Low-level herbivory by root-knot nematodes (Meloidogyne incognita) modifies root hair morphology and rhizodeposition in host plants (Hordeum vulgare) |
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Authors: | Susan Haase Liliane Ruess Günter Neumann Sven Marhan Ellen Kandeler |
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Institution: | 1. Institute of Soil Science and Land Evaluation, Soil Biology Section, University of Hohenheim, Emil-Wolff-Stra?e 27, 70599, Stuttgart, Germany 2. Institute of Plant Nutrition, University of Hohenheim, Fruwirthstr. 20, 70593, Stuttgart, Germany
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Abstract: | Low amounts of root infestation by plant parasitic nematodes are suggested to increase nutrient supply and in turn enhance
microbial activity and net mineralization rate in the rhizosphere. These effects are generally related to “leakage” of plant-derived
metabolites from damaged roots. Besides leakage, the present study examines other nematode–host interactions such as alterations
in root exudation and morphology, which were almost not considered yet. This includes undamaged root parts in order to assess
systemic plant response. The root-knot nematode Meloidogyne incognita (Kofoid and White 1919; Chitwood 1949) and barley (Hordeum vulgare L. cv. Europa) was used as model system. Host plants were grown in mini-rhizotrons inoculated with 0, 2,000, 4,000 or 8,000 M. incognita for 4 weeks. Root morphology, rhizodeposition (sugars, carboxylates, amino acids), and rhizosphere microbial communities
(PLFAs) were assessed. In treatments with 4,000 nematodes, shoot biomass, total N and P content increased by the end of the
experiment. Generally, an enhanced release of plant metabolites (sugars, carboxylates, amino acids) from the apical root zone
occurred 1 week after inoculation with 4,000 and 8,000 M. incognita, indicating root leakage. Low levels of root herbivory stimulated root hair elongation in both infected and uninfected roots.
These systemic changes in root morphology likely contributed to the increased sugar exudation in uninfected roots in all nematode
treatments at 3 weeks after inoculation. Root-knots formed a separate microhabitat within the root-system. They were characterised
by decreased rhizodeposition and increased fungal to bacterial ratio in the adhering rhizosphere soil. The present study provides
the first evidence that, apart from leakage, nematode root herbivory at background levels induces local and systemic effects
on root morphology and exudation, which in turn may affect plant performance. |
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Keywords: | Belowground herbivory Mini-rhizotrons PLFA Rhizosphere microorganisms Root exudation Root-knot nematodes |
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