The impact of heating on the hydraulic properties of soils sampled under different plant cover

The impact of heating on the peristence of water repellency, saturated hydraulic conductivity, and water retention characteristics was examined on soils from both forest and meadow sites in southwest Slovakia shortly after a wet spell. The top 5 cm of meadow soils had an initial water drop penetration time WDPT at 20°C of 457 s, whereas WDPT in the pine forest was 315 s for the top 5 cm and 982 s if only the top 1 cm was measured. Heating soils at selected temperatures of 50, 100, 150, 200, 250 and 300°C caused a marked drop in water drop penetration time WDPT from the initial value at 20°C. However, samples collected in different years and following an imposed cycle of wetting and drying showed much different trends, with WDPT sometimes initially increasing with temperature, followed by a drop after 200–300°C. The impact of heating temperature on the saturated hydraulic conductivity of soil was small. It was found for both the drying and wetting branches of soil water retention curves that an increase in soil water repellency resulted in a drop in soil water content at the same matric potential. The persistence of soil water repellency was strongly influenced by both the sampling site and time of sampling, as it was characterized by the results of WDPT tests.     

The use of steam/air mixtures for partially sterilizing soils infested with cucumber root rot pathogens

An apparatus for experimentally heating glasshouse soils in situ with steam/ air mixtures is described. Covering soil with a rigid hood enabled mixtures to be introduced at ground level at pressures sufficient to give reasonable rates of heat penetration. Heat-treating soils (66–100° C), in which cucumbers had previously grown poorly, increased yields of subsequent crops from (1) 33 to 39/43 kg/plot of four plants and (2) 95 to 178/191 kg/plot. These increases were associated with the eradication of a dark sclerotial pathogenic fungus causing tap root rot. Increasing partial sterilization temperatures increased concentrations of soluble and exchangeable soil Mn from 4 p.p.m. in unheated soil to 9, 43, 87 and 108 p.p.m. at 66, 77, 88 and 100° C respectively, these differences being paralleled by concentrations of Mn in leaf laminae. Cucumbers grown in soils sterilized at 88° C yielded 8 % more than those in soils treated at 100° C.     

Growth and survival of cowpea rhizobia in bauxitic silt loam and sandy clay loam soils

Survival of 4 cowpea Rhizobium strains, IRC291, MI-50A, JRW3 and JRC29, in two soil types (bauxitic silt loam and sandy clay loam) undergoing drying at 30°C and 37°C was examined. While all strains except JRW3 showed a general pattern of increase in their numbers during the first 3 weeks in sterile soils, none of the strains showed any increase in their population in non-sterile soils. Cowpea rhizobia showed better survival in non-sterile bauxitic silt loam than in clay loam soils at 30°C. However, the long-term survival (examined up to 6 months) of rhizobia in both soils was poor at 37°C as compared to 30°C. We also found that cowpea rhizobia survived better in soils undergoing drying than in moist soils at 30°C. Our results suggest that (a) cowpea rhizobia survived better in bauxitic silt loam than in clay loam soil and (b) the low indigenous cowpea rhizobial population in Jamaican soils may be due to their poor long-term survival and weak saprophytic competence.     

Development of a radio frequency heating system for sterilization of vacuum-packed fish in water

We developed equipment that quickly and uniformly heats packed whole fish in circulating tap water using radio frequency (RF) heating. Four vacuumed plastic-packed Pacific sauries in tap water were set in a radial arrangement between coaxial cylindrical electrodes in a closed vessel. For sterilization testing, Bacillus subtilis spores added in the center of the sauries were counted after treatment. For quality assurance, meat color and backbone hardness were measured after treatment. The temperature at the center of the sauries was increased up to 130 °C for 19 min using 9 kW RF heating, and up to 119 °C for 45 min using conventional heating (CH) at 120 °C. B. subtilis spores were decreased by five logarithmic orders using RF heating and by four logarithmic orders using CH. The RF-treated meat was brighter than the CH-treated meat, and the RF-treated backbone was softer than CH-treated one.     

Temperature response and flowering of white clover (Trifolium repens) varieties in controlled environments and the field

Floral initiation of 10 white clover varieties growing in three controlled day/night temperature regimes, 22“/10°C, 20°/10°C, 17°/10°C, was recorded. Effects of artificial soil heating on floral initiation of the same plants subsequently transferred to the field were also examined. In the controlled environments only a slight increase in day temperature (2–5°C) was necessary to significantly increase flowering. Defoliation at the three temperatures had contrasting effects on subsequent flower production. Results from the soil heating experiment suggested that increased temperature might compensate for short daylengths, by bringing forward reproductive bud initiation by 1 month. Soil heating increased the total number of inflorescences produced.     

Temperature Dependence of Methane Production in Tropical Rice Soils

Although CH 4 production is sensitive to temperature, it is not clear how temperature controls CH 4 production directly versus the production of organic substrates that methanogens convert into CH 4 . Therefore, this study was done to better understand how CH 4 production in rice paddy soil responded to temperature when the process was not limited by the availability of substrates. In a laboratory-incubation study using three Indian rice soils under flooded conditions, the effect of temperature on CH 4 production was examined. CH 4 production in acid sulphate, laterite, and alluvial soil samples under flooded conditions distinctly increased with increase in temperature from 15°C to 35°C. Laterite and acid sulphate soils produced distinctly less CH 4 than alluvial soils. CO 2 production increased with increase in temperature in all the soils. The readily mineralizable carbon C and Fe 2+ contents in soils were least at 15°C and highest at 35°C, irrespective of soil type. Likewise, a significant correlation existed between microbial population (methanogens and sulphate reducers) and CH 4 production. Comparing the temperature coefficients ( Q 10 ) for methane production within each soil type at low (15°C-25°C) and medium (25°C-35°C) temperature intervals revealed that these values were not uniform for both alluvial and laterite soils. But acid sulphate soil had Q 10 values that were near 2 at both temperature intervals. When these soil samples were amended with substrates (acetate, H 2 -CO 2 , and rice straw), there were stimulatory effects on methane production rates and consequently on the Q 10 values. The pattern of temperature coefficients was characteristic of the soil type and the nature of substrates used for amendment.     

Analysis of trace elements in animal tissues

Graphite furnace atomic absorption spectrophotometry is a method used for the measurement of low concentrations of manganese (ppb range). Despite the widespread use of this technique, there is considerable inconsistency concerning sample preparation and choice of instrumental parameters. In this paper, we determined manganese concentrations of National Bureau of Standards (NBS) bovine liver by both graphite furnace (Instrumentation Laboratory IL 555B) and flame atomic absorption following wet digestion of the sample with nitric acid. The following instrumental parameters for the graphite furnace were found optimal for the measurement of manganese in digested NBS bovine liver: inert gas flow=14 SCFH, drying temperature 100°C/15 s (step 1), 125°C/15 s (step 2), pyrolysis temperature 500°C/15 s (step 3), and 1000°C/15 s (step 4); atomization temperature 2250°C/10 s (step 5). For optimal results, the nitric acid concentration of the sample should be between 2 and 4M. There were no significant differences found for manganese concentrations determined by either peak height or peak area measurement. Additionally, no significant differences were found in manganese concentrations determined by flame or furnace methods. Assuming proper sample preparation and choice of instrumental parameters, values obtained for manganese concentration by graphite furnace and flame atomic absorption spectrophotometry are similar. Therefore, data obtained by these two methods can be compared directly.     

The Effects of Drying Temperature on the Extractability of Metals from Dredged Sediments

Dredged sediments may contain considerable amounts of metallic and/or organic pollutants. The risk of metal transfer from sediment deposits to soils can be evaluated using chemical extraction procedures; however, the temperatures at which samples are dried before metal extraction vary widely from one study to another. This led us to investigate the impact of drying temperature on the extractability of metals from dredged sediments. First, water-, CaCl ₂ - and DTPA-extractions were performed on 12 dredged sediments collected in France, with analyses being carried out on both raw (i.e. not dried) samples and on samples dried at 105°C. Higher extractable Cd and Zn contents were recorded for the samples dried at 105°C than for the raw samples. In order to assess the effect of drying temperature on metal extractability, we selected one sediment and carried out CaCl ₂ -, HNO ₃ - and DTPA-extractions on the raw sample and on samples dried at three different temperatures. In general, increasing the drying temperature led to an increase in the extractability of Cr and Cu for all three extraction methods. The CaCl ₂ -extractability of Ni and Zn decreased as drying temperature increased, except for the sample dried at 105°C. The HNO ₃ - and DTPA-extractabilities of these two metals were highest when the sediments were air-dried and then decreased with increasing drying temperature. Similar behavior was observed for Cd, except in the case of HNO ₃ -extractability. As the aim of chemical analysis using selective extraction is to measure the bio-available fractions of metals in soils and sediments, we suggest that extraction should be carried out on raw samples in order to simulate plant growth conditions.     

Life from the ashes: survival of dry bacterial spores after very high temperature exposure

We found that spores of Bacillus amyloliquefaciens rank amongst the most resistant to high temperatures with a maximum dry heat tolerance determined at 420 °C. We found that this extreme heat resistance was also maintained after several generations suggesting that the DNA was able to replicate after exposure to these temperatures. Nonetheless, amplifying the bacterial DNA using BOXA1R and (GTG)₅ primers was unsuccessful immediately after extreme heating, but was successful after incubation of the heated then cooled spores. Moreover, enzymes such as amylases and proteases were active directly after heating and spore regeneration, indicating that DNA coding for these enzymes were not degraded at these temperatures. Our results suggest that extensive DNA damage may occur in spores of B. amyloliquefaciens directly after an extreme heat shock. However, the successful germination of spores after inoculation and incubation indicates that these spores could have a very effective DNA repair mechanism, most likely protein-based, able to function after exposure to temperatures up to 420 °C. Therefore, we propose that B. amyloliquefaciens is one of the most heat resistant life forms known to science and can be used as a model organism for studying heat resistance and DNA repair. Furthermore, the extremely high temperature resistivity of these spores has exceptional consequences for general methodology, such as the use of dry heat sterilization and, therefore, virtually all studies in the broad area of high temperature biology.

     

The energetic cost of arousal from torpor in the marsupial Sminthopsis macroura : benefits of summer ambient temperature cycles

The costs of arousal from induced torpor were measured in the striped-faced dunnart (Sminthopsis macroura; ca. 25 g) under two experimental ambient temperature cycles. The sinusoidal-type temperature cycles were designed to evaluate the effects of passive, ambient temperature heating during arousal from torpor in these insectivorous marsupials. It was hypothesised that diel ambient temperature cycles may offer significant energy savings during arousal in animals that employ daily torpor in summer as a response to unpredictable food availability. The cost of arousal in animals in which passive, exogenous heating occurred was significantly lower than that in animals not exposed to an ambient temperature cycle. The total cost of all three phases of torpor (entry, maintenance and arousal) was almost halved when animals were exposed to an ambient heating cycle from 15 °C to 25 °C over a 24-h period. In all animals, irrespective of the experimental ambient temperature cycle employed, the minimum torpor body temperature was 17–18 °C. The body temperature (T_b) of animals exposed to exogenous heating increased from the torpor T_b minimum to a mean value of 22.59 °C before endogenous heat production commenced. This relatively small increase in T_b of ca. 5 °C through `free' passive heating was sufficient to account for the significant ca. three-fold decrease in the cost of arousal and may represent an important energetic aid to free-ranging animals. Accepted: 4 October 1998     

Temperature responses of carbon mineralization in conifer forest soils from different regional climates incubated under standard laboratory conditions

¹⁴C‐labelled straw was mixed with soils collected from seven coniferous forests located on a climatic gradient in Western Europe ranging from boreal to Mediterranean conditions. The soils were incubated in the laboratory at 4°, 10°, 16°, 23° and 30 °C with constant moisture over 550 days. The temperature coefficient (Q₁₀) for straw carbon mineralization decreased with increasing incubation temperatures. This was a characteristic of all the soils with a difference of two Q₁₀ units between the 4–10° and the 23? 30 °C temperature ranges. It was also found that the magnitude of the temperature response function was related to the period of soil incubation. Initial temperature responses of microbial communities were different to those shown after a long period of laboratory incubation and may have reflected shifts in microbial species composition in response to changes in the temperature regime. The rapid exhaustion of the labile fractions of the decomposing material at higher temperatures could also lead to underestimation of the temperature sensitivity of soils unless estimated for carbon pools of similar qualities. Finally, the thermal optima for the organic soil horizons (Of and Oh) were lower than 30 °C even after 550 days of incubation. It was concluded that these responses could not be attributed to microbial physiological adaptations, but rather to the rates at which recalcitrant microbial secondary products were formed at higher temperatures. The implication of these variable temperature responses of soil materials is discussed in relation to modelling potential effects of global warming.     

Effect of Thermal Treatment on the Physicochemical Properties of Emulsion Stabilized by Gelatin from Black Tilapia (Oreochromis mossambicus) Skin

This study investigated the influence of thermal treatment (30 °C to 110 °C, 30 min) on the physicochemical and rheological properties of an emulsion stabilized by black tilapia (Oreochromis mossambicus) skin at pH 4. The protein pattern of tilapia gelatin did not have any significant difference after the gelatin was heated within a temperature range of 30 °C to 70 °C. However, at 90 °C and 110 °C, denaturation occurred where α-, β- and γ-chains of the gelatin were degraded, leading to a concomitant increase in low molecular peptides. The emulsion stability was investigated through a particle size analyzer, zeta potential, microscopic observation and creaming index. The gelatin emulsion was physically stable at 30 °C to 70 °C with a mean droplet size of less than 13 μm. When the heating temperature was increased to 90 °C and 110 °C, the emulsion showed a pronounced increase in droplet size due to coalescence. The gelatin emulsion heated at 90 °C and 110 °C also displayed instability against creaming after storage at room temperature for 7 days. As the heating temperature increased, the gelatin emulsion exhibited a decrease in apparent viscosity and the flow behavior changed from shear thinning to Newtonian. The rheological data also showed that the storage modulus (G′) of emulsion became more frequency dependent as the heating temperature increased, indicating weak droplet interactions. The tilapia gelatin emulsion was physically unstable when subjected to thermal treatment above 70 °C. The data reported in this study provides useful insight into the formulation of acidic food emulsions that require thermal treatment.

     

Thermotolerance and thermal sensitization in a differentiating murine erythroleukemia cell line

• 1.1.|Friend erythroleukemia cells (FELC, a differentiating cell line) were heated at various temperatures and heating sequences. Heat treatments which ranged from 41.0 to 45.0°C and did not cause differentiation in FELC and inhibited the differentiation response to DMSO in FELC.
• 2.2.|Heating resulted in cell killing which increased with temperature and heating time. Protracted low temperature heating (40.0–42.0°C) or incubation at 37°C between two heat treatments at 45.0°C resulted in thermotolerance for both the endpoints of cell killing and differentiation.
• 3.3.|High temperature heating (45.0°C) before heating at 41.0–42.0°C resulted in increased thermal sensitivity to the latter heat treatments. This was observed for both the survival and differentiation endpoints.
• 4.4.|A comparison was made of the thermal sensitivity for the two endpoints of cell killing and differentiation.

     

Degradation of moist soil aggregates by rapid temperature rise under low intensity fire

Background and aims

Soil structure degradation by fire is usually attributed to qualitative and quantitative change of organic and inorganic binding agents, especially in high severity burns (>300 °C) that last for prolonged periods (> 1 hour). In contrast, controlled burns are typically managed to be low in intensity and severity. Such burns are considered benign to soil structural stability because organic matter and inorganic binding agents (e.g., gypsum) are relatively stable at such low temperatures. Recent observations at a controlled burn site in the eastern Great Basin (Nevada) showed soil aggregate breakdown found in shrub canopies where soil temperatures briefly exceeded 300 °C as well as interspaces between shrubs, where the temperatures were likely lower than beneath shrubs because of less surface biomass. These alterations cannot be explained in terms of thermal alteration of binding agents. This study was designed to test whether pressure created by rapidly vaporized pore water can cause aggregate breakdown.

Methods

We subjected three different sizes of aggregates (0.25–1, 1–2 and 2–4 mm) of soils derived from the eastern Great Basin burn site as well as from a forest and urban garden in California to rapid and slow (3 °C/min) heating rates. These treatments were conducted at 5 peak temperatures (75, 100, 125, 150 and 175 °C).

Results

Post-burn water stability of the aggregates showed that rapid heating rate caused more pronounced degradation of aggregate stability than slow heating. Moreover, the heating-rate dependent structural degradation increased with peak temperature. For the majority of the aggregates, the effect also increased with initial water content. In all the soils tested, there was no preferential loss of organic matter in the rapid-heating treatment that can explain the observed enhanced breakdown of aggregates.

Conclusions

Our observations indicate that soil structural degradation under low-intensity fire occurs as a result of mechanical stresses extorted by rapidly escaping steam from soil pores under rapid heating rate.     

Alleviating soil sickness caused by aerobic monocropping: responses of aerobic rice to soil oven-heating

“Aerobic rice” system is the cultivation of nutrient-responsive cultivars in nonflooded and nonsaturated soil under supplemental irrigation. It is intended for lowland areas with water shortage and for favorable upland areas with access to supplementary irrigation. Yield decline caused by soil sickness has been reported with continuous monocropping of aerobic rice grown under nonflooded conditions. The objective of this study was to determine the growth response of rice plant to oven heating of soil with a monocropping history of aerobic rice. A series of pot experiments was conducted with soils from fields where rice has been grown continuously under aerobic or anaerobic (flooded) conditions. Soil was oven heated at different temperatures and for various durations. Plants of Apo, an upland variety that does relatively well under the aerobic conditions of lowland, were grown aerobically without fertilizer inputs in all six experiments. Plants were sampled during vegetative stage to determine stem number, plant height, leaf area, and total biomass. Heating of soil increased plant growth greatly in soils with an aerobic history but a relatively small increase was observed in soils with a flooded history as these plants nearly reached optimum growth. A growth increase with continuous aerobic soil was already observed with heating at 90°C for 12 h and at 120°C for as short as 3 h. Maximum plant growth response was observed with heating at 120°C for 12 h. Leaf area was most sensitive to soil heating, followed by total biomass and stem number. We conclude that soil heating provides a simple and quick test to determine whether a soil has any sign of sickness that is caused by continuous cropping of aerobic rice.     

Reduction of the temperature sensitivity of soil organic matter decomposition with sustained temperature increase

The degree to which microbial communities adjust their decomposition of soil carbon over time in response to long-term increases in temperature is one of the key uncertainties in our modeling of the responses of terrestrial ecosystems to warming. To better understand changes in temperature sensitivity of soil microbial communities to long-term increases in soil temperature, we incubated 27 soils for one year with both short-term and long-term manipulations of temperature. In response to increasing temperature short-term from 20 to 30 °C, respiration rates increased more than threefold on average across soils. Yet, in response to long-term increases in temperature, respiration rates increased approximately half as much as they did to short-term increases in temperature. Short-term Q₁₀ of recalcitrant C correlated positively with long-term Q₁₀ measured between 10 and 20 °C, yet there was no relationship between short-term Q₁₀ and long-term Q₁₀ between 20 and 30 °C. In all, under laboratory conditions, it is clear that there is reduction in the temperature sensitivity of decomposition to long-term increases in temperature that disassociate short- and long-term responses of microbial decomposition to temperature. Determining the fate of soil organic matter to increased temperature will not only require further research on the controls and mechanisms of these patterns, but also require models to incorporate responses to both short-term and long-term increases in temperature.     

Factors influencing the potential mobility and bioavailability of exchangeable ammonium ion in dried lake sediments

Abstract

The effect of drying temperature and oxidation on the level of exchangeable ammonium ion found in sediments has been examined using samples collected from along a polluted creek and from shallow lake bays. The sediments were dried at temperatures between 20°C and 100°C (either in air or under a nitrogen atmosphere), and the ammonium ion content was extracted into 0.1 M KCl prior to analysis using an ion selective electrode. Exposure to air during the drying stage usually resulted in lower ammonium values, while increasing the drying temperature altered the amount of displaceable (i.e. available) ammonium ion extracted, generally in an upward direction. The amount detected (5–25 μ g^?1) varied between sites, and surface sediment values differed from the 10–50 cm core material results. The pH of the extracts varied with the drying temperature used, indicating that the heating process promoted some chemical changes in the test samples. The study has demonstrated that in nutrient level surveys, the analytical data produced can depend greatly on the sample preparation procedure selected. It also indicated the type of changes which could occur when dredged sediments are land dumped.     

Variations in soil culturable bacteria communities and biochemical characteristics in the Dongkemadi glacier forefield along a chronosequence

The variations in the soil culturable bacterial communities and biochemical parameters of early successional soils from a receding glacier in the Tanggula Mountain were investigated. We examined low organic carbon (C) and nitrogen (N) contents and enzymatic activity, correlated with fewer bacterial groups and numbers in the glacier forefield soils. The soil pH values decreased, but the soil water content, organic C and total N significantly increased, along the chronosequence. The soil C/N ratio decreased in the early development soils and increased in the late development soils and it did not correlate with the soil age since deglaciation. The activities of soil urease, sucrase, protease, polyphenol oxidase, catalase, and dehydrogenase increased along the chronosequence. The numbers of culturable bacteria in the soils increased as cultured at 25°C while decreased at 4°C from younger soils to older soils. Total numbers of culturable bacteria in the soils cultured at 25°C were significantly positively correlated to the soil total N, organic C, and soil water content, as well as the activities of soil urease, sucrase, dehydrogenase, catalase, and polyphenol oxidase. We have obtained 224 isolates from the glacier forefield soils. The isolates were clustered into 28 groups by amplified ribosomal DNA restriction analysis (ARDRA). Among them, 27 groups and 25 groups were obtained from the soils at 25°C and at 4°C incubation temperatures, respectively. These groups are affiliated with 18 genera that belong to six taxa, viz, Actinobacteria, Gammaproteobacteria, Bacteroidetes, Firmicutes, Alphaproteobacteria, and Betaproteobacteria. The dominant taxa were Actinobacteria, Gammaproteobacteria, and Bacteroidetes in all the samples. The abundance and the diversity of the genera isolated at 25°C incubation temperature were greater than that at 4°C.     

Influence of alternate submergence and drying of rice soils prior to resubmergence on available phosphorus

Summary Four acid rice-soils (0–20 cm, air-dry, and <2 mm) were subjected to 3 cycles, each consisting of 30-day submergence followed by air-drying at room temperature or oven-drying at 105°C for 3 days. The available phosphorus was determined colorimetrically by Bray's P-2 extractant (0.03N NH₄F+0.1N HCl) using 1:20 soil extractant ratio. The beneficial effect of 30-day submergence followed by drying of soil prior to resubmergence on native phosphorus was apparent in all soils studied except Shirgaon clay soil, which was probably due to presence of relatively more active Fe in that soil.     

Carbon quality and nutrient status drive the temperature sensitivity of organic matter decomposition in subtropical peat soils

Estimates of gaseous carbon (C) fluxes in wetlands are heavily based on temperature. However, isolating specific effects of temperature on anaerobic C processing from other controls (C quality and nutrients) has proven difficult. Here, we test the hypothesis that temperature sensitivity of soil organic matter (SOM) decomposition is more influenced by C quality than nutrient availability in subtropical freshwater, sawgrass (Cladium jamaicense)-based peats. Carbon age (characterized by depth: 0–10 and 10–20 cm) was used as a surrogate of C quality while two sites were selected with contrasting levels of nutrient (P) availability. In anaerobic laboratory incubations temperature was increased in 5 °C steps to assess the proportion of C available at a given temperature (i.e. thermo-labile C) as productions of gaseous (CO₂ and CH₄) and dissolved organic C (DOC) fractions. Thermo-labile C increased 3.1–3.6 times from 15 °C to 30 °C in all soils. Disproportionate increase in the production of gaseous forms versus DOC as well as CH₄:CO₂ was observed with warming. Observed Q₁₀ values followed the trend of CH₄ (~14) ? CO₂ (~2.5) > DOC (~1.7) and temperature sensitivity was more dependent on C quality than nutrient availability over the entire temperature range. Spectral analysis indicated more bio-available DOC production at higher temperature. Regression analysis also indicated that C quality primarily influenced SOM decomposition at lower temperature, while at higher temperature nutrient limitation dominantly controlled SOM decomposition. These findings confirm the role of C quality in temperature sensitivity of warm peat soils, but also indicate an increased importance of nutrient limitation at higher temperature.