Author
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Schreiner, Roger - Paul |
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Pinkerton, John |
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Submitted to: Soil Biology and Biochemistry
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 2/29/2008 Publication Date: 5/12/2008 Citation: Schreiner, R.P., Pinkerton, J.N. 2008. Ring nematodes (Mesocriconema xenoplax) alter root colonization and function of arbuscular mycorrhizal fungi in grape roots in a low P soil. Soil Biology and Biochemistry. 40:1870-1877. Interpretive Summary: The hypothesis that plant parasitic, ring nematodes alter the manner in which beneficial, mycorrhizal fungi colonize and function in grape roots by competing for carbohydrates was tested. Carbohydrate concentrations were manipulated in roots by reducing the supply from shoots by shading (50% sun) some plants, but not others (full sun). Ring nematodes and mycorrhizal fungi were added, or not, to the soils that grapevines (Pinot noir) were grown in. The most significant findings from this study were that: young grapevines required mycorrhizal fungi to grow and produce significant biomass in the experimental soil because they could not acquire enough phosphorus without these fungi ; ring nematodes suppressed arbuscules (specialized structures made by mycorrhizal fungi inside individual root cells that indicate nutrient transfer between plants and fungi) and reduced starch in fine roots without altering other fungal structures in roots; ring nematodes reduced phosphorus and potassium uptake of vines; but ultimately ring nematodes did not affect plant dry matter accumulation after a single growing season. Ring nematodes did not have a greater impact on mycorrhizal fungi in the shaded plants as compared to the plants in full sunlight, even though root carbohydrates were independently reduced in the shaded plants. Overall, our findings support the hypothesis that ring nematodes alter colonization of roots by mycorrhizal fungi and their ability to improve plant phosphorus uptake by competing for root carbohydrates, but suggest that other factors are also involved in the ring nematode suppression of mycorrhizal fungi in grape roots. Technical Abstract: A reduction of arbuscules in roots of grapevines (Vitis vinifera) observed when ring nematodes were added to field microplots led to the hypothesis that nematode feeding suppresses arbuscules by competing for root carbohydrates. This hypothesis was tested by growing ‘Pinot noir’ grapevines in a factorial experiment with 3 levels of initial nematode densities (0, 0.1, 1.0 nematodes g-1 soil), 2 levels of light (full sun, 50% sun), and 2 levels of AMF (nonAMF/+ AMF). Effects on plant growth were primarily driven by a light and AMF treatment interaction, such that low light increased stem dry matter accumulation at the expense of roots in +AMF vines only. Nematodes had only a minor influence on plant growth (leaf mass was reduced at the highest nematode density), but nematodes did not affect overall plant dry matter accumulation. Since nonAMF vines were severely limited by P and overall vine growth was so poor, the impact of nematode and light treatments were further analyzed in +AMF plants only. Nematode populations, AMF colonization, and root carbohydrates were differentially influenced by initial nematode density or light levels. Root biomass, and reducing sugar and starch concentrations in roots were reduced by low light, but the final nematode populations and arbuscule frequencies in roots were unaffected by light. Nematodes reduced arbuscules and starch concentrations in fine roots, but did not affect colonization by hyphae and vesicles. Nematodes reduced plant P and K uptake at the highest density, and low light reduced Mg uptake. These findings support the hypothesis that ring nematodes suppress arbuscules in roots via competition for root carbohydrates. However, the lack of a treatment interaction between light and nematodes in our study suggests that ring nematode-AMF interactions in grape roots are controlled by more than competition for photosynthate. |
