Effects of a humic acid and its size-fractions on the bacterial community of soil rhizosphere under maize (Zea mays L.)

Istituto di Chimica Agraria ed Ambientale, Università Cattolica del Sacro Cuore, Via Emilia Parmense 84, 29100 Piacenza, Italy.
Chemosphere (Impact Factor: 3.34). 09/2009; 77(6):829-37. DOI: 10.1016/j.chemosphere.2009.07.077
Source: PubMed


The effects of a humic acid (HA) and its size-fractions on plants carbon deposition and the structure of microbial communities in the rhizosphere soil of maize (Zea mays L.) plants were studied. Experiments were conducted in rhizobox systems that separate an upper soil-plant compartment from a lower compartment, where roots are excluded from the rhizosphere soil by a nylon membrane. The upper rhizobox compartment received the humic additions, whereas, after roots development, the rhizosphere soil in the lower compartment was sampled and sliced into thin layers. The lux-marked biosensor Pseudomonas fluorescens 10586 pUCD607 biosensor showed a significant increase in the deposition of bioavailable sources of carbon in the rhizosphere of soils when treated with bulk HA, but no response was found for treatments with the separated size-fractions. PCR-DGGE molecular fingerprintings revealed that the structure of rhizosphere microbial communities was changed by all humic treatments and that the smaller and more bioavailable size-fractions were more easily degraded by microbial activity than the bulk HA. On the other hand, highly hydrophobic and strongly associated humic molecules in the bulk HA required additional plant rhizodeposition before their bio-transformation could occur. This work highlights the importance of applying advanced biological and biotechnological methods to notice changes occurring in plant rhizodeposition and rhizosphere microbial activity. Moreover, it suggests correlations between the molecular properties of humic matter and their effects on microbial communities in the rhizosphere as mediated by root exudation.

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    • "They make up a significant component of soil organic matter and can improve soil properties such as aggregation (Piccolo et al. 1997) and water-holding capacity, and act as a nutrient 'reservoir' by complexing macro-and micro-nutrients (Canarutto et al. 1996; Chen et al. 2004a; Imbufe et al. 2005; Ferreras et al. 2006; Alagöz and Yilmaz 2009). The application of HS to soil has been found to stimulate seed germination, and increase the growth and yields of a variety of important agricultural species (Lee and Bartlett 1976; Piccolo et al. 1993; Nardi et al. 2002; Arancon et al. 2006; Eyheraguibel et al. 2008; Puglisi et al. 2009). However, the effect of adding HS to plants and soils varies with the origin and concentration of the HS applied, and the species of plant and soil type to which it is applied (Rose et al. 2014). "
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    ABSTRACT: Commercial products derived from lignite (brown coal), sold mainly as humate preparations, are widely promoted as plant growth stimulants leading to higher crop yields. These products are also claimed to improve key indicators of soil health including soil pH and microbial biomass. In a glasshouse setting, we investigated the effect of six lignite-derived amendments applied at the manufacturer's recommended rate on the early-stage growth of two pasture species, lucerne (Medicago sativa L.) and ryegrass (Lolium multiflorum Lam.). We used two soil types common to south-eastern Australia, and following an 8-week growing period, assessed soil pH, microbial biomass carbon and mycorrhizal colonisation as key indicators of soil health. We hypothesised that humic acid (HA) and macronutrients derived from the products would positively influence pasture growth and soil health indicators. Although significant growth effects were observed in response to some products, the effects were inconsistent across pasture and soil types. Treatment effects on tissue nutrient accumulation were rare, with the exception of increased potassium in ryegrass in one soil amended with raw brown coal, and decreased nitrogen in lucerne in the same soil amended with a granulated, slow-release humate product. Further, we found no consistent trends in mycorrhizal colonisation or microbial biomass carbon in response to individual treatments. Given the variable responses of the plant species and soil types to the amendments used here, we emphasise the need for further mechanistic studies to help understand how these amendments can be used to greatest effect.
    Crop and Pasture Science 09/2014; 65(9):899. DOI:10.1071/CP13433 · 1.48 Impact Factor
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    • "M from serving as a template for guiding evolution of future generations of organisms capable of rapidly utilizing it as an energy or nutrient source . Almendros and Dorado ( 1999 ) also consider the complexity of SOM and suggested that the disordered structure of these materials and the lack of the repeating units make them difficult to degrade . Puglisi et al . ( 2009 ) also pointed toward the structural complexity of SOM and suggested that it is the strength of their association rather than specific differences in molecular composition that could explain SOM ' s stability . Papa et al . ( 2010 ) attributed SOM ' s stability to its nanoscale structure and introduced a correlation between degradabilit"
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    ABSTRACT: The purpose of this study was to quantitatively assess the effect of organic matter self-assembly on its resistance to microbial mineralization. Humic acids isolated from leonardite, two peats and a mineral soil were used as organic matter samples because they provide a broad range of variability in terms of origin and the nature of their organic components. Using a benzene-methanol extraction the original humic acid samples were disassembled into humic components and a humic-lipid composite. The composite was further disassembled by using an alkaline aqueous extraction into humic amphiphilic and lipid components. Mixtures that reproduced the composition of self-assembled samples were prepared by mixing the solid individual fractions in the exact proportions that they were present in the original material. The original humic acid and their corresponding mixtures were added as the sole carbon source in separate aerobic cultures containing a microbial consortium isolated from a mineral soil. After incubation for 125 days mineralization of the self-assembled samples was shown to be higher by as much as 70% compared to their corresponding physical mixtures. The extent of mineralization of the self-assembled samples was not correlated to chemical composition base on the carbon-type distribution or hydrophobicity index derived from 13C solid-state NMR spectra. Mineralization of the physical mixtures and fractions did vary with chemical composition and was accompanied by preferential mineralization of alkyl carbon. These results suggest the microbial mineralization of humic acids is related to their self-assembly.
    Soil Biology and Biochemistry 06/2014; 73. DOI:10.1016/j.soilbio.2014.02.013 · 3.93 Impact Factor
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    • "HS have stimulating effects on amylolitic, proteolytic and denitrifying microorganisms (Visser, 1985), and have the ability of crossing the membrane of microorganisms and bioconcentrate within the cells (Kulikova et al., 2010). HS are also known to influence deeply the structure and activity of soil microbial communities (Dong et al., 2009; Puglisi et al., 2009) and to select phylogenetic distinct and abundant guilds, as in the case of microbial groups involved in nitrate reduction processes that are directly linked to the oxidation of the humic material (Van Trump et al., 2011). A general consensus considers HS as supramolecular associations of relatively small (b 1000 Da) hetereogeneous molecules, which are held together in only apparently large molecular sizes by weak linkages, such as hydrogen and hydrophobic bonds (Piccolo, 2002). "

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