Effect of simulated forest fire on the availability of N and P in mediterranean soils

The effect of soil burning on N and P availability and on mineralization and nitrification rates of N in the burned mineral soil was studied by combustion of soils in the laboratory. At a fire temperature of 600°C, there was a complete volatilization of NH₄ and a significant increase of pH, from 7.6 in the unburned soil to 11.7 in the burned soil. Under such conditions ammonification and nitrification reactions were inhibited. Less available P was produced immediately after the fire at 600°C, as compared to P amount produced at 250°C. Burning the soils with plants caused a decrease in NH₄-N and (NO₂+NO₃)-N concentrations in the soil as well as a reduction in ammonification and nitrification rates. Combustion of soil with plants contributed additional available P to the burned soil. The existence of a non-burned soil under the burned one played an important role in triggering ammonification and nitrification reactions.     

Cold temperature decreases bacterial species richness in nitrogen‐removing bioreactors treating inorganic mine waters

Explosives used in mining, such as ammonium nitrate fuel oil (ANFO), can cause eutrophication of the surrounding environment by leakage of ammonium and nitrate from undetonated material that is not properly treated. Cold temperatures in mines affect nitrogen removal from water when such nutrients are treated with bioreactors in situ. In this study we identified bacteria in the bioreactors and studied the effect of temperature on the bacterial community. The bioreactors consisted of sequential nitrification and denitrification units running at either 5 or 10°C. One nitrification bioreactor running at 5°C was fed with salt spiked water. From the nitrification bioreactors, sequences from both ammonia‐ and nitrite‐oxidizing bacteria were identified, but the species were distinct at different temperatures. The main nitrifiers in the lower temperature were closely related to the genera Nitrosospira and Candidatus Nitrotoga. 16S rRNA gene sequences closely related to halotolerant Nitrosomonas eutropha were found only from the salt spiked nitrification bioreactor. At 10°C the genera Nitrosomonas and Nitrospira were the abundant nitrifiers. The results showed that bacterial species richness estimates were low, <150 operational taxonomic units (OTUs), in all bioreactor clone libraries, when sequences were assigned to operational taxonomic units at an evolutionary distance of 0.03. The only exception was the nitrification bioreactor running at 10°C where species richness was higher, >300 OTUs. Species richness was lower in bioreactors running at 5°C compared to those operating at 10°C. Biotechnol. Bioeng. 2011;108: 2876–2883. © 2011 Wiley Periodicals, Inc.     

Ability of nitrapyrin,dicyandiamide and acetylene to retard nitrification in a mineral and an organic soil

Laboratory experiments were conducted to evaluate the efficacy of nitrapyrin, dicyandiamide (DCD) and acetylene (C₂H₂) as nitrification inhibitors in a silt loam and oragnic soil with and without added NH₄. Nitrapyrin (8 μg/g soil) and DCD (20 μg/g soil) were very effective in retarding nitrification of NH₄−N in the silt loam soil during 14 days of aerobic incubation at 30°C. However neither nitrapyrin, (20 μg/g soil) nor DCD (20 or 100 μg/g soil) were effective in retarding NO₃ production in the organic soil not amended with NH₄. Dicyandiamide was moderately effective in retarding nitrification (39% inhibition) at 100 μg/g concentration but nitrapyrin at 20 μg/g rate had little effect (8% inhibition) on nitrification in the organic soil amended with NH₄. In a separate experiment C₂H₂ was a very effective inhibitor in both soils when present in the flask atmosphere at 0.1% or 1% (v/v).     

Mineralization of soil nitrogen in three forest communities from the New England region of New South Wales

Nitrogen (N) mineralization rates and the temperature response patterns of mineral N production in surface (0–7.6 cm) soils were compared in laboratory incubation studies based on disturbed, composite samples. Seasonal variation in the field levels of mineral N, and mineralization potential of intact (7.6 × 5.6 cm diameter) soil cores, were also investigated. Ammonification proceeded rapidly in each soil. Nitrification did not occur in grassy forest (GF) soil but was active in both layered forest (LF) and mossy forest (MF) soils, especially the former. Total mineral N production was greatest in MF and least in LF. Ammonification in disturbed samples was maximal at 50°C in all three soils with a secondary peak at 10°C in LF soil. Nitrification in LF and MF soils was most rapid at 25°C. Several species of ammonifying bacteria with different temperature optima were isolated, indicating that the process of ammonification is a composite of the activities of a variety of decomposer microbes. Mean field levels of mineral N and NH₄–N throughout the year were greatest in MF and least in LF. Seasonal fluctuations in NH₄–N were evident, concentrations being universally low in mid-winter (about 1.5 μgg^-1), increasing to a maximum in late summer (about 5 μg g^-1 in LF: 16–18 μg g^-1 in GF and MF). Field levels of NO₃–N were more constant and never more than 5 μg g^-1 in any community. Both total mineralization and ammonification in intact cores were greatest in MF and least in LF while nitrification was greatest in LF and almost negligible in GF, thus confirming the results obtained with disturbed samples. The potential for mineralization was large in mid-winter when the amount of mineral N was very low, and small in late summer when field levels were higher: this is interpreted as indicating that seasonal climatic factors regulate the availability of substrates for decomposers. Spatial variability in field levels of mineral N and mineral N production in the laboratory was evidenced by significant ‘sampling site’ effects in each community: however, at the sampling intensity used, the presence of bark mounds around Eucalyptus saligna trees could not be shown to affect these attributes. The inability of GF soil to nitrify when incubated in the laboratory could not be ascribed to a high C/N ratio, low pH, lack of substrate ammonium, or a low population of autotrophic nitrifying bacteria. No attempt was made to investigate the presence of allelopathic nitrification inhibitors. No evidence was obtained to support the view that nitrification is atypical of climax communities in situ. The most productive forest (LF) had the greatest capacity to nitrify and the least productive community (GF) the smallest capacity to do so.     

Global patterns and controlling factors of soil nitrification rate

Soil nitrification, an important pathway of nitrogen transformation in ecosystems, produces soil nitrate that influences net primary productivity, while the by‐product of nitrification, nitrous oxide, is a significant greenhouse gas. Although there have been many studies addressing the microbiology, physiology, and impacting environment factors of soil nitrification at local scales, there are very few studies on soil nitrification rate over large scales. We conducted a global synthesis on the patterns and controlling factors of soil nitrification rate normalized at 25°C by compiling 3,140 observations from 186 published articles across terrestrial ecosystems. Soil nitrification rate tended to decrease with increasing latitude, especially in the Northern Hemisphere, and varied largely with ecosystem types. The soil nitrification rate significantly increased with mean annual temperature (MAT), soil nitrogen content, microbial biomass carbon and nitrogen, soil ammonium, and soil pH, but decreased with soil carbon:nitrogen and carbon:nitrogen of microbial biomass. The total soil nitrogen content contributed the most to the variations of global soil nitrification rate (total coefficient = 0.29) in structural equation models. The microbial biomass nitrogen (MBN; total coefficient = 0.19) was nearly of equivalent importance relative to MAT (total coefficient = 0.25) and soil pH (total coefficient = 0.24) in determining soil nitrification rate, while soil nitrogen and pH influenced soil nitrification via changing soil MBN. Moreover, the emission of soil nitrous oxide was positively related to soil nitrification rate at a global scale. This synthesis will advance our current understanding on the mechanisms underlying large‐scale variations of soil nitrification and benefit the biogeochemical models in simulating global nitrogen cycling.     

Temperature-dependent nitrogen transformations in acid oak-beech forest litter in the Netherlands

Laboratory incubation experiments have been carried out to quantify net nitrogen mineralization and nitrification in oak-beech litter at temperatures ranging from 0 to 30°C. Net mineralization was linearly proportional to temperature. Nitrification was inhibited at 0,5 and 30°C. As compared with soils under cultivation, there is only restricted knowledge of nitrification kinetics in acid forest litters, especially when temperature is considered. With these litter types, one should be cautious applying high incubation temperatures, which seldomly occur under field conditions.     

Experimental determination of nitrogen kinetic isotope fractionation: Some principles; illustration for the denitrification and nitrification processes

Summary A few principles relative to the presentation and use of nitrogen stable isotopic data are briefly reviewed. Some classical relationships between the isotope composition of a substrate undergoing a single-step unidirectional reaction, are introduced. They are illustrated through controlled experiments on denitrification in a soil, and through nitrification by pure cultures ofNitrosomonas europaea. In the latter case, the isotope fractionation is calculated from the isotopic composition of the residual substrate, then of the product and the result is shown to be statistically the same for the two procedures. The isotopic enrichment factor for denitrification is −29.4±2.4‰ at 20°C, and −24.6±0.9‰ at 30°C; for nitrification this factor is −34.7±2.5‰ under the experimental conditions employed.     

Effects of incubation temperature on the organic amendment‐mediated control of Fusarium wilt of tomato

Organic soil amendments play important roles in the reduction of plant diseases caused by soil‐borne plant pathogens. This study examined the combined effects of concentrations of organic amendments, temperature and period of incubation in soil on the management of Fusarium wilt of tomato caused by Fusarium oxysporum f. sp. lycopersici (Fol). In an experiment with substrate mixture, Fol reduction was higher when the soils were incubated at 35°C than at 30°C. Disease severity was proportionally reduced as the volume of amendment added increased. Furthermore, disease was significantly lower in substrates incubated for 30 days at both temperatures, as compared to substrates incubated for only 15 days. The most effective control was achieved with pelletised poultry manure (PPM). In experiments with natural sandy soil, the effects of amendments on Fol populations, measured by real‐time quantitative PCR with TaqMan probes, were significant. The highest decreases in Fol DNA resulted when the soil was amended with 2% PPM and incubated at 35°C. The reductions in DNA concentrations was most likely related to the accumulations of high concentrations of NH₃ (27.3 mM) in soils treated with 2% PPM and incubated at room temperature (RT; 23 ± 2°C), or at 35°C. Severity of plants grown in soils incubated at RT decreased by over 40%, and more than 73% when incubated at 35°C, regardless of the rate of PPM. The results indicate that the management with PPM, when combined with heating or solarisation, is an effective control measure against Fusarium wilt of tomato.     

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.     

Partial nitrification under limited dissolved oxygen conditions

Partial nitrification to nitrite is technically feasible and economically favourable, especially when wastewaters contained high ammonium concentrations or low C/N ratios. Partial nitrification can be obtained by selectively inhibiting nitrite-oxidizing bacteria (NOB) through appropriate regulation of the pH, temperature and dissolved oxygen (DO) concentrations. The effect of pH, DO levels and temperature on ammonia oxidation rate and nitrite accumulation was investigated in order to determine the optimal conditions for partial nitrification of synthetic wastewater with high ammonia concentration. The experiments performed at low DO levels to lower the total oxygen needed in the nitrification step, which means great saving in aeration. During the start-up stage pH and DO were set at 7.0–7.4 and 0.5 mg/l, respectively. The reactor was operated until complete partial nitrification was achieved. The effect of pH, DO on partial nitrification was studied, as pH was kept at 6.5, 7.5, 8.5, 9.5 and DO at 0.5±0.2, 1.5±0.2 and 2.5±0.2 mg/l, and temperature at 30 °C. The influence of temperature on k_a value was studied by keeping pH=7.5, DO=1.5 mg/l and temperature was controlled at 12, 20 and 30 °C, respectively. The results showed that partial nitrification to nitrite was steadily obtained and the optimal operational parameters were pH=7.5, DO=1.5 mg/l, T=30 °C based on ammonia oxidation rate and nitrite accumulation rate. The maximum k_a was achieved and to be 115.1×10⁻³ mg NH₄⁺–N (mg VSS h)⁻¹ under this condition.     

Analysis of Microbial Population Dynamics in a Partial Nitrifying SBR at Ambient Temperature

In this study, a lab-scale partial nitrifying sequencing batch reactor (SBR) was developed to investigate partial nitrification at ambient temperature (16–22 °C). Techniques of denaturing gradient gel electrophoresis (DGGE), cloning, and fluorescence in situ hybridization (FISH) were utilized simultaneously to study microbial population dynamics. Partial nitrification was effectively achieved in response to shifts of influent ammonium concentrations. DGGE results showed that higher ammonia concentration referred to lower ammonia-oxidizing bacteria (AOB) diversity in the SBR. Phylogenetic analysis revealed that all the predominant AOB was affiliated with Nitrosomonas genus. FISH analysis illustrated AOB was the predominant nitrifying bacteria of microbial compositions when SBR achieved partial nitrification (PN) at ambient temperature.     

Influence of soil temperature on root freezing tolerance of Scots pine (Pinus sylvestris L.) seedlings

The influence of soil temperature on the root freezing tolerance of one-year-old containerized Scots pine (Pinus sylvestris L.) seedlings was investigated. In addition, the TTC and electrolyte leakage methods were evaluated in terms of their suitability for use in detecting damage to roots caused by freezing. In mid-August, seedlings were placed in three thermostat-controlled soil beds in a greenhouse with an initial soil temperature of 14.3 °C. Soil temperature was lowered in two of the soil beds, resulting in temperatures of 10.7 and 5.3 °C respectively. Each soil temperature, i.e. 14.3, 10.7 and 5.3 °C was maintained for eight weeks. Starting in early September, damage to roots induced by artificial freezing was estimated biweekly by measuring electrolyte leakage, triphenyl tetrazolium chloride (TTC) reduction and potential root growth in a three-week cultivation test. In addition, the root freezing tolerance of seedlings placed outdoors was tested. Measurements showed that these seedlings were exposed to soil temperatures ranging from 13.0 °C in mid-August to 0.5 °C in November. Generally, the development of root freezing tolerance was more pronounced for seedlings exposed to lower (0.5 and 5.3 °C) soil temperatures compared with those exposed to higher (10.7 and 14.3 °C) ones. Root freezing tolerance was highest among the seedlings placed outdoors which were also exposed to the lowest soil temperatures registered in the study. To examine the effect of a temporary warm period, the soil temperature in one treatment was increased from 5.4 °C to 13.9 °C, maintained at the latter temperature for two weeks in October and then lowered to 5.7 °C. Root freezing tolerance was reduced by exposure to the warmer soil temperature. However, after four weeks at the colder soil temperature, the tolerance of the seedlings had returned to the level measured prior to exposure to the warm soil temperature. Methods based on the measurement of root electrolyte leakage and TTC reduction were both found to have limitations when used to detect root freezing damages in containerized seedlings. This revised version was published online in June 2006 with corrections to the Cover Date.     

Increased salinity improves the thermotolerance of mesophilic nitrification

Nitrification is a well-studied and established process to treat ammonia in wastewater. Although thermophilic nitrification could avoid cooling costs for the treatment of warm wastewaters, applications above 40 °C remain a significant challenge. This study tested the effect of salinity on the thermotolerance of mesophilic nitrifying sludge (34 °C). In batch tests, 5 g NaCl L^?1 increased the activity of aerobic ammonia-oxidizing bacteria (AerAOB) by 20–21 % at 40 and 45 °C. For nitrite-oxidizing bacteria (NOB), the activity remained unaltered at 40 °C, yet decreased by 83 % at 45 °C. In a subsequent long-term continuous reactor test, temperature was increased from 34 to 40, 42.5, 45, 47.5 and 50 °C. The AerAOB activity showed 65 and 37 % higher immediate resilience in the salt reactor (7.5 g NaCl L^?1) for the first two temperature transitions and lost activity from 45 °C onwards. NOB activity, in contrast to the batch tests, was 37 and 21 % more resilient in the salt reactor for the first two transitions, while no difference was observed for the third temperature transition. The control reactor lost NOB activity at 47.5 °C, while the salt reactor only lost activity at 50 °C. Overall, this study demonstrates salt amendment as a tool for a more efficient temperature transition for mesophilic sludge (34 °C) and eventually higher nitrification temperatures.     

The Effect of Temperature on the Bioventing of Soil Contaminated with Toluene and Decane

The effect of temperature on evaporation and biodegradation rates during soil bioventing (SBV) was studied for a mixture of toluene and decane in bench-scale soil columns at a continuous air flow and consecutively at two different flow rates. The effect of temperature on SBV was monitored by GC headspace analysis of contaminant, CO₂ and O₂ concentrations in the soil gas over time. Separation of evaporation and biodegradation processes into three different phases based on their rates was used together with Q₁₀ and E₁₀ (values that give the factor by which biodegradation and evaporation rates increase when the temperature is raised by 10 degrees) to compare quantitatively the removal kinetics at 10 and 20°C. Adsorption of toluene and decane onto soil (a phase partitioning process) at 20 and 10°C was described with linear Freundlich isotherms. A temperature decrease from 20 to 10°C resulted in an increase of soil-air partitioning coefficients by a factor of 1.8 and of 2.1 for toluene and decane, respectively. The mean Q₁₀ value for the biodegradation of toluene was found to be 2.2 for a temperature rise from 10 to 20°C. A toluene content in the soil gas above 75% of the saturation concentration inhibited biodegradation at both temperatures. The SBV efficiency was dependent on temperature with respect to remediation time. SBV at 20°C resulted in a 99.8% and a 98.7% reduction of toluene and decane initial concentrations, respectively. To reach similar results at 10°C, about 1.6 times as much time and 1.4 times as much air were required; however, at both temperatures the total amounts of biodegraded hydrocarbons were approximately the same. The evaporation-to-biodegradation ratios at 20°C were 82.5:17.5 for toluene and 16:84 for decane, whereas at 10 °C they were 71:29 and 2:98, respectively. A comparison of Q₁₀ values showed that, except during the initial phase of SBV, only a modest decrease in biodegradation rates should be expected after a decrease in temperature from 20 to 10°C. Flow rate reduction had a significant impact on the toluene evaporation rate at a higher temperature, whereas for decane this rate was only slightly affected by temperature. In contrast to decane, the ratio between toluene vapor pressures at 20 and 10°C may be used to predict the removal of toluene by evaporation during the above-mentioned phases of SBV, when evaporation is important.     

Root respiration in citrus acclimates to temperature and slows during drought

Citrus seedlings were grown in soil columns in which the root system was hydraulically separated into two equal layers; this enabled us to maintain roots in the upper layer without water for 110 d. The columns were placed into waterbaths modified so that soil temperatures in the top layer could be maintained at 25°C or at 35°C, while temperature in the bottom layer was maintained at 25°C. We hypothesized that, if citrus plants were grown in dry soil for an extended period, root mortality would increase if the cost of maintaining the roots was increased by elevating the soil temperature. However, during the drought period we did not observe any root mortality, even at the higher soil temperature. Moreover, we did not find that root respiration was increased by prolonged exposure to drought and higher soil temperature. We did find that root respiration rates slowed in dry soil. Furthermore, when the soil columns were switched from one temperature treatment to another, root respiration rates in wet soil rapidly increased when moved to a higher temperature or rapidly decreased when moved to a lower temperature. But after only 4 d, respiration rates returned to their original level; root respiration in dry soil was not affected by either short-or long-term shifts in soil temperature. Root respiration in citrus appears to acclimate rapidly to changes in soil temperature.     

From seed to seedling: A critical transitional stage for the Mediterranean psammophilous species Dianthus morisianus (Caryophyllaceae)

Abstract

Seed germination, seedling emergence and seed persistence in the soil were investigated for Dianthus morisianus (Caryophyllaceae), a psammophilous endemic species of Sardinia. Stored and freshly collected seeds were incubated in a range of constant temperatures (5–25°C) and an alternating temperature regime (25/10°C). The effect of seed burial depth on seedling emergence was investigated under controlled environmental conditions. Seed persistence in the soil was verified by in situ experimental seed burials. Seeds of this species were non-dormant, and all seed lots germinated both in the light and darkness, mainly at low temperatures (≤20°C), with a maximum at 15°C (≥95%). Optimal seedling emergence was obtained when seeds were buried at a depth of 1–2 cm, and a declining emergence with increasing depth was observed. D. morisianus was also unable to form a persistent soil seed bank. The fate of the seeds that, after dispersal, do not emerge from the soil in the spring is, therefore, presumably to die before the next favourable growing season.     

Thermophilic biological nitrogen removal in industrial wastewater treatment

Nitrification is an integral part of biological nitrogen removal processes and usually the limiting step in wastewater treatment systems. Since nitrification is often considered not feasible at temperatures higher than 40 °C, warm industrial effluents (with operating temperatures higher than 40 °C) need to be cooled down prior to biological treatment, which increases the energy and operating costs of the plants for cooling purposes. This study describes the occurrence of thermophilic biological nitrogen removal activity (nitritation, nitratation, and denitrification) at a temperature as high as 50 °C in an activated sludge wastewater treatment plant treating wastewater from an oil refinery. Using a modified two-step nitrification–two-step denitrification mathematical model extended with the incorporation of double Arrhenius equations, the nitrification (nitrititation and nitratation) and denitrification activities were described including the cease in biomass activity at 55 °C. Fluorescence in situ hybridization (FISH) analyses revealed that Nitrosomonas halotolerant and obligatehalophilic and Nitrosomonas oligotropha (known ammonia-oxidizing organisms) and Nitrospira sublineage II (nitrite-oxidizing organism (NOB)) were observed using the FISH probes applied in this study. In particular, this is the first time that Nitrospira sublineage II, a moderatedly thermophilic NOB, is observed in an engineered full-scale (industrial) wastewater treatment system at temperatures as high as 50 °C. These observations suggest that thermophilic biological nitrogen removal can be attained in wastewater treatment systems, which may further contribute to the optimization of the biological nitrogen removal processes in wastewater treatment systems that treat warm wastewater streams.     

Biochemical Properties of A Thermophilic Alkalophile

A thermophilic alkalophile (IC strain) which can grow well in an alkaline medium at over 55°C was isolated from soil samples, and identified as Bacillus licheniformis; its growth on a neutral medium was, however, very poor. This strain was able to grow at 37°C as well as at 55°C, but the specific growth rate at 55°C was about twice as high as that at 37°C under alkaliné conditions.

The intracellular pH remained below 9.5 when Na⁺ was present in the medium. Na ⁺ stimulated the alanine uptake by cells or membrane vesicles, but was not required ATP synthesis.

Intracellular enzymes were stable on heat treatment up to 60°C. The residual activity of enolase after heating at 60°C for 10 min was about 80%. Cytochrome oxidase in membrane vesicles was completely stable up to 58°C for 30 min. These enzymes were also resistant to SDS treatment, more than 50% of their activities remaining at 5% SDS.     

On the use of weather data in ecological studies along altitudinal and latitudinal gradients

Global warming has created a need for studies along climatic gradients to assess the effects of temperature on ecological processes. Altitudinal and latitudinal gradients are often used as such, usually in combination with air temperature data from the closest weather station recorded at 1.5–2 m above the ground. However, many ecological processes occur in, at, or right above the soil surface. To evaluate how representative the commonly used weather station data are for the microclimate relevant for soil surface biota, we compared weather station temperatures for an altitudinal (500–900 m a.s.l.) and a latitudinal gradient (49–68°N) with data obtained by temperature sensors placed right below the soil surface at five sites along these gradients. The mean annual temperatures obtained from weather stations and adjusted using a lapse rate of ?5.5°C km^?1 were between 3.8°C lower and 1.6°C higher than those recorded by the temperature sensors at the soil surface, depending on the position along the gradients. The monthly mean temperatures were up to 10°C warmer or 5°C colder at the soil surface. The within‐site variation in accumulated temperature was as high as would be expected from a 300 m change in altitude or from a 4° change in latitude or a climate change scenario corresponding to warming of 1.6–3.8°C. Thus, these differences introduced by the decoupling are significant from a climate change perspective, and the results demonstrate the need for incorporating microclimatic variation when conducting studies along altitudinal or latitudinal gradients. We emphasize the need for using relevant temperature data in climate impact studies and further call for more studies describing the soil surface microclimate, which is crucial for much of the biota.     

Incubation study on effects of adding varying levels of nickel (as sulphate) on nitrogen and carbon mineralisation in soil

The effects were studied of adding 10, 100 and 1000 ppm Ni (as sulphate) to a sandy soil (pH 5·9) on N and C mineralisation during subsequent aerobic incubation for 6 weeks at 30° C. With increasing Ni level, nitrification decreased to a greater extent than did N and C mineralisation. The toxic effects of 1000 ppm Ni were not much greater than those of 100 ppm Ni. Nitrification and N and C mineralisation were decreased by 68, 36 and 35% respectively with 1000 ppm Ni. Results are discussed in relation to exchangeable and EDTA-extractable Ni levels.