Elevated atmospheric CO2 changes phosphorus fractions in soils under a short rotation poplar plantation (EuroFACE)

Future high levels of atmospheric carbon dioxide (CO2) may increase biomass production of terrestrial plants and hence plant requirements for soil mineral nutrients to sustain a greater biomass production. Phosphorus (P), an element essential for plant growth, is found in soils both in inorganic and in organic forms. In this work, three genotypes of Populus were grown under ambient and elevated atmospheric CO2 concentrations (FACE) for 5 years. An N fertilisation treatment was added in years 4 and 5 after planting. Using a fractionation scheme, total P was sequentially extracted using H2O, NaOH, HCl and HNO3, and P determined as both molybdate (Mo) reactive and total P. Molybdate-reactive P is defined as mainly inorganic but also some labile organic P which is determined by Vanado-molybdophosphoric acid colorimetric methods. Organic P was also measured to assess all plant available and weatherable P pools. We tested the hypotheses that higher P demand due to increased growth is met by a depletion of easily weatherable soil P pools, and that increased biomass inputs increases the amount of organic P in the soil. The concentration of organic P increased under FACE, but was associated with a decrease in total soil organic matter. The greatest increase in the soil P due to elevated CO2 was found in the HCl-extractable P fraction in the non-fertilised treatment. In the NaOH-extractable fraction the Mo-reactive P increased under FACE, but total P did not differ between ambient and FACE. The increase in both the NaOH- and HCl-extractable fractions was smaller after N addition. The results showed that elevated atmospheric CO2 has a positive effect on soil P availability rather than leading to depletion.We suggest that the increase in the NaOH- and HCl-extractable fractions is biologically driven by organic matter mineralization, weathering and mycorrhizal hyphal turnover.

Arbuscular mycorrhizal modulation of diazotrophic and denitrifying microbial communities in the (mycor)rhizosphere of Plantago lanceolata

Impacts of divergent arbuscular mycorrhizal (AM) fungi, Glomus intraradices and Gigaspora margarita, on denitrifying and diazotrophic bacterial communities of Plantago lanceolata in nutrient-limited dune soil were assessed. We hypothesized AM species-related modifications that were confirmed in respective bacterial nirK and nifH sequence polymorphism -based community clustering and community variance allocation. The denitrifying community appeared more responsive to AM fungi than the nitrogen-fixing community. Nevertheless, the main explanatory variable, in both cases, was plant age. We conclude that AM fungi can modify N-cycling microbial rhizosphere communities and future work should aim to verify the functional significance and mechanistic basis.

Environmental controls on the production of calcium carbonate by earthworms

Lumbricus terrestris earthworms produce calcium carbonate (CaCO3) granules with unknown physiological function. To investigate carbon sequestration potential, the influence of temperature and CO2 concentration ([CO2]) on CaCO3 production was investigated using three soils, five temperatures(3-20 C) and four atmospheric [CO2] (439-3793 ppm). Granule production rates differed between soils, but could not be related to any soil characteristics measured. Production rates increased with temperature, probably because of higher metabolic rate, and with soil CO2 concentration. Implications for carbon sequestration are discussed. CaCO3 production in earthworms is probably related to pH regulation of blood and tissue fluid in the high CO2 environment of the soil.

Influence of organic fertilization on the number of culturable diazotrophic endophytic bacteria isolated from sugarcane

The numbers of culturable diazotrophic endophytic bacteria (CDEB) from roots stems and leaves of sugarcane submitted to organic inorganic or no fertilization were compared In order to determine the size of the N(2) fixing populations the Most Probable Number technique (MPN) was used The quantification of diazotrophic bacteria by using the acetylene reduction assay (ARA) was more accurate than observing the bacterial growth in the vials to confirm N(2) fixing capability the detection of gene nifH was performed on a sample of 105 Isolated bacteria The production of extracellular enzymes involved in the penetration of the plants by the bacteria was also studied The results showed that organic fertilization enhances the number of CDEB when compared with conventional fertilization used throughout the growing season The maximum number of bacteria was detected in the roots Roots and stems presented the greatest number of CDEB in the middle of the cropping season and in leaves numbers varied according to the treatment Using two pairs of primers and two different methods the nifH gene was found in 104 of the 105 tested isolates Larger amounts of pectinase were released by isolates from sugarcane treated with conventional fertilizers (66%) whereas larger amounts of cellulase were released by strains isolated from sugarcane treated with organic fertilizers (80%) (C) 2010 Elsevier Masson SAS All rights reserved

Co-accumulation of microbial residues and particulate organic matter in the surface layer of a no-till Oxisol under different crops

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Fluorapatite solubilization by Aspergillus niger in vinasse medium

Fluorapatite solubilization by Aspergillus niger using diluted vinasse at a relative density of 45° Brix may be an alternative to the usual processes for obtaining soluble phosphate. After 13 days of culture, a production of 1.2g l-1 soluble phosphate was obtained for 5g l-1 fluorapatite added to the vinasse, as well as production of 11 gl-1 dry mycelial mass and a substantial reduction of the polluting components of the medium, i.e. a 78 and 94% reduction of total and reducing sugars, respectively, and a 48 and 80% reduction of total and soluble solids, respectively. In less diluted medium, increased sugar content led to a greater production of dry mass but also to a reduction of soluble phosphate content. When fluorapatite concentration in vinasse was increased from 5.0 to 7.5 or 10.0 g l-1, soluble phosphate accumulation increased by 0.28 and 0.15 g l-1, respectively. Addition of ammonium nitrate or rotary shaking of the culture mixture did not lead to the production of larger amounts of soluble phosphate than obtained in the absence of these factors. © 1990.

Use of lipopolysaccharides to characterize Bradyrhizobium spp.

Three methods of extraction of lipopolysaccharide (LPS) were compared-the conventional hot phenol-water method with 40% phenol, a modified form of this method using 10% phenol, and the hot saline method. Good recovery of LPS was achieved by each of the three methods, with the LPS found in the aqueous phase with the two phenol-based procedures. The application of SDS-PAGE to the LPS extracts, followed by silver staining, showed similar banding with all three methods of extraction. When the hot saline extraction LPS fraction from eight strains of Bradyrhizobium spp. and eight strains of Bradyrhizobium japonicum was compared with SDS-PAGE, characteristic profiles were achieved. Serological analysis of eight strains of Bradyrhizobium spp., using antisera prepared against whole cells in agglutination reactions, showed extensive sharing of antigens. When antisera was prepared using outer membrane LPS, extracted by the hot saline method, the amount of cross-reaction was reduced greatly. The results indicated that LPS provide an efficient means of obtaining monospecific antisera to be used for serological identification of strains of Bradyrhizobium spp. and that the hot saline extraction method is recommended for a fast, simple and efficient way to obtain LPS and characterize this bacterium.

Ammonia volatilization losses from surface-applied urea with urease and nitrification inhibitors

Urease inhibitor (UI) and nitrification inhibitor (NI) have the potential to improve N-use efficiency of applied urea and minimize N losses via gaseous emissions of ammonia (NH 3) to the atmosphere and nitrate (NO3-) leaching into surface and ground water bodies. There is a growing interest in the formulations of coating chemical fertilizers with both UI and NI. However, limited information is available on the combined use of UI and NI applied with urea fertilizer. Therefore the aim of this study was to investigate the effects of treating urea with both UI and NI to minimize NH 3 volatilization. Two experiments were set up in volatilization chambers under controlled conditions to examine this process. In the first experiment, UR was treated with the urease inhibitor NBPT [N-(n-butyl) thiophosphoric acid triamide] at a rate of 1060 mg kg -1 urea and/or with the nitrification inhibitor DCD (dicyandiamide) at rates equivalent to 5 or 10% of the urea N. A randomized experimental design with five treatments and five replicates was used: 1) UR, 2) UR + NBPT, 3) UR + DCD 10%, 4) UR + NBPT + DCD 5%, and 5) UR + NBPT + DCD 10%. The fertilizer treatments were applied to the surface of an acidic Red Latosol soil moistened to 60% of the maximum water retention and placed inside volatilization chambers. Controls chambers were added to allow for NH 3 volatilized from unfertilized soil or contained in the air that swept over the soil surface. The second experiment had an additional treatment with surface-applied DCD. The chambers were glass vessels (1.5 L) fit with air inlet and outlet tubings to allow air to pass over the soil. Ammonia volatilized was swept and carried to a flask containing a boric acid solution to trap the gas and then measured daily by titration with a standardized H 2SO 4 solution. Continuous measurements were recorded for 19 and 23 days for the first and second experiment, respectively. The soil samples were then analyzed for UR-, NH4+-, and NO3--N. Losses of NH 3 by volatilization with unamended UR ranged from 28 to 37% of the applied N, with peak of losses observed the third day after fertilization. NBPT delayed the peak of NH 3 losses due to urease inhibition and reduced NH 3 volatilization between 54 and 78% when compared with untreated UR. Up to 10 days after the fertilizer application, NH 3 losses had not been affected by DCD in the UR or the UR + NBPT treatments; thereafter, NH 3 volatilization tended to decrease, but not when DCD was present. As a consequence, the addition of DCD caused a 5-16% increase in NH 3 volatilization losses of the fertilizer N applied as UR from both the UR and the UR + NBPT treatments. Because the effectiveness of NBPT to inhibit soil urease activity was strong only in the first week, it could be concluded that DCD did not affect the action of NBPT but rather, enhanced volatilization losses by maintaining higher soil NH4+ concentration and pH for a longer time. Depending on the combination of factors influencing NH 3 volatilization, DCD could even offset the beneficial effect of NBPT in reducing NH 3 volatilization losses. © 2012 Elsevier Ltd.

Non-labile plant C contributes to long-lasting macroaggregation of an Oxisol

Decomposition of plant material influences soil aggregation dynamics in ways that are still poorly understood, especially for Oxisols, in which oxides are believed to play a dominant role. In an incubation experiment, we investigated (i) the effect of plant material addition from selected monocot and dicot species on soil organic C (SOC), carbohydrate composition, fungal and total microbial biomass, and aggregation of an Oxisol; and (ii) the relationship among these properties and C mineralization patterns. The experiment was carried out at 25 °C for 180 d after addition of 11 plant materials (4 g C kg-1 soil) and a control (no plant material added). Mineralization of C during the incubation was described considering two pools of C (labile and non-labile) using a first-order plus linear fitting. Compared to the control, corn materials showed larger pentose input, greater mineralization rates for the non-labile C pool (k), greater soil pentose content (xylose + arabinose) and larger mean weight diameter of soil water-stable aggregates at 180 d of incubation. These effects were independent of changes in SOC content, suggesting that total C accrual and macroaggregation may be decoupled processes in this Oxisol. Our results support the hypothesis that the non-labile plant C pool contributes to the long-lasting stability of macroaggregates of this Oxisol and that this effect is mediated by plant and soil pentoses. We propose that plant pentose content and the decomposition rate of the slow pool (k) are useful parameters for the prediction of plant effects on aggregation dynamics of Oxisols and the selection of soil conservation practices. © 2012.

Diversidade bacteriana em solos, vinhaça e semicompostagem relacionados ao cultivo de cana-de-açúcar

Pós-graduação em Microbiologia Agropecuária - FCAV