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13 páginas, 4 figuras y 3 tablas, The widespread use of both heavy metals and antibiotics in livestock farming, followed by their subsequent arrival on agricultural soils through manure and slurry spreading, has become a problem of vital importance for human health and the environment. In the current research, a laboratory experiment was carried out for 42 d to study tolerance and co-tolerance of three tetracycline antibiotics (tetracycline, TC; oxytetracycline, OTC; chlortetracycline, CTC) in soils polluted with heavy metals (As, Cd, Zn, Cu, Ni, Cr, and Pb) at high concentrations (1000 mg kg-1 of each one, separately). Pollution induced community tolerance (PICT) of the bacterial community was estimated using the leucine incorporation technique. The log IC50 (logarithm of the concentration causing 50 % inhibition in bacterial community growth) values obtained in uncontaminated soil samples for all the heavy metals tested showed the following toxicity sequence: Cu > As > Cr ≥ Pb ≥ Cd > Zn > Ni. However, in polluted soil samples the toxicity sequence was Cu > Pb ≥ As ≥ Cd ≥ Cr ≥ Ni ≥ Zn. Moreover, at high heavy metal concentrations, the bacterial communities showed tolerance to the metal itself, this taking place in the long term for all the metals tested. The bacterial communities of the soil polluted with heavy metals showed also long-term co-tolerance to TC, OTC, and CTC. This kind of study, focusing on the eventual increases of tolerance and co-tolerance of bacterial communities in agricultural soil, favored by the presence of different kinds of pollutants, is of crucial importance, mostly bearing in mind that the appearance of antibiotic resistance genes in soil bacteria could be transmitted to human pathogens., This study has been funded by the Spanish Ministry of Economy and Competitiveness through the projects CGL2015-67333-C2-1-R and CGL2015-67333-C2-2-R (FEDER Funds). David Fernández-Calviño holds a Ramón y Cajal contract (RYC-2016-20411), financed by the Spanish Ministry of Economy, Industry and Competitiveness. Vanesa Santás-Miguel holds a pre-doctoral fellowship (ED481A-2020/089) financed by Xunta de Galicia.

The presence of antibiotics in soils may increase the selection pressure on soil bacterial communities and cause tolerance to these pollutants. The temporal evolution of bacterial community tolerance to different concentrations of tetracycline (TC), oxytetracycline (OTC) and chlortetracycline (CTC) was evaluated in two soils. The results showed an increase of soil bacterial community tolerance to TC, CTC and OTC only in samples polluted with the highest antibiotic concentrations tested (2000 mg kg−1). The magnitude of those increases was higher in the soil with the lower organic carbon content (1.6%) than in the soil with an organic carbon content reaching 3.4%. In the soil with low organic carbon content, the time-course evolution showed a maximum increase in the tolerance of bacterial communities to tetracycline antibiotics between 45 and 100 incubation days, while for longer incubation times (360 days) the tolerance decreased. In the soil with high organic carbon content, a similar behavior was found for OTC. However, for CTC and TC, slightly increases and decreases (respectively) were found in the bacterial community tolerance at intermediate incubation times, followed by values close to zero for TC after 360 days of incubation, while for CTC they remained higher than in the control. In conclusion, soil pollution due to tetracyclines may cause bacterial community tolerance to these antibiotics when present at high concentrations. In addition, the risk is higher in soils with low organic matter content, and it decreases with time., This study has been funded by the Spanish Ministry of Economy and Competitiveness through the projects CGL 2015-67333-C2-1-R and -2-R (FEDER Funds) and by Xunta de Galicia via BV1 research group (ED431C 2017/62-GRC). David Fernández Calviño holds a Ramón y Cajal contract (RYC-2016-20411) financed by the Spanish Ministry of Economy, Industry and Competitiveness. Vanesa Santás-Miguel and Laura Rodríguez González holds a pre-doctoral fellowship (ED481A-2020/089 and ED481A-2021/309, respectively) financed by Xunta de Galicia.

The effect of fire severity and recurrence on the recovery of enzymatic activities (β-glucosidase, urease, acid phosphatase) and bacterial activity was monitored. Unburned and burned soil samples from soil affected by a high severity wildfire and by a low severity experimental fire were subjected in laboratory to a temperature gradient to simulate different fire severities. These samples were subjected to a second laboratory heat treatment to simulate the effect of recurrence. Soil temperature was measured and used to calculate the degree-hours reached by the soil. The results showed: a) a strong effect of repeated soil heating at different temperatures on soil microbial activity; b) a different sensitivity of enzymatic activities and bacterial activity to fire, c) the magnitude of changes in these biochemical properties was related to the extent of heat supplied to samples and the previous fire/heat history, and d) degree-hours are adequate to quantify the severity of heat treatments and to examine their effects on soil microbial activity. The relationships between degree-hours and the different biochemical properties analyzed clearly demonstrate that the usefulness of these biochemical properties to detect the soil microbial community response to the heat stress followed the order: urease activity > acid phosphatase activity >β-glucosidase activity ≫ bacterial activity., This study was supported by the Ministerio Español de Economía y Competitividad (AGL2012-39686-C02-01), the National Institute of Agricultural Research of Spain (INIA) through project RTA2017-00042- C05-02 cofunded by FEDER, and by Fundación MAPFRE. A. Barreiro and A. Lombao were recipients of FPU grants from the Ministerio Español de Educación (AP2010-2284, AP2010-1900).

The increase of bacterial community tolerance to Cu, and of cotolerance to the antibiotics tetracycline (TC), oxytetracycline (OTC) and chlortetracycline (CTC), was studied in three soils spiked with six different Cu concentrations (resulting in 0, 125, 250, 500, 750 and 1000 mg kg&minus, 1 into soils) in a laboratory experiment, after 42 days of incubation. The results show significant increases of bacterial community tolerance to the metal when soil Cu concentrations were between 125 and 500 mg kg&minus, 1. Moreover, Cu soil pollution also caused cotolerance to the three antibiotics studied but for higher Cu concentrations (1000 mg kg&minus, 1).

Wildfires are a major problem in Mediterranean forest ecosystems, affecting the same area year after year. Their severity is increasing, partly due to climate change and hence, every now and then, virulent fires of high severity spread ravage this region. The aim of this study was to evaluate the influence of fire regime (recurrence, severity) in soil microbial community structure analyzing the phospholipid fatty acid (PLFA) and the microbial functional diversity assessing the level physiological profiling technique (CLPP). Samples of a soil affected by a high severities wildfire and a soil affected by a low severity experimental fire were heated under laboratory conditions at different temperatures to simulate different fire severity. To simulate fire recurrence, the heating treatment was repeated after one month of incubation. The fire severity was estimated as the amount of heat supplied to samples by degree-hour methodology. A marked impact of fire regime on soil microorganisms was detected; the microbial community response varied depending on previous history of fire and the magnitude of changes in PLFA pattern and CLPP, was related to the amount of heat supplied to the samples. Wildfires had a greater impact on microbial community structure than subsequent soil heating in the laboratory. The total biomass and the biomass of specific groups of microorganisms decreased notably as a consequence of wildfire and minor changes were detected due to the experimental fire and soil heating under laboratory conditions. The results clearly showed the usefulness of PLFA pattern to study the effect of fire regimes and associated direct and indirect changes in soil microorganisms and in soil quality. The data also indicated that the degree-hour methodology rather than maximum temperature is adequate to simulate fire severity and evaluate the impact of thermal shock on soil ecosystems., This study was supported by the Ministerio Español de Economía y Competitividad (AGL2012-39686-C02-01), the National Institute of Agricultural Research of Spain (INIA) through project RTA2017-00042-C05-02, cofunded by FEDER and by Fundación Mapfre. A. Barreiro and A. Lombao were recipients of FPU grants from the Ministerio Español de Educación (AP2010-2284, AP2010-1900).

© 2020 by the authors., Soil properties determining the thermal transmissivity, the heat duration and temperatures reached during soil heating are key factors driving the fire-induced changes in soil microbial communities. The aim of the present study is to analyze, under laboratory conditions, the impact of the thermal shock (infrared lamps reaching temperatures of 100 °C, 200 °C and 400 °C) and moisture level (0%, 25% and 50% per soil volume) on the microbial properties of three soil mixtures from different sites. The results demonstrated that the initial water content was a determinant factor in the response of the microbial communities to soil heating treatments. Measures of fire impact included intensity and severity (temperature, duration), using the degree-hours method. Heating temperatures produced varying thermal shock and impacts on biomass, bacterial activity and microbial community structure., This research was funded by Spanish Ministry of Economy and Competitiveness (AGL2012-39686-C02-01) and for the for the MAPFRE foundation. A. Barreiro and A. Lombao are recipients of FPU grant from Spanish Ministry of Education. The authors thank S.J. González-Prieto for his valuable help with the statistical analyses.

Antibiotics discharged to the environment constitute a main concern for which different treatment alternatives are being studied, some of them based on antibiotics removal or inactivation using by-products with adsorbent capacity, or which can act as catalyst for photo-degradation. But a preliminary step is to determine the general characteristics and magnitude of the degradation process effectively acting on antibiotics. A specific case is that of sulfonamides (SAs), one of the antibiotic groups most widely used in veterinary medicine, and which are considered the most mobile antibiotics, causing that they are frequently detected in both surface- and ground-waters, facilitating their entry in the food chain and causing public health hazards. In this work we investigated abiotic and biotic degradation of three sulfonamides (sulfadiazine –SDZ-, sulfachloropyridazine –SCP-, and sulfamethazine –SMT-) in aqueous media. The results indicated that, in filtered milliQ water and under simulated sunlight, the degradation sequence was: SCP > SDZ ≈ SMT. Furthermore, the rate of degradation clearly increased with the raise of pH: at pH 4.0, half-lives were 1.2, 70.5 and 84.4 h for SCP, SDZ and SMT, respectively, while at pH 7.2 they were 2.3, 9.4 and 13.2 h for SCP, SMT and SDZ. The addition of a culture medium hardly caused any change in degradation rates as compared to experiments performed in milliQ water at the same pH value (7.2), suggesting that in this case sulfonamides degradation rate was not affected by the presence of some chemical elements and compounds, such as sodium, chloride and phosphate. However, the addition of bacterial suspensions extracted from a soil and from poultry manure increased the rate of degradation of these antibiotics. This increase in degradation cannot be attributed to biodegradation, since there was no degradation in the dark during the time of the experiment (72 h). This indicates that photo-degradation constitutes the main removal mechanism for SAs in aqueous media, a mechanism that in this case was favored by humic acids supplied with the extracts from soil and manure. The overall results could contribute to the understanding of the environmental fate of the three sulfonamides studied, aiding to program actions that could favor their inactivation, which is especially relevant since its dissemination can involve serious environmental and public health risks.

The ecosystem response to fire is often linked to fire severityand recurrence, with potentially large consequences on bothaboveground and below–ground processes. Understandingthe fire impact has become increasingly important in the light ofrecent changes to disturbance regimes due to climate change.Although the impacts on the above vegetation and the belowsoil physical and chemical properties are well documented, itremains unclear how fire affects the fine-scale microorgan-isms. Microbial communities are responsible for drivingessential ecosystem processes and particularly sensitive tochanges induced in soil quality by wildfire or prescribed firedisturbances. This work is a review of the last three years’literature, dealing with the fire impact on mass, activity, anddiversity of soil microorganisms from soil A horizon.

The effects of adding two winery wastes, perlite waste (PW) and bentonite waste (BW), to an acid vineyard soil were assessed using some chemical and biological soil properties in a field study that lasted 18 months. The addition of PW (up to 81 Mg ha −1 ) had neither significant nor permanent effects on soil characteristics such as the pH, organic matter content or nutrient concentrations, the amounts of copper or zinc, or the electrical conductivity. Moreover, no persistent negative effects were found on the enzymatic activities after PW application. In contrast, soil that was amended with up to 71 Mg BW ha −1 showed increases in its soil pH values, exchangeable potassium and water soluble potassium and phosphorus contents. In addition, it caused significant increases in the electrical conductivity and water-soluble Cu. In addition, the phosphomonoesterase enzymatic activity decreased significantly (up to 28%) in response to the amendment with 71 Mg BW ha −1 . These results showed that adding BW and PW to the soil may be a good agronomic practice for recycling these types of wastes. However, in the case of PW, its use as a soil amendment must be performed with caution to control its possible harmful effects.

The effect of tetracycline toxicity on the growth of soil bacterial communities was assessed using 22 agricultural soils with different pH values (between 4.1 and 7.4) and organic carbon concentrations (1.1–10.9%). Samples from all these soil types were spiked with different concentrations of tetracycline, and bacterial community growth was estimated after 1, 8, and 42 days of incubation, by using the H leucine incorporation method. Although tetracycline toxicity persisted in the soil during the incubation period, its magnitude gradually decreased with time. Moreover, tetracycline toxicity largely depends on soil characteristics, decreasing as a function of increasing organic matter, clay content, and effective exchangeable cation capacity (eCEC), and decreasing soil pH values. Further, an equation that allows the prediction of the direct effect of tetracycline on the growth of soil bacterial community was developed considering easily determinable parameters as the input; this equation will help achieve quick assessment of potentially hazardous situations., This study has been funded by the Spanish Ministry of Economy and Competitiveness through the projects CGL2015-67333-C2-1-R and -2-R (FEDER Funds). David Fernández Calviño holds a Ramón y Cajal con- tract (RYC-2016-20411), financed by the Spanish Ministry of Economy, Industry and Competitiveness.

Veterinary antibiotics reaching soils and water bodies are considered emerging pollutants deserving special attention. In this work, dissipation of tetracycline (TC), oxytetracycline (OTC) and chlortetracycline (CTC) is investigated. Dissipation experiments in filtered water, using simulated sunlight, resulted in the following degradation sequence: TC

In the present work, the effect of two by-products (pine bark and crushed mussel shell) on microbial biomass and community structure was studied in a soil from a mine tailing located in a copper mine. In a laboratory experiment, different doses (0, 12, 24, 48, 96 and 192 Mg ha-1) of pine bark, crushed mussel shell or mixtures of both by-products were added to the soil. The amended soil samples were incubated for one year at 60% of water holding capacity, and then 33 phospholipid fatty acids (PLFAs) were extracted from these samples and quantified. The PLFAs concentrations were used for different microbial biomass estimations: total biomass, bacterial biomass, fungal biomass, gram-positive (G+) biomass and gram-negative (G-) biomass. The addition of crushed mussel had no significant effects on the total soil microbial biomass, either bacterial of fungal biomass. However, the addition of pine bark increased the total microbial biomass in the soil (up to 40%), mainly due to increases in the fungal biomass (it increased 1600%). No synergistic effects were observed when the soil was amended with both, pine bark and crushed mussel shell. The main community structure changes were due to the addition of pine bark to the soil, and were also due to modifications in fungal communities. Our results suggest that the microbial biomass was mainly limited in the mine soil by low organic matter concentrations, and therefore, practices increasing the amount of soil organic matter should be priorities for soil reclamation. En el presente trabajo se estudió el efecto de dos subproductos (corteza de pino y concha de mejillón triturada) sobre la biomasa y estructura microbiana de un suelo procedente de una escombrera localizada en una mina de cobre. En un experimento realizado en laboratorio fueron añadidas al suelo diferentes dosis (0, 12, 24, 48, 96 and 192 Mg ha-1) de corteza de pino, concha de mejillón triturada y mezclas de ambos subproductos. Las muestras de suelo enmendado fueron incubadas durante un año al 60% de la capacidad de campo, y posteriormente 33 ácidos grasos de los fosfolípidos (PLFAs) fueron extraídos de estas muestras y cuantificados. La concentración de PLFAs fue utilizada para realizar distintas estimaciones de la biomasa microbiana: biomasa total, biomasa bacteriana, biomasa fúngica, biomasa de bacterias gram + y biomasa de bacterias gram -. La adición de concha de mejillón triturada no tuvo efectos significativos sobre la biomasa total ni sobre la biomasa bacteriana o fúngica. Sin embargo, la adición de corteza de pino al suelo incrementó la biomasa total del suelo (hasta un 40%), debido mayormente al incremento de la biomasa fúngica (se incrementó un 1600%). Tampoco se observaron efectos sinérgicos cuando el suelo fue enmendado con una mezcla de corteza de pino y concha de mejillón triturada. Los mayores cambios en la estructura de las comunidades microbianas fueron debidos a la adición de corteza de pino al suelo, y fueron además debidas a cambios en las comunidades fúngicas. Nuestros resultados sugieren que la biomasa microbiana del suelo de mina está mayormente limitada por la concentración de materia orgánica y, por tanto, deben ser priorizadas prácticas de manejo que contribuyan a incrementarla para la rehabilitación de este tipo de suelos. Neste trabalho foi estudado o efeito de dois subprodutos (casca de pinheiro e concha de mexilhão triturada) na biomassa e estrutura microbiana de um solo procedente de uma escombreira localizada numa mina de cobre. Numa experiência de laboratório, doses diferentes (0, 12, 24, 48, 96 e 192 Mg ha-1) de casca de pinheiro, concha de mexilhão triturada e misturas de ambos os subprodutos foram adicionados ao solo. Amostras de solo corrigido com os resíduos foram incubadas durante um ano a 60% da sua capacidade de retenção de água, e subsequentemente, 33 ácidos gordos dos fosfolípidos (PLFAs) foram extraídos a partir destas amostras e quantificados. A concentração de PLFAs foi usada para estimar vários tipos de biomassa microbiana: biomassa total, biomassa bacteriana, biomassa fúngica, biomassa de bactérias gram positivas e biomassa de bactérias gram negativas. A adição de concha de mexilhão triturada não teve nenhum efeito significativo na biomassa total ou na biomassa bacteriana ou fúngica. Porém, a adição de casca de pinheiro aumentou a biomassa microbiana do solo (até 40%), principalmente devido ao aumento da biomassa fúngica (a qual aumentou de 1600%). Não foi observado nenhum efeito de sinergismo quando o solo foi corrigido com uma mistura de casca de pinheiro e concha de mexilhão triturada. As maiores alterações na estrutura das comunidades microbianas foram produzidas pela adição de casca de pinheiro ao solo, as quais resultaram em alterações nas comunidades fúngicas. Os resultados sugerem que a biomassa microbiana do solo de mina é, maioritariamente limitada pela concentração de matéria orgânica. Assim, práticas que contribuam para o seu aumento devem ser prioritárias para a reabilitação deste tipo de solos. SI

Bentonite based organic-mineral wastes contains high concentrations of organic matter and plant nutrients and hence presents a high potential as a soil amendment. However, it also can have high salinity and high copper concentrations that may cause negative effects on microorganisms when the soil is amended with this type of wastes. In this work, the effect of soil amendment with a bentonite based winery waste on soil carbon mineralization was studied in acidic vineyard soils as an indicator of soil quality. The carbon mineralization in the waste is significantly lower and slower than that in the studied vineyard soils despite its significantly higher amount of organic carbon. However, when the bentonite winery waste was added to the soils, the carbon mineralization showed positive priming effects (increased between 78 and 337%). Therefore, reductions in the carbon mineralization, and hence changes on short-term organic matter turnover are not expected after bentonite waste amendment in acid soils.

Stable and labile soil organic compounds play different roles in the soil. It is a question of how far soil organic matter (SOM) fractions with different labilities vary as a function of climatic and management conditions. In order to answer this question stable (organic C -C-, total N -N-, organic P -Po-), and labile SOM fractions (total carbohydrates -CHt- and hot water soluble carbohydrates -CHw-) were measured monthly for two years in the 10-cm soil top-layer of an Entic Haplustoll, under conventional tillage (CT), vertical tillage (VT) and no-till (NT). Results showed that contents of all analyzed organic fractions were higher in NT than in VT and CT in almost all sampling dates. All organic compounds were less variable with time in NT and VT than in CT, in agreement with the smaller soil disturbance of NT and VT compared to CT. The more labile fractions varied as a function of short term changes in the climatic conditions, mainly temperature. Under soil disturbing tillage systems, the most stable fractions tended to decrease and the more labile to increase with time. This was attributed to the transformation of the more stable into the more labile fractions, possibly due to the disruption of aggregates produced by tillage that favored SOM mineralization. Po was the less variable compound, even under the most disturbing tillage conditions. The quotients C/N, CHt/C and CHw/C evolved similarly in all tillage systems, indicating that that tillage systems change the amount but not the quality of SOM.

The enormous quantity of plant waste produced from greenhouse tomato crops is an environmental problem that should be solved by recycling that waste into valuable organic products through low-cost technologies, such as vermicomposting. Feasibility of vermicomposting greenhouse tomato-plant waste (P) using paper-mill sludge (S) as complementary waste was investigated by this study. Earthworm development in P, S, and two mixtures of both wastes was monitored over 24 weeks and compared with that in cow dung (D), an optimum organic-waste to be vermicomposted. The effectiveness of vermicomposting to biostabilize those wastes was assessed by analysing phospholipid fatty acid composition, chemical features, plant-nutrient content, metal concentration, enzyme activities, and germination index (GI). A commercial vermicompost was also analyzed and taken as a reference of vermicompost quality. Earthworms did not survive in P alone, but a mixture of P with S at a ratio of 2:1 or 1:1 resulted in earthworm development similar to that observed in D. Phospholipid fatty acid analysis revealed that earthworm activity strongly transformed initial microbiota inhabiting the wastes, giving rise to vermicompost microbial communities which were similar to that of a commercial vermicompost. Both mixtures of P and S were properly biostabilized through vermicomposting, as indicated by decreases in their C:N ratio and enzyme activities together with increases in their degree of maturity (GI ~ 100 %) after the process. This study demonstrates that the vermicomposting of tomato-plant waste together with paper-mill sludge allows the recycling of both wastes, thereby improving the environmental sustainability of greenhouse crops.

The aim of this study was to assess the influence of pH on copper mobilization in two copper-rich acid soils (from vineyard and mine) amended with crushed mussel shell. Crushed mussel shell amended soils (0–48 Mg ha−1) were subjected to the effect of several acid and alkali solutions in a batch experiment in order to study their copper release. Copper distribution was studied in decanted soils from batch experiments using a sequential extraction procedure, whereas the effect of crushed mussel shell on copper release kinetics was studied using a stirred flow reactor. When soils were treated with acid solutions, the copper mobilization from non-amended soils was significantly higher than from the amended samples. Major changes in copper fractionation were an increase of the acid soluble fraction in acid-treated vineyard soil samples with shell dose. For the mine soil, the oxidable fraction showed a relevant diminution in acid-treated samples at the highest crushed mussel shell dose. For both soils, copper desorption rates diminished up to 86 % at pH 3 when crushed mussel shell was added. At pH 5, copper release rate was very slow for both soils decreasing up to 98 % for the mine soil amended with the highest shell dose, whereas no differences were observed at pH 7 between amended and non-amended soils. Thus, crushed mussel shell addition could contribute to reduce potential hazard of copper-enriched soils under acidification events.

Wildfires are a global problem that can require the application of fire-fighting chemicals for combating them. These compounds can have negative effects on forest ecosystems; however, there are few studies about their influence on the soil microbial community. The aim of this work is to analyse under field conditions the impact of a prescribed fire and the addition at normal field doses of three different fire-fighting chemicals (foaming agent, ammonium polyphosphate, Firesorb) on different soil properties, 10 years after the fire and retardant addition. The study was performed in a Humic Cambisol under scrubland located in Galicia (NW Spain). Several physical, physicochemical, chemical (water holding capacity, pH, electric conductivity, total C and N, hydro-soluble C and carbohydrates), biochemical and microbiological [biomass C, enzyme activities, respiration, bacterial growth, fungal biomass and growth, biomass and community composition by the phospholipid fatty acid (PLFA) pattern] properties were analysed in the 0–2- and 2–5-cm soil layers. A marked effect of soil depth and no effects of prescribed fire on most analysed properties were observed, suggesting that soil chemical quality was recovered after 10 years, although changes in microbial community composition were still detected 10 years after the prescribed fire and the retardant addition. The PLFA pattern combined with principal component analysis allows us to differentiate the microbial communities according to both soil depth and soil treatment. The ammonium polyphosphate was the fire-fighting chemical with the strongest effects on the composition of soil microbial communities, which is in accordance with marked changes observed in vegetation., This research was supported by the Spanish Ministry of Education and Science through the projects AGL2001-1242-CO4-01 and AGL2008-02823. A. Barreiro is a recipient of an FPU grant from the Spanish Ministry of Education (AP2010-2284). Part of this work has been funded with a PFU program grant awarded to A. Barreiro (short stays).

Pollution induced community tolerance (PICT) has been suggested as an end-point measurement less affected by confounding environmental factors compared to standard methods of microbial growth, activity and community composition. We evaluated the use of PICT to determine Cu toxicity in vineyard soils polluted with Cu based fungicides (25-1120 mg Cu kg(-1)). These soils also varied in pH (4.3-7.3), organic C (0.31-6.91%) and texture (14-56% silt). PICT was estimated as bacterial community tolerance to Cu measured by the [H-3]leucine incorporation method. Bacterial tolerance to Cu increased 9 times in the most polluted compared to the unpolluted soils. Cu tolerance was also affected to a minor degree by pH, organic C and soil texture. Lower bacterial tolerance was found in soils with high pH and organic C, probably due to Cu becoming less bioavailable in soils with high pH and organic C content. The silt content appeared to increase bacterial tolerance, probably due to fine soil particles decreasing Cu bioavailability during the PICT detection phase. Despite the effects of other environmental factors, the main determinant of increased bacterial community tolerance to Cu was the pollution level. PICT measured with the leucine incorporation technique thus appears to be a sensitive and stable concept to evaluate toxic impacts, unless soils with very different pH, organic C or texture are studied. (C) 2011 Elsevier Ltd. All rights reserved.

Atrazine is one of the most used herbicides worldwide; however, consequences of its long-term agricultural use are still unknown. A laboratory study was performed to examine changes in microbial properties following ethylamino-15N-atrazine addition, at recommended agronomic dose, to five acidic soils from Galicia (NW Spain) showing different physico-chemical characteristics, as well as atrazine application history. Net N mineralization was observed in all soils, with nitrate being the predominant substance formed. The highest values were detected in soils with low atrazine application history. From 2% to 23% of the atrazine-15N was found in the soil inorganic-N pool, the highest values being detected after 9 weeks in soils with longer atrazine application history and lower indigenous soil N mineralization. The application of atrazine slightly reduced the amount of soil N mineralized and microbial biomass at short term. Soluble carbohydrates and β-glucosidase and urease activity decreased with incubation time, but were not significantly affected by the single application of atrazine. Microbial community structure changed as consequence of both soil type and incubation time, but no changes in the phospholipid fatty acid (PLFA) pattern were detected due to recent atrazine addition at normal doses. The saturated 17- to 20-carbon fatty acids had higher relative abundance in soils with a longer atrazine history and fungal biomass, as indicated by the PLFA 18:2ω6,9, decreased with the incubation time. The results suggested that the PLFA pattern and soil N dynamics can detect the long-term impact of repeated atrazine application to agricultural soils.

The immediate effect of low and high severity wildfires on the main soil properties, as well as their short‐ and medium‐term evolution under field conditions, was examined. The study was performed with three pine forest soils (two Leptosols and one Humic Cambisol, developed over granite and basic schist, respectively), located in the Atlantic humid temperate zone (Galicia, NW Spain). Samples were collected from the A‐horizon (0–5 cm depth) of the burnt and the corresponding unburnt soils, immediately and 3, 6 and 12 months after the wildfires. Most properties analysed exhibit immediate fire‐induced changes and different evolution depending on fire severity and soil type. In general, immediately after the fire pH and soil properties related to nutrients availability increased and cation exchange capacity decreased, whereas properties related to soil organic matter content (C, N, Fe and Al oxides) had a variable effect depending mainly on the soil studied; all these modifications were accentuated by fire severity. These effects were attenuated in the short term in the soil affected by a low severity wildfire, but they lasted for at least 1 year in the soils affected by high severity wildfires, particularly in the Leptosols. The results showed the importance of the fire as a disturbance agent in the dynamic of nutrients and soil organic matter that is directly related with soil quality in the Galician forest ecosystems., This study was supported by the Consellería de Educación y Ordenación Universitaria de la Xunta de Galicia and by the Comisión Interministerial de Ciencia y Tecnología (CICYT), Spain.

Copper-based fungicides have been applied in vineyard soils for a long time, which has resulted in increasing soil Cu concentration. However, information relating to non-target effects of these fungicides on microorganisms of these soils is scarce. The aim of this study was to determine the potential enzyme activities of vineyard soils in relation to Cu content and evaluate the potential risks of long-term application of Cu-based fungicides. For this purpose, a wide range of soil samples, having different total, exchangeable and bioavailable Cu contents, were collected from six regions of quality wines located in the NW Iberian Peninsula, and the activity of dehydrogenase, β-glucosidase, urease and phosphatase were measured. Overall, the results obtained indicate adverse effects of Cu on dehydrogenase, β-glucosidase and phosphatase activities and an inconsistent effect on urease activity. Threshold Cu concentrations at which changes in the enzyme activities became evident were 150–200 mg total Cu kg −1 and 60–80 mg bioavailable Cu kg −1 .

Worldwide, fire-fighting chemicals are rapidly gaining acceptance as an effective and efficient tool in wildfires control and in prescribed burns for habitat management. However, despite its widespread use as water additives to control and/or slow the spread of fire, information concerning the impact of these compounds on soil ecosystems is scarce. In the present work we examine, under field conditions, the response of the microbial communities to three different fire-chemicals at normal doses of application. The study was performed with a Humic Cambisol over granite under heath, located in the temperate humid zone (Galicia, NW Spain) with the following treatments: unburned soil (US) and burned soil added with water alone (BS) or mixed with the foaming agent Auxquímica RFC-88 at 1% (BS + Fo), Firesorb at 1.5% (BS + Fi) and FR Cross ammonium polyphosphate at 20% (BS + Ap). The microbial mass (microbial C), activity (β-glucosidase, urease) and community structure [phospholipids fatty acids (PLFA) pattern] were measured on soil samples collected at different sampling times during a 5 year period after a prescribed fire. The results showed a negative short-term effect of the fire on the microbial properties. The microbial biomass and activity levels tended to recover with time; however, changes in the microbial community structure (PLFA pattern) were still detected 5 years after the prescribed fire. Compared to the burned soil added with water, the ammonium polyphosphate and the Firesorb treatments were the fire-fighting chemicals that showed a higher influence on the microbial communities over the whole study period. Our data indicated the usefulness of the PLFAs analysis to detect the long-term impact of both fire and fire-fighting chemicals on the soil microbial communities and hence on the soil quality of forest ecosystems., This study was supported by the Consellería de Educación y Ordenación Universitaria de la Xunta de Galicia (08MRU002400PR) and by the Ministerio de Ciencia e Innovación (AGL2008-02823), Spain.

The phospholipid fatty acid (PLFA) pattern of vineyard soils from the Northwest of the Iberian Peninsula was studied to identify soil factors determining the microbial community structure, with special emphasis on effects of Cu pollution and pH. A wide range of soil samples, collected from six winegrowing regions (Rias Baixas, Ribeiro, Ribeira Sacra, Monterrei, Valdeorras and Vinhos Verdes) was analyzed. Physicochemical properties, including total Cu content, five different Cu fractions and available Cu, were also determined. Total Cu varied between 33 and 1120 mg kg(-1) and pH(water) between 4.3 and 7.3. Soil pH rather than Cu content was most important in determining the composition of the microbial community. An increase in the relative concentrations of the monounsaturated PLFAs 16:1 omega 5, 16:1 omega 7c, 17:1 omega 8 and 18:1 omega 7 and a decrease of br18:0. i17:0, 17:0 and cy19:0 was correlated to an increase in pH. A significant effect of Cu was also found, with an increase in the branched fatty acids 10Me17:0, i16:0, 10Me18:0, a17:0 and br17:0 as consequence of Cu pollution. This change in the PLFA pattern was correlated to both the total and available fractions of Cu. Although the PLFA pattern was a useful tool to assess factors affecting the microbial composition, it is difficult to differentiate between these factors. (C) 2010 Elsevier B.V. All rights reserved.

The occurrence of total Cu and Cu fractions (exchangeable Cu, Cu bound to organic matter, Cu bound to amorphous inorganic materials, Cu bound to crystalline Fe and Al oxides and residual Cu) was studied in 170 surface layers of soils from seven vineyard regions located in the NW Iberian Peninsula (Rias Baixas, Ribeira Sacra, Ribeiro, Monterrei, Valdeorras, O Bierzo and Vinhos Verdes). The data showed that long-term application of Cu-based fungicides has led to increased concentrations, mainly in superficial vineyard soil layers. Thus, 64% of the samples showed total Cu levels higher than 100 mg kg − 1 , threshold for soil contamination. Total Cu content in Ribeiro (248 ± 130 mg kg − 1 ) and Ribeira Sacra (259 ± 118 mg kg − 1 ) soils were significantly higher than those observed for the rest of the vineyard regions (169 ± 90, 139 ± 122, 115 ± 42, 103 ± 42 and 100 ± 48 mg kg − 1 in Valdeorras, Rias Baixas, O Bierzo, Vinhos Verdes and Monterrei, respectively). Cu distribution among various soil fractions also differed between winegrowing regions; however, in general, Cu in these vineyard soils is present mainly in less mobile fractions (average values were 48 ± 12% for Cu bound to soil organic matter; 15 ± 9% for Cu associated to amorphous inorganic materials; 12 ± 9% for Cu bound to crystalline Fe and Al oxides and 23 ± 12% for residual Cu), whereas exchangeable Cu constituted approximately 3 ± 3% of total Cu. All soil samples were separated in three well differentiated groups according to their physical, chemical and Cu fractionation data (Ribeiro, Ribeira Sacra and Monterrei samples; O Bierzo, Valdeorras and Monterrei samples; Rias Baixas and Vinhos Verdes samples), being soil type, climate and fungicide application as the most determinant factors for soil quality.

To detect effects of Cu pollution, the Cu tolerance of soil bacterial communities extracted from several vineyards located in NW Spain was measured. Bacterial community tolerance was estimated by means of the thymidine (TdR) and leucine (Leu) incorporation techniques using either IC(50) values (the log of the metal concentration that reduced incorporation to 50%) or the percentage of activity at one specific Cu concentration (10(-6) mol L(-1)). The tolerance measurements by the TdR incorporation technique were similar to those obtained by the Leu incorporation method, indicating that the two methods were equivalent in terms of suitability for detecting the toxicity of Cu to soil bacterial communities. The two tolerance indices considered (IC50 values and percentage of activity) were closely correlated (r = 0.975, P < 0.001), showing that both were equally good in measuring Cu tolerance of the bacterial community. An increased bacterial community tolerance to Cu, indicating a pollution effect, was observed in vineyard soils with more than 100 mg Cu kg(-1) soil. Thus, the long-term use of Cu in vineyards has a toxic effect on the soil bacterial community, resulting in an increased tolerance. An effect of increased levels of Cu could not be detected when measuring bacterial community activity, pointing to the increased sensitivity to detect toxicity in field studies using tolerance measurements.

The impact of a wildfire on some selected physicochemical, chemical (water retention, pH, electrical conductivity, free Fe and Al oxides, total C, extractable C), biochemical (microbial C, soil respiration, bacterial activity, β-glucosidase, urease and phosphatase activities) and microbiological properties (analysis of phospholipid fatty acids, PLFA pattern) was evaluated in Fragas do Eume Natural Park (NW Spain). Soil samples were collected three months after the wildfire from the A horizon (0–2.5 and 2.55 cm) of the unburnt and burnt soil under climax vegetation (Quercus) and non-autochthonous vegetation (Eucalyptus). The results indicated that, independent of the vegetation considered, the wildfire induced short-term modifications of most soil properties analysed, more accentuated changes being those related to labile fractions of the soil organic matter (extractable C and microbial biomass C, negative effects) as well as those in pH and bacterial growth values (positive effects). The fire effect was often more noticeable in the 0–2.5 cm layer than in the 2.5–5 cm layer. The results of a principal component analysis performed with the matrix of the physicochemical and biochemical data showed that vegetation was the most important factor controlling the overall quality of these soils and that wildfire is also an important source of variation in soil quality. This is in agreement with the PLFA pattern, differentiating clearly the Quercus soil samples from the Eucalyptus ones and, to a lesser extent, the burnt soil samples from the corresponding unburnt ones. Medium- and long-term consequences of these microbial changes in the functioning of the plant–soil system should be investigated in order to preserve the biodiversity of the Natural Park., This study was supported by the Ministerio Español de Economía y Competitividad (AGL2012-39686-C02-01) and by Fundación MAPFRE (MA-12-AYU-374). A. Barreiro and A. Lombao are recipients of FPU grants from Spanish Ministry of Education (AP2010-2284, AP2010-1900).

Microbial community DNA was extracted directly from an arable soil experimentally polluted with Cd, Cu, Ni, Pb or Zn, and incubated for 34 months. Broad-scale measurements of changes in microbial community structure were assessed by applying %G+C profiling and community hybridisation techniques to the DNA, and compared with phospholipid fatty acid (PLFA) profiles. %G+C profiles, statistically compared using parameterisation and principal component analysis, differed between treatments. Community hybridisation revealed a range of DNA similarities between treatments. The combination of these two techniques facilitated the interpretation of the data. The differences between the treatments determined by DNA analysis were consistent with the PLFA patterns, and revealed that: (i) microbial communities in metal contaminated soils were different from those in uncontaminated soil, (ii) the microbial community in Cu contaminated soil was different from those in soils contaminated with the other metals, and (iii) the microbial communities in soils contaminated with Pb and Ni were indistinguishable from one another.

The effect of long-term elevated soil Pb levels on soil microbiota was studied at a forest site in Norway, where the soil has been severely contaminated with Pb since the last period of glaciation (several thousand years). Up to 10% Pb (total amount, w/w) has been found in the top layer. The microbial community was drastically affected, as judged from changes in the phospholipid fatty acid (PLFA) pattern. Specific PLFAs that were high in Pb-enriched soil were branched (especially br17:0 and br18:0), whereas PLFAs common in eukaryotic organisms such as fungi (18:2omega6,9 and 20:4) were low compared with levels at adjacent, uncontaminated sites. Congruent changes in the PLFA pattern were found upon analyzing the culturable part of the bacterial community. The high Pb concentrations in the soil resulted in increased tolerance to Pb of the bacterial community, measured using both thymidine incorporation and plate counts. Furthermore, changes in tolerance were correlated to changes in the community structure. The bacterial community of the most contaminated soils showed higher specific activity (thymidine and leucine incorporation rates) and higher culturability than that of control soils. Fungal colony forming units (CFUs) were 10 times lower in the most Pb-enriched soils, the species composition was widely different from that in control soils, and the isolated fungi had high Pb tolerance. The most commonly isolated fungus in Pb-enriched soils was Tolypocladium inflatum. Comparison of isolates from Pb-enriched soil and isolates from unpolluted soils showed that T. inflatum was intrinsically Pb-tolerant, and that the prolonged conditions with high Pb had not selected for any increased tolerance.

Synthetic polymers are currently being used as water additives to control wildfires and prescribed burns. This laboratory study examines the effects of one of these acrylic-based polymers (Firesorb) on some biochemical properties (microbial biomass C, hydrolysis of FDA, β-glucosidase, urease and N mineralization) of two coarse textured soils (loamy sand and sandy loam) under pinewood located at Galicia (NW Spain). Firesorb was added to unheated and heated soil samples at two levels of application (1 and 3 times the recommended dose) and measurements were made after 6 and 12 weeks of aerobic incubation. The results obtained for both soils at different incubation times were found to be comparable. Except for N mineralization, which was reduced by Firesorb addition, in both unheated and heated soils, the Firesorb-treated samples showed similar or significantly higher values for the biochemical parameters analyzed than those in the untreated control soils. This finding suggests that under these assay conditions the synthetic polymer used as a fire-fighting chemical had no adverse effects on soil microbial communities.

Bacterial activities, estimated using the thymidine and leucine incorporation techniques, were measured in soil artificially contaminated with five different metals (Cd, Cu, Ni, Pb, Zn) at two different concentrations and in an uncontaminated control. The activity of the bacteria was followed during 14 months of incubation under laboratory conditions. After an initial decrease, which was correlated to the level of metals added, the bacterial activity recovered. Peak activities, much higher than those of the uncontaminated control, were detected after different incubation times for the different metal treatments. Cu contaminated soils showed peak activities after 1 month of incubation, while for Zn, Pb, and especially Ni, peak activities were not found until up to after 1 year of incubation. The leucine/thymidine incorporation ratio (mol/mol) did not differ over time, but significant differences were found between different metal treatments. Thus, while the uncontaminated control, and Cd, Zn and Ni treated soils had ratios around 20, the Cu contaminated soils had high ratios, around 50. The Pb contaminated soils, on the other hand, had low ratios (around 7). This was interpreted as an indication of different bacterial communities in the different treatments, where the Cu treated soils differed most from the other soils, while Cd, Zn or Ni application gave rise to similar communities. Other techniques to characterize soil microorganisms have earlier indicated the same effect of the metals on the bacterial community.

The effects of temperature on the growth rate and metal toxicity in soil bacterial communities extracted from unpolluted and polluted soils were investigated using the thymidine and leucine incorporation techniques. An agricultural soil, which was contaminated in the laboratory with Cu, Cd, Zn, Ni or Pb, and an uncontaminated forest soil were used. Measurements were made at 0°C and 20°C. Leucine incorporation was found to be as sensitive to heavy metals as thymidine incorporation in the short-term trial used to indicate heavy metal tolerance. Similar IC50 values (the log of the metal concentration that reduced incorporation to 50%) were also obtained at 0 and 20°C, independently of the technique used. Metal tolerance could thus be measured using both techniques at any temperature in the range 0–20°C. In the long-term experiment different temperature-growth relationships were obtained on the basis of the rate of thymidine or leucine incorporation into bacterial assemblages from unpolluted and polluted soils, as judged from the minimum temperature values. This could not be attributed to the metal addition alone since different patterns were observed when different metals were added to the soil. Thus, the minimum temperature for thymidine incorporation was similar in Cu-polluted and unpolluted soil, while in soils polluted with Cd and Zn the minimum temperature increased by 2°C, and Ni and Pb additions increased the minimum temperature by 4°C compared to the unpolluted soil. This suggested that heavy metal pollution led to bacterial communities showing different temperature characteristics to those in the corresponding unpolluted soil. Similar observations were deduced from the minimum temperatures required for leucine incorporation. Three groups of bacterial communities were distinguished according to the growth response to temperature in polluted soils, one group in Cu-polluted soil, a second group in soil polluted with Zn and Cd, and a third group in soils polluted with Ni and Pb.

A thymidine incorporation technique was used to determine the tolerance of a soil bacterial community to Cu, Cd, Zn, Ni, and Pb. An agricultural soil was artificially contaminated in our laboratory with individual metals at three different concentrations, and the results were compared with the results obtained by using the plate count technique. Thymidine incorporation was found to be a simple and rapid method for measuring tolerance. Data obtained by this technique were very reproducible. A linear relationship was found between changes in community tolerance levels obtained by the thymidine incorporation and plate count techniques ( r = 0.732, P < 0.001). An increase in tolerance to the metal added to soil was observed for the bacterial community obtained from each polluted soil compared with the community obtained from unpolluted soil. The only exception was when Pb was added; no indication of Pb tolerance was found. An increase in the tolerance to metals other than the metal originally added to soil was also observed, indicating that there was multiple heavy metal tolerance at the community level. Thus, Cu pollution, in addition to increasing tolerance to Cu, also induced tolerance to Zn, Cd, and Ni. Zn and Cd pollution increased community tolerance to all five metals. Ni amendment increased tolerance to Ni the most but also increased community tolerance to Zn and, to lesser degrees, increased community tolerance to Pb and Cd. In soils polluted with Pb increased tolerance to other metals was found in the following order: Ni > Cd > Zn > Cu. We found significant positive relationships between changes in Cd, Zn, and Pb tolerance and, to a lesser degree, between changes in Pb and Ni tolerance when all metals and amendment levels were compared. The magnitude of the increase in heavy metal tolerance was found to be linearly related to the logarithm of the metal concentration added to the soil. Threshold tolerance concentrations were estimated from these linear relationships, and changes in tolerance could be detected at levels of soil contamination similar to those reported previously to result in changes in the phospholipid fatty acid pattern (Å. Frostegård, A. Tunlid, and E. Bååth, Appl. Environ. Microbiol. 59: 3605-3617, 1993).

30: 147-152., Extractable atrazine and its metabolites (hydroxyatrazine, deethylatrazine and deisopropylatrazine) were evaluated in agricultural soils from the températe humid zone (Galicia, NW Spain) under laboratory conditions. The experiment was performcd with five soils with different properties (organic C, soil texture and atrazine application history), both unamended and treated with atrazine at field application rate. Measurements ot" the atrazine compounds were made at different time intervals (1, 3, 6, 9 and 12weeks) during a 3-month incubation period. Results showed that only hydroxyatrazine was detected in the extractable fraction ot" the unamended soils, with valúes remaining relatively constant throughout the incubation period. Atrazine addition notably increased the concentration of the parent compound and its degradation producís; deisopropylatrazine and hydroxyatrazine were the main metabolites detected in the extractable fraction of the treated soils, whereas deethylatrazine was not detected. After 7 days incubation, valúes of total extractable residues, expressed as percentage ot" initially added atrazine, ranged from 75 to 86% (25-68% of atrazine, 7-11% of hydroxyatrazine and 9-57% of deisopropylatrazine). The valúes decreased rapidly during the first 3 weeks of incubation, showing valúes of 2-8% in soils with higher atrazine application and from 28 to 30% in soils with lower application history. At the end of the incubation, 2-8% ot" total extractable residues were still detected (0-4% of atrazine, 2-3% of hydroxyatrazine and 0-2% of deisopropylatrazine), indicating a residual eft'ect of atrazine addition. These variations in the extractable fraction indicated that most added atrazine was rapidly degraded, especially in soils with higher application history.

Mineralization of atrazine and formation of extractable and non-extractable "bound" residues were followed under laboratory conditions in two contrasting soils (organic C, texture, and atrazine application history) from northern Spain. The soils, a Humic Cambisol (MP) and a Gleyic Cambisol (G) were incubated with labeled atrazine (ring-13C atrazine) at field application dose and measurements were made at different time intervals during 3 mo. Fate and behavior of atrazine along the incubation showed different patterns between the two soils, the time taken for degradation of 50% (DT50) being 9 and 44 d for MP and G soils, respectively. In MP soil, with 40 yr of atrazine application and lower organic C and clay content, more than 89% of U-13C-atrazine added was mineralized after 12 wk, with most mineralization occurring within the first 2 wk. G soil, with 10 yr of atrazine application, exhibited a more progressive U-13C-atrazine mineralization, reaching 54% of initially added atrazine at 12 wk. Hydroxyatrazine and deisopropylatrazine were the metabolites founded in the extractable fraction, demonstrating that both chemical and biological processes are involved in atrazine degradation. Soil G showed during all the incubation times an extractable residues fraction greater than that in MP soil, indicating a high potential risk of soil and water contamination. Rapid microbial degradation through s-triazine ring cleavage was proposed to be the main decomposition pathway of atrazine for the two soils studied. Bound residues pool also differed notably between soils accounting for 9 and 41% of initially added atrazine, the higher values shown by soil with higher organic matter and clay content (G soil).

The content of atrazine and its metabolites (hydroxyatrazine, deethylatrazine and deisopropylatrazine) as well as the activities of two soil enzymes (urease and β-glucosidase) were evaluated in an acid agricultural soil, located in a temperate humid zone (Galicia, NW Spain), with an annual ryegrass–maize rotation under conventional tillage (CT) and no tillage (NT). Samples were collected during two consecutive years from the arable layer at two depths (0–5 cm and 5–20 cm) and different times after atrazine application. Hydroxyatrazine and deisopropylatrazine were the main metabolites resulting from atrazine degradation in the acid soil studied, the highest levels being detected in the surface layer of the NT treatment. A residual effect of atrazine was observed since hydroxyatrazine was detected in the arable layer (0–5 cm, 5–20 cm) even one year after the herbicide application. Soil enzyme activities in the upper 5 cm layer under NT were consistently higher than those in the same layer under CT. Urease and β-glucosidase activities decreased with depth in the profile under NT but they did not show any differences between the two depths for the plots under CT. For both tillage systems enzyme activities also reflected temporal changes during the maize cultivation; however, no consistent effect of the herbicide application was observed., This study was supported by the Secretaría Xeral de Investigación e Desenvolvemento da Xunta de Galicia (Proyecto PGIDT01PXI40002PR), Spain.

The physical and chemical characteristics of four composted urban refuses (one of them amended with CaCO3 during the composting process) from Spanish industrial composting plants were studied from the point of view of their use as organic fertilizers. The four composts were very fine in texture with low bulk density and high salinity. The pH was close to neutrality; the organic matter content ranged from 42 to 60% and the C/N ratio from 16 to 22 (7 for the amended urban refuse). Most of the total N was in organic forms; NH4+-N largely predominatedNO3−-N in the composts, except for the amended composted refuse where the predominant inorganic form was NO3−-N. Calcium was the most abundantnutrient followed by K, Na, Mg and P. Most of the Ca and Na were in available forms; available K and Mg were lower and available P very small. Total Al and Fe were extremely abundant followed by Zn, Mn, Pb, Cu, Cr, Ni and Cd. The percentage of available Mn was very high, followed by available Cu and Pb in two of the composts, and available Zn and Cd. Available Al, Fe, Ni and Cr were very low or negligible. Most of the total Zn, important percentages of total Pb, Mn, Al and Fe, but very low proportions of total Cr and Ni and only traces of Cd, were complexed with organic matter; these compounds seemed to be soluble organo-metallic complexes, except part of those formed by Al and Cd that could be stable complexes. Although the four composted refuses were unbalanced with regard to the main nutrients they all had potential agronomic value. Total C contents and C/N ratios in the three non-amended composts were in the range for stabilized composts; however, the NH4+-N content seemed to point to the presence of non-stabilized substances., This research was supported by the COTOP (Xunta de Galicia, Spain).

Microbial biomass and activity were determined in three Cambisols and two Rankers developed over different kinds of rocks. The soils contained 0·3−1·7 g C kg−1 soil as biomass, which represented 0·8−1·5% of the total C. Whether the fumigation-incubation or fumigation-extraction method was employed, non-significant differences were found in microbial biomass values. The microbial density, which ranged from 107 to 108 microorganisms g−1 soil, was drastically reduced by CHCl3-fumigation; however, the liberation of cell metabolites significantly increased the microbial growth rate. During 10 days of soil incubation at 25°C 0·1−0·2 g C kg−1 soil (0·1−0·5% of total soil C) was released and 1−5 mg N 100 g−1 soil (0·1−1·5% of total soil N) was mineralized. A significant increase (approximately threefold) in the average C and N mineralization was found as a consequence of microbial lysis by fumigation. The results indicated that these soils have a considerable quantity of microbial biomass but a relatively low metabolic activity and that C and N mineralization may be significantly improved when microbial constituents are liberated into the soil., This research was supported by Conselleria de Educaci6n de La Xunta de Galicia.

A fumigation-extraction method that measures the fraction of the biomass rendered extractable to K2SO4 after microbial cells lysis by chloroform was used to estimate microbial biomass C and N in forest soil samples unheated or heated at 160, 350 or 600°C for 30 min, 2 or 4 h. The biomass C and N of the unheated samples were 1011 μg C g−1 and 124 μg N g−1 dry soil. Chloroform fumigation of the heated samples did not solubilize non-microbial soil organic matter. The microbial C and N in the heated samples were reduced to undetectable amounts regardless of the temperature and duration of heating. After restoring the microbial population in the heated soils by inoculation with fresh unheated soil and incubation, microbial biomass C and N were detected in the samples heated at 160°C (441 μg C g−1 and 42 μg N g−1 dry soil) and 350°C (63 μg C g−1 and 11 μg N g−1 dry soil) whereas the values in samples heated at 600°C were below the limits of detection. The decrease in biomass values were in accordance with a decrease in the number of microorganisms and hyphal length the recovery of which was inversely related to the temperature of heating. The results suggest that the fumigation-extraction technique can be used to estimate microbial biomass C and N in heated soils., This investigation was supported by the Comision Interministerial de Ciencia y Tecnologia and by Conselleria de Education of the Xunta de Galicia.