Specific Respiration Rate Research Articles

Effect of Reforestation on Microbiological Activity of Postagrogenic Soils in European Russia

We have studied the microbiological activity of postagrogenic soddy–podzolic, gray, and dark gray forest soils representing succession stages of natural reforestation on former agricultural lands in various forest zones. The chosen succession chronoseries of postagrogenic soils are uniform and include arable soil, abandoned lands of various ages, and forest cenoses. The content of organic carbon (Corg) and total nitrogen (N), pH, water holding capacity (WHC), basal respiration (Vbasal), microbial biomass carbon (Cmic), and ecophysiological parameters of the status of microbial communities (metabolic coefficient qCO2; the Cmic: Corg ratio, and specific rate of basal respiration calculated as the Vbasal: Corg ratio) are determined in mixed soil samples taken from 0–10 and 10–20 cm layers. It has been revealed that the transformation of arable soils into abandoned lands constantly occupied by meadow or forest vegetation usually results in the progressive accumulation of organic carbon in the 0–10-cm layer. This causes more active soil respiration and a significant increase in the pool of microbial carbon. Parallel to this, the processes of podzol formation upon the development of forest vegetation result in a pronounced increase in acidity in the 10–20 cm layer, which causes a decrease in Vbasal and Cmic in soils of forest cenosis. For all the studied chronoseries of postagrogenic soils, the correlation between microbiological parameters (Vbasal and Cmic) and the general soil properties (Corg, N, and WHC) is the closest. The following factors (in decreasing order) exert effect on the dynamics of all the studied properties at postagrogenic evolution: forest zone/soil type > age of abandoned land ˜ depth in the arable layer.

Effects of soil warming on specific respiration rate and non-structural carbohydrate concentration in fine roots of Chinese fir seedlings

A field mesocosm experiment with Chinese fir (Cunninghamia lanceolata) seedlings was conducted in Chenda State-Owned Forest Farm, Sanming, Fujian Province. The effects of soil warming (ambient +5 ℃) on specific respiration rates and nonstructural carbohydrate (NSC) concentrations in fine roots were measured by the ingrowth core method, to reveal the belowground responses and the adaptability of Chinese fir to global warming. The results showed that soil warming caused significant changes of fine root NSC in the second year. The NSC and starch concentrations in 0-1 mm fine roots, and the NSC and sugar concentrations in 1-2 mm fine roots decreased signifi-cantly in January. The NSC, sugar and starch concentrations in 0-1 mm roots and the starch concentration in 1-2 mm roots increased in July. Soil warming had no significant effect on fine root NSC in the third year. The specific root respiration rate of the 0-1 mm roots significantly increased in July of the second year but significantly decreased in July of the third year in the warmed plots. Compared with the 0-1 mm roots, soil warming had no significant effect on the specific root respiration rate of the 1-2 mm roots. In conclusion, the responses of fine root respiration to soil warming depended on the duration of warming. Fine root respiration partly acclimated to soil warming with increasing duration of soil warming, which kept fine root NSC being relatively stable.

Substrate-Limited and -Unlimited Coastal Microbial Communities Show Different Metabolic Responses with Regard to Temperature.

Bacteria are the principal consumers of dissolved organic carbon (DOC) in the ocean and predation of bacteria makes organic carbon available to higher trophic levels. The efficiency with which bacteria convert the consumed carbon (C) into biomass (i.e., carbon growth efficiency, Y) determines their ecological as well as biogeochemical role in marine ecosystems. Yet, it is still unclear how changes in temperature will affect Y and, hence, the transfer of consumed C to higher trophic levels. Here, we experimentally investigated the effect of temperature on metabolic functions of coastal microbial communities inoculated in both nutrient-limited chemostats and nutrient–unlimited turbidostats. We inoculated chemostats and turbidostats with coastal microbial communities into seawater culture medium augmented with 20 and 100 μmol L−1 of glucose respectively and measured CO2 production, carbon biomass and cell abundance. Chemostats were cultured between 14 and 26°C and specific growth rates (μ) between 0.05 and 6.0 day−1, turbidostats were cultured between 10 and 26°C with specific growth rates ranging from 28 to 62 day−1. In chemostats under substrate limitation, which is common in the ocean, the specific respiration rate (r, day−1) showed no trend with temperature and was roughly proportional to μ, implying that carbon growth efficiency (Y) displayed no tendency with temperature. The response was very different in turbidostats under temperature-limited, nutrient-repleted growth, here μ increased with temperature but r decreased resulting in an increase of Y with temperature (Q10: 2.6). Comparison of our results with data from the literature on the respiration rate and cell weight of monospecific bacteria indicates that in general the literature data behaved similar to chemostat data, showing no trend in specific respiration with temperature. We conclude that respiration rates of nutrient-limited bacteria measured at a certain temperature cannot be adjusted to different temperatures with a temperature response function similar to Q10 or Arrhenius. However, the cellular respiration rate and carbon demand rate (both: mol C cell−1 day−1) show statistically significant relations with cellular carbon content (mol C cell−1) in chemostats, turbidostats, and the literature data.

Individual and combined inhibition of phenol and thiocyanate on microbial activity of partial nitritation.

This study evaluated the individual and interactive effect of phenol and thiocyanate (SCN-) on partial nitritation (PN) activity using batch test and response surface methodology. The IC50 of phenol and SCN- on PN sludge were 5.6 and 351mg L-1, respectively. The PN sludge was insensitive to phenol and SCN- at levels lower than 1.77 and 43.3mg L-1, respectively. A regression model equation was developed and validated to predict the relative specific respiration rate (RSRR) of PN sludge exposed to different phenol and SCN- concentrations. In the range of independent variables, the most severe inhibition was observed with a valley value (17%) for RSRR, when the phenol and SCN- concentrations were 4.08 and 198mg L-1, respectively. An isobole plot was used to judge the combined toxicity of phenol and SCN-, and the joint inhibitory effect was variable depending on the composition and concentration of the toxic components. Furthermore, the toxic compounds showed independent effects, which is the most common type of combined toxicity.

Carbon Availability Modifies Temperature Responses of Heterotrophic Microbial Respiration, Carbon Uptake Affinity, and Stable Carbon Isotope Discrimination.

Microbial transformations of organic carbon (OC) generate a large flux of CO2 into the atmosphere and influence the C balance of terrestrial and aquatic ecosystems. Yet, inherent heterogeneity in natural environments precludes direct quantification of multiple microbial C fluxes that underlie CO2 production. Here we used a continuous flow bioreactor coupled with a stable C isotope analyzer to determine the effects of temperature and C availability (cellobiose concentration) on C fluxes and 13C discrimination of a microbial population growing at steady-state in a homogeneous, well-mixed environment. We estimated C uptake affinity and C use efficiency (CUE) to characterize the physiological responses of microbes to changing environmental conditions. Temperature increased biomass-C specific respiration rate and C uptake affinity at lower C availability, but did not influence those parameters at higher C availability. CUE decreased non-linearly with increasing temperature. The non-linear, negative relationship between CUE and temperature was more pronounced under lower C availability than under relatively high C availability. We observed stable isotope fractionation between C substrate and microbial biomass C (7~12‰ depletion), and between microbial biomass and respired CO2 (4~10‰ depletion). Microbial discrimination against 13C-containing cellobiose during C uptake was influenced by temperature and C availability, while discrimination during respiration was only influenced by C availability. Shifts in C uptake affinity with temperature and C availability may have modified uptake-induced 13C fractionation. By stressing the importance of C availability on temperature responses of microbial C fluxes, C uptake affinity, CUE, and isotopic fractionation, this study contributes to a fundamental understanding of C flow through microbes. This will help guide parameterization of microbial responses to varying temperature and C availability within Earth-system models.

A model analysis of climate and CO2 controls on tree growth and carbon allocation in a semi-arid woodland

Many studies have failed to show an increase in the radial growth of trees in response to increasing atmospheric CO2 concentration [CO2] despite the expected enhancement of photosynthetic rates and water-use efficiency at high [CO2]. A global light use efficiency model of photosynthesis, coupled with a generic carbon allocation and tree-growth model based on mass balance and tree geometry principles, was used to simulate annual ring-width variations for the gymnosperm Callitris columellaris in the semi-arid Great Western Woodlands, Western Australia, over the past 100 years. Parameter values for the tree-growth model were derived from independent observations except for sapwood specific respiration rate, fine-root turnover time, fine-root specific respiration rate and the ratio of fine-root mass to foliage area (ζ), which were calibrated to the ring-width measurements by approximate Bayesian optimization. This procedure imposed a strong constraint on ζ. Modelled and observed ring-widths showed quantitatively similar, positive responses to total annual photosynthetically active radiation and soil moisture, and similar negative responses to vapour pressure deficit. The model also produced enhanced radial growth in response to increasing [CO2] during recent decades, but the data do not show this. Recalibration in moving 30-year time windows produced temporal shifts in the estimated values of ζ, including an increase by ca 12% since the 1960s, and eliminated the [CO2]-induced increase in radial growth. The potential effect of CO2 on ring-width was thus shown to be small compared to effects of climate variability even in this semi-arid climate. It could be counteracted in the model by a modest allocation shift, as has been observed in field experiments with raised [CO2].

Effect of body size and temperature on respiration of Galaxias maculatus (Pisces: Galaxiidae)

ABSTRACTBody mass and temperature are primary determinants of metabolic rate in ectothermic animals. Oxygen consumption of post-larval Galaxias maculatus was measured in respirometry trials under different temperatures (5–21 °C) and varying body masses (0.1–>1.5 g) spanning a relevant range of thermal conditions and sizes. Specific respiration rates (R in g O2 g−1 d−1) declined as a power function of body mass and increased exponentially with temperature and was expressed as: R = 0.0007 * W −0.31 * e 0.13 * T. The ability of this model to predict specific respiration rate was evaluated by comparing observed values with those predicted by the model. Our findings suggest that the respiration rate of G. maculatus is the result of multiple interactive processes (intrinsic and extrinsic factors) that modulate each other in ‘meta-mechanistic’ ways; this would help to explain the species’ ability to undergo the complex ontogenetic habitat shifts observed in the lakes of the Andean Patagonic range.

Effects of precipitation exclusion on fine-root biomass and functional traits of Cunninghamia lanceolata seedlings.

A precipitation exclusion experiment was set up in Cunninghamia lanceolata seedling plots in Chenda State-Owned Forest Farm, Sanming, Fujian Province, which included 50% precipi-tation reduction and ambient precipitation (control). Using soil coring and in-growth core me-thods, changes in fine-root functional traits of C. lanceolata seedlings, including fine-root biomass, morphology, stoichiometry, specific root respiration, and nonstructural carbohydrates, were exa-mined after 1 year's precipitation exclusion. The results showed that precipitation exclusion significantly decreased biomass of 0-1 mm diameter roots but had no effect on 1-2 mm diameter roots. However, adaptive morphological changes occurred in the precipitation exclusion treatment. The specific root length (SRL) of the 0-1 and 1-2 mm diameter roots increased by 21.1% and 30.5%, respectively, and root tissue density (RTD) significantly decreased and specific root surface area (SRA) significantly increased in the 0-1 mm diameter roots. Precipitation exclusion led to increase in nitrogen concentration in fine roots, but the absorption capacity for phosphorus was impeded, resulting in increased root N:P, which implied a nutritional imbalance in fine roots. Precipitation exclusion did not significantly change fine root specific respiration rate and nonstructural carbohydrate (NSC) content. However, the soluble sugar content and the ratio of soluble sugar to starch were significantly decreased, and the starch content was increased by 33.3% in the 1-2 mm diameter roots, indicating an adaptation response of C. lanceolata seedlings to reduced precipitation by increasing the storage of nonstructural carbohydrate in fine roots.

특정 호흡수에서 행한 통제호흡이 심박변이도에 미치는 영향에 대한 예비연구

Objectives We observed what effects of Paced Breathing(PB) in specific respiration rate have on heart rate variability (HRV) according to Sasang Constitution.Methods HRV of 72 healthy participants in sitting position was recorded while they carried out usual breathing, 0.2Hz, 0.1Hz, and 0.05Hz PB each 5 minutes in consecutive order. Five minute of relaxation was permitted between each breathing. Finally, HRV indices were statictically analyzed of 32 participants (SOEUM: 11, SOYANG: 10, TAEEUM: 11) after data out of accord with respiration rate or outliers were excluded.Results and Conclusions According to respiration rates, there was no statistical significance of HRV among Sasang Constitution. Regardless of Sasang Constituion, 0.2Hz PB increased mean heart rate and decreased natural logarithmic low frequency(lnLF) oscillation of HRV without the change of natural logarithmic high frequency(lnHF), while 0.1Hz PB increased lnLF and standard deviation of N-N interval(SDNN), and slightly decreased lnHF without the change of mean heart rate. 0.05 Hz PB also showed the same effect as 0.1Hz PB, but was impracticable.

Litter heterogeneity modulates fungal activity, C mineralization and N retention in the boreal forest floor

The implications of forest floor heterogeneity for fungal activity, nutrient retention and carbon sequestration within the forest floor remain poorly documented. This information would be particularly relevant to situations where large changes in fresh litter occur such as following stand replacing disturbances. Numerous laboratory studies have documented mycelial translocation of simple forms of C and nutrients between contrasting substrates, allowing fungi to overcome local deficiencies. In slightly more complex but less controlled conditions, we assessed how factors contributing to forest floor heterogeneity—decay state, litter origin and tree species—individually affect fungal activity during decomposition. We also assessed how the juxtaposition of litters of contrasting nutrient and C status (decay state) alter fungal activity within individual substrates. We expected fungal biomass to be reallocated to C-rich litters while lignocellulolytic activity would increase in all juxtaposed litters. A microcosm experiment was conducted in which wood and leaf litters of one softwood species (Pinus banksiana) and one hardwood species (Populus tremuloïdes) were incubated alone or in combination with litters of contrasting decay states. Litter mass loss, change in N content, C mineralization, fungal biomass, specific respiration rate and lignocellulolytic activity were measured after 15 and 30 weeks. The decay state of litter had the most pronounced and consistent effects on fungal activity, with higher fungal biomass and lignocellulolytic enzyme activity in well decomposed litters and higher mass loss, C mineralization and specific respiration rate in fresh litters. In juxtaposed litters, fungal biomass was initially reallocated to fresh litters when incubated with well decomposed litters. Cellulolytic activity also increased by 30% in juxtaposed fresh litters while Mn-peroxidase activity increased by 42% in both fresh and well decomposed litters. With the longer incubation period, C mineralization and specific respiration of fungal biomass increased in juxtaposed well decomposed wood, indicating an increase in overflow metabolism presumably in response to an increase in labile C. Fresh litters that were juxtaposed increased their N content while that of single litters decreased. A better understanding of fine scale mechanisms affecting litter decomposition could improve our ability to forecast ecosystem response to disturbance.

Temperature-mediated changes in microbial carbon use efficiency and <sup>13</sup>C discrimination

Abstract. Understanding how carbon dioxide (CO2) flux from ecosystems feeds back to climate warming depends in part on our ability to quantify the efficiency with which microorganisms convert organic carbon (C) into either biomass or CO2. Quantifying ecosystem-level respiratory CO2 losses often also requires assumptions about stable C isotope fractionations associated with the microbial transformation of organic substrates. However, the diversity of organic substrates' δ13C and the challenges of measuring microbial C use efficiency (CUE) in their natural environment fundamentally limit our ability to project ecosystem C budgets in a warming climate. Here, we quantify the effect of temperature on C fluxes during metabolic transformations of cellobiose, a common microbial substrate, by a cosmopolitan microorganism growing at a constant rate. Biomass C specific respiration rate increased by 250 % between 13 and 26.5 °C, decreasing CUE from 77 to 56 %. Biomass C specific respiration rate was positively correlated with an increase in respiratory 13C discrimination from 4.4 to 6.7 ‰ across the same temperature range. This first demonstration of a direct link between temperature, microbial CUE, and associated isotope fluxes provides a critical step towards understanding δ13C of respired CO2 at multiple scales, and towards a framework for predicting future ecosystem C fluxes.

Inhibition of the partial nitritation by roxithromycin and Cu(II)

To facilitate the application of partial nitritation (PN) – anaerobic ammonium oxidation process in nitrogen removal from livestock wastewater, the inhibition of roxithromycin (ROX) and Cu(II) on the PN sludge was examined using a respirometric method. The results showed that the IC50 of ROX and Cu(II) on PN sludge were 346 and 74.3mgL−1, respectively. The relative specific respiration rate (SRR) of ammonia-oxidizing bacteria (AOB) decreased from 87.4% to 17.7% with the ROX concentration increased from 0 to 500mgL−1. When the concentration of Cu(II) increased from 0 to 160mgL−1, the SRRs of AOB and nitrite-oxidizing bacteria decreased by 85.5% and 11.2%, respectively. According to the isobole plots analysis, combined suppression by ROX and Cu(II) was synergistic. Fourier transform infrared spectroscopy analyses showed that ROX exposure altered the positions of CO bonds, and the intensity of the absorption peak at 2100cm−1 changed under Cu(II) exposure.

Changes in very fine root respiration and morphology with time since last fire in a boreal forest

We examined the physiological and morphological responses of individual fine root segments in boreal forests stands with different age since the last fire to determine changes in specific fine root respiration and morphological traits during forest succession. We investigated the respiration of fine roots divided into three diameter classes (<0.5, 0.5–1.0, and 1.0–2.0 mm) in a Finnish boreal Pinus sylvestris L. in forest stands with 5, 45, 63, and 155 years since the last fire. Specific respiration rates of <0.5 mm roots in 155-year-old stands were 74 %, 38 %, and 31 % higher than in 5-, 45-, and 63-year-old stands, respectively. However, the respiration rates of thicker diameter roots did not significantly change among stands with respect to time after fire. Similarly, fire disturbance had a strong impact on morphological traits of <0.5 mm roots, but not on thicker roots. Root respiration rates correlated positively with specific root length (length per unit mass) and negatively with root tissue density (mass per unit volume) in all stand ages. The linear regression lines fitted to the relationships between root respiration and specific root length or root tissue density showed significantly higher intercepts in 63- and 155-year-old than in 5-year-old stands. Significant shifts in the intercept of the common slope of respiration vs. morphology indicate the different magnitude of the changes in physiological performance among the fire age class. Despite a specific small geographic area, we suggest that the recovery of boreal forests following wildfire induces a strategy that favors carbon investment in nutrient and water exploitation efficiency with consequences for higher respiration, length, and lower tissue density of very fine roots.

Respiration, worker body size, tempo and activity in whole colonies of ants

Ants are social, and their metabolism should be measured on at least two levels: (i) the individual workers and brood of which the colony is composed and (ii) the colony in its entirety. Whole colony respiration, tempo (size‐free running speed in body lengths per second) and whole colony activity were simultaneously measured for 15 species of ants in four subfamilies, and these data are related to average worker and whole‐colony weight, activity, percentage brood and percentage fat. Across all 15 species, whole colony respiration rate (μL CO2 h−1) is linearly related to whole colony live weight (log–log slope = 1.0). Colonies composed of large workers respire less than colonies composed of an equal live weight of small workers, and colonies with high tempos respire more than lower tempo colonies of equal weight. The tempos and respiration rates of smaller ants tend to be higher, and a higher tempo exacts a cost in higher respiration independent of the effect of small body size. Individual worker respiration (μL CO2 h−1) scales to worker live weight with an exponent of 0.76. Whole colony specific respiration rate (μL CO2 g−1 h−1) is unrelated to colony live weight. The regressions of respiration rates against colony and worker dry weight, lean weight and metabolic weight have similar slopes to those of live weight but different intercepts. Respiration is not related to worker percentage fat, percentage brood or activity. Ant ecology, tempo, body size, polymorphism and colony size are discussed in relation to respiration.

Quantification of the transient and long-term response of Saccharomyces cerevisiae to carbon dioxide stresses of various intensities

Carbon dioxide (CO2) is a major compound of microbial metabolism both as a substrate and as a product but high dissolved carbon dioxide concentrations have long been known to affect yeast physiology.This work investigates the energetic aspects of the transient and long-term responses of yeast chemostat cultures submitted to different step-increases of the dissolved CO2 concentrations.It was demonstrated that a CO2 shift-up triggered a transient metabolic response characterized by an increase of the specific respiration rate (up to +37%), the mobilization of storage sugars, excretion of ethanol and acetate (up to 50mgL−1) and by the uptake of potassium (+30mM) and magnesium (+20mM) ions. The energy generation by the yeast metabolism temporarily increased and a transient decrease in the biomass synthesis was observed. This short-term response was not dependent of the amplitude of the shift-up and could not be explained by pH homeostasis only. Moreover, on the long-run CO2 created an energy drain that was proportional to its concentration as the YATP value decreased from 12.7gXmoleATP−1 to 9.57gXmoleATP−1 when the dissolved CO2 concentration was increased from 1.4mM to 17.09mM. Succinate excretion was also observed for CO2 enriched cultures and its production rate was found proportional with increasing CO2 concentrations. Finally, we pointed out that yeast cells may adapt to high CO2 concentrations in the long-run.This work illustrates the regulation of physiologic and metabolic homeostasis of yeast cells when facing CO2 stress.

Seasonal change in acclimatised respiration rate of Temora longicornis

We investigated the seasonal changes in the respiration rate (R) of adult Temora longicornis (Muller) acclimatised to in situ conditions over 1 yr. Mean (±1 SE) R varied from 50.5 ± 2.8 nl O2 ind. −1 h −1 in December to 73.2 ± 3.53 nl O2 ind. −1 h −1 in August for copepods of mean body dry weight (DW) of 33.5 ± 1.1 and 26.3 ± 0.95 μg, respectively. Males represented ~8% of the total measurements, and their respiration did not differ significantly from that of females. R scaled isometrically with dry weight (DW), i.e. the allometric exponent of the power function (R = aDW b ) did not differ significantly from unity (b = 0.83 to 1.35). The relationship between in situ weight- specific respiration rate (Rsp) and temperature (T) was described by a sigmoid trend with Q10 ranging from 1 to 2.88 (mean 1.57 to 1.89). In contrast, the acclimated and acutely measured Rsp of copepods maintained under optimal feeding conditions in the laboratory increased exponentially with temperature and were characterised by higher mean Q10 of 2.05 and 2.41, respectively. Acclimatised ln R increased significantly with ln DW, T, ln chlorophyll a (ln Chl) and ln egg production rate (ln EPR). Our results indicate that seasonal changes in T. longicornis respiration rate are not simply determined by body mass and temperature but also reflect copepod nutritional and reproductive condition. We argue that predictive ecological models using fixed thermal coefficient values may overestimate copepod respiration, particularly under ambient conditions limiting growth and reproduction. Our findings have important implications for the calculation of carbon flow in marine food-webs and for understanding how zooplankton physiology responds to changes in global temperature.

Effects of oxytetracycline on populations and community metabolism of an aquatic microcosm

AbstractTo investigate the ecological impacts of a widely‐used antibiotic agent oxytetracycline (OTC), we prepared an aquatic microcosm consisting of two green algae (Chlorella sp. and Scenedesmus sp.), a blue‐green alga (Tolypothrix sp.), a protozoan (Cyclidium sp.), two rotifers (Philodina sp. and Lecane sp.), an aquatic oligochaete (Aeolosoma hemprichi), and bacteria. We investigated the effects of OTC on population abundance of composite species, gross primary production (GPP), and community respiration (CR). We linked population abundance, GPP and CR to understand the relationship between these measures. First, ‘experimental respiration rate of heterotrophs’ (HRexp) was obtained by CR minus algal respiration that is calculated by 0.35 × GPP. Next, the population respiration of each heterotroph was calculated from the direct measure of population abundance and the assumed constant of per‐capita respiration. We defined the sum of the population respirations across all heterotrophs as ‘theoretical respiration rate of heterotrophs’ (HRtheo). Finally, relative community metabolism (RCM) of the heterotrophic community was obtained by calculating the ratio of HRexp to HRtheo that indicates changes in specific respiration rates as a whole in the community. The influence of OTC on RCM was larger than on CR, thus the effect of OCT on the metabolism of heterotrophs was far more severe than expected from CR. RCM can magnify the rate of change in the original data, and facilitate the detection of influences in ecotoxicological studies.

On Relation of Filtration and Respiration in the Frat Oyster (Ostrea edulis) at Different Water Temperature

Dependence of filtration and respiration rate in the flat oyster on water temperature was studied. Parameters of the exponential equation of relation of the considered functions with the body mass within the temperature interval 10−23°C were determined. Specific filtration rate varied over the range 0.88−2.37 l/hour·g, regression coefficient − 0.435−0.513, specific respiration rate varied over the range 0.291−0.725 mg O2/hour·specimen, regression coefficient − 0.688−0.773. Relation F/R (index of filtering activity) at different temperature varied insignificantly − from 4.41 to 4.82 l/ml O2. Relatively stable relation of filtration and respiration rates over natural seasonal temperature rhythm indicates compensatory modification of filtration and metabolism intensity under changing temperature.

Acclimation and soil moisture constrain sugar maple root respiration in experimentally warmed soil

The response of root respiration to warmer soil can affect ecosystem carbon (C) allocation and the strength of positive feedbacks between climatic warming and soil CO2 efflux. This study sought to determine whether fine-root (<1 mm) respiration in a sugar maple (Acer saccharum Marsh.)-dominated northern hardwood forest would adjust to experimentally warmed soil, reducing C return to the atmosphere at the ecosystem scale to levels lower than that would be expected using an exponential temperature response function. Infrared heating lamps were used to warm the soil (+4 to +5 °C) in a mature sugar maple forest in a fully factorial design, including water additions used to offset the effects of warming-induced dry soil. Fine-root-specific respiration rates, root biomass, root nitrogen (N) concentration, soil temperature and soil moisture were measured from 2009 to 2011, with experimental treatments conducted from late 2010 to 2011. Partial acclimation of fine-root respiration to soil warming occurred, with soil moisture deficit further constraining specific respiration rates in heated plots. Fine-root biomass and N concentration remained unchanged. Over the 2011 growing season, ecosystem root respiration was not significantly greater in warmed soil. This result would not be predicted by models that allow respiration to increase exponentially with temperature and do not directly reduce root respiration in drier soil.

Organic amendments affect δ13C signature of soil respiration and soil organic C accumulation in a long‐term field experiment in Sweden

SummaryThe contribution of young and old soil organic carbon (SOC) pools to soil CO2 fluxes and specific respiration rates of these fluxes was determined by using δ13C signatures in the Ultuna long‐term continuous soil organic matter experiment (C‐SOME). Initiated in 1956, the experiment had a range of treatments amended organically and with mineral nitrogen fertilizer under C3 cultivation until 1999, and thereafter under C4 (maize) cultivation. In 2011, soil respiration was measured in situ prior to planting, during growth and after harvest. The contributions from C4‐ and C3‐C as well as their specific respiration rates were estimated from δ13C differences in SOC and CO2 fluxes. The contributions from C4‐C sources were further separated into autotrophic and heterotrophic respiration by comparing respiration rates before and after harvest. Between 165 and 385 g C4‐C m−2 accumulated during 10 years of maize growth, contributing between 4.9 and 8.1% to the total SOC stock. Although recent C4‐C had an average specific respiration rate that was 8.4–22.6 times greater than C3‐C, total soil respiration was generally equally split between C3‐C and C4‐C. Both pools are therefore important sources of CO2 in the overall C budget, and a crucial factor in accounting for SOC stock change caused by management. Experimental treatments influenced specific respiration rates of C4 plant material and accumulation of SOC stock, demonstrating how greater SOC accumulation can be favoured by high‐quality C inputs.