Thermal characteristics of soil organic matter measured by DSC: A hint on a glass transition

Glass transitions have been reported for purified humic acids only. In this study, a glass transition was detected in a sample of a sandy forest soil by Differential Scanning Calorimetry (DSC). The glass transition temperature was 79°C for air‐dried samples and 77°C for pre‐moistened samples. In addition to the glass transition, an exothermic process around 30°C was detected in pre‐moistened samples. This could be due to water loss of soil organic matter. However, the nature of this process is not yet understood. This study showed that the macromolecular behaviour of SOM, as indicated by DSC, reacts to the moisture state of soil organic matter.     

Water-soluble organic materials in paddy soil ecosystem

Abstract

Column experiments were conducted to analyze the effect of the temperature on the amounts of organic materials in the leachate, especially organic acids and methane, from samples of the plow layer soil amended with rice straw. Total amount of inorganic carbon in the leachate during the 30-d period of incubation in relation to the temperature was 18°C < 25°C ≤ 30°C > 37°C > 45°C. Total amount of organic carbon in the leachate was signiicantly larger under 45°C incubation than that at other temperatures.

Acetic acid was the dominant organic acid in the leachate regardless of the temperature. Butylic and propionic acids were also present in large amounts in the early and the late period of incubation of temperatures ranging between 18 and 37°C, while only acetic acid was the dominant organic acid during the 30-d period of incubation at 45°C.

The total amount of methane in leachate during the 30-d period of incubation was very small at 18°C, while very large at 25, 30, and 37°C. It decreased nearly to one half at 45°C compared with that at 30°C. Based on the values of δ¹³CH₄ in the leachate, 3 different stages were recognized in the predominant processes of methane production in the submerged paddy soil amended with rice straw: the stage when methane production from CO₂-B₂ was predominant followed by the stages of methane production from acetic acid and from CO₂-H₂ in this order. The second stage coincided with the time of decrease of the organic acid contents in the leachate. Under 45°C incubation, methane production from CO₂-H₂ was predominant throughout the 30-d period of incubation.     

Seasonal effects on photoassimilated carbon-14 in the root system of blue grama and associated soil organic matter

Blue grama (Bouteloua gracilis (H.B.K.) Lag.) was grown at day (14 h) and night temperatures of 25° and 15°C, respectively, in a ¹⁴CO₂-atmosphere during the last 31 of the 55 days from germination to seed set (period 1). An air-tight seal separated the shoot and root spheres. This period was followed by 21 days of a 14°C day (10 h) and 38°C night regime, and 29 days of continuous ?5°C (period 2), and 26 days of the original temperature and light conditions (period 3). Distribution of the assimilated ¹⁴C at the end of period 1 was: roots 33%; root-derived organic matter in the soil 23%; and 22% was released as CO₂. The washed root mass to root-derived soil organic matter ratio of the labelled ¹⁴C was 60 to 40. A root mass decrease of 45% over the cool and frost period changed this ratio to 23 to 77. Polysaccharides and 0.1 n NaOH-extractable organic matter decreased while potential dehydrogenase activity and total organic P increased during this same period, thereby confirming field related observations. Measured dehydrogenase activity overwinter may have two different origins. As total C content of the soil did not increase under the conditions of the experiment, it was postulated that a portion of the observed increase in total C in the field overwinter was of inorganic rather than organic origin.     

Effects of successive soil freeze-thaw cycles on soil microbial biomass and organic matter decomposition potential of soils

Abstract

Effects of soil freeze-thaw cycles on soil microbial biomass were examined using 8 soil samples collected from various locations, including 4 arable land sites and 2 forest sites in temperate regions and 2 arable land sites in tropical regions. The amounts of soil microbial biomass C and N, determined by the chloroform fumigation and extraction method, significantly decreased by 6 to 40% following four successive soil freeze-thaw cycles (- 13 and 4°C at 12 h-intervals) compared with the unfrozen control (kept at 4°C during the same period of time as that of the freeze-thaw cycles). In other words, it was suggested that 60 to 94% of the soil microorganisms might survive following the successive freeze-thaw cycles. Canonical correlation analysis revealed a significantly positive correlation between the rate of microbial survival and organic matter content of soil (r = 0.948*). Correlation analysis showed that the microbial survival rate was also positively correlated with the pore-space whose size ranged from 9.5 to 6.0 μm (capillary-equivalent-diameter; r = 0.995**), pH(KCI) values (r = 0.925**), EC values (r = 0.855*), and pH (H₂O) values (r = 0.778*), respectively. These results suggested that the soil physicochemical properties regulating the amount of unfrozen water in soil may affect the rate of microbial survival following the soil freeze-thaw cycles. The potential of organic matter decomposition of the soils was examined to estimate the effects of the soil freeze-thaw cycles on the soil processes associated with the soil microbial communities. The soil freeze-thaw cycles led to significant 6% increase in chitin decomposition and 7% decrease in rice straw decomposition (p < 0.05), suggesting that the partial sterilization associated with the soil freeze-thaw cycles might disturb the soil microbial functions.     

Physical factors influencing decomposition of organic materials in soil aggregates

Glucose or starch labelled with ¹⁴C was mixed thoroughly into slurried soils. Aggregates of different sizes were obtained from the soils as they dried. The labelled substrates were considered to be distributed in both micro- and macropores in the aggregates. Control samples (labelled substrates in macropores only) were prepared by adding the labelled carbohydrates after the formation of the aggregates. The various samples were sterilized by γ-irradiation and stored at ?15°C.Samples were wetted to about ?20kPa, inoculated with soil organisms, and incubated for 4 weeks at 28°C in closed systems, which enabled regular measurement of ¹⁴CO₂ released.Based on the ¹⁴CO₂ released, it was concluded that starch was protected from microbial attack when present in micropores in aggregates made from fine sandy loam.After incubation samples were dried and rewetted. The flush of ¹⁴CO₂ released was twice as big for samples containing labelled starch compared with glucose, showing that disruption of aggregates, containing residual starch, and rearrangements of soil components are as important as chemical and biological factors in causing the flush of CO₂ resulting from wetting a soil. Mechanical disruption of the aggregates resulted in a similar flush of ¹⁴CO₂.     

Carbon mineralization in an arid soil amended with thermally-dried and composted sewage sludges

Soil amendment with sewage sludge (SS) from municipal wastewater treatment plants is nowadays a common practice for both increasing soil organic matter and nutrient contents and waste disposal. However, the application of organic amendments that are not sufficiently mature and stable may adversely affect soil properties. Composting and thermal drying are treatments designed to minimize these possible deleterious effects and to facilitate the use of SS as a soil organic amendment. In this work, an arid soil either unamended or amended with composted sewage sludge (CSS) or thermally-dried sewage sludge (TSS) was moistened to an equivalent of 60% soil water holding capacity and incubated for 60 days at 28 °C. The C–CO₂ emission from the samples was periodically measured in order to study C mineralization kinetics and evaluate the use of these SS as organic amendments. In all cases, C mineralization decreased after the first day. TSS-amended soil showed significantly higher mineralization rates than unamended and CSS-amended soils during the incubation period. The data of cumulative C–CO₂ released from unamended and SS-amended soils were fitted to six different kinetic models. A two simultaneous reactions model, which considers two organic pools with different degree of biodegradability, was found to be the most appropriate to describe C mineralization kinetics for all the soils. The parameters derived from this model suggested a larger presence of easily biodegradable compounds in TSS-amended soil than in CSS-amended soil, which in turn presented a C mineralization pattern very similar to that of the unamended soil. Furthermore, net mineralization coefficient and complementary mineralization coefficient were calculated from C mineralization data. The largest losses of C were measured for TSS-amended soil probably due to an extended microbial activity. The results obtained thus indicated that CSS is more efficient for increasing total organic C in arid soils.     

Microbial biomass and activity indices after organic substrate addition to a selenium-contaminated soil

High concentrations of Se in soil might have negative effects on microorganisms. For this reason, the effect of organic substrate addition (glucose + maize straw) on Se volatilisation in relation to changes in microbial biomass and activity indices was investigated using an artificially Se-contaminated soil. Microbial biomass N was reduced on average by more than 50% after substrate addition, but adenylate energy charge (AEC) and metabolic quotient qCO₂ were both increased. The Se content decreased by nearly 30% only with the addition of the organic substrate at 25°C. No significant Se loss occurred without substrate at 25°C or with substrate at 5°C. In the two treatments with substrate addition, the substrate-derived CO₂ evolution was about 30% lower with Se addition than without. In contrast, Se had no effect on any of the other soil microbial indices analysed, i.e. microbial biomass C, microbial biomass N, adenosine triphosphate (ATP), AEC, ATP-to-microbial biomass C, and qCO₂.     

Temperature sensitivity of soil organic matter decomposition varies with biochar application and soil type

Biochar application has the potential to improve soil fertility and increase soil carbon stock, especially in tropical regions. Information on the temperature sensitivity of carbon dioxide(CO_2) evolution from biochar-amended soils at very high temperatures, as observed for tropical surface soils, is limited but urgently needed for the development of region-specific biochar management targeted to optimize biochar effects on soil functions. Here, we investigated the temperature sensitivity of soil respiration to the addition of different rates of Miscanthus biochar(0, 6.25, 12.5, and 25 Mg ha~(-1)) in two types of soils with contrasting textures. Biochar-amended soil treatments and their controls were incubated at constant temperatures of 20, 30, and 40℃. Overall, our results show that: i) considering data from all treatments and temperatures, the addition of biochar decreased soil CO_2 emissions when compared to untreated soils;ii) CO_2 emissions from biochar-amended soils had a higher temperature sensitivity than those from biochar-free soils; iii) the temperature sensitivity of soil respiration in sandy soils was higher than that in clay soils; and iv) for clay soils, relative increases in soil CO_2 emissions from biochar-amended soils were higher when the temperature increased from 30 to 40℃, while for sandy soils, the highest temperature responses of soil respiration were observed when increasing the temperature from 20 to 30℃. Together, these findings suggest a significantly reduced potential to increase soil organic carbon stocks when Miscanthus biochar is applied to tropical soils at high surface temperatures, which could be counteracted by the soil-and weather-specific timing of biochar application.     

The proportional mineralisation of microbial biomass and organic matter caused by air-drying and rewetting of a grassland soil

During the first few days after rewetting of an air-dried soil (AD-RW), microbial activity increases compared to that in the original moist soil, causing increased mineralisation (a flush) of soil organic carbon (C) and other nutrients. The AD-RW flush is believed to be derived from the enhanced mineralisation of both non-biomass soil organic matter (due to its physical release and enhanced availability) and microbial biomass killed during drying and rewetting. Our aim was to determine the effects of AD-RW on the mineralisation of soil organic matter and microbial biomass during and after repeated AD-RW cycles and to quantify their proportions in the CO₂-C flushes that resulted. To do this, a UK grassland soil was amended with ¹⁴C-labelled glucose to label the biomass and then given five AD-RW cycles, each followed by 7 d incubation at 25 °C and 50% water holding capacity. Each AD-RW cycle increased the amount of CO₂-C evolved (varying from 83 to 240 μg g⁻¹ soil), compared to the control with, overall, less CO₂-C being evolved as the number of AD-RW cycles increased. In the first cycle, the amount of biomass C decreased by 44% and microbial ATP by 70% while concentrations of extractable C nearly doubled. However, all rapidly recovered and within 1.3 d after rewetting, biomass C was 87% and ATP was 78% of the initial concentrations measured prior to air-drying. Similarly, by 2 d, extractable organic C had decreased to a similar concentration to the original. After the five AD-RW cycles, the amounts of total and ¹⁴C-labelled biomass C remaining in the soil accounted for 60 and 40% of those in the similarly incubated control soil, respectively. Soil biomass ATP concentrations following the first AD-RW cycle remained remarkably constant (ranging from about 10 to 14 μmol ATP g⁻¹ biomass C) and very similar to the concentration in the fresh soil prior to air-drying. We developed a simple mathematical procedure to estimate the proportion of CO₂-C derived from biomass C and non-biomass C during AD-RW. From it, we estimate that, over the five AD-RW cycles, about 60% of the CO₂-C evolved came from mineralisation of non-biomass organic C and the remainder from the biomass C itself.     

14C-labelled maleic hydrazide degradation in soil: Influence of temperature,moisture, clay and organic material

¹⁴C-labelled maleic hydrazide (MH) was added to each of three soils at a concentration of 4 mg kg^?1, and its degradation measured by the release of ¹⁴CO₂ after 2 days. Between 1 and 30°C, at a constant moisture content (full field capacity), the mean degradation rate increased by a factor of 3 for each temperature increment of 10°C (Q₁₀ = 3). The mean activation energy was 78 kJ mol^?1. Above 35°C, the degradation rate decreased.At soil moisture contents between wilting point and 80–90% of field capacity, the degradation rate doubled with an increase in moisture content of 50% of field capacity (constant temperature, 25°C). Above field capacity, the degradation rate was either unchanged or decreased. Below wilting point the degradation was very slow, even after 2 months.The rate of decomposition of MH at all temperatures and moisture contents was lowest in the soil with the highest content of organic matter and the lowest clay content. This soil had the highest Freundlich K value, and presumably adsorbed MH the most strongly, although the lower clay content may also play a role in the lower decomposing capacity of this soil.     

Priming effect of small glucose additions to 14C-labelled soil

Soil was freed of its organic matter by heating it to 400°C. Plants were grown in a ¹⁴CO₂ atmosphere and from them a labelled “soil organic matter” (humus) was prepared by composting the plant material for more than 3 yr in the modified soil under laboratory conditions. The influence of small additions of unlabelled glucose on the decomposition of the labelled soil organic matter was studied. Shortly after the addition of glucose there was a small extra evolution of ¹⁴CO₂, which lasted about 1 day. It is claimed that the extra evolution of ¹⁴CO₂ was caused by conversion of labelled material in the living biomass and was not due to a real priming action, i.e. an accelerated decomposition of humic substances or dead cellular material.     

Modeling aerobic decomposition of rice straw during the off-rice season in an Andisol paddy soil in a cold temperate region of Japan: Effects of soil temperature and moisture

Submerged rice paddies are a major source of methane (CH₄) which is the second most important greenhouse gas after carbon dioxide (CO₂). Accelerating rice straw decomposition during the off-rice season could help to reduce CH₄ emission from rice paddies during the single rice-growth season in cold temperate regions. For understanding how both temperature and moisture can affect the rate of rice straw decomposition during the off-rice season in the cold temperate region of Tohoku district, Japan, a modeling incubation experiment was carried out in the laboratory. Bulk soil and soil mixed with 2% of δ¹³C-labeled rice straw with a full factorial combination of four temperature levels (?5 to 5, 5, 15, 25°C) and two moisture levels (60% and 100% WFPS) were incubated for 24 weeks. The daily change from ?5 to 5°C was used to model the freezing–thawing cycles occurring during the winter season. The rates of rice straw decomposition were calculated by (i) CO₂ production; (ii) change in the soil organic carbon (SOC) content; and (iii) change in the δ¹³C value of SOC. The results indicated that both temperature and moisture affected the rate of rice straw decomposition during the 24-week aerobic incubation period. Rates of rice straw decomposition increased not only with high temperature, but also with high moisture conditions. The rates of rice straw decomposition were more accurately calculated by CO₂ production compared to those calculated by the change in the SOC content, or in its δ¹³C value. Under high moisture at 100% WFPS condition, the rates of rice straw decomposition were 14.0, 22.2, 33.5 and 46.2% at ?5 to 5, 5, 15 and 25°C temperature treatments, respectively. While under low moisture at 60% WFPS condition, these rates were 12.7, 18.3, 31.2 and 38.4%, respectively. The Q₁₀ of rice straw decomposition was higher between ?5 to 5 and 5°C than that between 5 and 15°C and that between 15 and 25°C. Daily freezing–thawing cycles (from ?5 to 5°C) did not stimulate rice straw decomposition compared with low temperature at 5°C. This study implies that to reduce CH₄ emission from rice paddies during the single rice-growth season in the cold temperate regions, enhancing rice straw decomposition during the high temperature period is very important.     

Optimized conditions for determination of total soil organic matter in diverse samples by mass loss on ignition

Reliable measurement of soil organic matter (SOM) contents is crucial to assessment of soil health, productive longevity and the effects of climate change. In this study, the loss‐on‐ignition (LOI) method has been used to determine the SOM of dried soil samples with a wide range of clay, sand and silt contents from the Agricultural Laboratory Proficiency (ALP) program. Regressions of ALP participant data against LOI measurements at 350–650°C indicate that the extent of SOM oxidation depends more on the ignition temperature and time than on the sample compositions. Thus, LOI data from ignition at 350–550°C for 12 h relative to ignition at 650°C for 12 h converge at 650°C and the average coefficient of variance decreases to ≈ 4% at 650°C. Also examined are regressions of soil organic C from direct dry combustion as standards with LOI measured at 360°C for 2 h, LOI measured at 650°C for 12 h and with the Walkley‐Black procedure used in the ALP program.     

Persistence and effect of dexon on soil respiration

The effect of the fungicide Dexon (p-dimethylaminobenzenediazo sodium sulfonate) on CO₂ production from soil amended or not with organic matter, was studied for 60 days. Dexon was found to retard the breakdown of glucose and paddy straw added to soil. Inhibition of CO₂ production occurred during the early stages of glucose decomposition and in the case of straw throughout the period of study. Dehydrogenase activity in the soil was also found to be reduced by this fungicide. Total organic carbon content increased when straw was added to soil in the presence of Dexon. On the other hand, addition of Dexon alone to soil caused a decrease in the amount of organic carbon. Its effect on nitrogen content of the soil was marginal. Dexon had almost completely disappeared from the soil by 60 days.     

Temperature response of ammonia and greenhouse gas emission from manure amended silty clay soil

Soil temperature plays an important role in organic matter decomposition, thus likely to affect ammonia and gaseous emission from land application of manure. An incubation experiment was conducted to quantify ammonia and greenhouse gas (GHG) (N₂O, CO₂ and CH₄) emissions from manure and urea applied at 215?kg N ha^?1 to Fargo-Ryan silty clay soil. Soil (250?g) amended with solid beef manure (SM), straw-bedded solid beef manure (BM), urea only (UO), and control (CT) were incubated at 5, 10, 15, and 25 °C for 31 days at constant 60% water holding capacity (WHC). The cumulative GHGs and NH₃ emission generally increased with temperature and highest emission observed at 25 °C. Across temperature levels, 0.11–1.3% and 0.1–0.7% of the total N was lost as N₂O and NH₃, respectively. Cumulative CO₂ emission from manure was higher than UO and CT at all temperatures (P?<?0.05). Methane accounted for <0.1% of the total C (CO₂?+?CH₄) emission across temperatures. The Q₁₀ values (temperature sensitivity coefficient) derived from Arrhenius and exponential models ranged 1.5–3.7 for N₂O, 1.4–6.4 for CO₂, 1.6–5.8 for CH₄, and 1.4–5.0 for NH_3. Our results demonstrated that temperature significantly influences NH₃ and GHG emissions irrespective of soil amendment but the magnitude of emission varied with soil nutrient availability and substrate quality. Overall, the highest temperature resulted in the highest emission of NH₃ and GHGs.     

Denitrification and C,N mineralization as function of temperature and moisture potential in organic and mineral horizons of an acid spruce forest soil

The influence of temperature (T) and water potential (ψ) on the denitrification potential, C and N mineralization and nitrification were studied in organic and mineral horizons of an acid spruce forest soil. The amount of N₂O emitted from organic soil was 10 times larger than from the mineral one. The maximum of N₂O emission was in both soils at the highest water potential 0 MPa and at 20°C. CO₂ production in the organic soil was 2 times higher than in mineral soil. Net ammonification in organic soil was negative for most of the T‒ψ variations, while in mineral soil it was positive. Net nitrification in organic soil was negative only at the maximum water potential and temperature (0 MPa, 28°C). The highest rate was between 0 and −0.3 MPa and between 20 and 28°C. In mineral soil NO₃⁻ accumulated at all T‒ψ variations with a maximum at 20^oC and −0.3 MPa. We concluded that in organic soil the immobilization of NH₄⁺ is the dominant process in the N‒cycling. Nevertheless, decreasing of total N mineralized at 0 MPa and 20—28^oC can be explained by denitrification.     

Rate of decomposition of organic matter in soil as influenced by repeated air drying-rewetting and repeated additions of organic material

Repeated air drying and rewetting of three soils followed by incubation at 20°C resulted in an increase in the rate of decomposition of a fraction of ¹⁴C labeled organic matter in the soils. The labeled organic matter originated from labeled glucose, cellulose and straw, respectively, metabolized in the soils during previous incubation periods ranging from 1.5 to 8 years.Air drying and rewetting every 30th day over an incubation period of 260–500 days caused an increase in the evolution of labeled CO₂ ranging from 16 to 121 per cent as compared to controls kept moist continuously. The effect of the treatment was least in the soil which had been incubated with the labeled material for the longest time.Additions of unlabeled, decomposable organic material also increased the rate of decomposition of the labeled organic matter. The evolution of labeled CO₂ during the 1st month of incubation after addition was in some cases 4–10 times larger than the evolution from the controls. During the continued incubation the evolution decreased almost to the level of the controls, indicating that the effect was related to the increased biological activity in the soils during decomposition of the added material.Three additions of organic material during the period of incubation resulted totally in an increase over the controls ranging from 36 to 146 per cent.     

Effect of temperature and flooding duration on phosphate sorption in an acid sulphate soil from Vietnam

Phosphate sorption in soil is controlled largely by Fe-oxihydroxides, and so important changes in P dynamics are expected when the redox potential is modified. Such changes in P sorption when acid soil is flooded, as for rice cultivation, have been evaluated. Samples from an acid sulphate soil in the Mekong Delta of Vietnam were flooded for up to 56 d at 20°C and 30°C. Some of the samples incubated at 30°C were dried in open air for 30 d after flooding. Small redox potential (Eh<0) and pH>6 were rapidly reached in soil flooded at 30°C; less drastic reducing conditions (Eh ?0.2 V) and pH 4–5 occurred at 20°C. Phosphate sorption increased during flooding. The increase was twofold at 20°C, and 10-fold at 30°C. Phosphate sorption index decreased in the soil that was air dried after flooding at 30°C, but still remained two to three times greater than before flooding. These results were compared to the changes in oxalate-extractable Fe, i.e. poorly crystalline or amorphous Fe-oxihydroxides. The increase of P sorption per unit increase of oxalate-Fe was seven to eight fold larger at 30°C than at 20°C.     

Kinetics of native and added carbon mineralization on incubating at different soil and moisture conditions in Typic Ustochrepts and Typic Halustalf

The carbon dynamics in soils is of great importance due to its links to the global carbon cycle. The prediction of the behavior of native soil organic carbon (SOC) and organic amendments via incubation studies and mathematical modeling may bridge the knowledge gap in understanding complex soil ecosystems. Three alkaline Typic Ustochrepts and one Typic Halustalf with sandy, loamy sand, and clay loam texture, varying in percent SOC of 0.2; S₁, 0.42; S₂, 0.67; S₃ and 0.82; S₄ soils, were amended with wheat straw (WS), WS + P, sesbania green manure (GM), and poultry manure (PM) on 0.5% C rate at field capacity (FC) and ponding (P) moisture levels and incubated at 35 °C for 1, 15, 30 and 45 d. Carbon mineralization was determined via the alkali titration method after 1, 5, 7 14, 21, and 28 d. The SOC and inorganic carbon contents were determined from dried up (50 °C) soil samples after 1, 15, 30, and 45 d of incubation. Carbon from residue mineralization was determined by subtracting the amount of CO₂-C evolved from control soils. The kinetic models; monocomponent first order, two-component first order, and modified Gompertz equations were fitted to the carbon mineralization data from native and added carbon. The SOC decomposition was dependent upon soil properties, and moisture, however, added C was relatively independent. The carbon from PM was immobilized in S₄. All the models fitted to the data predicted carbon mineralization in a similar range with few exceptions. The residues lead to the OC build-up in fine-textured soils having relatively high OC and cation exchange capacities. Whereas, fast degradation of applied OC in coarse-textured soils leads to faster mineralization and lower build-up from residues. The decline in CaCO₃ after incubation was higher at FC than in the P moisture regime.     

Effect of temperature on the respiration rate of forest soil organic layer along an elevation gradient in the Polish Carpathians

The aim of our studies was to determine the relation between temperature and the respiration rate of the forest soil organic layer along an altitudinal gradient while controlling the effects of the soil characteristics. The respiration rate was measured in laboratory conditions at different temperatures, 0, 10, 20, and 30°C, in samples collected in the Polish part of the Western Carpathians at 600, 800, 1,000, and 1,200 m above sea level from four different mountains, which were later treated as replicates. The increase in the average respiration rate between two consecutive temperatures was expressed as Q ₁₀ coefficients. Among the nutrients measured in the soil organic layer, only the total organic N concentration significantly increased with elevation. The temperature effect was significant for both the respiration rate and the Q ₁₀ values. The calculated Q ₁₀ values were highest for the temperature range between 10 and 20°C, and the lowest values were obtained from the highest temperature range (20–30°C). The altitude effect was significant for the respiration rate but not for the Q ₁₀ values, indicating that the temperature sensitivity of the soil respiration did not change much along the studied altitudinal gradient.