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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    • "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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    • "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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