT to a wide range of literature data on the response of soil microbial processes to temperature with a focus on respiration but also including different soil enzyme activities, nitrogen and methane cycling. Our theory agrees closely with a wide range of experimental data and predicts temperature optima for these microbial processes. MMRT also predicted high relative temperature sensitivity (as assessed by Q₁₀ calculations) at low temperatures and that Q₁₀ declined as temperature increases in agreement with data synthesis from the literature. Declining Q₁₀ and temperature optima in soils are coherently explained by MMRT which is based on thermodynamics and heat capacity changes for enzyme‐catalysed rates. MMRT also provides a new perspective, and makes new predictions, regarding the absolute temperature sensitivity of ecosystems – a fundamental component of models for climate change.