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Soil microbial traits and functions play a central role in soil organic carbon (SOC) dynamics. However, at the macroscale (regional to global) it is still unresolved whether (i) specific environmental attributes (e.g., climate, geology, soil types) or (ii) microbial community composition drive key microbial traits and functions directly. To address this knowledge gap, we used 33 grassland topsoils (0-10 cm) from a geoclimatic gradient in Chile. First, we incubated the soils for 1 week in favorable standardized conditions and quantified a wide range of soil microbial traits and functions such as microbial biomass carbon (MBC), enzyme kinetics, microbial respiration, growth rates as well as carbon use efficiency (CUE). Second, we characterized climatic and physicochemical properties as well as bacterial and fungal community composition of the soils. We then applied regression analysis to investigate how strongly the measured microbial traits and functions were linked with the environmental setting versus microbial community composition. We show that environmental attributes (predominantly the amount of soil organic matter) determined patterns of MBC along the gradient, which in turn explained microbial respiration and growth rates. However, respiration and growth normalized for MBC (i.e., specific respiration and growth) were more linked to microbial community composition than environmental attributes. Notably, both specific respiration and growth followed distinct trends and were related to different parts of the microbial community, which in turn resulted in strong effects on microbial CUE. We conclude that even at the macroscale, CUE is the result of physiologically decoupled aspects of microbial metabolism, which in turn is partially determined by microbial community composition. The environmental setting and microbial community composition affect different microbial traits and functions, and therefore both factors need to be considered in the context of macroscale SOC dynamics.

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The main challenge in treating aged soils highly contaminated with total petroleum hydrocarbons (TPH) is to enhance their bioavailability for microbial degradation. Hydrocarbons in soils undergo chemical changes that make them more resistant to biodegradation. This study investigates toluene's efficacy in enhancing the biodegradation of aged hydrocarbon-contaminated soil containing 292,000 mg TPH kg-1 dry soil. Toluene's effect was compared between solid phase (SOP) and slurry phase (SLP) treatments using a microbial consortium isolated from Cyperus laxus rhizosphere. TPH biodegradation and microbial respiration were measured, the latter to estimate the respiratory quotient (RQ, the ratio between moles of carbon dioxide released and moles of oxygen absorbed during respiration). Toluene significantly accelerated TPH biodegradation in both treatments, achieving ~ 30% higher removal than in a non-solvent control, possibly through improved bioavailability of aromatic compounds and other low molecular weight compounds. According to the RQ analysis, toluene enhanced microbial respiratory processes and hydrocarbon catabolism with higher hydrocarbon mineralization (RQ = ~ 0.5) in both SOP and SLP assays. Our results reveal toluene's potential to increase hydrocarbon availability and microbial degradation efficiency in aged contaminated soils; its use in various bioremediation techniques could be of broad applicability across diverse soil types and pollutants.

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This study evaluated the use of sugarcane filter cake and nitrogen, phosphorus and potassium (NPK) fertilization in the bioremediation of a soil contaminated with diesel fuel using a completely randomized design. Five treatments (uncontaminated soil, T1; soil contaminated with diesel, T2; soil contaminated with diesel and treated with 15 % (wt) filter cake, T3; soil contaminated with diesel and treated with NPK fertilizer, T4; and soil contaminated with diesel and treated with 15 % (wt) filter cake and NPK fertilizer, T5) and four evaluation periods (1, 60, 120, and 180 days after the beginning of the experiment) were used according to a 4 × 5 factorial design to analyze CO2 release. The variables total organic carbon (TOC) and total petroleum hydrocarbons (TPH) remaining in the soil were analyzed using a 5 × 2 factorial design, with the same treatments described above and two evaluation periods (1 and 180 days after the beginning of the experiment). In T3 and T5, CO2 release was significantly higher, compared with the other treatments. Significant TPH removal was observed on day 180, when percent removal values were 61.9, 70.1, 68.2, and 75.9 in treatments T2, T3, T4, and T5, respectively, compared with the initial value (T1).

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This study aimed to evaluate the effects of two rehabilitation systems in sites contaminated by Zn, Cu, Pb, and Cd on biological soil attributes [microbial biomass carbon (Cmic), basal and induced respiration, enzymatic activities, microorganism plate count, and bacterial and fungal community diversity and structure by denaturing gradient gel electrophoresis (DGGE)]. These systems (S1 and S2) consisted of excavation (trenching) and replacement of contaminated soil by uncontaminated soil in rows with Eucalyptus camaldulensis planting (S1-R and S2-R), free of understory vegetation (S1-BR), or completely covered by Brachiaria decumbens (S2-BR) in between rows. A contaminated, non-rehabilitated (NR) site and two contamination-free sites [Cerrado (C) and pasture (P)] were used as controls. Cmic, densities of bacteria and actinobacteria, and enzymatic activities (ß-glucosidase, acid phosphatase, and urease) were significantly higher in the rehabilitated sites of system 2 (S2-R and S2-BR). However, even under high heavy metal contents (S1-R), the rehabilitation with eucalyptus was also effective. DGGE analysis revealed similarity in the diversity and structure of bacteria and fungi communities between rehabilitated sites and C site (uncontaminated). Principal component analysis showed clustering of rehabilitated sites (S2-R and S2-BR) with contamination-free sites, and S1-R was intermediate between the most and least contaminated sites, demonstrating that the soil replacement and revegetation improved the biological condition of the soil. The attributes that most explained these clustering were bacterial density, acid phosphatase, ß-glucosidase, fungal and actinobacterial densities, Cmic, and induced respiration.

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This study investigated the microbial metabolism in Bermuda-grass Tifton 85 areas after potable-water and effluent irrigation treatments. The experiment was carried out in Lins/SP with samples taken in the rainy and dry seasons (2006) after one year and three years of irrigation management, and set up on an entirely randomized block design with four treatments: C (control, without irrigation or fertilization), PW (potable water + 520 kg of N ha-1 year-1); TE3 and TE0 (treated effluent + 520 kg of N ha-1 year-1) for three years and one year, respectively. The parameters determined were: microbial biomass carbon, microbial activity, and metabolic quotient. Irrigation with wastewater after three years indicated no alteration in soil quality for C and ET3; for PW, a negative impact on soil quality (microbial biomass decrease) suggested that water-potable irrigation in Lins is not an adequate option. Microbial activity alterations observed in TE0 characterize a priming effect.

RESUMO

The accumulation and decomposition of litter in soils under forests depend on climatic and biotic conditions. This work evaluated the effect of monthly rainfall and temperature on total bacteria, and on the dehydrogenase and respiration microbial activities. The effects of organic matter, total organic C and soil moisture were also evaluated. Performed from April, 1999 to March, 2000 in an Eucalyptus-cultivated and Pinus-cultivated Oxisol (Typic Haplustox), the study showed that climate and the soil variables affect the total number of bacteria and the microbial activities. The highest air temperatures and rainfall intensities were found during the Summer and, consequently, all the studied variables were maximal during this period. Minimal values varied from Autumn to Winter or, for some parameters, up to Spring. A positive correlation proved the influence of the organic matter, organic C and soil moisture on the total bacteria and on the respiratory and dehydrogenase activities. Litter content was also higher in the Summer as compared to the Winter, but it correlated only with the total bacteria (r = 0.52***). However, the correlation between the litter content and organic matter (r = 0.64***) and soil moisture (r = 0.49**) suggest that the soil organic matter may have influenced microbial activity. All variables found in the Eucalyptus soil were higher than that of Pinus soil, probably favored by the best soil fertility and higher pH value.

O acúmulo e decomposição da serapilheira em solos de florestas dependem das condições climáticas e bióticas. Este trabalho avaliou as variações mensais no número de bactérias totais e nas atividades da desidrogenase e da respiração microbiana, relacionando-as à quantidade de serapilheira depositada e aos teores de matéria orgânica e de água do solo. O estudo foi realizado de abril de 1999 a março de 2000 em um Latossolo Vermelho-Escuro plantado com eucalipto e com Pinus. Houve influência do clima e das variáveis do solo nas bactérias totais e a atividade microbiana. Todas as variáveis ajustaram-se a equações de 3º grau. Durante o verão, foram obtidos os maiores valores de temperatura e de chuvas e, consequentemente, todas as variáveis estudadas apresentaram seus valores máximos neste período, e os valores mínimos no outono-inverno ou, para alguns parâmetros, até mesmo na primavera. A correlação positiva comprovou a influência da matéria orgânica e da água do solo no número de bactérias e nas atividades respiratórias e da desidrogenase. O teor de serapilheira sobre o solo também foi maior no verão do que no inverno, mas só apresentou correlação com as contagens de bactérias (r = 0,52***). Contudo, a correlação entre os teores de serapilheira e os de matéria orgânica (r = 0,64***) e de água do solo (r = 0,49**) demonstra que a matéria orgânica pode ter influenciado a atividade microbiana. Todas as variáveis analisadas no solo de eucalipto foram maiores do que no de Pinus, provavelmente favorecidas pela melhor fertilidade e maior valor do pH.

RESUMO

The accumulation and decomposition of litter in soils under forests depend on climatic and biotic conditions. This work evaluated the effect of monthly rainfall and temperature on total bacteria, and on the dehydrogenase and respiration microbial activities. The effects of organic matter, total organic C and soil moisture were also evaluated. Performed from April, 1999 to March, 2000 in an Eucalyptus-cultivated and Pinus-cultivated Oxisol (Typic Haplustox), the study showed that climate and the soil variables affect the total number of bacteria and the microbial activities. The highest air temperatures and rainfall intensities were found during the Summer and, consequently, all the studied variables were maximal during this period. Minimal values varied from Autumn to Winter or, for some parameters, up to Spring. A positive correlation proved the influence of the organic matter, organic C and soil moisture on the total bacteria and on the respiratory and dehydrogenase activities. Litter content was also higher in the Summer as compared to the Winter, but it correlated only with the total bacteria (r = 0.52***). However, the correlation between the litter content and organic matter (r = 0.64***) and soil moisture (r = 0.49**) suggest that the soil organic matter may have influenced microbial activity. All variables found in the Eucalyptus soil were higher than that of Pinus soil, probably favored by the best soil fertility and higher pH value.

O acúmulo e decomposição da serapilheira em solos de florestas dependem das condições climáticas e bióticas. Este trabalho avaliou as variações mensais no número de bactérias totais e nas atividades da desidrogenase e da respiração microbiana, relacionando-as à quantidade de serapilheira depositada e aos teores de matéria orgânica e de água do solo. O estudo foi realizado de abril de 1999 a março de 2000 em um Latossolo Vermelho-Escuro plantado com eucalipto e com Pinus. Houve influência do clima e das variáveis do solo nas bactérias totais e a atividade microbiana. Todas as variáveis ajustaram-se a equações de 3º grau. Durante o verão, foram obtidos os maiores valores de temperatura e de chuvas e, consequentemente, todas as variáveis estudadas apresentaram seus valores máximos neste período, e os valores mínimos no outono-inverno ou, para alguns parâmetros, até mesmo na primavera. A correlação positiva comprovou a influência da matéria orgânica e da água do solo no número de bactérias e nas atividades respiratórias e da desidrogenase. O teor de serapilheira sobre o solo também foi maior no verão do que no inverno, mas só apresentou correlação com as contagens de bactérias (r = 0,52***). Contudo, a correlação entre os teores de serapilheira e os de matéria orgânica (r = 0,64***) e de água do solo (r = 0,49**) demonstra que a matéria orgânica pode ter influenciado a atividade microbiana. Todas as variáveis analisadas no solo de eucalipto foram maiores do que no de Pinus, provavelmente favorecidas pela melhor fertilidade e maior valor do pH.