Session 2. Soil-Root-Microbe Interaction & their Effects on the Transformation & Bioavailability of Nutrients

ISMOM 2008 – ORAL ABSTRACTS J. Soil Sci. Plant Nutr. 8 (3) 2008 111 Session 2. Soil-Root-Microbe Interaction & their Effects on the Transformation & Bioavailability of Nutrients S2-O1 Changes on Soil Phosphorus Fractions by Phosphorus Solubilising Fungi after Rock Phosphate Addition D. Pinochet* and E. Valenzuela Facultad de Ciencias Agrarias, Facultad de Ciencias, Universidad Austral de Chile, Valdivia, Chile. *E-mail: Soils have significant amount of phosphorus which is not immediately available to crops and only a small fraction becomes available during crop season. When rock phosphate is applied to soils a significant P accumulation occurs in the inorganic P fractions extracted with HCl (Figure 1). The aim of this study was to evaluate changes on soil P fractions after rock P applications due to native solubilising fungi collected previously from an Andisol (Valenzuela et al., 2002). Soil samples of an Andisol, Valdivia soil Series, 15.4% OM, pH 5.6 with 8.5 mg kg-1 P-Olsen were incubated, for 90 days to 25ºC and 70% of maximum water holding capacity, with 1500 mg P kg-1 applied as North Caroline rock phosphate. The treatments were native fungi Aspergillus niger 1 (H1) and Aspergillus niger 2 (H2). A Aspergillus niger strain CBS was used as a control (HC) and a sample with no fungi addition (RP). Phosphorus fractions were measured in 1 g of soil samples using three replicates by Tiessen and Moir method (Pinochet et al., 2001). Results showed a decrease on inorganic P fractions extracted with HCl both diluted and concentrated extractions, which represents mainly P associated with Calcium, indicating that fungi solubilised rock P in soils. Also, fungi did not decrease labile organic P fraction extracted with NaOH and increased organic P extracted with HCl which represent non labile P associated to fulvic and humic acid. This study shows that Aspergillus niger native and CBS control strains solubilise rock P applied to soil increasing labile inorganic without decreasing labile organic P. 1400 1000 control RP 800 PR Phosphorus delta (mg/kg) Phosphorus (mg/kg) 1200 1000 800 600 400 200 RF + HC RF + H1 600 RF + H2 400 200 0 -200 0 Pi Resin Pi Po Bicarbonate Pi Po NaOH Pi HCl d Pi Po HCl c Pi Digestion Pi Resin Pi Po Bicarbonate Pi HCl d Pi Po HCl c Pi Digestion Soil Phosphorus Fractions Soil Phosphorus Fractions Figure 1. P Distribution after incubation without (control) and rock P addition Pi Po NaOH Figure 2. Changes in soil P fractions over non applied P control (delta P). Keywords: Soil phosphorus fractions; Aspergillus niger; rock phosphate. References D. Pinochet, G. Epple and R. MacDonald,. (2001). R C. Suelo Nut. Veg. 1: 58-69. F.E. Valenzuela D. Pinochet and P. Carias M. (2002). Mycotaxon 81: 357-366. ISMOM 2008 – ORAL ABSTRACTS J. Soil Sci. Plant Nutr. 8 (3) 2008 112 Session 2. Soil-Root-Microbe Interaction & their Effects on the Transformation & Bioavailability of Nutrients S2-O2 Oxalate Crystal Formation in Fine Lateral Roots of Eucalyptus sp. Induced by Ectomycorrhizal Fungi J. Zambrano-Gonzalez1*, M. Dutra-Costa2, I. Ribeiro da Silva3, J. Lima-Neves3, N. Félix de Barros3 and A. Chaer-Borges2 1 Laboratorio de Biotecnología. CHEMTEC S.A.E. Capitán Felipe Gómez 1087, Ñemby, Paraguay. 2 Departamento de Microbiología, Universidade Federal de Viçosa-UFV. CEP 36571-000 Viçosa, Minas Gerais, Brasil. 3 Departamento de Solos, Universidade Federal de Viçosa-UFV, CEP 36571000 Viçosa, Minas Gerais, Brasil. *E-mail: The accumulation of calcium oxalate crystals (CaOx) was evaluated in fine lateral roots and ectomycorrhizas of Eucalyptus sp. cultivated for 2.5 years in an area with typical topography with concave-convex side in the region of Viçosa, MG. Approximately 2,100 fine lateral roots, mycorrhizal and nonmycorrhizal, randomly collected in the study area, were diaphanized and analyzed by light microscopy for CaOx visualization. Ectomycorrhizal morphotypes were analyzed by scanning electron microscopy for the presence of calcium oxalate crystals on the mantle surface. Seventy percent of the total number of lateral roots observed showed the accumulation of CaOx in the root cortex cells either in the form of druses or grains. The conspicuous presence of CaOx was observed in 56.2% of the ectomycorrhizae and in 17.5% of the nonmycorrhizal lateral fine roots, evidencing the role of the ectomycorrhizal association in the storage of calcium in the roots of Eucalyptus sp. In the ectomycorrhizae druses were the predominant CaOx forms, while in nonmycorrhizal roots crystalline grains were most frequent. In the topographical positions studied (top, slope, lowland), ten ectomycorrhizal morphotypes were observed which varied as to the content of CaOx in the root cortex, suggesting distinct capacities of each ectomycorrhizal fungal species to supply calcium to the host plant. The analysis of the mantle surface of the different ectomycorrhizal morphotypes by scanning electron microscopy did not evidence the presence of CaOx in this structure, confirming that under the conditions evaluated, the accumulation of calcium crystals in the association is limited to the root cortex. This the first report on the occurrence of CaOx in the ectomycorrhizae of eucalypts under the prevalent conditions of Brazilian soils, suggesting a role for the association in supplying calcium to the plant in areas with low calcium availability. Keywords: Oxalate; Eucaliptus sp.; ectomycorrhizal fungi. ISMOM 2008 – ORAL ABSTRACTS J. Soil Sci. Plant Nutr. 8 (3) 2008 113 Session 2. Soil-Root-Microbe Interaction & their Effects on the Transformation & Bioavailability of Nutrients S2-O3 A Single Root Model for the Impact of Root Exudates on the Fate of Phosphorus in Soils S. Klepsch1,2*, A. Schnepf1, D. Leitner1, J. Santner1, M. Puschenreiter1 and W.W. Wenzel1 1 University of Natural Resources and Applied Life Sciences, Vienna, Institute of Soil Research, Peter-Jordan Strasse 82, A-1190 Vienna, Austria. 2Austrian Research Centers GmbH - ARC, A-2444 Seibersdorf, Austria. *E-mail: A mechanistic single root model for rhizosphere processes is proposed, which describes the effect of root exudates on the bioavailability phosphorus (P). The model includes reaction kinetics between root exudates, different forms of P, dissolved organic carbon, metal ions, and the respective sorbed species. Equilibrium and kinetic sorption processes, besides complexation, mineralization, dissolution/precipitation, degradation and decay processes are implemented in the model. Interaction between soil microorganisms, P and exudates will additionally be accounted for. Time-dependent boundary conditions imply exudation of organic ligands, and uptake of phosphate ions at the root surface. All dissolved species are subject to diffusive/dispersive processes resulting in a system of coupled 1-dimensional partial differential equations. The model will be applied to study the P nutrition of oil seed ra (...truncated)